Class 12 Physics Semiconductor Electronics n-p-n transistor

n-p-n transistor

Circuit Diagram

  • Biasing –
    • Forward bias- The emitter base junction is forward biased which means the n type emitter is connected to the negative pole of the battery and the p type base is connected to the positive pole of the same battery VEE
    • Reverse bias – The collector base junction is reverse biased which means the ptype base is connected to the negative pole of the battery and the n type emitter is connected to the positive pole of the same batter Vcc
  • Current –
    • The emitter current IE, base current IB and the collector current is as indicated in the circuit diagram
  • Resistance –
    • The emitter-base junction has low resistance while the base-collector junction has a high resistance

Working

  • The electrons are the majority carriers in the emitter n type semiconductor. This is repelled by the negative terminal of the battery VEE resulting in emitter current IE
  • The base being lightly doped and thin, the electron density is less. Hence, only 5% of the electrons entering the base combine with the holes resulting in base current IB. The base current is 5% of IE
  • The remaining 95% of the electrons pass over to the collector on account of the high positive potential of the battery Vcc. This results in collector current Ic which is 95% of IE
  • When the electron coming from the emitter combines with the hole in the base, the deficiency of hole in the base is compensated by the flow of holes from the positive terminal of the battery VEE to the base through the connecting wire
  • The current in the n-p-n transistor and the external circuit is due to  the flow of electrons
  • From the circuit, we fine IE = IB + Ic

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