0-30V Power Supply - doesn't work

[RubicK]

Hello, i have made this power supply and it doesn't work. When i turn it on, U2 is heating very much, current is around 100mA, potensiometers doesn't do anything, voltage on output is abou 0,2V. I have checked PCB and connection of each part, but i didn't found a mistake, please help i realy don't know what to do.

Thank you,
RubicK, Czech Republic

 

[audioguru2]

Hi Rubick,
Welcome to our forum. ;D
U2 would get hot if Q1 is conducting when it shouldn't. Also, if Q1 is conducting then the output voltage will be very low like your project.
Check Q1, R13, R14 and the parts that make the negative 5.6V supply.

 

[RubicK]

I have checked parts you have written, but i have nothing found. I am a beginner in electronics, so it is hard form me to find a mistake. I tryed to disconnect Q1 from the PCB. Voltage on output was about 30V but i couldn't regulate it. Can you also tell me what parts makes that 5,6V negative Voltage? Thanks

 

[audioguru2]

Hi Rubick,
Disconnecting Q1 made the output voltage high so the negative 5.6V supply must not be working.
This sketch shows its parts and how they work with each half-wave from the transformer.

View attachment 38123

 

[RubicK]

Oh thats unbelievable! I have been bulding this supply according translated article:

http://www.hw.cz/Teorie-a-praxe/Konstrukce/ART1438-Napajeci-zdroj-0-30V-s-regulovatelnym-proudem-2mA--3A.html

Author of this text made a mistake in part list, he wrote that R3 is 220kOhm instead of 220 Ohm, could this be that mistake? i measured voltage in front of R3 and it was about 6,1V then i measured it behind and it was about 0,6V

 

[RubicK]

I founded next 2 errors: R2 must be 82Ohms instead of 82k, and R17 must be 33Ohm instead of 33k!!!

I hope that this errors couldn't damage any part on PCB...

 

[audioguru2]

A copy of a copy isn't the same as the original, is it?
Check all parts values with the parts list in our projects section. Then your project will probably work as poorly as others that were built. Then look at the topic about fixing it and making it more reliable in our forum.
I recommend this parts list:

View attachment 38129

 

[RubicK]

I cannot download that image, it always downloads a 0 byte file.

 

[audioguru2]

Can't you see a PNG file type? Here it is as a GIF:

View attachment 38130