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                                                       Power supply  

A power supply is an electronic device that supplies electric energy to an electrical load. The primary function of a power supply is to convert one form of electrical energy to another. As a result, power supplies are sometimes referred to as electric power converters. Some power supplies are discrete, stand-alone devices, whereas others are built into larger devices along with their loads. Examples of the latter include power supplies found in desktop computers and consumer electronics devices.
Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source. Depending on its design, a power supply may obtain energy from various types of energy sources, including electrical energy transmission systems, energy storage devices such as a batteries and fuel cells, electromechanical systems such as generators and alternators, solar power converters, or another power supply.
All power supplies have a power input, which receives energy from the energy source, and a power output that delivers energy to the load. In most power supplies the power input and output consist of electrical connectors or hardwired circuit connections, though some power supplies employ wireless energy transfer in lieu of galvanic connections for the power input or output. Some power supplies have other types of inputs and outputs as well, for functions such as external monitoring and control.

  
A simple desktop power supply with power output connector seen at lower-left and power input connector (not shown) located at the rear

General classification

A rackmount, adjustable regulated DC power supply

Functional

Power supplies are categorized in various ways, including by functional features. For example, a regulated power supply is one that maintains constant output voltage or current despite variations in load current or input voltage. Conversely, the output of an unregulated power supply can change significantly when its input voltage or load current changes. Adjustable power supplies allow the output voltage or current to be programmed by mechanical controls (e.g., knobs on the power supply front panel), or by means of a control input, or both. An adjustable regulated power supply is one that is both adjustable and regulated. An isolated power supply has a power output that is electrically independent of its power input; this is in contrast to other power supplies that share a common connection between power input and output.

Mechanical

Power supplies are packaged in different ways and classified accordingly. A bench power supply is a stand-alone desktop unit used in applications such as circuit test and development. Open frame power supplies have only a partial mechanical enclosure, sometimes consisting of only a mounting base; these are typically built into machinery or other equipment. Rack mount power supplies are designed to be secured into standard electronic equipment racks. An integrated power supply is one that shares a common printed circuit board with its load.

Power conversion method

Power supplies can be broadly divided into linear and switching types. Linear power converters process the input power directly, with all active power conversion components operating in their linear operating regions. In switching power converters, the input power is converted to AC or to DC pulses before processing, by components that operate predominantly in non-linear modes (e.g., transistors that spend most of their time in cutoff or saturation). Power is "lost" (converted to heat) when components operate in their linear regions and, consequently, switching converters are usually more efficient than linear converters because their components spend less time in linear operating regions.

Types

DC power supply

A DC power supply is one that supplies a constant DC voltage to its load. Depending on its design, a DC power supply may be powered from a DC source or from an AC source such as the power mains.

AC-to-DC supply

Schematic of basic AC-to-DC power supply, showing (from L-R) transformer, full-wave bridge rectifier, filter capacitor and resistor load

Some DC power supplies use AC mains electricity as an energy source. Such power supplies will sometimes employ a transformer to convert the input voltage to a higher or lower AC voltage. A rectifier is used to convert the transformer output voltage to a varying DC voltage, which in turn is passed through an electronic filter to convert it to an unregulated DC voltage.
The filter removes most, but not all of the AC voltage variations; the remaining AC voltage is known as ripple. The electric load's tolerance of ripple dictates the minimum amount of filtering that must be provided by a power supply. In some applications, high ripple is tolerated and therefore no filtering is required. For example, in some battery charging applications it is possible to implement a mains-powered DC power supply with nothing more than a transformer and a single rectifier diode, with a resistor in series with the output to limit charging current.

Linear regulator

The function of a linear voltage regulator is to convert a varying DC voltage to a constant, often specific, lower DC voltage. In addition, they often provide a current limiting function to protect the power supply and load from overcurrent (excessive, potentially destructive current).
A constant output voltage is required in many power supply applications, but the voltage provided by many energy sources will vary with changes in load impedance. Furthermore, when an unregulated DC power supply is the energy source, its output voltage will also vary with changing input voltage. To circumvent this, some power supplies use a linear voltage regulator to maintain the output voltage at a steady value, independent of fluctuations in input voltage and load impedance. Linear regulators can also reduce the magnitude of ripple and noise on the output voltage.

AC power supplies

An AC power supply typically takes the voltage from a wall outlet (mains supply) and lowers it to the desired voltage. Some filtering may take place as well.
In modern use, AC power supplies can be divided into single phase and three phase systems. "The primary difference between single phase and three phase AC power is the constancy of delivery." ^[1] AC power Supplies can also be used to change the frequency as well as the voltage, they are often used by manufacturers to check the suitability of their products for use in other countries. 230V 50 Hz or 115 60 Hz or even 400 Hz for avionics testing.

Switched-mode power supply

 

In a switched-mode power supply (SMPS), the AC mains input is directly rectified and then filtered to obtain a DC voltage. The resulting DC voltage is then switched on and off at a high frequency by electronic switching circuitry, thus producing an AC current that will pass through a high-frequency transformer or inductor. Switching occurs at a very high frequency (typically 10 kHz — 1 MHz), thereby enabling the use of transformers and filter capacitors that are much smaller, lighter, and less expensive than those found in linear power supplies operating at mains frequency. After the inductor or transformer secondary, the high frequency AC is rectified and filtered to produce the DC output voltage. If the SMPS uses an adequately insulated high-frequency transformer, the output will be electrically isolated from the mains; this feature is often essential for safety.
Switched-mode power supplies are usually regulated, and to keep the output voltage constant, the power supply employs a feedback controller that monitors current drawn by the load. The switching duty cycle increases as power output requirements increase.
SMPSs often include safety features such as current limiting or a crowbar circuit to help protect the device and the user from harm.^[2] In the event that an abnormal high-current power draw is detected, the switched-mode supply can assume this is a direct short and will shut itself down before damage is done. PC power supplies often provide a power good signal to the motherboard; the absence of this signal prevents operation when abnormal supply voltages are present.
Some SMPSs have an absolute limit on their minimum current output.^[3] They are only able to output above a certain power level and cannot function below that point. In a no-load condition the frequency of the power slicing circuit increases to great speed, causing the isolated transformer to act as a Tesla coil, causing damage due to the resulting very high voltage power spikes. Switched-mode supplies with protection circuits may briefly turn on but then shut down when no load has been detected. A very small low-power dummy load such as a ceramic power resistor or 10-watt light bulb can be attached to the supply to allow it to run with no primary load attached.
The switch-mode power supplies used in computers have historically had low power factors and have also been significant sources of line interference (due to induced power line harmonics and transients). In simple switch-mode power supplies, the input stage may distort the line voltage waveform, which can adversely affect other loads (and result in poor power quality for other utility customers), and cause unnecessary heating in wires and distribution equipment. Furthermore, customers incur higher electric bills when operating lower power factor loads. To circumvent these problems, some computer switch-mode power supplies perform power factor correction, and may employ input filters or additional switching stages to reduce line interference.

Programmable power supply

Programmable power supplies

A programmable power supply is one that allows remote control of its operation through an analog input or digital interface such as RS232 or GPIB. Controlled properties may include voltage, current, and in the case of AC output power supplies, frequency. They are used in a wide variety of applications, including automated equipment testing, crystal growth monitoring, semiconductor fabrication, and x-ray generators.
Programmable power supplies typically employ an integral microcomputer to control and monitor power supply operation. Power supplies equipped with a computer interface may use proprietary communication protocols or standard protocols and device control languages such as SCPI.

Uninterruptible power supply

 

An uninterruptible power supply (UPS) takes its power from two or more sources simultaneously. It is usually powered directly from the AC mains, while simultaneously charging a storage battery. Should there be a dropout or failure of the mains, the battery instantly takes over so that the load never experiences an interruption. In a computer installation, this gives the operators time to shut down the system in an orderly way. Other UPS schemes may use an internal combustion engine or turbine to continuously supply power to a system in parallel with power coming from the AC. The engine-driven generators would normally be idling, but could come to full power in a matter of a few seconds in order to keep vital equipment running without interruption. Such a scheme might be found in hospitals or telephone central offices.

High voltage power supply

A 30 kV high voltage power supply with Federal Standard connector, used in electron microscopes

A high voltage power supply is one that outputs hundreds or thousands of volts. A special output connector is used that prevents arcing, insulation breakdown and accidental human contact. Federal Standard connectors are typically used for applications above 20 kV, though other types of connectors (e.g., SHV connector) may be used at lower voltages. Some high voltage power supplies provide an analog input that can be used to control the output voltage. High voltage power supplies are commonly used to accelerate and manipulate electron and ion beams in equipment such as x-ray generators, electron microscopes, and focused ion beam columns, and in a variety of other applications, including electrophoresis and electrostatics.
High voltage power supplies typically apply the bulk of their input energy to a power inverter, which in turn drives a voltage multiplier or a high turns ratio, high voltage transformer, or both (usually a transformer followed by a multiplier) to produce high voltage. The high voltage is passed out of the power supply through the special connector, and is also applied to a voltage divider that converts it to a low voltage metering signal compatible with low voltage circuitry. The metering signal is used by a closed-loop controller that regulates the high voltage by controlling inverter input power, and it may also be conveyed out of the power supply to allow external circuitry to monitor the high voltage output.

Specification

The suitability of a particular power supply for an application is determined by various attributes of the power supply, which are typically listed in the power supply's specification. Commonly specified attributes for a power supply include:

• Input voltage type (AC or DC) and range
• Efficiency of power conversion
• The amount of voltage and current it can supply to its load
• How stable its output voltage or current is under varying line and load conditions
• How long it can supply energy without refueling or recharging (applies to power supplies that employ portable energy sources)
• Operating and storage temperature ranges

Power supply applications

Power supplies are a fundamental component of many electronic devices and therefore used in a diverse range of applications. This list is a small sample of the many applications of power supplies.

Computer power supply

A modern computer power supply is a switch-mode power supply that converts AC power from the mains supply, to several DC voltages. Switch-mode supplies replaced linear supplies due to cost, weight, and size improvement. The diverse collection of output voltages also have widely varying current draw requirements.

Electric Vehicle power supply

Electric vehicles are those which rely on energy created through electricity generation. A power supply unit is part of the necessary design to convert high voltage vehicle battery power.^[4]

Welding power supply

Main article: Welding power supply

Arc welding uses electricity to melt the surfaces of the metals in order to join them together through coalescence. The electricity is provided by a welding power supply, and can either be AC or DC. Arc welding typically requires high currents typically between 100 and 350 amperes. Some types of welding can use as few as 10 amperes, while some applications of spot welding employ currents as high as 60,000 amperes for an extremely short time. Older welding power supplies consisted of transformers or engines driving generators. More recent supplies use semiconductors and microprocessors reducing their size and weight.

Aircraft power supply

Both commercial and military avionic systems require either a DC-DC or AC/DC power supply to convert energy into usable voltage.

AC adapter

Switch-mode mobile phone charger

 

An AC adapter is a power supply built into an AC mains power plug. AC adapters are also known by various other names such as "plug pack" or "plug-in adapter", or by slang terms such as "wall wart". AC adapters typically have a single AC or DC output that is conveyed over a hardwired cable to a connector, but some adapters have multiple outputs that may be conveyed over one or more cables. "Universal" AC adapters have interchangeable input connectors to accommodate different AC mains voltages.
Adapters with AC outputs may consist only of a passive transformer (plus a few diodes in DC-output adapters), or they may employ switch-mode circuitry. AC adapters consume power (and produce electric and magnetic fields) even when not connected to a load; for this reason they are sometimes known as "electricity vampires", and may be plugged into power strips to allow them to be conveniently turned on and off.

Overload protection

Power supplies often have protection from short circuit or overload that could damage the supply or cause a fire. Fuses and circuit breakers are two commonly used mechanisms for overload protection.^[5]
A fuse contains a short piece of wire which melts if too much current flows. This effectively disconnects the power supply from its load, and the equipment stops working until the problem that caused the overload is identified and the fuse is replaced. Some power supplies use a very thin wire link soldered in place as a fuse. Fuses in power supply units may be replaceable by the end user, but fuses in consumer equipment may require tools to access and change.
A circuit breaker contains an element that heats, bends and triggers a spring which shuts the circuit down. Once the element cools, and the problem is identified the breaker can be reset and the power restored.
Some PSUs use a thermal cutout buried in the transformer rather than a fuse. The advantage is it allows greater current to be drawn for limited time than the unit can supply continuously. Some such cutouts are self resetting, some are single use only.

Current limiting

Some supplies use current limiting instead of cutting off power if overloaded. The two types of current limiting used are electronic limiting and impedance limiting. The former is common on lab bench PSUs, the latter is common on supplies of less than 3 watts output.
A foldback current limiter reduces the output current to much less than the maximum non-fault current.

Terminology

• SCP - Short circuit protection
• OPP - Overpower (overload) protection
• OCP - Overcurrent protection
• OTP - Overtemperature protection
• OVP - Overvoltage protection
• UVP - Undervoltage protection
• UPS - Uninterruptable Power Supply
• PSU - Power Supply Unit
• SMPSU - Switch-Mode Power Supply Unit   

                                                              X  .  I  Direct current (DC)

Direct current (DC) is the unidirectional flow of electric charge. A battery is a good example of a DC power supply. Direct current may flow in a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current.^[1]
The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.^[2][3]
Direct current may be obtained from an alternating current supply by use of a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current with an inverter or a motor-generator set.
Direct current is used to charge batteries and as power supply for electronic systems. Very large quantities of direct-current power are used in production of aluminum and other electrochemical processes. It is also used for some railways, especially in urban areas. High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.

 

Direct Current (red line). The vertical axis shows current or voltage and the horizontal 't' axis measures time and shows the zero value.

History of electric power transmission

Brush Electric Company's central power plant with dynamos generating direct current to power arc lamps for public lighting in New York. Beginning operation in December 1880 at 133 West Twenty-Fifth Street, the high voltages it operated at allowed it to power a 2-mile (3.2 km) long circuit.^[4]

Direct current was produced in 1800 in Italian Physicist Alessandro Volta's battery, his Voltaic pile.^[5] The nature of how the current flowed was not well understood until French physicist André-Marie Ampère discovered the current traveled in one direction from positive to negative.^[6] When French instrument maker Hippolyte Pixii built the first dynamo electric generator in 1832, he found that as the magnet used passed the loops of wire each half turn, it caused the flow of electricity to reverse, generating an alternating current.^[7] At Ampère's suggestion, Pixii later added a commutator, a type of "switch" where contacts on the shaft work with "brush" contacts to produce direct current.
The late 1870s and early 1880s saw electricity starting to be generated at power stations. These were initially set up to power arc lighting (a popular type of street lighting) running on very high voltage (usually higher than 3000 volt) direct current or alternating current.^[8] This was followed by the wide spread use of low voltage direct current for indoor electric lighting in business and homes after inventor Thomas Edison launched his incandescent bulb based electric "utility" in 1882. Because of the significant advantages of alternating current over direct current in using transformers to raise and lower voltages to allow much longer transmission distances, direct current was replaced over the next few decades by alternating current in power delivery. In the mid-1950s, high-voltage direct current transmission was developed, and is now an option instead of long-distance high voltage alternating current systems. For long distance underseas cables (e.g. between countries, such as NorNed), this DC option is the only technically feasible option. For applications requiring direct current, such as third rail power systems, alternating current is distributed to a substation, which utilizes a rectifier to convert the power to direct current.

Various definitions[edit]

Types of direct current

The term DC is used to refer to power systems that use only one polarity of voltage or current, and to refer to the constant, zero-frequency, or slowly varying local mean value of a voltage or current.^[9] For example, the voltage across a DC voltage source is constant as is the current through a DC current source. The DC solution of an electric circuit is the solution where all voltages and currents are constant. It can be shown that any stationary voltage or current waveform can be decomposed into a sum of a DC component and a zero-mean time-varying component; the DC component is defined to be the expected value, or the average value of the voltage or current over all time.
Although DC stands for "direct current", DC often refers to "constant polarity". Under this definition, DC voltages can vary in time, as seen in the raw output of a rectifier or the fluctuating voice signal on a telephone line.
Some forms of DC (such as that produced by a voltage regulator) have almost no variations in voltage, but may still have variations in output power and current.
In regard to radio frequency applications, DC commonly denotes a frequency of 0 Hz. An example of this is the phrase "DC to daylight", meaning a radio system which can receive or transmit in a frequency range from 0 Hz to some higher frequency. Most radio systems do not provide DC coverage.

Circuits

A direct current circuit is an electrical circuit that consists of any combination of constant voltage sources, constant current sources, and resistors. In this case, the circuit voltages and currents are independent of time. A particular circuit voltage or current does not depend on the past value of any circuit voltage or current. This implies that the system of equations that represent a DC circuit do not involve integrals or derivatives with respect to time.
If a capacitor or inductor is added to a DC circuit, the resulting circuit is not, strictly speaking, a DC circuit. However, most such circuits have a DC solution. This solution gives the circuit voltages and currents when the circuit is in DC steady state. Such a circuit is represented by a system of differential equations. The solution to these equations usually contain a time varying or transient part as well as constant or steady state part. It is this steady state part that is the DC solution. There are some circuits that do not have a DC solution. Two simple examples are a constant current source connected to a capacitor and a constant voltage source connected to an inductor.
In electronics, it is common to refer to a circuit that is powered by a DC voltage source such as a battery or the output of a DC power supply as a DC circuit even though what is meant is that the circuit is DC powered.

Domestic

This symbol which can be represented with Unicode character U+2393 (​⎓​) is found on many electronic devices that either require or produce direct current.

DC is commonly found in many extra-low voltage applications and some low-voltage applications, especially where these are powered by batteries or solar power systems (since both can produce only DC).
Most electronic circuits require a DC power supply.
Domestic DC installations usually have different types of sockets, connectors, switches, and fixtures from those suitable for alternating current. This is mostly due to the lower voltages used, resulting in higher currents to produce the same amount of power.
It is usually important with a DC appliance to observe polarity, unless the device has a diode bridge to correct for this.

Automotive

Most automotive applications use DC. The alternator is an AC device which uses a rectifier to produce DC. Usually 12 V DC are used, but a few have a 6 V (e.g. classic VW Beetle) or a 42 V electrical system.

Telecommunication

Through the use of a DC-DC converter, higher DC voltages such as 48 V to 72 V DC can be stepped down to 36 V, 24 V, 18 V, 12 V, or 5 V to supply different loads. In a telecommunications system operating at 48 V DC, it is generally more efficient to step voltage down to 12 V to 24 V DC with a DC-DC converter and power equipment loads directly at their native DC input voltages, versus operating a 48 V DC to 120 V AC inverter to provide power to equipment.
Many telephones connect to a twisted pair of wires, and use a bias tee to internally separate the AC component of the voltage between the two wires (the audio signal) from the DC component of the voltage between the two wires (used to power the phone).
Telephone exchange communication equipment, such as DSLAMs, uses standard −48 V DC power supply. The negative polarity is achieved by grounding the positive terminal of power supply system and the battery bank. This is done to prevent electrolysis depositions.

High-voltage power transmission

 

High-voltage direct current (HVDC) electric power transmission systems use DC for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses.

Other

Applications using fuel cells (mixing hydrogen and oxygen together with a catalyst to produce electricity and water as byproducts) also produce only DC.
Light aircraft electrical systems are typically 12 V or 20 V DC.

DC/DC Power Supplies

A DC-to-DC converter is a class of power supply which converts a source of direct current (DC) from one voltage level to another. They can essentially step-up, step-down or invert a DC voltage. Future Electronics is proud to offer a wide range of DC/DC Converter Power Suppliers including: Bias Power, SL Power (Condor), Cosel, Friwo, Mean Well, Murata Power Solutions, Power One, Recom Power, Vicor and Wall Industries.

Choosing the Right DC to DC Power Supply:

When you are looking for the right DC to DC power supply, with FutureElectronics.com parametric search, no matter the application (or need, such as open frame or encapsulated) , you can filter the results by various attributes: by Type (Open Frame or Encapsulated), by form factor (1/4 Brick, ½ Brick 1/8 Brick), by Isolation (Isolated, Non-Isolated), by Number of Outputs (Single or Dual), by Output Voltage (1 W, 2 W, 3 W, 5 W,10 W,15 W, 20 W, 30 W, 50 W), by Input Voltage (-15 V / 15 V, -12 V / 12 V, -5 V / 5 V, 3.3 V, 5 V, 5.5 V, 12 V,15 V, 24 V) and by Package Style (DIP-24, DIP-6, SIP-3, SIP-4, SIP-7, SIP-8).

Applications for DC/DC Converter Power Supplies:

DC to DC converters are important in portable electronic devices such as cellular phones and laptop computers, which are supplied with power primarily from batteries. Portable devices often contain several sub-circuits, each with its own voltage level requirement, different from that supplied by a battery or an external supply. A DC to DC converter offers a method to increase voltage from a partially lowered battery voltage, thereby saving space instead of using multiple batteries to accomplish the same thing.
Other power supply applications and uses include: low noise amplifiers, signal processing, data acquisition - including sensors, automatic test equipment, laboratory test equipment, control circuits. In short, Future Electronics has the right DC DC power supply solution for your needs.

DC to DC Converters in R&D Quantities or Production Ready Packaging

     

 

 

A power supply is an electronic circuit that converts an ac voltage to dc voltage. It is basically consisting of the following elements: transformer, rectifier, filter and regulator circuits. Power supply units (PSU) are used in computers, amateur radio transmitters and receivers, and all other electronic equipment that use dc voltage as an input. Uninterruptible power supply is a must for computers which holds volatile data from time to time. This prevents corruption of data due to power failure and low voltage.

Transformer

The transformer is a static device that transfers electrical energy from the primary winding to the secondary winding without affecting the frequency. It is used to step-up or step-down the ac voltage level and isolates the remainder of the electronic system from the ac power.

The primary winding of the transformer is connected to an ac voltage source that produces alternating current while the secondary is connected to a load. The primary and secondary windings are not physically connected to each other but due to electromagnetic induction following Faraday's law, there is an induced voltage in the secondary winding. There are three main functions of transformers namely: stepping the voltage up, stepping the voltage down and providing isolation between the primary and secondary circuits.

A simple power supply used in desktop computers. This unit supplies the regulated voltage necessary for computer to operate properly. | Source

Rectifier

The rectifier is a device used to change the ac power into pulsating dc. The basic rectifier is the diode. This diode is a unidirectional device that operates as rectifier in the forward direction. The three basic rectifier circuits using diodes are the half-wave, full-wave center-tapped and full-wave bridge type.

Filter

The filter of the power supply is used to keep the ripple component from appearing in the output. It is designed to convert pulsating DC from rectifier circuits into a suitably smooth dc level. The two basic types of power supply filters are the capacitance filter (C-filter) and RC-filter. The C-filter is the simplest and most economical filter available. On the other hand, RC-filter is used to reduce the amount of ripple voltage across a capacitor filter. Its primary function is to pass most of the dc component while attenuating the ac component of the signal.
Ripple and Ripple factor
Ripple is the unwanted ac component of the signal after rectification. It is unwanted because it can destroy or damage the load. This is the main reason why filters are installed in power supply - to prevent high ripples. The job of the filter is to smoothen the signal and suppress the ac component or variations. Ripple factor is the ratio of the root mean square of the ripple voltage to the value of dc component at the output voltage. It is sometimes expressed in percentage or in peak-to-peak value. The ripple factor determines the effectivity of a filter being used in the circuit.

 

A sample full-wave bridge rectifier circuit with RC filter. The filter is used to reduce the ac component of the signal. | Source

Voltage Regulators

A voltage regulator is designed to provide a very steady or well regulated dc output. It is always ideal to have a steady output voltage so that the load will operate properly. The output level is maintained regardless of the variation of the input voltage. The commonly used transistor voltage regulators are the series voltage regulator and the shunt voltage regulator.
Series voltage regulator
The series element controls the amount of the unregulated input voltage that goes to the output as a regulated output. The regulated output voltage is sampled by a circuit that provides a feedback to the comparator circuit and is compared to a reference voltage.


Shunt voltage regulator
The shunt voltage regulator provides regulation by shunting current away from the load to regulate the output voltage.

 

A typical schematic diagram of LM317. The major component, LM317 IC is used as adjustable voltage regulator. | Source

IC Voltage Regulators

A regulator Integrated Circuit (IC) unit contains the circuitry - the reference source, comparator, amplifier, control device, and the overload protector - inside a single IC. There are also adjustable voltage regulators which allow the user to set the desired output level. Other IC regulators have fixed output values. It is said that IC regulators are superior compared to transistor voltage regulators when it comes to linearity of the output voltage.  


Power supplies or power supply units, PSU, form an essential part of very many items of electronics equipment.
The most common form takes in AC power from the mains supply and delivers a DC voltage to the item requiring power.
Accordingly power supplies are widely used in a variety of forms - some large supplying high levels of current, other power supplies, much smaller providing lower levels of power.

Power supply basics

The aim of a DC power supply is to provide the required level of DC power to the load using an AC supply at the input. Different applications require different attributes, but more often than not these days DC power supplies provide an accurate output voltage - this is regulated using electronic circuitry so that it provides a constant output voltage over a wide range of output loads.
In most power supplies there are number of different elements. These may not all be present in every design.

• Input transformer:   The input transformer is used to transform the incoming line voltage down to the required level for the power supply. Typically the input transformer provides a step down function. It also isolates the output circuit from the line supply.
• Rectifier:   The power supply rectifier converts the incoming signal from an AC format into raw DC. Either half wave or more commonly full wave rectifiers may be used as they make use of both halves of the incoming AC signal.
• Smoothing:   The raw DC from the rectifier is far from constant falling to zero when the AC waveform crossed the zero axis, and then rising to its peak. The addition of a reservoir capacitor here fills in the troughs in the waveform, enabling the next stage of the power supply to operate. Large value capacitors are normally used within this stage.
• Regulator:   This stage of the power supply takes the smoothed voltage and uses a regulator circuit to provide a constant output virtually regardless of the output current and any minor fluctuations in the input level.

Power supply regulation

There are two basic forms of power supply used in electronics equipment:

• Unregulated:   This form of power supply was the only type used many years ago. It simply consisted of a rectifier section and this was followed by capacitor or capacitor and inductor smoothing. There was no regulation to steady the voltage. If a large current was drawn the voltage would fall as a result of the resistive losses, and also the smoothing would not be as effective and the level of hum would rise.
• Voltage regulated:   As transistor circuitry became more commonplace, regulated power supplies became more common. Today they are almost universally used. They typically incorporate a voltage reference, and the output voltage is compared to this and altered accordingly by control circuitry within the regulated power supply.

In addition to this, regulated power supplies may be further subdivided:

• Linear regulated power supply:   Linear regulated power supplies use an analogue approach. A series element - a semiconductor transistor or FET - is controlled allow the correct voltage at the output for any current within the operating range.
  
  

  Note on Linear Power Supplies:

  Linear power supplies are widely used for applications where low noise and ripple are required. As the name suggests, they use linear technology - typically a series linear regulator element to drop voltage. As such they dissipate power, but without any switching mode, they are able to offer high levels of performance
   
• Switching regulator power supply:   The switching regulator format for a power supply uses a large output reservoir capacitor. A series element - a transistor or FET - is switched on and off to keep the voltage on the capacitor within the required limits.
  
  

  Note on Switch Mode Power Supplies:

  Switch mode power supplies and switch mode regulators have many advantages in terms of efficiency, size and weight. Their design can be more involved than might be thought at first. Yet with a good understanding, these switch mode power supplies, SMPSs, switch mode regulators and switch mode controllers can be successfully designed and built..
   

Each type of power supply regulation technique has its own advantages and disadvantages. As a result different types of regulator are used in different applications, although with technology improving, switching regulators are being used increasingly.

Regulator type	Advantages	Disadvantages
Linear regulator	Very low level of noise Straightforward technology	Low level of efficiency High levels of heat may need to be dissipated Large size compared to switching regulator
Switching regulator	Highly efficient Can be made very compact Low amounts of heat need to be removed	Ripple and noise can be higher than linear regulator EMC issues need to be addressed as switching spikes can cause interference

As a result of the different properties of each type of power supply regulator, linear regulators tend to be used in applications where very low levels of noise and ripple are required and heat dissipation may not be such a problem. Hi-fi amplifiers are one such area. Switching mode regulators are used more widely as they can be made very compact, they are very efficient and the levels of ripple, spikes and noise can normally be low enough for most applications. 

When choosing any DC power supply, the specification is of key importance. A variety of DC power supply specifications will be quoted, each detailing a different element of the performance of the power supply.
For different applications, different power supply specifications will be important. However each one needs to be considered when choosing or specifying a suitable power supply.

Power supply voltage and current specification

The voltage and current are the two most important parameters and will naturally be quoted in volts and amps. Sometimes the output power in watts may be quoted.

Line regulation specification

Line regulation is the variation in output voltage when the input or line voltage changes. It is normally quoted in millivolts variation or as a percentage of the output voltage and should be a few millivolts (e.g. 5 mV) or around 0.01% of the maximum output voltage for most supplies for a change of line voltage anywhere within the operating range.

Power supply specification for load regulation

Load regulation is the variation in output voltage for a change in the load. It is normally quoted as a in millivolts variation or as percentage of the maximum output voltage It might typically be a few millivolts (e.g. 5 mV) or 0.01% for a step load change from 0 to 100% load. It is normally quoted for a constant line voltage and steady temperature.

Power supply specification for ripple and noise

The ripple and noise on the output is combined as a single measurement. For linear supplies, ripple frequency will normally be at twice the line frequency. For switching supplies ripple and spikes will arise from the switching action of the supply. The ripple components are often given as rms figures, but for switching supplies a peak to peak measurement is more useful because it shows the extent of the spikes arising from the switching. Most good supplies should offer noise and ripple figures of better than 10 mV rms and for switching supplies figures of 50mV or less should be achievable in many cases, although very high current supplies may have slightly higher values.

Power supply stability specification

Stability of the output voltage is important for some applications and is quoted for many supplies. Typically the output voltage will be measured over a period of time under constant load and input voltage and the voltage drift measured. Typically, this will be a few millivolts (e.g. five to ten) over a period of ten hours.

Temperature stability specification

The temperature stability might also be important. This is measured as a percentage or absolute voltage change per degree C. Typically, this might be in the region of 0.02% / degree C or 2 mV / degree C.

Power Management

- in-depth technical information and articles about all forms of power management and power sources from DC power supplies to DC-DC converters, batteries and green power sources.

DC power supplies

• DC power supply basics
• DC power supply specifications
• Switch mode power supply
• Linear power supply
• Digital power supply

• Uninterruptible power supply, UPS
• Power Management Bus PMBus
• Wireless / inductive charging
• Qi wireless charging
• A4WP wireless charging
• Power factor correction, PFC

Battery technology

Battery technology is an area of power management electronics that is growing in importance and sophistication with the ever increasing number of battery power electronics products.

• Battery technology basics
• Nickel cadmium / NiCad battery
• Nickel Metal Hydride NiMH battery

• Lithium-ion, Li-ion battery
• Lead acid battery
• Battery management system technology

Green energy

With the focus on reducing environmental effects of power management, technologies such as energy harvesting are been more widely investigated.

• Energy harvesting technologies

• Fuel cells

Analysis

• Modern Power Supply System Design
• Isolation & Partial Discharge Testing of DC-DC Converters for Gate Drive Applications
• Power Density Dominates Server Design: Outlook for 2016
• Wireless Charging for the Automotive Environment
• LED Lighting Power Supplies
• Digital vs Analogue Power Supplies - Finding the right balance
• Integrated Power Considerations
• Understanding custom battery packs: options and applications
• Understanding Power Supply Reliability
• The Art of Selecting Power Supplies

 

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Solar Cell, Solar Module & Solar Array Test ( DC problematic )

The goal of achieving ever increasing solar cell efficiency and reduced cost demands accurate, repeatable, fast, and reliable test results. The research, design, and development work necessary to achieving superior performing, highly manufacturable solar cells, modules and arrays requires high performance test equipment.
Producing quality solar modules and arrays in a production environment requires the characterization and sorting of solar cells. Matching the I-V performance of solar cells destined for installation in a common module or array is necessary for achieving optimum output power capability. Maximizing productivity and module or array performance means making fast, accurate and reliable measurements.
Measuring the forward I-V performance of a solar cell, module, or array involves loading the device with a constant voltage, varying the voltage in increments from zero to the device open circuit voltage (Voc), and measuring the output current. Zero volts corresponds to the maximum available short circuit current (Isc). At Voc, the measured output current of the device is zero. Measuring the reverse I-V performance of a shadowed (dark) solar device requires the application, in increments, of a reverse polarity voltage.    

Why do electronic circuits need their power supply to be DC, or rectified AC?

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I'm pretty sure the answer to this should be obvious - even to me ... It's been a while I've been reading and attempting to construct simple electronic circuits. The supply almost always is either through a battery/cell, or AC duly rectified to DC. I have the impression electronic circuits rarely ever work off an AC supply. Is this impression correct? If yes, why is an electronic circuit rarely (if ever) powered/biased using straight AC?

1. AC flips polarity very often. Most semiconductor devices have been designed with very particular polarity conditions in mind. If one were to reverse the polarity between two inputs on many different components, you would get magic smoke coming out of it. For example take mosfet operation. An NMOS is expected to block current from drain to source until the gate is activated. If you have AC across drain to source, then it allows current to flow backwards (losing gate control). It's not impossible to design an electronic circuit with active devices around AC, but it makes it much more challenging. I should also qualify this statement: many electronics circuits do have signals with AC components to them, but they usually have a DC offset to them to prevent the polarity switching. That would be something like 5VppAC with a 2.5V DC offset would be an AC signal from 0-5 V. That remains the same polarity at all times even though it's passing an AC signal. 2.   A keyword - in context with the question - is LINEARITY. Let us take the simple example of an electronic circuit, which is widely used: Transistor-based "linear" amplifiers (lumped circuits or integrated). Transistors are highly non-linear devices. In order to produce sinusoidal output signals exhibiting low signal distortion it is necessary to use only a certain part of the input-output charcteristic. Hence, we use a dc voltage/dc current to BIAS the device at a suitable operating point (within a limited quasi-linear part of the input-output function). Then, the input signal causes a swing around this operating point resulting in an acceptable output quality  3. You are right, circuit are seldom powered with AC. Some analog circuit may work on AC, but digital doesn't. This is due to the very nature of how it has been design and how it has proven to be efficient and easy to implement. There are system which uses AC signal to encode data on some very old systems, but it requires lots of high power components, which is not practical with current technology. An example would be old casino slot machines which used an analog signal to make the reels turn and the coin dispenser drop coins one by one. Also, some mechanical counters used AC signal toggling to count. Transistors as they are now are designed to be efficient with DC signals (if you consider digital data as DC, since some purist would say it actually is offset AC). It is what is the most power efficient and space-wise efficient in integrated circuits. Also, encoding data on AC signal (while possible) is much more complex than with DC signal, since you can use a simple edge detection mechanism. In order to do so with AC, you need to use peek detectors or circuits like that, which is not practical. Now if you want to understand why technology moved toward DC, consider this: imagine you are trying to turn on/off complex circuits with DC, it is easy, because your signal has only two states: full on and full off. With AC, you would have (as a guess): an AC signal or no signal. Relays could be compatible with your AC signal, but they work simply because of magnetic field. In order for your relay to remain firmly on, you would need to rectify your signal (so it doesn't swing) thus yielding rectified AC... In short, it is both due to historical and technological reasons  4.   First electron tube was the diode and the main property is to produce DC voltage from AC (one way). Triode tube is based on diode (DC) and was the first device with stable amplifyication or switching properties. This was realized controlling the electron flow from a negative cathode to a positive anode via a grid. So the weak grid voltage modulates a DC voltage (dc swing) and those an amplifier is made. This device needed mainly by Telegraphy and early Radios area . To use an AC power makes the amplification extremily coplex and finaly useless. After that a lot of applications with electron tubes introduced in the market and industry around the globe. Transistor invented as a direct replacement of triode tubes, based exactly at the same concept, and today IC’s consists of million transistors that needs a DC power. However there is a semiconductor device like Thiristor or Triac that can be powered with AC power, but in most cases needs a zero-crossing circuit with a proper input signal that should be related somehow with the frequency of the AC power and so on  5.   Most interesting circuits maintain some internal state, that means: they store information. In order to do this, the circuits needs electrical energy. Pure AC (current and voltage in phase) by its nature regularly goes through a period in which no energy is supplied. This makes it difficult to make a circuit that can store state: it is as if the circuit has to start anew every AC period. You can circumvent this problem by storing energy in some other form (magnetic, mechanic, in a capacitor, etc) but why bother? DC can supply energy all the time, so most circuits work with DC. The above is mostly about digital circuits. An analog circuit could be AC powered, but then the AC component would be present in the output, which in most cases would present a problem (especially when the output is fed into a human ear).  6. only one reason used for DC supply for meter. Basically let say one example DC supply store AC supply not be store that reason only reason . In case of AC supply needs to connection of supply that is not possible you works on a hight its ac wires required for supply of meter thats reason we shifted in DC supply which is best way of meter.Most electronic system or circuit used in DC supply that of minimum voltages. Mostly electronic Engineers are bounded of (0 to 12 V)play in that ranges of voltage thats to be up range for higher power likely heavy generator required of v (120 to 200 V) for excitation for running Alternator only minimum times required for DC supply Alternating Current (AC) vs. Direct Current (DC) ≡ Pages Contributors: ShawnHymel Favorited Favorite 24 Share Use this URL to share: Share on Google+ Share on Tumblr Submit to reddi Share on Twitter Share on Facebook Pin It Thunderstruck! Where did the Australian rock band AC/DC get their name from? Why, Alternating Current and Direct Current, of course! Both AC and DC describe types of current flow in a circuit. In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction. Most of the digital electronics that you build will use DC. However, it is important to understand some AC concepts. Most homes are wired for AC, so if you plan to connect your Tardis music box project to an outlet, you will need to convert AC to DC. AC also has some useful properties, such as being able to convert voltage levels with a single component (a transformer), which is why AC was chosen as the primary means to transmit electricity over long distances. What You Will Learn The history behind AC and DC Different ways to generate AC and DC Some examples of AC and DC applications Recommended Reading What is Electricity What is a Circuit? Voltage, Current, Resistance, and Ohm’s Law Electric Power Alternating Current (AC) Alternating current describes the flow of charge that changes direction periodically. As a result, the voltage level also reverses along with the current. AC is used to deliver power to houses, office buildings, etc. Generating AC AC can be produced using a device called an alternator. This device is a special type of electrical generator designed to produce alternating current. A loop of wire is spun inside of a magnetic field, which induces a current along the wire. The rotation of the wire can come from any number of means: a wind turbine, a steam turbine, flowing water, and so on. Because the wire spins and enters a different magnetic polarity periodically, the voltage and current alternates on the wire. Here is a short animation showing this principle:   Generating AC can be compared to our previous water analogy: To generate AC in a set of water pipes, we connect a mechanical crank to a piston that moves water in the pipes back and forth (our “alternating” current). Notice that the pinched section of pipe still provides resistance to the flow of water regardless of the direction of flow. Waveforms AC can come in a number of forms, as long as the voltage and current are alternating. If we hook up an oscilloscope to a circuit with AC and plot its voltage over time, we might see a number of different waveforms. The most common type of AC is the sine wave. The AC in most homes and offices have an oscillating voltage that produces a sine wave. Other common forms of AC include the square wave and the triangle wave: Square waves are often used in digital and switching electronics to test their operation. Triangle waves are found in sound synthesis and are useful for testing linear electronics like amplifiers. Describing a Sine Wave We often want to describe an AC waveform in mathematical terms. For this example, we will use the common sine wave. There are three parts to a sine wave: amplitude, frequency, and phase. Looking at just voltage, we can describe a sine wave as the mathematical function: V(t) is our voltage as a function of time, which means that our voltage changes as time changes. The equation to the right of the equals sign describes how the voltage changes over time. VP is the amplitude. This describes the maximum voltage that our sine wave can reach in either direction, meaning that our voltage can be +VP volts, -VP volts, or somewhere in between. The sin() function indicates that our voltage will be in the form of a periodic sine wave, which is a smooth oscillation around 0V. 2π is a constant that converts the freqency from cycles (in hertz) to angular frequnecy (radians per second). f describes the frequency of the sine wave. This is given in the form of hertz or units per second. The frequency tells how many times a particular wave form (in this case, one cycle of our sine wave - a rise and a fall) occurs within one second. t is our dependent variable: time (measured in seconds). As time varies, our waveform varies. φ describes the phase of the sine wave. Phase is a measure of how shifted the waveform is with respect to time. It is often given as a number between 0 and 360 and measured in degrees. Because of the periodic nature of the sine wave, if the wave form is shifted by 360° it becomes the same waveform again, as if it was shifted by 0°. For simplicity, we sill assume that phase is 0° for the rest of this tutorial. We can turn to our trusty outlet for a good example of how an AC waveform works. In the United States, the power provided to our homes is AC with about 170V zero-to-peak (amplitude) and 60Hz (frequency). We can plug these numbers into our formula to get the equation (remember that we are assuming our phase is 0): We can use our handy graphing calculator to graph this equation. If no graphing calculator is available we can use a free online graphing program like Desmos (Note that you might have to use ‘y’ instead of ‘v’ in the equation to see the graph). Notice that, as we predicted, the voltage rise up to 170V and down to -170V periodically. Additionally, 60 cycles of the sine wave occurs every second. If we were to measure the voltage in our outlets with an oscilloscope, this is what we would see (WARNING: do not attempt to measure the voltage in an outlet with an oscilloscope! This will likely damage the equipment). NOTE: You might have heard that AC voltage in the US is 120V. This is also correct. How? When talking about AC (since the voltage changes constantly), it is often easier to use an average or mean. To accomplish that, we use a method called “Root mean squared.” (RMS). It is often helpful to use the RMS value for AC when you want to calculate electrical power. Even though, in our example, we had the voltage varying from -170V to 170V, the root mean square is 120V RMS. Applications Home and office outlets are almost always AC. This is because generating and transporting AC across long distances is relatively easy. At high voltages (over 110kV), less energy is lost in electrical power transmission. Higher voltages mean lower currents, and lower currents mean less heat generated in the power line due to resistance. AC can be converted to and from high voltages easily using transformers. AC is also capable of powering electric motors. Motors and generators are the exact same device, but motors convert electrical energy into mechanical energy (if the shaft on a motor is spun, a voltage is generated at the terminals!). This is useful for many large appliances like dishwashers, refrigerators, and so on, which run on AC. Direct Current (DC) Direct current is a bit easier to understand than alternating current. Rather than oscillating back and forth, DC provides a constant voltage or current. Generating DC DC can be generated in a number of ways: An AC generator equipped with a device called a “commutator” can produce direct current Use of a device called a “rectifier” that converts AC to DC Batteries provide DC, which is generated from a chemical reaction inside of the battery Using our water analogy again, DC is similar to a tank of water with a hose at the end. The tank can only push water one way: out the hose. Similar to our DC-producing battery, once the tank is empty, water no longer flows through the pipes. Describing DC DC is defined as the “unidirectional” flow of current; current only flows in one direction. Voltage and current can vary over time so long as the direction of flow does not change. To simplify things, we will assume that voltage is a constant. For example, we assume that a AA battery provides 1.5V, which can be described in mathematical terms as: If we plot this over time, we see a constant voltage: What does this mean? It means that we can count on most DC sources to provide a constant voltage over time. In reality, a battery will slowly lose its charge, meaning that the voltage will drop as the battery is used. For most purposes, we can assume that the voltage is constant. Applications Almost all electronics projects and parts for sale on SparkFun run on DC. Everything that runs off of a battery, plugs in to the wall with an AC adapter, or uses a USB cable for power relies on DC. Examples of DC electronics include: Cell phones The LilyPad-based D&D Dice Gauntlet Flat-screen TVs (AC goes into the TV, which is converted to DC) Flashlights Hybrid and electric vehicles Battle of the Currents Almost every home and business is wired for AC. However, this was not an overnight decision. In the late 1880s, a variety of inventions across the United States and Europe led to a full-scale battle between alternating current and direct current distribution. In 1886, Ganz Works, an electric company located in Budapest, electrified all of Rome with AC. Thomas Edison, on the other hand, had constructed 121 DC power stations in the United States by 1887. A turning point in the battle came when George Westinghouse, a famous industrialist from Pittsburgh, purchased Nikola Tesla’s patents for AC motors and transmission the next year. AC vs. DC Thomas Edison In the late 1800s, DC could not be easily converted to high voltages. As a result, Edison proposed a system of small, local power plants that would power individual neighborhoods or city sections. Power was distributed using three wires from the power plant: +110 volts, 0 volts, and -110 volts. Lights and motors could be connected between either the +110V or 110V socket and 0V (neutral). 110V allowed for some voltage drop between the plant and the load (home, office, etc.). Even though the voltage drop across the power lines was accounted for, power plants needed to be located within 1 mile of the end user. This limitation made power distribution in rural areas extremely difficult, if not impossible. Nikola Tesla George Westinghouse ) With Tesla’s patents, Westinghouse worked to perfect the AC distribution system. Transformers provided an inexpensive method to step up the voltage of AC to several thousand volts and back down to usable levels. At higher voltages, the same power could be transmitted at much lower current, which meant less power lost due to resistance in the wires. As a result, large power plants could be located many miles away and service a greater number of people and buildings. Edison’s Smear Campaign Over the next few years, Edison ran a campaign to highly discourage the use of AC in the United States, which included lobbying state legislatures and spreading disinformation about AC. Edison also directed several technicians to publicly electrocute animals with AC in an attempt to show that AC was more dangerous than DC. In attempt to display these dangers, Harold P. Brown and Arthur Kennelly, employees of Edison, designed the first electric chair for the state of New York using AC. The Rise of AC In 1891, the International Electro-Technical Exhibition was held in Frankfurt, Germany and displayed the first long distance transmission of three-phase AC, which powered lights and motors at the exhibition. Several representatives from what would become General Electric were present and were subsequently impressed by the display. The following year, General Electric formed and began to invest in AC technology. Edward Dean Adams Power Plant at Niagara Falls, 1896 Westinghouse won a contract in 1893 to build a hydroelectric dam to harness the power of Niagara falls and transmit AC to Buffalo, NY. The project was completed on November 16, 1896 and AC power began to power industries in Buffalo. This milestone marked the decline of DC in the United States. While Europe would adopt an AC standard of 220-240 volts at 50 Hz, the standard in North America would become 120 volts at 60 Hz. High-Voltage Direct Current (HVDC) Swiss engineer René Thury used a series of motor-generators to create a high-voltage DC system in the 1880s, which could be used to transmit DC power over long distances. However, due to the high cost and maintenance of the Thury systems, HVDC was never adopted for almost a century. With the invention of semiconductor electronics in the 1970s, economically transforming between AC and DC became possible. Specialized equipment could be used to generate high voltage DC power (some reaching 800 kV). Parts of Europe have begun to employ HVDC lines to electrically connect various countries. HVDC lines experience less loss than equivalent AC lines over extremely long distances. Additionally, HVDC allows different AC systems (e.g. 50 Hz and 60 Hz) to be connected. Despite its advantages, HVDC systems are more costly and less reliable than the common AC systems. In the end, Edison, Tesla, and Westinghouse may have their wishes come true. AC and DC can coexist and each serve a purpose.   You should now have a good understanding of the differences between AC and DC. AC is easier to transform between voltage levels, which makes high-voltage transmission more feasible. DC, on the other hand, is found in almost all electronics. You should know that the two do not mix very well, and you will need to transform AC to DC if you wish to plug in most electronics into a wall outlet. With this understanding, you should be ready to tackle some more complex circuitry and concepts, even if they contain AC. Types of Power Supplies       Regulated power supplies usually refers to a power supply capable of supplying a variety of output voltages useful for bench testing electronic circuits, possibly with continuous variation of the output voltage, or just some preset voltages. Almost all electronic devices used in electronic circuits need a dc source of power to operate. A regulated power supply essentially con­sists of an ordinary power supply and a volt­age regulating device. The output from an ordinary power supply is fed to the voltage regulating device that provides the final output. The output voltage remains constant irrespective of variations in the ac input voltage or variations in output (or load) current but its amplitude is varied according to the load requirement. Some of these types of power supplies are discussed below. SMPS The industry drive to more diminutive, lighter and more productive electronics systems has prompted the advancement of the SMPS, nothing but Switch Mode Power Supply. There are some topologies normally used to actualize SMPS. A switched-mode power supply is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. In this by employing high switching frequencies, the sizes of the power transformer and associated filtering components in the SMPS are dramatically reduced in comparison to the linear. DC to DC converters and DC to AC converters belong to the category of SMPS. In a linear regulator circuit the excess voltage from the unregulated dc input supply drops across a series element and hence there is power loss in proportion to this voltage drop, whereas in switched mode circuit the unregulated portion of the voltage is removed by modulating the switch duty ratio. The switching losses in modern switches (like: MOSFETs) are much less compared to the loss in the linear element. The majority of electronic DC loads are supplied from standard power sources. Unfortunately, standard source voltages may not match the levels required by microprocessors, motors, LEDs, or other loads, especially when the source voltage is not regulated like battery sources and other DC as well AC sources. SMPS Block Diagram: The main idea behind a switch mode power supply (SMPS) can be easily understood from the concept of conceptual explanation of a DC-DC converter. If the system input is AC then the 1st stage is to convert to DC. This is called rectification. The SMPS with a DC input does not require the rectification stage. Many newer SMPS will use a special Power factor correction (PFC) circuit. By following the sinusoidal wave of the AC input, we can make the input current. And rectified signal is filtered by the input reservoir capacitor to produce the unregulated DC input supply. The unregulated DC supply is given to high frequency switch. For higher frequencies, components with more level capacitance and inductance are required. In this MOSFETs may be used as synchronous rectifiers, these have even lower conducting stage voltage drops. The high switching frequency, switches the input voltage across the primary of the power transformer. The drive pulses are normally fixed frequency and variable duty cycle. The output of the secondary transformer is rectified and filtered. Then it is sent to output of the power supply. Regulation of the output to provide a stabilized Dc supply is carried out by the control or feedback block.    Most SMPS. Systems operate on a fixed frequency pulse width modulation basis, where the duration of the on time of the drive to the power switch is varied on a cycle by cycle basis. The pulse width signal given to the switch is inversely proportional to the output of the output voltage. The oscillator is controlled by the voltage feedback from a closed loop regulator. This is usually achieved by using a small pulse transformer or an opto-isolator, hence adding to the component count. In an SMPS, the output current flow depends on the input power signal, the storage elements and circuit topologies used, and also on the pattern used to drive the switching elements. By using LC filters the output waveforms are filtered. Advantages of SMPS: Greater efficiency because the switching transistor dissipates little power Lower heat generation due to higher efficiency Smaller in size Lighter weight Reduced harmonic feedback into the supply main Applications of SMPS: Personal computers Machine tool industries Security systems   Along with SMPS another circuit for regulated supply and back up purpose is discussed below. Linear Power Supplies Work bench power supply with backup A work bench power supply is a DC power supply unit which can provide different regulated DC voltages which is used for the purpose of testing or trouble shooting. A simple circuit of regulated power supply with battery backup has been designed which can be used as a work bench power supply. It gives 12 volts, 9 volts and 5 volts regulated DC to power prototypes while testing or trouble shooting. It also has a battery back up to continue the work if power fails. Low battery indication is also provided to confirm the battery status. It Consists of Three Major Sections: A rectifier and a filter unit which converts the AC signal to regulated DC signal using the combination of transformer, diodes and capacitors. A Battery used as an alternative, which can be recharged during the main power supply and used as a source of power in case of absence of main supply. A battery charge indicator which gives an indication of the battery charge and discharge. A 14-0-14, 500 mA transformer, rectifier diodes D1, D2 and smoothing capacitor C1 form the power supply section. When the mains power is available, D3 forward biases and provides more than 14 volts DC to IC1 which then gives regulated 12 volts that can be tapped from its output. At the same time, IC2 gives regulated 9 volts and IC3 regulated 5 volts from their outputs. A 12 volt 7.5 Ah rechargeable battery is used as backup. When mains power is available, it charges via D3 and R1. R1 limits the current for charging. To prevent overcharging, if the power supply is switched for long time and the battery is not using, Trickle charge mode is safe. The charging current will be around 100-150 mA. When the mains power fails, D3 reverse biases and D4 forward biases and battery takes the load. A UPS battery is an ideal choice.    Zener diode ZD and the PNP transistor T1 form the low battery indicator.  This kind of arrangement is used in Inverters to indicate the low battery status. When the battery voltage is above 11 volts, Zener conducts and keeps the base of T1 high so that it remains off. When the battery voltage drops below 11 volts, the Zener turns off and T1 forward biases. (Zener diode conducts only when the voltage through it is above 1 volt or higher than its rated voltage. So here the 10 volt zener conducts only if the voltage is above 11 volts.) LED then lights to indicate the need for battery charging. VR1 adjusts the correct off point of the Zener .Charge the battery fully and measure its terminal voltage .If it is above 12 volts, adjust the wiper of the preset VR1 in the middle position, and slightly turn it till LED turns off. Do not turns the Preset to the extreme ends. Battery should always contain sufficient voltage above 12 volts (Fully charged battery will show around 13.8 volts) then only IC1 gets sufficient input voltage.    In this circuit diagram, given a regulated power supply circuit that though a fixed-voltage regulator U1-LM7805 not only gives a variable but also auto switch off features. This is achieved by a potentiometer which is connected between the regulator IC common terminal and ground. For every 100-ohm increment in the in-circuit value of the resistance of potentiometer RV1, the output voltage increases by 1 volt. Thus, the output varies from 3.7V to 8.7V (taking into account 1.3-volt drop across diodes D7 and D8). When no load is connected across its output terminals, then the supply is that it switches itself off. This is achieved with the help of transistors Q1 and Q2, diodes D7 and D8, and capacitor C2. When a load is connected at the output, potential drop across diodes D7 and D8 (approximately 1.3V) is sufficient for transistors Q2 and Q1 to conduct. As a result, the relay gets energized and remains in that state as long as the load remains connected. At the same time, capacitor C2 gets charged to around 7-8 volt potential through transistor Q2. But when the load ( a lamp here in series with S2 )  is disconnected, transistor Q2 is cut off. However, capacitor C2 is still charged and it starts discharging through base of transistor Q1. After some time (which is basically determined by value of C2), relay RL1 is de-energized, which switches off the mains input to primary of transformer TR1. To resume the power again, switch S1 Push button should be pressed momentarily. The delay in switching off the power supply varies directly with the capacitor value. A transformer with a secondary voltage of 12V-0V, 250mA was used, it can nevertheless be changed as per user’s requirement (up to 30V maximum. and 1-ampere current rating). For drawing more than 300mA current, the regulator IC must be fitted with a small heat sink over a mica insulator. When the transformer’s secondary voltage increases beyond 12 volts (RMS), potentiometer RV1 must be re-dimensioned. Also, the relay voltage rating should be predetermined. Variable Power Supply using LM338 DC power supply is often required to power electronic devices. While some require a regulated power supply, there are many applications where the output voltage needs to be varied. Variable power supply is the one where we can adjust the output voltage according to the requirements. Variable power supply can be used in many applications like applying variable voltage to DC motors, applying variable voltages to High voltage DC-DC converters to adjust the gain, etc. It is mostly used in testing electronic projects. The main component in a variable power supply is any regulator whose output can be adjusted using any means like a variable resistor. Regulator ICs like LM317 provide a adjustable voltage from 1.25 to 30V. Another way is using LM33 IC. Here a simple variable power supply circuit using LM33 is used which is a high current voltage regulator. LM 338 is the high current voltage regulator that can supply an excess of 5 amperes current to the load. Output voltage from the regulator can be adjusted from 1.2 volts to 30 volts. It requires only two external resistors to set the output voltage. LM 338 belongs to the LM 138 family which is available in 3 terminal package. It can be used in applications such as adjustable power supply, constant current regulator, battery chargers etc. A high current variable supply is essential to test high power amplifier circuits, during trouble shooting or servicing. This allows the power supply to be used with high transient loads and speeds start up under full load condition. The over load protection remains functional even if the adjust pin is disconnected accidentally. Circuit Description The basic circuit consists of the following parts: A Step down Transformer to cause a drop in ac voltage of 230V. A rectifier module to rectify the AC signal. A smoothing electrolyte capacitor to filter out the dc signal and remove the ac ripples. LM338 A variable resistor Working of the Circuit The variable power supply using LM338 positive voltage regulator is shown below. The power is derived from a 0-30 volts 5 ampere step down transformer. The 10 amps rectifier module rectifies the low volt AC to DC which is made ripple free by the smoothing capacitor C1. Capacitor C2 and C3 improves the transient responses. Output voltage can be adjusted through the Pot VR1 to the desired voltage from 1.2 volts to 28 volts.D1 protects against C4 and D2 protect against C3 when switched off. Regulator requires heat sink. Vout = 1.2V (1+ VR1 / R1) + I AdjVR1.   Unregulated Linear Power Supply Unregulated power supplies contain a step-down transformer, rectifier, filter capacitor, and a bleeder resistor. This type of power supply, because of simplicity, is the least costly and most reliable for low power requirements. The main disadvantage is that the output voltage is not constant. It will vary with the input voltage and the load current, and the ripple is not suitable for electronic applications. The ripple can be reduced by changing the filter capacitor to an LC (inductor-capacitor) filter, but the cost becomes more. Unregulated Linear Power Supply Input transformer The input transformer is used to convert the incoming line voltage down to the required level of the power supply. It also isolates the output circuit from the line supply. Here we are using a step-down transformer. Rectifier The rectifier used to convert the incoming signal from an AC format into raw DC. Please refer these links, Different types of rectifiers available are half wave rectifier and full-wave rectifier. Filter Capacitor The pulsated DC from the rectifier is fed to the smoothing capacitor. It will remove the unwanted ripples in the pulsated DC. Bleeder Resistor Bleeder Resistor is also known as a power supply drain resistor. It is connected across the filter capacitors to drain their stored charge so that the power system supply is not dangerous. Regulated Linear Power Supply Regulated linear power supplies are same to the unregulated linear power supply except that a 3-terminal regulator is used in place of the bleeder resistor. The main aim of this supply is to provide the required level of DC power to the load. The DC power supply uses an AC supply as the input. Different applications require different levels of attributes voltages, but nowadays the DC power supplies provide an accurate output voltage. And this voltage is regulated by an electronic circuitry so that it provides a constant output voltage over a wide range of output loads. Regulated Power Supply Block Diagram Here the basic circuit diagram for Regulated Linear Power Supply given below. Regulated Linear Power Supply Smoothing Once rectified from an AC signal, the DC needs to be smoothed to remove the varying voltage level. Large value capacitors are generally used for this purpose. Voltage Regulator A linear regulator has an active (BJT or MOSFET) pass device (series or shunt) controlled by a high gain differential amplifier. It compares the output voltage with a precise reference voltage and adjusts the pass device to maintain a constant level output voltage. There are two main types of linear power supplies. Read more about Different Types of Voltage Regulators with Working Principle. Series regulator  This is the most widely used regulators for linear power supplies. As the name implies a series element is placed in the circuit as shown in below figure, and its resistance varied via the control electronics to ensure that the correct output voltage is generated for the current taken. Concept of the Series Voltage Regulator or Series Pass Regulator Shunt regulator The shunt regulator is less widely used as the main element within a voltage regulator. In this, a variable element is placed across the load as shown in below. There is a source resistor placed in series with the input, and the shunt regulator is varied to make sure that the voltage across the load remains constant.           Switch Mode Power Supply (SMPS) The SMPS has a rectifier, filter capacitor, series transistor, regulator, transformer, but is more complicated than the other power supplies that we have discussed. Switching Mode Power Supply The above-shown schematic is a simple block diagram. The AC voltage is rectified to an unregulated DC voltage, with the series transistor and the regulator. This DC is chopped to a constant high-frequency voltage which enables the size of the transformer to be dramatically reduced and allows for a much smaller power supply. The disadvantages of this type of supply are that all of the transformers have to be custom-made and the complexity of the power supply does not lend itself to low production or economical low power applications. Please refer this link to Know All About SMPS. Switch Mode Power Supply (SMPS) Uninterruptible Power Supply (UPS) UPS is a Backup power source that, in the case of power failure or fluctuations, allows enough time for an orderly shutdown of the system or for a standby generator to start up. UPS consists usually of a bank of rechargeable batteries and power sensing and conditioning circuitry. Furthermore read about the UPS circuit diagram and different types, please refer this link to read more about UPS Circuit Diagram and Working. Uninterruptible Power Supply (UPS) This is all about different types of power supplies which include linear power supplies, switching mode power supply, uninterrupted power supply. Furthermore, to implement electronics and electrical projects or any information regarding the types of power supply fell free to give your feedback to give your suggestions, comments in the comment section below.