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Thread: TL494 halbridge like ATX problem

  1. #31
    Thanks for very informative reply!

    Regarding voltage drop:
    I observed very strange waveform on switching transistors, when converter is loaded about 50W.
    This is how I connected scope, on the other transistor it's the same.
    On the first screenshot when lighter load (few watts) the voltage on the collector is just fine, going from 325V to ground - very small voltage drop on transistors. But on the second screenshot, with higher load 50W there's smaller voltage swing - higher voltage drop on transistors? Is that becaouse of too small base current? Could this create voltage drop on the output and heat up transistors?
    I used a base drive transformer from old atx, maybe I should rewind it? Do You have some Idea for numbers of turns?

    And lastly, I changed number of turns of secondary to 2x10 and using 4x0,6 wire to fit it in window.

    Thanks, Fifi

  2. #32
    .... Silvio's Avatar
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    Yes i can also see that the pulses are not symmetrical.
    This could be the highside i guess. Try to change the capacitor feeding the gate to correct. Try a different value and see for any changes. The task is to pulse the gate hard at all times. Try a higher aux supply like 15 or 17v feeding oscillator circuit and BDT primary. If gate is not drven hard enough then transistors enter linear mode and get hot.

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