Three types of multi-functional Homebrew 6/8Amps, 20- and 30 Ampere regulatable power supplies:
RE PSR28A68, PSR30A20 and PSR30A30


RE-PSR28A6
rev4.1.1

By Guy, de ON6MU


This is an easy to make power supply which has stable, clean and regulatable output voltage. By using two 2N3055 transistors we become more then 2 times the amount of amps then the power supply delivers, making it real though to brake ;). Although you could use this design to deliver 20 amps (with some modifications, see below page), I did not needed such much power. Make sure you mount them on a huge heat sink, as the 2N3055 transistors can get very hot at full load. Also use thick wires.

Although the LM-317 power regulator will kick in on shortcircuit, overload and thermal overheating, the fuses in the primary section of the transformer and the fuse F2 at the output will secure your power supply. The rectified voltage of: 30 volt x SQR2 = 30 x 1.41 = 42.30 volt measured on C1. So all capacitors should be rated at 50 volts. Caution: 42 volt is the voltage that could be on the output if one of the transistors should blow.

P1 allows you to 'regulate' the output voltage to anything between 0 and 28 volts. The LM317 lowest voltage is 1.2 volt. To have a zero voltage on the output I've put 3 diodes D7,D8 and D9 on the output of the LM317 to the base of the 2N3055 transistors. The LM317 maximum output voltage is 30 volts, but using the diodes D7,D8 & D9 the output voltage is approx 30v - (3x 0.6v) = 28.2volt.

Calibrate your build-in voltmeter using P3 and, of course, a good digital voltmeter.

P2 will allow you to set the limit of the maximum available amps at the output +Vcc. When using a 100 Ohm/1watt varistat the current is limited to approx. 3 Amps @ 47 Ohm and +- 1 Amp @ 100 Ohms.

Note:
The collectors of the finals needs to be soldered with a wire all together if the transistors even if they are isolated from the heatsink or not. If you do not isolated the finals from the heatsink, then please make sure the heatsink does not make contact with the chassis (metal casing where you plan to build the PS into).
Remember to use thick wires suitable for transfering the current needed according to the power supply you tend to build.

 

RE-PSR28A68 Power supply Schematic 1

Part list for 6/8 Amp regulatable power supply (PSR28A68):

Less maximum output voltage needed?
In operation, the LM317 develops a nominal 1.25V reference voltage, VREF, between the output and adjustment terminal.
The reference voltage is impressed across program resistor R1 and, since the voltage is constant, a constant current I1 then flows through the output set resistor R2, giving an
output voltage of

Since the 100 uA current from the adjustment terminal represents an error term, the LM317 was designed to minimize IADJ and make it very constant with line and load changes.
To do this, all quiescent operating current is returned to the output establishing a minimum load current requirement. If there is insufficient load on the output, the output will rise.

Less amps needed?
Well, without much modification you can:
- only one 2N3055, will give you 4...5 amps.
- the bridge rectifier (D1...D4) only needs 4 x 1N5401 (any +/- 3 amp diodes as only halve of the max. amp is needed, so we have some room when short-circuited)
- one 4700uF (C2) is sufficient
- F2 = 6 amp
- D5, D10 = 1N4001

The power supply insides

 

Heat sink
 Remember to isolate the transistors from the chassis/radiator! Use a radiator (heat sink) of appropriate size and surface area; insulating and heat-conducting spacer or at least a thin mica; hot adhesive and thermal paste.

Finished power supply:

 

 

Note: You can add a 3th 2N3055 and use for R9=27 Ohm, to make a 10/12 ampere power supply of the design stated above.

 

Mark, PA4M, made a 3 ampere version by using just one 2N3055 and build into a Zetagi power supply box. He reported a very good linearity of the output voltage over the entire range.

Thanks Mark for the feedback and pictures!

 

20 ampere regulatable power supply 1...30volt
RE-PSR30A20
(total revision)

RE-PSR30A20 Schematic 2

 

Major revision of the entire project.

PSR30A20/30 Specs

Today's highlight!

Part list PSR30A20 or PSR30A30
20/30 Ampere regulatable power supply (30 amp version values in blue):

Optional (and can be left out together with R9) S2, which switches between +- 5 Amps and full output current. R9 can be replaced by a 47 or even a 100 ohms potentiometer of 4watt for adjustable output amps, but be sure you can reach 0 ohms as any resistance limits the max. output current!

The relay is used to switch off the power supply voltage when the mains (S1) are/is switched off. So no delay do to the discharge of C2, and so preventing output voltages from not return to zero immediately. You can leave it out if you do not care about slow discharge of the voltage when turned off, or add a heavy duty secondary switch.

A MB2504 is used as it is a 25 ampere rectifier bridge which also should be cooled. Or you could use eight BYW29 8 amp diodes (TO220 pinning) mounted on a heat sink.

Mount a little heatsink on the LM317 IC. Be sure that C3, C4, C5 and C6 are mounted as close as possible to LM317!

Use heavy bread wires that can deliver 20/30 amps

Remember to isolate the 2N3055 transistors from the chassis!
Use a radiator (heat sink) of appropriate size and surface area; insulating and heat-conducting spacer or at least a thin mica; hot adhesive and thermal paste.
20/30 amp needs proper large heat sink and remember to use pretty thick wires!
Note:
The collectors of the finals needs to be soldered with a wire all together if the transistors even if they are isolated from the heatsink or not. If you do not isolated the finals from the heatsink, then please make sure the heatsink does not make contact with the chassis (metal casing where you plan to build the PS into).

This revision has been improved with a feedback control on the output voltage (Q5, R11,C11,D8), giving increased stability. However, the lowest voltage is about 1.35v, while in the previous design (schematic 1) the voltage can by zero.
When problems with spikes or irregular voltage control then try to disconnect Q5 and take it from there.

Special thanks to Andrew B. concerning the feedback of the output voltage.

Less maximum output voltage needed?
In operation, the LM317 develops a nominal 1.25V reference voltage, VREF, between the output and adjustment terminal.
The reference voltage is impressed across program resistor R1 and, since the voltage is constant, a constant current I1 then flows through the output set resistor R2, giving an
output voltage of

Since the 100 uA current from the adjustment terminal represents an error term, the LM317 was designed to minimize IADJ and make it very constant with line and load changes.
To do this, all quiescent operating current is returned to the output establishing a minimum load current requirement. If there is insufficient load on the output, the output will rise.

More of my projects: 78h05_powersupply

This is how Ivan Lops made it:
click to enlarge
Many thanks Ivan!!

4 ampere regulatable power supply 1...18volt
RE-PSR4A18

This how Morten LA9DNA build it:
click to enlarge
Thanks Morten!

 

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