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On/Off Ratio

  1. Aug 1, 2009 #1
    Research-related question:

    What is the typical on/off ratio of a silicon transistor? This seems like basic information, but I can't find it anywhere.

    Also, how high does the on/off ration need to be in order for transistors (say, in a logic circuit) to function correctly?

    Thanks!
     
  2. jcsd
  3. Aug 1, 2009 #2

    negitron

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    Science Advisor

    What do you mean by "on/off ratio"? This is not a conventional transistor terminology. A transistor which is fully off has zero volts base bias with respect to the emitter and passes approximately zero current (there is some very slight leakage, but this is ignored in practice). A transistor which is fully on has a saturated gate condition with a bias voltage of (for silicon) about .7 volts and passes a collector-emitter current equal to the base current times beta (the DC current gain of that particular transistor).
     
  4. Aug 1, 2009 #3
    Do you mean the duty cycle in a typical application? or do you mean the ratio of on-current to off-current for a given transistor? If the latter, it kinda looks like you are interested in efficiency. The static on-current to off-current ratio in modern transistors is typically extremely high and not an issue. The real problem in efficiency is how quickly the transistor can switch on and off. You characterize that with, for example, a time domain plot of current when it switches. Google transistor slew rate, for example.
     
  5. Aug 1, 2009 #4
    0% to 100%.
     
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