PNP Transistor With Three LED's as a Switch


 Three modes of Operating Region of Transistors are:

  1. Active Region
  2. Saturation Region
  3. Cut-off Region

1- Active Region Characteristics:

  • In 'Active Region' , the transistor operate as an 'Amplifier'
  • The Junction Base-Emitter is forward Biased.
  • The Junction Collector-Base is Reverse Biased.

2- Saturation Region Characteristics:

  • ​​In 'Saturation' region, the transistor operates as an 'Closed Switch'.
  • The 'Base' Electrode is Connected to Supply Voltage [ Vcc ]
  • The Junction Base-Emitter Voltage is greater than 0.6V i.e VBE > 0.6V.
  • The Junction Base-Emitter is Forward Biased.
  • The Junction Collector-Base is Forward Biased.
  • Maximum Saturation Collector Current [ Ic ] flows, i.e [ Ic=Vcc/R]
  • This condition of transistor is act as a 'Fully-ON' and this is 'Saturation Region'.
  • Collector to Emitter Voltage [ VCE ] is approximately equal to Zero ideally. i.e [ VCE = 0V ]

​3- Cut-Off Region Characteristics:

  • In 'Cut-off' region, the transistor operate as an 'Open Switch'.​
  • The 'Base' Electrode is Grounded to zero Voltage [ 0V ].
  • The Junction Base-Emitter Voltage is less than 0.6V i.e VBE < 0.6V.
  • The Junction Base-Emitter is Reverse Biased.
  • The Junction Collector-Base is Reverse Biased.
  • No Collector Current [ Ic ] flows, i.e [ Ic=0 ].
  • This condition of transistor is act as a 'Fully-OFF ' and this is 'Cut-Off Region'.
  • Collector to Emitter Voltage [ VCE ] is approximately equal to Supply Voltage [ VCC ] [ VCE = VCC ]

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