Tomi Engdahl's Linear Power Supply Page
Index
Linear power supplies use dissipative regulator components
to achieve regulation. This dissipative regulation means
conversion of excessive power to heat. When using a linear
regulator you have usually an unregulated power supply which gives
somewhat higher voltage than your electronics needs. You put a
dissipative regulator between the power source and your electronics
circuit. This regulator keeps the voltage on the output stable
(as long as the input voltage is high enough). The regulator itself
converts the the power determined by voltage difference (unregulated voltage - output voltage) times output current to need.
Linear power supplies are generally easy to construct
(there are very easy to use ICs for this or they can be
built quite easily using discrete components) and can easily give
good quality output voltage (stable output voltage and
low noise). The disadvantage of them is low
effiencely (lots of heat dissipated in power supply).
The linear regulator used in regulated linear power supplies,
utilises simple techniques of controlled energy dissipation to achieve a regulated output voltage independent of line and load variation. It is, therefore, inherently inefficient, especially when a wide input voltage range has to be catered for.
When building a linear regualated power supply which takes
mains voltage and outputs low voltage, the following parts are needed;
a buly low frequency mains transformer, large heat-sinking is required to dissipate the heat generated by the regulating element and very large filter capacitors are required to store enough energy at the voltage to maintain the output for a reasonable length of time when the mains source is removed (during mains AC voltage zero crossing).
Note that linear power supplies can be a non-linear load to the mains
power. The reason for this is how the rectifier circuit and the
filtering capacitors work together with the transformer AC output.
The rectifier connected to the transformer secondary starts to
conduct when the output voltage from the transformer secondary is
higher than the voltage in the filtering capacitor. This usually
happens at 30-75 degrees from mains zero crossing depending on
the circuit load and filtering capacitor size. Usually the rectifier
stops to conduct quite quicly after the highest secondary voltage
is reached (at 90 degress from zero crossing). This means that
the current goes to the rectifier capacitor only for some
part of the mains voltage (high current then) and most of the
time no current goes to the filtering capacitor. This is clearly
a non-linear load.
- A Designer's Guide to the L200 Voltage Regulator - STMicroelectronics Application Note in pdf format
- Change improves regulators reliability - standard circuit for adjustable, 3-terminal regulators (LM317, LM350, etc) suffers from a designed-in fault: If the potentiometer R2s wiper loses contact, the regulators output goes high
- DMOS delivers dramatic performance gains to LDO regulators - LDO regulators with pnp pass elements nearly obsoleted the early npn linear regulators
- Emitter-Follower Boosts Linear Regulator's Output Current - an external emitter-follower increases the output current while maintaining the low quiescent current of this LDO regulator
- Extend the input range of a low-dropout regulator - Because of process limitations, all ICs have an input-voltage limitation. This limitation can be cumbersome when you try to step down a high supply voltage to a lower, regulated voltage using a dc/dc converter, such as a linear regulator. Adding a FET to the input of a linear regulator creates a dc/dc converter with a wider input-voltage range than the range of the regulator alone. The excess voltage and, therefore, power occurs in the FET.
- Full Wave Rectification - This article describes how full wave rectification using four diodes works.
- Full-wave DC power supply - This is a simulation of a simple DC power supply based on a full-wave rectifier. This power supply uses center-tapped transformer and two diodes. This type of circuit is also known as a biphase rectifier.
- Increasing Regulator Current - Although the 78xx series of voltage regulators are available with different current outputs, you can boost the available current output with this circuit. A power transistor is used to supply extra current to the load the regulator, maintaining a constant voltage.
- Inside a Power-Cube Transformer - How those little things convert mains AC to safe low voltage DC
- Increasing Regulator Current - you can boost the available current output of 78xx series of voltage regulators with this circuit
- Keep linear regulators in their safe zone - thermal characteristics of regulators depend on their operating conditions and the system's load
- Method of Determining Secondary Current Ratings in D.C. Circuits - This document gives you the equations for Half Wave Rectifier (HWR), Full Wave Center Tap (FWCT), Full Wave Bridge (FWB) and Dual Complementary Rectifies (DCR). Also example circuits are given. This document gives also information how to add a regulator to the power supply output.
- Power supplies - theory
- Rectifier Applications Handbook
- Transformer Facts Technical Bulletin No.1: Application Notes on Rectifier Transformers
- Understanding linear regulators - Linear regulators convert unregulated dc voltage to regulated dc voltage. are good vehicles to use to begin a voltage-regulator study.
- Unregulated Power Supply - sample circuits and some information which describes it's operation and calculation of component values
- Unregulated power supply design
- Voltage regulators (stabilizers) 78xx a 79xx by ST - warning about some possible problem if the regulator load is too low
- Zener Voltage Regulator CALCULATOR
An unregulated power supply is by far the simplest linear power supply type. It consists of a mains transformer, rectifier and a output voltage filtering capacitor.
The ac from the transformer secondary is rectified by a rectifier of some type. Typically a block rectifier or four individual diodes such as 1N4004 types are used as rectifier. In some applications a centre tapped transformer and two diodes are used for rectification. The principal advantage of a bridge rectifier is you do not need a centre tap on the secondary of the transformer.
After the rectifier the power supplies generally have some form of filtering capacitor which converts the voltage from rectifier (varies between 0V and full rectifier voltage generally at twice of mains frequency) to a smooth DC voltage.
An unregulated power supply generally gives somewhat higher output voltage when it is not loaded at all (genrally around 1.4 times nominal voltage). The output voltage starts to drop as the load increases, and they give the nominal output voltage at the nominal load current. If the load increses from this, the output voltage drips below nominal voltage until maximum output current is reached (after that some protective elements like overheating protector or fuse stops the excessive current from flowing).
In general, most devices that are battery powered can handle a voltage of at least 10% higher. And they usually work also with somewhat lower voltages. This is because most transistors and Analog ICs are designed to work within a range of voltages. This is why an unregulated power supplies can be used with many such circuits.
What is a "wall wart"? I'm sure you have a number of these things around; I sure do. These are those little (or not so little) black (but sometimes white) cubes with AC power connector blades on one face. You plug it into the wall and it converts the AC voltage to DC voltage at some specified current. Once you plug it into the AC outlet, it sits there like a black (or white) wart on your wall, thus the term of endearment, "wall wart." Typical wallwart includes an unregulated power supply as described above.
Most AC adapter is nothing more than a step down
transformer (probably a 10:1 coil ratio to get 12V AC output from 120V AC),
a bridge rectifier (to convert AC to DC), and maybe a capacitor to filter
the ripple.
Very many devices need well regulated power.
The most typival approach used electronics devices is to to use a transformers that
work directly from the domestic electricity supply at 60 Hz (in the U.S.A, 50 Hz in some other countries)
and this is followed by rectifier + regulator circuitry that uses linear regulation.
In this type of regulator a transistor, or a special IC, is used as a series resistor whose value
of resistance is controlled so as to maintain the output voltage constant despite variations in load.
This work well, is quite simple to make, but is quite inefficient as a lot of power is wasted as heat (wasted heat is define by formula: drop voltage over regulator (volts) * current taken (in amperes) = power loss (in watts)).
Linear regulation works wery well in low power applications where some lost heat is no problem
(in higher power applications switched more power supplies are nowadays preferred because of less
wasted power).
- 12 Volt 30 Amp Power Supply - This circuit uses a single 7812 IC voltage regulator and multiple outboard pass transistors (TIP2955). This power supply can deliver output load currents of up to 30 amps.
- 12V RMS to 10V Voltage Regulator - will take a 12V RMS sinusoidal input from a transformer and provide a 10V DC output at 100 mA with very good regulation
- 12 Volt to 9 Volt DC Converter
- 13.8V 20A power supply - Regulated DC power supply, short circuit safe, and with current limiter. This PSU has been especially designed for current-hungry ham radio transceivers. It delivers safely around 20Amps at 13.8V. For lower currents, a separate current limiting output, capable of 15ma up to a total of 20A has been added. The base of this design is a simple 12V regulator (7812) and power transistors.
- 48 Volt Phantom Power Supply - This is a simple 48 V regulated linear power supply design that will provide up to 60 mA of current. This circuit is based on the Texas Instruments TL783C high voltage adjustable linear regulator IC. This circuit is short circuit protected.
- 78xx regulator board - circuit board and ccircuit for making voltage regulators based on 78xx ICs, in pdf format, text in Finnish
- A constant 5 volts DC power supply - This is an example of a power supply to power anything requiring 5 volts DC. This circuit takes low voltage AC in (9-16V AC).
- Active preloading provides sinking capability - a simple add-on circuit enables a unipolar power supply, usually a current-sourcing circuit only, to sink current from a load
- Circuit reduces VCC ripple in audio band - regulator circuit which reduces noise and ripple by at least 35 dB over the audio range of 100 Hz to 20 kHz and provides a clean source of 5V power for driving audio circuits in portable applications such as cellular phones and multimedia notebook computers
- DC power supply - simple circuit based on 78xx fixed voltage regulator IC, those ICs are available for some fixed voltages between 5 and 24V
- Discrete LDO Regulator - The discrete LDO design presented here came about because of the need for an LDO (low drop-out regulator) for 5V designs. There are better performing LDO parts, but they tend to be either single sourced or expensive. This one can be made from common components. The performance parameters are very crude : 5V nominal at up to 10mA from 6-16V.
- Explanamtion and experiment about regulated DC power supply - many power supply designs for different voltages, built from discrete components
- High Current Power Supply - takes very few parts and outputs up to 10A, regulation not very good
- Increasing Regulator Current - you can boost 78xx regulator output with one power transistor
- Linear supply uses switch-mode regulation - You can use simple circuits to implement small, regulated plug-in power supplies. This basic and versatile 5V supply uses a zener diode and an emitter-follower transistor.
- Logic PSU with Over Voltage Protection - 5 volt regulated power supply for TTL and 74LS series integrated circuits, includes output overvoltage fault protection
- Low-drop regulator - outputs 5V at 1A, constructed from discrete components, in postscript file format
- MOSFET circuit ups regulator's output current - use a current mirror and a power MOSFET to increase the output-current capability of an IC-voltage regulator
- Power Supply for Preamplifiers - gives +/-15V outputs and takes power from external AC power supply
- Regulated 12 Supply - provides a regulated 12 volts at 0.5 amp to a load, built from discrete components
- Regulated 12 Volts DC Power Supply for Vacuum Tube Heaters - this 7812 based circuit circuit can be used with low-hum audio applications such as microphone preamps and for other applications that require well regulated 12 volts
- Regulated Power Supply - This circuit uses tandard 78xx series regulators
- Regulator excels in noise and line rejection - certain electronic circuits require extremely low-noise power supplies and this circuit provides very good quality power output
- Regulator generates sub-bandgap voltages - 100-mA regulator that uses a dual linear-regulator IC to produce output voltages below 1.25V from 2.9 to 5.5V input-voltage range
- Sam's Schematic Collection of various circuits - includes many regulated power supply circuits
- Simple 5V power supply for digital circuits
- The Spyder - an Eight-Output Pedalboard Power Supply - outputs regulated 9V DC
- Universal DC-DC Convertor - This circuit will generate a smaller DC output voltage from a larger DC input voltage.It is quick and simple to make and by changing the value of the zener diode, the circuit can be universally adapted to provide other output voltages. The circuit and all diagrams represent a DC convertor with 12V battery input and 9Volt DC output.
- Voltage Regulator - simple regulated 12V power supply using one transistor regulator circuit
- Zener Diode Calculator - This calculator is designed to give the wattage and resistance of the circuit power resistor, the voltage and wattage rating of the Zener diode and general design schematic for the circuit. Enter the maximum and minimum voltage inputs; enter the voltage output and the anticipated current rating. Click on Calculate and the results will be displayed.
- 0-30 VDC Stabilized Power Supply With Current Control 0.002-3A - This is a high quality power supply with a continuously variable stabilised output adjustable at any value between 0 and 30VDC. The circuit also incorporates an electronic output current limiter that effectively controls the output current from a few milliamperes (2 mA) to the maximum output of three amperes that the circuit can deliver. This feature makes this power supply indispensable in the experimenters laboratory as it is possible to limit the current to the typical maximum that a circuit under test may require, and power it up then, without any fear that it may be damaged if something goes wrong. There is also a visual indication that the current limiter is in operation so that you can see at a glance that your circuit is exceeding or not its preset limits.
- 0-30 Volt Laboratory Power Supply - This circuit provides 0-30 volts, at 1 amp, maximum, using a discrete transistor regulator with op-amp feedback to control the output voltage. This power supply has constant current mode suitable for charging batteries.
- 0 - 300V Adjustable Power suppy - This is a simple circuit which can provide an adjustable voltage source of 0 to 330 Volt. The supply is short-ciruit proof: the current is limited to about 100mA.
- 10 amp Power Supply - This is a simple regulated power supply that can give adjustable voltage from 3 volts to 18 volts. The current capacity is 10 amperes. This circuit is overcurrent protected. This circuit can be modified for higher current ratings if needed.
- 1.2-25VDC at 4A power supply schematic - built using discrete transistors and 741 opamp, read circuit description
- 1A Variabe Power Supply - This circuit takes in 240V AC and outputs a regulated DC at voltage sange of 2-15V DC up to 1.5A.
- Adjustable power supply using LM317 - voltage regulator for 1.2V to 35V output voltages and up to 1A load
- Adjustable Power Supply - well filtered variable 1.2-30 volts at 5 amps using LM338K
- Build a Variable Voltage Supply for Cheap - This is a variable voltage 1.5A supply that can be built cheaply and used for bench experimeting. With a 24VDC wall wart, this board can produce anywhere from 23V to 1.2V
- High Current Regulated Supply - uses pair of 3N3055 transistors to give out currents up to 15A
- L200 Regulator Circuit - easy to build a power supply with one single L200 IC, offers a variable current limit of up to 2 A, as well as voltage regulation
- Variable 3 - 24 Volt / 3 Amp Power Supply - regulated power supply can be adjusted from 3 to 25 volts and is current limited
- Säädettävä jännitelähde 0-24V 4A - 0-24V 4A adjustable power supply, text in Finnish
- Variable Power Supply - based on versatile L200 voltage regulator, independent voltage (3-15V) and current (10mA-2A) limits
- Variable Regulated Power Supply - This is a simple, but low-ripple powersupply, and an excellent project if you're starting out in electronics. It will suit your needs for most of your bench testing and prototype applications. The output is adjustable from 1.2 volts to about 30 volts. Maximum current is about 1.5 amp.
The circuits here are not linear port supplies, so having them here near dual polarity power supplies seemed to be a good idea.
The circuits in in this category are are generally simple switched mode power supplies.
Tomi Engdahl <tomi.engdahl@hut.fi>
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