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Diode Voltage Drop — Parallax Forums

Diode Voltage Drop

piguy101piguy101 Posts: 248
edited 2011-06-21 12:58 in General Discussion
Some of you may remember the thread about my power supply a few days back, and now I have another question. It appears that the voltage drop of my diodes and LEDs changes as when I raise the current, the voltage drop increases slightly. (A few tenths of a volt) Also, at a very low current the diode voltage drop is about half the rated voltage drop. Is this all exposed to happen?

Comments

  • LeonLeon Posts: 7,620
    edited 2011-06-21 12:45
    The diode voltage drop depends on the diode type and the current.
  • Tracy AllenTracy Allen Posts: 6,667
    edited 2011-06-21 12:52
    That is the way diodes work. The current is an exponential function of voltage, and conversely, if you push a current through a diode, the voltage across it is a logarithmic function of the current. For example, the graph shows the current vs voltage curve of the substrate diode in a propeller. At around 500 µA forward current, the voltage is about 0.58. That voltage changes with current. 6 microamps gives 0.4 V. 10 mA gives about 0.8 V. People talk about a threshold, but it is a soft threshold.
    Prop_catch_diode_current_2.png
    Prop_catch_diode_current_2.png
    588 x 498 - 31K
  • piguy101piguy101 Posts: 248
    edited 2011-06-21 12:58
    Okay thanks. I will be operating at around 13V and 600mA so I will have exceeded that "threshold".
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