Voltage regulators are available as easy to use three last integrated circuits – one terminal for the input voltage, one for the output voltage, and i for the ground (0V). The most commonly used are from the 78XX series – 7812 for 12 Volts, and 7805 for five Volts etc. Also of item use for renewable energy generators are very efficient low dropout regulators such equally the LM2940 serial – LM2940CT-12 for 12 Volt etc.

1 mutual shortfall of these common regulators is they are rated at just one Amp output electric current. It is unremarkably possible to apply them with college currents, but a large heatsink and/or fan is essential. Regulators for college currents than 1 Amp are available, but tend to exist expensive, and still require good heatsinking.

Power transistor used with an LM78XX voltage regulator for high currents

Pictured above is a circuit from the Fairchild LM7812 datasheet. This uses a power transistor and apower resistor to take on some of the workload enabling college currents to be regulated. With this ready, the power transistor and power resistor demand heatsinking, and selecting the correct specification of transistor and resistor, and getting everything set up is not particularly easy.

One alternative is instead to parallel connect multiple three terminal regulators, with each regulator handling up to ane Amp of electric current.

Parallel Connecting Mulitple Voltage Regulators

Voltage regulators such as the LM7812 cannot simply be connected in parallel without additional circuitry. Each voltage regulator, though nominally rated at the aforementioned voltage, will in practice output a slightly dissimilar voltage – for example, 3 LM7812's could output 11.98, 12.01, and 12.06 respectively.

This tiny deviation in voltage has the disastrous consequence of making the regulator with the everyman output voltage trying to carry all of the current. This will cause information technology'south internal thermal protection to trigger (as the regulator overheats) finer removing that regulator from the circuit and kicking off a chain reaction up through the remaining parallel-connected regulators.

Two LM7812 voltage regulators connected in parallel for a maximum output current of 2 Amp

The circuit shown in a higher place* (from the EDN article High-Current Supply uses Standard Iii-terminal Regulator) has 2 LM7812 voltage regulators continued in parallel for a maximum total output electric current of ii Amps – double the rated current of one LM7812.
* Diodes D1, D2, and D should be 1N4007 co-ordinate to the EDN article, but common 1N4001 diodes volition be fine as they are rated upward to 50V which is more than enough. The capacitors are supposed to be C=47,000uF, C1 and C2 are 4,700uF, just as a 47,000uF capactitor is expensive and physically very large we tested this regulator using a 4,700uF for C, and one,000uF for C1 and C2 and had no problems.

An even simpler fashion to parallel connect multiple voltage regulators together is to add very low (beneath 1 Ohm) ballast/equalising resistors in series with the regulator outputs. Doing and then should make the regulators share current equally and therefore operate together without problems. It is worth noting nonetheless that this approach to load balancing makes the voltage regulation a bit less accurate.

Connecting 7812's in parallel with load balancing 0.25 Ohm resistors series connected to the outputs - 6 Amp 12 V regulated.

An instance of this simplistic approach in employ can be seen in the above experimental 12V 6A power supply* in which six LM7812 regulators were connected in parallel with 0.25 Ohm load balancing resistors (fabricated upwards of 4 1 Ohm resistors in parallel) continued in series with the output from each 7812 regulator. The schematic shows the key elements in this 6 Amp 12 Volt regulator.
* The original excursion diagram was published on the Wroclaw University of Engineering science website dorsum when we first published this article in 2006/7. Unfortunately that article is no longer online.

High Electric current Variable Voltage Regulation

Where you need to have a user variable voltage output, the LM317 is an excellent adjustable voltage regulator to apply. The output voltage is adapted using a couple of resistors, and one of these resistors tin can be replaced with a potentiometer to requite an adjustable output.

Adjustable high current power supply with LM317 voltage regulator

While the LM317T for example is limited to a continuous output of i-i.5A subject to sufficient heatsinking, ane or more than power transistors can be added as shown above to make an adjustable high current power supply. Click here for full details: LM317 Adjustable Power Supply.

Comments

Hullo from Kentucky Us!

In regard to this page, I have drawn upward a couple of 78xx high current circuits you might similar to consider. I've used them for a 30amp ability supply with a 7815 regulator.

Current regulation with a 78xx regulator

High current regulator using 78xx regulator and MJE3055 NPN transistors

REUK Added Info: The MJE3055 is an NPN silicon power transistor rated at upwardly to 60V, up to 75 Watts, and upwardly to ten Amps. Click here to view the MJE3055 Datasheet for more information.
If you are unable to find the MJE3055, any NPN ability transistor with a similar rating can be used instead. Click hither to view a selection of NPN power transistors.

I have since switched to using the better LM723 regulator so that I tin can suit the voltage and information technology is far more reliable than the 78xx. I accept used the LM723 for a 105amp supply.

REUK Added Info:The LM723 is a voltage regulator rated for outputs of 150mA at an adjustable voltage from 2V to 37V. By adding transistors every bit shown in the schematics to a higher place loftier output currents at the regulated voltage can be output. Click hither to view theLM723 datasheet.
The LM723 is available in the Britain from effectually 30 pence. Click here to buy an LM723 at present.

I've learned a few things on your site so I idea I'd pass along a piffling in return.

Ken Weaver, 17th August 2009

The benefit of this outset schematic is that the output is actually regulated; the PNP is fully in the feedback loop.
However in Ken's circuit, the bases of the 3055 are regulated, but not the emitters, where the output is taken. Thus for every current ratio of 2.7 the voltage drops by 25mV.

Nick, tenth July 2012