Forward based on EPR-12 doesn't want to start
Hi all.
I'm still struggling with forward converter based on EPR-12 project. In attachment you find PDF with schematic. Don't concern with upper block - it's PFC but for test purposes is disabled.
When I increase input voltage up to 200VDC circuits tries to start. You can see voltage wave taken from D on oscilloscope -> attached. But after a while it stops and voltage on D is constant and equal about 200VDC. This process repeats. The only thing I can see and hear is: unstable voltage on output 5V which changes from 5 do 10 and "strange" sound -> like a "spark". Looking at C pin - voltage is also changing. Does this mean that TOP is in auto-restart mode?
I checked feedback side and I didn't found any possible problem at this side. Why is this happening? I thought that maybe main transformer is "not good enough". But I've checked this with my local supplier and also have used transformer from ERP-12 directly since my project is the same. In both cases I have exactly the same problem.
What's wrong with this?
Thanks,
Marcin
Comments
Brilliant! It appeared that I had "cold point" close to optocoupler. Now my supply is working "almost fine". Almost because I have 5.9V and 15V instead of 5 and 12V.
For the particular reason I use transformer taken from EPR-12 so it can't be this part. What other element on the schema can influence output voltage? My schema is almost the same like EPR-12. I found that I use 3.9V Zener diode in L pin circuit against 4.3V in EPR-12. Could this be the problem?
... and this is strange: described Zener diode which I used for the project is 3,9V but in EPR-12 on the schema there is 1N5229 which is 4.3V but in PIXls contains 6.8V Zener used within DLIM circuit. So which one is suitable for the project and if this Zener could be the problem for not having output 5V/12V ?
You are not getting any feedback. Check to see if you have at least 12v on C22 which gives bias for transistor output of opto coupler. If you have bias on C22 then you could place a 2K resistor directly from bias from C22 to control pin. This should make supply come up stabily so you can investigate where regulation loop is open. But first you have to make sure there is 12V on C22.