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Embedded Systems Transistors

Embedded Systems Transistors. E. B. C. N. P. N. B. NPN. E. Bipolar Transistor. C. C. B. PNP. E. NPN rules: The collector must be more positive than the emitter B-E and B-C behave like diodes B-E forward biased B-C reverse biased Limitations on I C , I B , and V CE

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Embedded Systems Transistors

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  1. Embedded SystemsTransistors

  2. E B C N P N B NPN E Bipolar Transistor C C B PNP E • NPN rules: • The collector must be more positive than the emitter • B-E and B-C behave like diodes • B-E forward biased • B-C reverse biased • Limitations on IC, IB, and VCE • When rules (1)-(3) are obeyed, IC=hFEIB=IB hFE (current gain) ~ 100 iC governed by transistor action

  3. E B N P N small IC large ICE + + Bipolar Transistor C

  4. E B N P N Transistor Action C B C reverse biased forward biased IC=IB E

  5. 10 V lamp 0.1A 10 V C B E 1K Transistor Saturation switch closes: VBE=0.6V IB=9.4V/1K=9.4mA ICE=(IB)=100(9.4) =940mA to get that much current through the lamp VC would have to go significantly below ground, which is illegal by rule #1 “The collector must be more positive than the emitter” the transistor is saturated---only enough IC currentflows through the transistor to keep the collector 0.05 to 0.2 V more positive than the emitter.

  6. Emitter-Follower • VE = VB-0.6V • when Vin > 0.6V • big current/power gain at Vout=Vin-0.6V • impedance buffer Vin Vout

  7. Power Transistors • Darlington pairs • hFE=(hFE)2 • TIP102/106

  8. Push-Pull Amplifier Stages NPN can only “source” current “crossover” distortion PNP can only “sink” current

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