hyland 0-30v psu output osillates

[paul .a larner]

ive built this psu as per the schematic,the issues i have are,the output is 30v  with the voltage pot fully ccw,if i turn the current piot almost fully ccw the output drops to 0 with the led on,if i turn the current slightly cw it oscillates from 0v to 30v about every 3 seconds,the led flashes in time with this also,im using mc34071 opamps ,the only thing i havent changed is d7,its stil the 5.1v zenner,q2 is a bd137 and im using 4x 2n3055 pass transistors with 0.1r emitter resistors,any ideas on whats causing this wierd behaviour?,cheers m3vuv.

 

[HarryA1]

Do you have a better schematic? It's hard to read this one. Can you reference where you got the schematic or the kit?

 

[Guy Shemesh]

Hi Paul

Check your VRef circuit around U1, it seems very suspicious to me. To which Vref voltage you are designing for ? 

I would replace this small circuit altogether.. seems like a mistake in the schematics there. 

Best of Luck

Guy

ePiccolo Engineering

 

[paul .a larner]

heres a better schematic i hope,the first is the same as mine,my rv1 is 5k,2nd schem is origina,also i still have q1 in my version,should i remove it?,cheers m3vuvl.





heres a better original version

 

[HarryA1]

At 3 seconds pulsing you could see that with a multimeter. I would start at the output of U2 looking for pulses; if so look at its input and likewise back to U1 and U2 outputs and inputs. The op amps U1 - U3 (TL081) are short circuit protected.

"When shutdown occurs and less power is dissipated, the circuit cools as desired. The shutdown circuit is then disengaged and the circuit heats up. Again shutdown occurs and so forth."

 

[lafnian1990]

ive built this psu as per the schematic,the issues i have are,the output is 30v  with the voltage pot fully ccw,if i turn the current piot almost fully ccw the output drops to 0 with the led on,if i turn the current slightly cw it oscillates from 0v to 30v about every 3 seconds,the led flashes in time with this also,im using mc34071 opamps ,the only thing i havent changed is d7,its stil the 5.1v zenner,q2 is a bd137 and im using 4x 2n3055 pass transistors with 0.1r emitter resistors,any ideas on whats causing this wierd behaviour?,cheers m3vuv.

View attachment 43994

It seems to me that you can set a slider rheostat to control