Additional heat is dissipated from power transistor by using

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RRB ALP Electronics Mechanic 23 Jan 2019 Official Paper (Shift 2)
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  1. mica sheet and heat sink
  2. silicon paste.
  3. mica sheet
  4. heat sink

Answer (Detailed Solution Below)

Option 4 : heat sink
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Heat Sink

  • A heat sink is a mechanical device. It is connected to a power transistor in order to dissipate heat generated.
  • The heat flows through the heat sink and is radiated to the surrounding air. If a heat sink is not used then all the heat has to be transferred from a transistor case to the surrounding air causing the case temperature to increase.
  • In a transistor, the collector-to-base junction temperature rises because of self-heating. The self-heating is due to the power dissipated at the collector junction.
  • This power dissipation at the junction causes the junction temperature to rise, and this in turn increases the collector current which causes a further increase in power dissipation.
  • If the phenomenon continues then it may result in permanent damage to the transistor. This is known as thermal runaway.
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