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PMP20588: No output voltage, mosfet doesn't switch

willem deschryver
Prodigy 10 points
Part Number: PMP20588
Other Parts Discussed in Thread: LM5022, TL431, TL431LI

Hi,

I'm a student in electronics and for a project i made an exact copy of the reference design PMP20588.

After soldering I fail to get any voltage after the transfo.

Some measerments:

Uvlo = 3,1V

Vin = 24,1 V

Vsec of transfo = 0V

Voltage across the mosfet is also 24 V so it won't switch.

I didn't soldered R4 yet to ensure i have a correct voltage before i go further with the network stuff.

Thank you for your help

Willem

  • 0 in reply to David Strasser
    TI__Intellectual 2440 points

    Willem,

    Check the voltage on the VCC pin of the LM5022.  If it is approximately 7V then the turn-on regulator is working.  Next look at the SS pin on the LM5022.  It should be approximately 5V.  If it is not, there is a fault, most likely on the current sense.   If the SS pin is at 5V, there is probably something not connected correctly with the feedback.  The COMP pin on the LM5022 should be between approximately 1-5V for the converter to switch.

    Thanks,

    David

  • 0
    Prodigy 10 points

    Hi David.

    Thank you for your help. I found the problem. D11 was wrongly placed.

    Currently i have another issue that my output voltage is only 17V when in change the voltage divider nothing changes on the output.

    When i change the resistor parallel over the octocoupler i'm able to increase the output voltage because more current flows through the octocoupler. But when i increase the load on the output, my voltage spikes to 100+ V.

    The only component that is not original is the regulated shunt, since i couldn't get a hold on the original one.

    I use the TL 431LIBEDBZRQ1

    Thanks for all the help.

    Willem

  • 0 in reply to willem deschryver
    TI__Intellectual 2440 points

    Willem,

    The TL431LI is an improved version of the TL431 and should be a drop-in replacement in the SOT-23-3 package.

    Is the optocoupler the "A" version with the 80-160% CTR?

    Check the value of the resistor in series with the opto diode.

    Thanks,

    David

  • 0
    Prodigy 10 points

    Hi,

    Resistor values are all correct.

    I have the FOD817CSD

    This will probably the problem.

    Thank you !

    Willem