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Michael Preedom12
Prodigy 40 points

Tool/software: WEBENCH® Design Tools

This is a related question that I am doing or conducting research on for a project I am working on when the forward current through a certain germanium junction diode in 20mA, the voltage drop across the diode is 0.15 volts. If the current through the diode is doubled to 40 mA, the voltage drop across the diode will be: 1) less than 0.15  volts; 2) approximately 0.15 volts; 3) between 0.15 and 0.3 volts; 4) exactly 0.3 volts.

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    TI__Guru**** 191445 points

    Michael,

    It will depend on the specific diode.  For a Germanium diode, the forward knee voltage is 0.3 V, so if you have 0.15 V at 20 mA, then you are not yet forward biased.  40 mA may or may not be enough to forward bias the diode.  It will depend where the two current points lie in the V-I curve relative to the knee point.  Take for example the 1N34A.  Its forward voltage is 1 V at 5 mA, so it would be well into forward bias already at 15 mA.  For 1N270, the forward voltage is 1 V at 200 mA, so 20 mA or 40 mA is unlikely to forward bias the diode.  Source of data:

    www.americanmicrosemi.com/.../