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PMP10344: Start up issues

Part Number: PMP10344

Hi everyone.

I made a power supply based on PMP10344 with voltage and current adjustments and a new transformer. Now i'm having issues starting up the power supply, it's suposedly to start at around 90V, but in reality it only starts at around 180V. I noticed that the load makes a diference here, less load equals lower starting voltage, but I can't change that and I don't know how to solve this. Anyone have any suggestions?

  • Hi Arion, 

    The startup voltage is controlled by high voltage start up resistors and bias cap, that gets the converter started. Then the bias winding takes over from the transformer, so if you made changes to that transformer, we need to know what you did. I am asking the original designer to take a look, but we need to know what you changed to be able to help.



  • Hi Robert.
    I will attach a schematic file here.


    I hope it helps.

  • Hi Arion,

    I reviewed your schematic and had a few observations. It looks like the collector and emitter are flipped on Q3. This is supposed to speed up the turn-off timing, but it may not work as expected with the way you have it drawn.

    Also the primary inductance is much lower in your design, 128 uH down from 350 uH in the original. What is the max output current for this design?

    In regards to start-up, it will be a function of the start-up resistors and the VDD cap. Since you have two series caps with two, 1 MegOhm resistors, I would expect a relatively long time constant. That is, it may be able to start up with a low-line input, but it may take a while for the VDD cap to reach the 21 V spec to start switching. Can you take a measurement of the VDD voltage when applying a 90 Vac input to this design?



  • Hi John.

    I had not seen this difference, thank you! I will fix that.

    The max output current is 3A. When I changed the Rs1, Rs2, Rcs and Rlc to get 27V and 3A I considered the 128uH in the calculation.

    Will try to get a VDD measurement as soon as possible, but it oscillates between 8V and 21V, as expected, I saw that this means a fault is occurring, and I don't what fault could it be. 


  • Hi Arion,

    The fault may be from Q3 being flipped, have you been able to test with this change made?

    For debugging the fault condition can you also capture the AUX winding waveform? That might give insight to a possible OVP fault.



  • Hi John,

    I made the change and it worked. My turn-on voltage was 160V before and now is 75V.

    Thank you!!