Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

PN diode forward bias

  1. Apr 26, 2010 #1
    Probably a really stupid question but for a pn diode in complete forward bias i.e 6volts (switch on 0.7volts), does it behave like a normal resistor or is it a squared resistance till say 200 volts and is there a forward voltage breakdown mechanism. I can only find I V curves that got to about 1.5 volts.
  2. jcsd
  3. Apr 26, 2010 #2
    Forward biased diodes operate (ideally) on an exponential curve. Forward bias voltages of 6V or 200 V are not practical. The current that correspondes to these cases is too large and no practical device can operate in this way. As you have noted 1.5 V might be a practical limit (give or take).

    Also, it follows from the exponential behavior that the behavior is not a "normal resistance" nor is it a "squared resistance".

    Perhaps you are confusing forward bias and reverse bias. Reverse biased voltages can be larger, and there are breakdown mechanisms (Zener and avalanch effects for example).

    See the following link for more details.

  4. Apr 26, 2010 #3
    Thanks, I wasnt confusing reverese bias, I just didnt know if that exponential resistance flattened out. Thanks for clearing it up.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook