AOUT_LC PSU problem.

Testing/Troubleshooting
1

hi,

I’ve tried to build TKs PSU

http://ucapps.de/mbhp/mbhp_opl3_psu.pdf

but encountered a little problem.

The Output voltage is ok, i get my +12V and -12V from the 7812 and 7912

as well as +/- 5V cause i modified the layout a little bit.

But the transformator is getting real hot.

heres my design.

http://web7.webfeeling-server.net/PSU.gif

I use a 2x15V AC 12VA trafo.

so thats 2 times 400mA… should be enough

since the PSU has a low parts count and i double and tripple checked all connections I don’t think its a connection problem or soldering error.

do i just need a bigger trafo or what could be the cause that it becomes so hot?

best,

julian

2

Have you measured the current being supplied by the transformer?  If it’s less than 400mA per side and the transformer is still getting hot, maybe you’ve got a faulty transformer?

That layout image looks very nice, what did you use to draw it?

3

the transformer is getting hot with nothing connected to the PSU…

so there is no consumer who could pull more than 400mA…

if i don’t connect the transformer to the PSU PCB it’s not getting warm and delivers about 18V AC as it should.

the picture was made with a software called ‘lochmaster’

a breadboard layout software.

so long,

julian

4

Hi Julian,

I built a similar PSU and also had this problem. The transformer was getting hot and was also vibrating a bit. My transformer is from Conrad and they have only “2x15 V” transformers, that means it doesn´t have a real center tap but two parallel windings each giving 15 V. The problem disappeared when I changed the wiring to the transformer. You have to choose the right two of the four secondary pins to connect together to the virtual Ground.

I made myself up an explanation - no idea if this is correct: As the windings lie parallel for the whole distance, the electrons have to be “pushed” through the transformer from -15V to +15V in the same direction to not work against each other, so it is essential that you connect the end of one winding to the START of the other one.

Seppoman

5

This topic is quite old, but I had the same problem only yesterday.

I used this schematic to build the PSU, which I downloaded from the website a while ago:

It proposes the use of TWO rectifiers. The result was a humming transformator which nearly catched fire.

When I followed the link to this schematic on the website today, the proposed PSU used only ONE rectifier, so I changed my board to that.

Now the PSU seems to work fine. Is it possible, that the originally published schematic was impossible to work properly?

Regards,

Leonhard

6

Is it possible, that the originally published schematic was impossible to work properly?

yes, therefore it has been removed from my website.

Please remove it from your webserver as well

Best Regards, Thorsten.