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High voltage attenuation

Discussion in 'Electronic Design' started by Jon Slaughter, Dec 11, 2009.

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  1. I have a circuit that has around 500V on it. I want to reduce the voltage to
    some sub-circuits. Effectively there is a load that has around 500V and I
    wish to attenuate this with regulation. A simple emitter follower with
    degeneration should do the trick. The bjt needs to be on the high side
    because of the common ground between the different subcircuits.

    The only problem is actually programming the base current. I want to avoid
    having high voltages on a pot that will be used to set the voltage
    attenuation for safety reasons(else I would just use the pot directly
    instead of the bjt).

    I eventually want to program the base using a uC instead. The load current,
    which should be irrelevant to the problem, is around 50mA. I don't need full
    scale range but from about max Vcc(95%+) to around 1/4 Vcc. The main thing
    is proper attenuation and regulation(which can be done with caps
    afterwards). It does not have to work "fast" either.

    Any ideas?
  2. But this changes ground. The bjt essentially becoming a low side resistor
    with the load being "lifted" off ground by the the bjt. This causes a
    problem with transfering signals between circuits since they will be
    shifted. If could "restore ground" somehow then I guess it would work.

    What do you mean by "power-sequence issues"?

    I'm not sure I follow. Simply adding capacitance across the bjt and emitter
    to ground is not any better(although maybe slower)?
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