This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TL2845: Frequency Change at Light Load

Part Number: TL2845

Hello,

We’re seeing the PWM switching frequency increase by 2x at no-load / light-load in a flyback topology.
Is this expected behavior?

There is a comment in the datasheet discussing TLx844 and TLx845 output frequency is one-half the oscillator frequency.
Could this be the issue?

Thank you, Keith

  • Keith,

    Thanks for the note. This is a fixed frequency controller and should not do that. The internal oscillator relative to the output isn't really a concern here.

    Sometimes we see frequency DROP at light load even as a fixed frequency controller  if duty required is less than min on time so it starts dropping pulses but not INCREASING frequency.

    They have repeated this with multiple units?

    Can they try adding small pre-load resistor to output to make sure this isn't a stability issue?

    Regards

    John

  • Hello,

    When we tested the design, it seemed to be unstable.  There would be bursting of the output as you increased the output current, and eventually the supply would enter a state where it would over-current and shutdown.

    We found the issue to be an incorrect diode was populated in the circuit.  It was not an ultra-fast recovery type, so it was continuously conducting.

    Thank you very much for your help.  Keith

  • Keith,
    Thanks for closing the loop here with us! (Pun absolutely intended. ) :)
    Glad y'all got it figured out.
    Regards,
    John