Need help with bench PS

[Deleted member 49011]

Is the heat sink the transistor is on actually pressed up against the case with thermal material between it ? The screw are isolated by the plastic washers , but pressing the heatsink up against the case with thermal material on and That's what it looks like in the picture wont guarantee isolation from the heatsink , you need washers on both sides .

If that's not the case , then ignore this post : P

 

[Zeebit]

Thermal compound is the only thing between the transistor and the heatsink so they are connected but the heatsink is insulated from the chassis.

 

[djQUAN]

I found the culprit on your problem with the CC not working on low voltages.

Your op amp V+ supply is connected to the output. Since it is powered from the output, with a dead short, the op amp is running on a really low supply voltage.

I put in a solder jumper in mine for a reason and tested it. Mine has the op amp + supply powered from the main high current rail and the - connected to the negative supply.

As for the oscillation, I believe having the board directly on top of the transformer has something to do with it. You should test it placed away from the transformer. And also the 0.2ohm shunt resistor leads are too long. It should be mounted on the board with short leads as it is part of the op amp feedback.

 

[Zeebit]

So I need to power the op amp straight from the main power rail and remove the connection to Vout?

Edit: djQUAN, I've connected the op amp V+ supply to the main power rail (after the filter caps) and disconnected it from the 317's Vout. The ouput voltage is now stuck at maximum. Do I need to connect the op amp V+ supply to both the main power rail and the 317's Vout at the same time?

another edit: I've connected the op amp V+ supply both to the main power rail and the 317's Vout. The voltage output is still stuck at max and its gone into CC mode.