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Transistors

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how bipolar transistor

how bipolar transistor

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Transcript

  • 1. N Type P Typeextra electrons holes (missing electrons) depletion zone
  • 2. N P Nemitter base collector
  • 3. N P Nemitter base collector
  • 4. Electron Flow N P Nemitter base collector
  • 5. Electron Flow N P Nemitter base collector
  • 6. • Emitter is grounded (zero voltage)• Base has a small positive voltage• Collector has a large positive voltage• Electrons flow from emitter into P layer.• Base (P layer) is lightly doped, so few holes get filled by extra electrons.• Most electrons build up in base (P layer).
  • 7. Electron Flow N P Nemitter base collector
  • 8. • Positive voltage at base and collector attract electrons in middle P layer.• Some current flows from emitter to base.• Most current flows from emitter to collector.• Base voltage determines flow from emitter. – If base voltage is too low, no current flows from emitter to base or from emitter to collector. – The higher the base voltage, the more base current and collector current flows.• Bipolar transistors are current amplifiers.
  • 9. Hole Flow N P Nemitter base collector
  • 10. P N Pemitter base collector
  • 11. P N Pemitter base collector
  • 12. Current for Hole Flow P N Pemitter base collector
  • 13. Current for Electron Flow P N Pemitter base collector
  • 14. • Bipolar transistors act like 2 back-to-back diodes• base-emitter diode is forward biased – current can flow from base to emitter• base-collector diode is reverse biased – current can not flow from collector to base • some leakage current will flow – if base current flows, causes collector to emitter current to flow
  • 15. No signal voltage on base,So transistor turned off. No base current (emitter to base)
  • 16. No signal voltage on base,So transistor turned off. Current can NOT flow from Collector to base to input No base to emitter current.
  • 17. All supply voltage dropped on R2 because transistor is an openNo signal voltage on base,So transistor turned off. No collector to emitter current No voltage from output to ground, so no current flows No base to emitter current.
  • 18. Small signal voltage applied to base, Transistor turned on. LARGE current must flow to output collector current flows small base current flows
  • 19. All supply voltage dropped on R2 All supply current to outputNo collector to emitter current
  • 20. No voltage on base transistor is off
  • 21. Voltage on the base turns transistor turns onsmall base current causes LARGE collector current
  • 22. Replace NPN with PNP and just reverse the polarity
  • 23. Replace NPN with PNP and just reverse the polarity
  • 24. Switches or Regulators• Transistors are manufactured to be either switches or regulators.• Switches need to turn on and off FAST!• Need enough base bias voltage to overcome barrier – 0.7 V for silicon transistor – 0.3 V for germanium transistor
  • 25. Switches or Regulators• How does a transistor work as a regulator?
  • 26. DCAC voltage on basecauses AC current
  • 27. DCAC voltage on basecauses AC current
  • 28. DC
  • 29. DC open base allows collector current to flow
  • 30. Small input signal current results inlarger output signal current
  • 31. Output signal current is at samefrequency as input but largeramplitudeRegulator transistorscan act as amplifiers