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

Using an L.E.D. as a diode to control current flow?

  1. Nov 23, 2011 #1
    I'm trying to make a small crystal radio and have managed to wire up the antenna and the head phone jack but I haven't got any diodes suitable for the voltages I'm using. I have some LEDs but will these dissipate too much current or cause any harmonics or interference with the signal?
  2. jcsd
  3. Nov 23, 2011 #2


    User Avatar
    Science Advisor

    It might work, but LEDs tend to tolerate only low reverse voltages (say, a few volts rather than the 700 volts of a 1N4007 power diode or even the 100 volts of a 1N4148 signal diode). In forward mode, they also usually have a much higher voltage drop (1.5 to 4 V) as compared to the ballpark for most diodes (0.3 to 0.7 V)
  4. Nov 24, 2011 #3


    User Avatar
    Science Advisor

    For a crystal radio, you will need diodes that turn on easily with a very low voltage.

    Suitable diodes are small signal Schottky diodes, like the BAT85, or point contact Germanium diodes.

    These Germanium diodes are fairly scarce now, but you may find them on Ebay or somewhere.
    Like these:

    LEDs are not suitable, nor are any kind of Silicon diode.

    I haven't got any diodes suitable for the voltages I'm using.

    What does this mean? A crystal radio (aka crystal set) does not normally use any input power apart from what comes from the antenna.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook