Low voltage drop diodes or equivalents

Discussion in 'General Electronics Chat' started by Wendy, Jan 30, 2009.

  1. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    I'm not where I can do the experiments, so I'll lay it out. When I can do some tests I'll post them. I'm after a diode that drops a lot less than the usual 0.6V forward drop.

    The Schottky diode is exactly what I'm talking about. Ready sources for this component may not always be handy however.

    I seem to remember that a conventional transistor will do something similar if the base is connected to the collector as shown.

    [​IMG]

    So can anyone confirm or deny this thought? Any other characteristics to worry about, such as acting as a Zener diode (I seem to remember such being stated a while back). For the sake of arguements lets assume a 2N2222.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, a transistor will act like a Zener if you run current through the emitter the wrong way; around 5v.

    Better to just keep a few Schottky diodes on hand, like 1N5817's, etc.
     
  3. Wendy

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  4. kubeek

    AAC Fanatic!

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    You could also try synchronous rectifiers (not sure if that is the right term), which basically are transistors switched on for the positive polarity and off for the negative.Hope someone with more knowledge about them will contribute.
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    If you connect the base to the collector the transistor won't work as a Schottky diode. Vce will equal 0.7V (approximately) because if it goes lower the transistor will turn off because the base-emitter diode will not be forward biased. Thus, Vbe=Vce will be such that it can cause the corresponding Ic to flow.
     
  6. beenthere

    Retired Moderator

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    Is this for low power usage? If so, see if you can find germanium units, like the famous 1N34. Vf should be on the order of .2 volts.
     
  7. Wendy

    Thread Starter Moderator

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    Actually germanium would be fine, I'm thinking alternatives (and hopefully outside the box). You don't want active circuitry with this, it is a component. Time to break out a protoboard...
     
  8. beenthere

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    I suppose you could grab a 2N404 and get similar results with the B-E junction.
     
  9. Wendy

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    That is funny, just for fun I looked long and hard for a germanium transistor. They can be had, but not easily. That project was for a low insertion voltage regulator.

    About the OP, another fine myth busted, 0.64V. I didn't see any obvious zener action using a 9V Battery (8.5V) and a 2.4KΩ resistor. Did see obvious thermal drift (temperature probe anyone?).
     
  10. bertus

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    Apr 5, 2008
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