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I this power supply good?

Discussion in 'Electronic Basics' started by little billy, Aug 2, 2004.

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  1. little billy

    little billy Guest


    Is the following psu any good

    The voltage reference is taken from the output,
    wouldn't it have made more sense to had some sort
    of zener diode reference, I mean, any input ripple
    is going to be present in the output, and worse still
    it will be amplified by Q1 so the output ripple
    will be even worse than the input ripple. This
    circuit is bad, isn't it?
  2. Define good. It probably works for some things and is certainly
    simple ot make. It is not as good as a lab grade adjustable supply
    that costs a hundred bucks or so.
    You should think of this circuit as using the turn on voltage of a
    transistor as its reference (both for the voltage setpoint and the
    current limit). Of course this is not a very sharp or temperature
    stable reference, but it may serve your purposes, which I am not aware
  3. little billy

    little billy Guest

    I think I was wrong about this circuit. It is alright. What sort of
    ripple can I expect to get at the output compared to the input, i.e.
    by how much will the ripple be reduced, and how does that compare with
    a proper laboratory regulated power supplies ?

    Did you see my other power supply question a few postings before,
    what's your take on R7, why is it 220R, what does it do ?
  4. Without some calculation or a simulation, I can't say. The reduction
    ratio is approximately equal to the voltage gain around the control
    loop at the ripple frequency. This one is simple enough to easily be
    put into LTspice with an input consisting of an AC ripple voltage
    riding on a DC bias.

    You can download a free copy of LTspice at:
    Sorry, I didn't take the time to think through how that circuit works.
  5. Rich Grise

    Rich Grise Guest

    It's adjustable. You turn the knob and use a meter to
    tell you if it's the voltage you want.

    Hope This Helps!
  6. little billy

    little billy Guest

    Hi again,

    It seems that the output ripple is almost as bad as the input ripple,
    take a look at my simulation results

    Either something is wrong, or this circuit goes to the bin.

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