Diode question

Discussion in 'Homework Help' started by thrival, Jul 1, 2009.

  1. thrival

    Thread Starter New Member

    Nov 18, 2006
    When a diode is being sold, typically there's a voltage rating not to be
    exceeded, i.e. 10kv. I presume that's the reverse bias rating. Also say
    that voltage rating applies for say, 10mA of current.

    But what about forward bias? How much current/voltage can the diode
    withstand? Would it be safe to compute the reverse bias ratings in watts
    and stay within that parameter, even though voltage and current may vary
    in the forward bias mode, i.e. so long as said watt rating isn't exceeded?

    Reason is I need to run more current through a given diode than it's rated for.
    Voltage will be much less than it's rating in the forward direction. Some heavy-
    duty (microwave) diodes have large R drops, which are unacceptable for my
    application, hence the need for a ligher duty diode to handle more current at
    less voltage.
  2. Papabravo


    Feb 24, 2006
    In the reverse direction a diode can withstand large voltages at very small leakage currents until breakdown occurs.

    In the forward direction, at forward voltages above 0.6 to 0.7 Volts the current is unlimited. That is why you will always see a resistor in series with an LED to limit the exponential rise in current associated with small changes in forward voltage.

    Schottky diodes have a lower threshold, typically 0.2 to 0.3 Volts.

    Forward and reverse characteristics are essentially unrelated. You can draw no conclusions about the one from the other.
  3. David Lewis


    Jun 29, 2009
    A heatsink or cooling fan may help the diode carry more current. Resistivity decreases rapidly as the junction gets hotter (high thermal coefficient of conductivity), so stay in the safe operating area to avoid thermal runaway.