Category: Symmetric Power Supply 0-70V @ 5A

Symmetric Power Supply 0-70V @ 5A

I want to build a new symmetrical power supply with the following demands:

-PC controlled via USB

-Current limited


-The set value and the actual value of the voltage and current can be read on lcd displays.

My order of transformers at pollin:
pollin bestelling

The start of the build (I mounted the transformers on a piece of treaded rod and mounted it on a angle bracket)
pollin bestelling
pollin bestelling

Symmetric Power Supply 0-70V @ 5A – Update

I got another order today. This time from Reichelt.

reichelt bestelling
-5 MJ2955 Transistors
-8 Relays 12V 10A
-8 resistors 0.1 Ohm 5W.
-Spacers to mount the pcb’s

Symmetric Power Supply 0-70V @ 5A – Update

I mounted the resistors and transistors on the heat sink:

And I made a switching pcb.

Symmetric Power Supply 0-70V @ 5A – Update

This update is not from today but from the past year. I have done a couple of small changes and didn’t post them on the site at that time. Now it is time to finely do that.

The first change was that I mounted the transformers in the other direction. This way I’m saving space and I have wound some extra coils at 2 transformers to power the logic.

A picture of how the power supply looks like at the moment
Foto voeding

I also decided that I’m going to use rotary encoders instead of touch ic’s. Therefore I ordered some rotary encoders at Sure Electronics. I’m going to use 4 of them in this power supply.

Rotary EncoderRotary Encoder

Symmetric Power Supply 0-70V @ 5A – Update

I bought some bigger heat sink for cheap. (Thanks Ben and Robert). I have put those new heat sinks on this power supply. With this heat sink it doesn’t need a fan, because the ribs run in the other direction and the heat sink is much bigger. I cut 5cm of the case at the back and mounted the heat sinks. In the middle I’ve put a panel for the power connector and in the future a usb connector.

Nieuwe koelbloken

Nieuwe koelbloken

I also made a new switch pcb because I was not happy anymore with the old design. The triacs to switch the 230V side of the transformers are driven by an PIC12F629. I have put a low power powersupply on this pcb to generate 2*5V from the extra windings I made around the transformers.

Schema schakelprint V2

Print schakelprint V2


R1, R2, R3 220R
R4, R11 33K
R6 0R33 5W
R5 3K3
R7, R8, R9, R10 1K
C1 470µF 25V
C2 100nF
C3, C4 10µF 25V
C5, C6 1000µF 25V
C7, C8, C9, C10 100nF SMD 0805
D1 1N4007
D2 5V1
D3, D4, D5, D6 1N4007 SMD
B1, B2 rectifier
IC1 PIC12F629 (Code) (Hex)
IC2 7812
IC3 7912
K1, K2, K3, K4 Relays
LED1 LED 5MM red
Q1, Q2, Q3, Q4 BC848 SMD
T1, T2, T3 TIC206D

Print schakelprint V2

Print schakelprint V2

Print schakelprint V2

Print schakelprint V2

Symmetric Power Supply 0-70V @ 5A – Update

After a long time I restarted building on this power supply. I found a circuit where I’m going to base it on.


I’m not going to use this circuit exactly, but the main part I do.

In this design they used TIP142 transistors. In my version I used MJ2955 transistors. I was doubting if I would change the design or change the transistors on the heat sink. After a lot of thinking I opted for the second option. The new transistors are mounted directly on the heat sink, where the old ones used an bracket. This should provide a better cooling.


I didn’t trust the big capacitors I first planned to use any more. 1 of the 2 is so dehydrated that if you shake it you hear the inners rumbling louse. Instead of buying new big capacitors I opted to buy a few smaller ones. This is cheaper and gives a lower ESR. To mount them I made a pcb. Per side I use 3 capacitors of 3300µF 100V. That gives a capacity of 9900µF per side, this should be more than enough.


The next update will be the analog print. This design is 90% ready so it should not take too long (if no other project gets in between.)

Symmetric Power Supply 0-70V @ 5A – Update

This update was already planned in October 2009, but I didn’t put it on my site until now.

I made a pcb for the help power supply. First I added a few extra coils on the main transformers, but the voltage was too low, so I removed them and bought some print transformers

The pcb:


The analog print is also finished

When I wanted to test the analog print I looked at my circuit drawings before. Then I noticed that the analog print works on 2*5V while the power supply outputs 2*12V. So I designed the digital pcb and put a 7805 and a 7905 voltage regulator on that.

I made a small pcb to connect the lcd with the digital pcb. The connector from the lcd had a two small pitch to solder strong wire to it. So I glued the pcb on the lcd, connected it with small wires to the lcd and soldered “big strong” wires on it to go to the digital pcb.