Introduction
As is commonly the case, this supply was born of necessity. There is absolutely nothing special about the circuit, except that as shown, it is quite capable of up to 20 Amps intermittently or 10A continuous. Simply use a bigger transformer, bridge rectifier and more capacitors and output transistors to get more current. The basic circuit should be good for up to 100A or so, using a 5A TO3 regulator IC, but it can obviously be increased further (if you really do need a 500A supply!). There is no reason that the supply cannot be made smaller as well (did I hear someone say "Perish the thought." ?). Using fewer transistors and a smaller transformer it will work from 1A upwards.

This is not a project intended for beginners or powering opamps (or other similar frivolous purposes :) it is intended solely for powering (nominally) 12V car audio accessories.

Regulation is not especially wonderful. It could have been made much better, but at the risk of instability and increased complexity, particularly as the current capability is increased. As it happens, the relatively poor regulation is actually a benefit the supply is intended for testing car power amplifiers and the like, and even with the heaviest wire, there will always be some voltage drop, and this is mimicked very well by the supply.

As a result, the tests that are carried out using this supply will be much closer to reality than if a supply with perfect regulation were used. It can also be used as a battery charger (with care!), as the noload voltage is very stable.
This project requires knowledge of mains wiring. If you are unfamiliar with (or justifiably scared of) the household mains supply DO NOT ATTEMPT CONSTRUCTION.

WARNING Never use leadacid batteries indoors unless extremely good ventilation is provided. Do not smoke or allow a naked flame within 10 metres of a charging battery, as highly explosive gases are generated during charging. These batteries contain sulphuric acid, which is highly corrosive and will cause severe burns. Exercise safe working and handling practices at all times.

Description
The power supply circuit is shown in Figures 1 and 2. A 7812 positive 3terminal regulator is used for the main regulation, and this is followed by as many power emitter followers as needed for the current you require. The transistors are not critical. I used 2N3771 devices (50V, 20A, 200W) simply because I had a whole bunch of them in my junkbox. These are pretty much ideal, but I suggest that you use whatever you can get cheaply. If you use 2N3055s (as indicated in the schematic), expect to use four transistors for the first 10A, and one transistor for each additional 5A peak (or 4A continuous) output capability to ensure an adequate safety margin. The voltage rating is unimportant, as the main supply will only be about 22V with an 18V transformer. Title:POWER CONVERTER Document Type and Number:European Patent EP1814216 Kind Code:A1
Abstract:There are provided: sets of pairs of main circuit switching elements (4u), (4x) that supply power to a load, connected in series with a DC power source; freewheel diodes (5u), (5x) connected in antiparallel with these main circuit switching elements; and a reverse voltage application circuit (8) that applies reverse voltage smaller than the DC voltage source to the freewheel diodes when these freewheel diodes cut off. The reverse voltage application circuit includes a current suppression circuit (10) that suppresses the main circuit current flowing in the lowvoltage DC voltage power source on reverse recovery of the freewheel diodes.
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Inventors:MOCHIKAWA, Hiroshi,c/o Toshiba Corporation (11, Shibaura 1chome,Minatoku, Tokyo 1050023, JP)
KOYAMA, Tateo,c/o Toshiba Corporation (11, Shibaura 1chome,Minatoku, Tokyo 1050023, JP)
Application Number:EP20050806591 Publication Date:08/01/2007 Filing Date:11/15/2005 View Patent Images:Images are available in PDF form when logged in. To view PDFs, Login or Create Account (Free!) Referenced by:View patents that cite this patent Export Citation:Click for automatic bibliography generation Assignee:KABUSHIKI KAISHA TOSHIBA (11, Shibaura 1chome, Minatoku, Tokyo 1050023, JP)
International Classes:H02M7/5387; H02M7/48 Foreign References:JPH10327585B
Attorney, Agent or Firm:Hoffmann, Eitle (Patent und Rechtsanw?lte Arabellastrasse 4, 81925 München, DE)
Claims:1. A power conversion device comprising: (1) a set of pairs of main circuit switching elements that supply power to a load and are connected in series with a DC voltage source; (2) a freewheel diode connected in antiparallel with said main circuit switching element; and (3) a reverse voltage application circuit that applies reverse voltage smaller than said DC voltage source to said freewheel diode on cutoff of said freewheel diode, wherein said reverse voltage application circuit is constituted by a series circuit comprising: (a) an auxiliary power source of lower voltage than said DC voltage source; and (b) (i) a reverse voltage application switching element of lower voltage withstanding ability than said main circuit switching element, that is turned ON during reverse recovery of said freewheel diode; and
(ii) a highspeed auxiliary diode of shorter recovery time than said freewheel diode; and wherein said auxiliary circuits comprise: (i) a low voltage DC voltage power source of lower voltage than a voltage of said DC voltage source; (ii) a current suppression circuit that suppresses said main circuit current flowing in said lowvoltage DC voltage power source on reverse recovery of said freewheel diode, and that is connected in series with said lowvoltage DC voltage power source, and (iii) a high frequency capacitor of low internal impedance even in a high frequency band, connected in parallel with series circuit of a lowvoltage DC voltage power source and said current suppression circuit. there are literally thousands of dedicated IC voltage regulators. Nearly every manufacturer has a range of regulators to suit nearly every requirement. Let's look at the very common LM340X series or the equivalent 78XX series. Firstly they come in a variety of voltage ranges from 5, 12 and 15V for LM340XX and 78XX. With these devices we can build a high current power supply.
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HIGHER POWER REGULATED POWER SUPPLY
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What is a regulated power supply?
Today, there are literally thousands of dedicated IC voltage regulators. Nearly every manufacturer has a range of regulators to suit nearly every requirement.

Let's look at the very common LM340X series or the equivalent 78XX series. Firstly they come in a variety of voltage ranges from 5, 12 and 15V for LM340XX and 78XX. With these devices we can build a high current power supply.

They also come in a variety of current ratings and package sizes. Common packages are TO92, TO5, TO220 and TO3. The first two, TO92 and TO5 are generally unavailable to the hobbyist because suppliers like to keep reduced stock lines and so tend only to stock the TO220 and TO3 types. In fact you can pay more for a TO92 type (rated at 100 ma) than you would for a TO220 type (rated at 1.5A)

When you have a requirement for a project of say 12V, or even 5V if it's a digital project, then these are the types you use. LM3405, LM34012 or 7805 or 7812 are the types.

There are of course negative voltage regulators with the numbers LM320XX or 79XX which are substantially the same as those discussed here excepting they are negative. We will not consider them further.

Assume your project calls for a basic fixed 12V D.C. to operate. Looking back to our earlier tutorial we apply all the same principles. Look at the original schematic.