21 December 2019

Comparison between Transistor and Vacuum Tubes


Advantages of Transistor over Vacuum tubes
High voltage gain
  • The voltage gain of the transistor is high as compare to vacuum tubes.
  • The voltage gain of the triode is less than 75 whereas the voltage gain of the transistor is greater than 300.

Lower supply voltage
  • The transistor requires very small DC supply voltage whereas the vacuum tubes require higher DC supply voltage for its operation.

Light weight circuit
  • This low voltage DC supply requirement makes its suitable for light weight transistor circuit as compare to heavier vacuum tube circuit.

Size
  • The size of the transistor is much smaller than vacuum tubes.

Heating
  • The vacuum tube require heater whereas the transistor does not require it.

Power supply
  • The power supply of vacuum tube becomes bulky due to weight of heater.

Life
  • The life of vacuum tube is limited up to thousand hours due to heaters however the life of transistor is many years.

Mechanically strong
  • The transistors are mechanically stronger than vacuum tubes. 

Application
  • The transistorare integrated with other semiconductor device in the integrated circuits ( ICs ).

Disadvantages of Transistor over Vacuum tubes
Power dissipation
  • The power dissipation of transistor is in terms of watt whereas the power dissipation of vacuum tube in kW. 
  • The transistor cannot be used in the high power application i.e. high power motor drive, transmitter etc.

Effect of input impedance
  • The input impedance of the vacuum tube is high therefore the input control circuit draws negligible current whereas the input impedance of the transistor is low therefore it draws high current from control circuit. Therefore the vacuum tubes is used in oscilloscope, electronic voltmeter etc.

Effect of temperature
  • The operating parameter performance of the transistor depends upon temperature. As the temperature changes, its operating parameter also changes however small change in temperature slightly affect the performance parameter of vacuum tubes.

Performance parameter
  • The transistor parameters such as current amplification factor ( β ) , base to emitter voltage ( VBE ) are not same for same serial number / category of transistor.

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