benny8902

All OpAmps are the same, MC34071. You know, it doesn't bother me much that the LED is on, as long as the rest is working like a charm. ;)

Problem solved. I have replaced the BD139 and added a heat sink. Now it works great. Thank you for your help and for the design. Just one more thing. My current limiting LED stays on all the time, though the current is not limited. When it goes into limiting stage, the LED lights brighter. What could I do to turn it off when it is not needed to be on? Voltage divider made out of 10K and 1K resistors? I have unconnected the LED and measured 19VDC on the pins in normal stage, 29VDC in current limit.

No way the heat sink would be too small. See the pictures attached. Also I have noticed that U2 gets hot. Any ideas, why?

The transformer is just fine, it's a 30$ 150VA toroidal transformer. It's good quality. Something else was the problem. I have found it. I have integrated a multimeter on the same board, I have mounted a 7824, a 7812 and a 7805 for the uC and the LCD display. It wasn't a good solution. When I was connecting the display, the output voltage was rising quickly, so i've bought a 5W 20V zener diode and a 5W 220 Ohms resistor for voltage regulation. This way it worked just perfectly. Now I have another problem. I have shorted the output to see the value of the current and I think I blew it. Now the output voltage is 39.6V, no matter what. Are the MC34071s blown? Or one of them?

Hello. I built it, it works, but it doesn't work correctly. Input voltage on C1 rises up to 57V!!! And I don't know why. Is it because R1 has 22k instead of 2.2k? The lady from the electronics shop messed up the values. Output voltage varies from 0-30V, though. Should I be worried about the input voltage?

It's because I already have all the parts, but the capacitor. Also in the country I live 12000uF capacitors are a bit hard to get. I could order one from Farnell, UK, but the delivery would cost me as much as the capacitor and it's not worth it. Thank you for your replies, I will try with the one I can get. I hope it will be ok.

So I should use a 2200uF capacitor in parallel? Would that be ok?

audioguru, I have an other question: does C1 have to be exactly 12000uF? I've found only 10000uF. Do I have to add two more 1000uF in parallel (or one 2200uF [?]) or the circuit will work without problems only with the 10000uF capacitor?

What if the transformer is bigger? Like 150VA. would that be a problem?