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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:
    http://webpages.charter.net/dawill/Images/H Bridge Transformer Driver 2.gif
    Simple, but needs bipolar supplies.
    About 2 years ago:
    http://webpages.charter.net/dawill/Images/H Bridge Transformer Driver.gif
    Good performance when the snubber's current is continuous. Tedious.
    This morning:
    http://webpages.charter.net/dawill/Images/H 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
    (~2.4V!).

    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?

    Tim
     
  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
    fashion?
     
  3. Tim Williams

    Tim Williams Guest

    Same problem as this one, no?

    What do you do with the flyback energy?

    Tim
     
  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. ;-)

    Tim
     
  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.

    Tim
     
  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.

    Tim
     
  9. James Arthur

    James Arthur Guest

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

    James Arthur
     
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