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UCC28510: It does not start PWM by flyback converter

Ilja Galkin
Prodigy 40 points
Part Number: UCC28510


Hi!
I'm doing a device - LED driver: 22V and 4A. The design of my device is almost completely identical to the reference design from the datasheet. When you start the device using the lamp it lights up and flashes showing short-circuit and overcurrent. At the gate of the transistor GT1 is present for PFC PWM the desired frequency (200 kHz), but the duty cycle always >90% and approaches 100%, creating a short circuit. At the gate of the transistor flyback Converter PWM is missing and there is always 0V.
Tell me what can be the error? I will be grateful for your help and advice!

My design: LED control.pdf

  • 0
    TI__Mastermind 40580 points
    Hello Ilja,

    I have notified the appropriate team of your issue and you should receive a response from one of them soon.
    If they cannot find the error after examining the schematic diagram, I anticipate that they will request oscilloscope waveforms.
    Please prepare to acquire various waveforms in advance, to help speed up debug.

    Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    TI__Mastermind 34465 points

    Hi Ilja,

    I would like to see some waveforms. The bus voltage is set at about 430V. What does this look like at startup ?

    The pfc stage should start up with about 110Vdc on the bus. This corresponds to about 80Vac input.

    Please measure the voltage across C28 .

    You should  really begin testing your power supply with a variable resistive load. I don't know what your LED load looks like but a string of LEDs is a constant voltage load and you cannot simply connect it to fixed voltage (23V) output.

    Please look at the no load condition and slowly increase the load in,say, 50 Ohm steps.

    Regards,

    John Griffin

  • 0 in reply to John Griffin1
    Prodigy 40 points

    Thanks for the quick response, John!

    1) I changed R3 and R7 to the resistors 510 kOhm. This value for 390V

    2) I enable on the device when the line voltage is 230V.

    The signals are measured with no output load:

    1) Capacitor C28, the signal amplitude is about 320V -

    2) Gate VT2 -

  • 0 in reply to John Griffin1
    Prodigy 40 points
    When the load (50, 100 Ohm and lamp) is connected, the situation is not changed.
  • 0 in reply to John Griffin1
    Prodigy 40 points

    It's waveform on the pin number 9 (VCC) at startup -