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pwm for a boost converter

Discussion in 'Electronic Design' started by [email protected], Mar 23, 2007.

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  1. Guest

    Re: this schematic:

    If I change C1 to 500 pF, would I get a 20 kHz PWM frequency?

    Would any other modifications be necessary to achieve 20 kHz?

    I'm trying to build a boost converter, and I'd like to use a variation
    on this circuit to perform the switching.


  2. Guest

    Ditto. Those 555 circuits are like using a crescent wrench instead of
    a socket. Eh, maybe pliers instead of a socket.
  3. Tim Williams

    Tim Williams Guest

    C1 smaller (than shown), and the pot smaller (maybe 10k).

    500pF is a little on the low side for a 555 but will still work. I think
    20kHz is about right for that (or 0.005uF with a 10k pot).

    I heartily recommend an UC3844 or similar chip for doing a boost converter.
    The current protection will keep your transistor from exploding, a notable

    I was messing around with a BS boost circuit (two comparators and an op-amp,
    plus the obvious hardware) just tonight and popped two power transistors.
    :( Car batteries can sink a lot of current...

  4. Terry Given

    Terry Given Guest

    AKA "adjustable nut-fucker"
  5. Rich Grise

    Rich Grise Guest

    When some newbie would show up in our shop to ask to borrow a
    crescent wrench, we'd ask, "Metric or Standard?" :)

  6. Left or right handed?
  7. Tim Williams

    Tim Williams Guest

    Heh, I realize that those are useless distinctions which can actually
    apply -- the only chiral part is the adjustment screw, while the wrench
    length is measured in perhaps 8" or 200mm.

    Now, a bucket of vacuum...

  8. James Arthur

    James Arthur Guest

    That's not a very good general-purpose power supply, as others have
    noted. Why not use one from my pal Bill Bowden?

    Be sure and use a suitable (fast) rectifier, like a 1n5819 schottky,
    or a fast-recovery type.

    James Arthur
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