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Why don't they make this easier

Discussion in 'Electronic Design' started by Tim Williams, Jun 15, 2009.

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  1. Tim Williams

    Tim Williams Guest

    I've tried various methods over the years to drive gate drive transformers
    with a positive-zero-negative-zero waveform. None of them are very good...

    For instance, I did this oh about 4 years ago: Bridge Transformer Driver 2.gif
    Simple, but needs bipolar supplies.
    About 2 years ago: Bridge Transformer Driver.gif
    Good performance when the snubber's current is continuous. Tedious.
    This morning: Bridge Transformer Driver 3.gif
    (A and B are open collector outputs.) Current sources stabilize output
    fairly well, but double followers make sucky offset when current reverses

    The common problem in all three is getting a TL494 or etc. to drive MOSFETs.
    It'd be so much nicer if they had a complementary bipolar, or better yet
    FET, output (ala SG3525 (almost) or UC3842).

    What do you do to drive a GDT?

  2. Fred Bartoli

    Fred Bartoli Guest

    Tim Williams a écrit :
    And what about a CT primary and just a pair of mostfets in a push-pull
  3. Tim Williams

    Tim Williams Guest

    Same problem as this one, no?

    What do you do with the flyback energy?

  4. Fred Bartoli

    Fred Bartoli Guest

    Tim Williams a écrit :
    But way much simpler...

    Sorry I thought you were running at 50-50 duty cycle...
  5. Tim Williams

    Tim Williams Guest

    I have a couple TC4420s, but was hoping for something with less 'gusto'.
    Besides, 6A in 10ns scares me. ;-)

  6. Tim Williams

    Tim Williams Guest

    Ahh, but I have a heatsink, so that doesn't matter to me. 100-200mA is
    plenty of drive for this application. What's more, I need about that much
    to drive the GDT at the lowest frequency. I don't think I can get more than
    1A peak through the GDT without a lot of interleaving anyway. Mere '3904s
    are fine, but alas, take an annoying amount of space to wire up.

    And another thing- a pair of TC4420 is as expensive as one of the IGBTs.

  7. Tim Williams

    Tim Williams Guest

  8. Tim Williams

    Tim Williams Guest

    Hmmmmmm, weird. A 555 stacked with a half bridge driver. Constant duty
    cycle output (i.e., fixed dead time), so it's no good for a forward
    converter. Resonant apps I guess. Thing is, you need a variable resistor
    to control frequency. A pair of current mirrors on Ct, with diode steering
    from Rt or whatever, would be a fine substitute. Mismatched currents will
    PWM the output (unbalanced PWM), which would be great for a class D power
    amplifier, but not good for a resonant switcher. Matched current mirrors
    would do okay.

    Thing is, I'm not sure I want fixed duty cycle. I may still want to vary
    power output by varying duty cycle (ala forward converter, TL494 et al.)
    rather than frequency. That's impossible with this chip.

    Besides, I want my control circuit grounded to ground. None of the IRxxxx
    chips I've seen can accommodate that, at least without a big stinking
    isolation transformer supplying the HV side.

    Come to think of it, I have a few IR2101s that I could just run at 0V as
    dual drivers for my immediate goal. That might work out. Still not an
    ideal solution, a weak dual TC4420 is really what I want, but I happen to
    have some of these on hand.

  9. James Arthur

    James Arthur Guest

    A series resistor 'weakens' the best of 'em.

    James Arthur
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