too much voltage?

Discussion in 'The Projects Forum' started by Gadersd, Jul 10, 2013.

  1. Gadersd

    Thread Starter Member

    Dec 8, 2012
    Can I use any voltage for semiconductors? If I had a diode and the fwv was 1.7, could I supply 1000v to it but use a 99.83k resistor to keep the current at 10ma? Would this damage the diode? I know that excessive voltage will damage things like capacitors and ics, but would things like diodes and transistors be fine on any voltage as long as the current is small enough?
  2. LDC3

    Active Member

    Apr 27, 2013
    Let's see:
    Vres = 1000V - 1.7V
    Ires = Vres / R
    = 998.3V / 99830Ω
    = 10mA
    P = I^2R
    = (0.01A)^2 * 99830Ω
    = 9.983W
    It appears that your resistor gets fried first, and since it usually shorts out, it will then fry your diode.
  3. wayneh


    Sep 9, 2010
    But in theory, if your resistor could tolerate the power dissipation, it would protect the diode while operating. Almost all the voltage would be dropped across the resistor.

    However, I'm not sure what would happen in the brief instant before current is flowing. Diodes have switching times and seeing 1000V for even a microsecond might be a big problem. Smoke and flash problem.

    Resistors can only provide protection when current is flowing at a predictable level. Using a resistor to, for instance, protect a 12V radio powered by a 24V supply is a bad choice because the current draw is not constant or predictable. That's why folks use voltage regulators in such cases.