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

I got another order today. This time from Reichelt.

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

I mounted the resistors and transistors on the heat sink:

And I made a switching pcb.

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

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.

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.

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.

Partlist:

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.)

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:

Mounted:

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.