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Question

The regenerative process where the collector junction temperature increases the collector current and vice versa is called _____.

This question was previously asked in
RRB ALP 2018 CBT 2 Fitter Question Paper (21-Jan-2019) (Shift 3)
The correct answer is
thermal runaway

Understanding Thermal Runaway

The process described, where an increase in collector junction temperature leads to an increase in collector current, which in turn further increases the temperature, is known as thermal runaway.

This is a positive feedback mechanism:

  • Higher Temperature  →  Higher Collector Current ($I_C$)
  • Higher $I_C$  →  Increased Power Dissipation ($P_D \approx V_{CE} \times I_C$)
  • Increased $P_D$  →  Higher Junction Temperature

This cycle escalates, potentially damaging the semiconductor device. The phrase "and vice versa" emphasizes this self-reinforcing loop.

Evaluating Other Options

  • Temperature Stability: This refers to maintaining a stable operating point despite temperature variations, the opposite of runaway.
  • Positive Feedback: While thermal runaway utilizes positive feedback, the term itself is more general. The question describes a specific consequence of positive feedback in this context.
  • Oscillation: This involves periodic fluctuations, not a continuous escalating increase in current and temperature.
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Important Questions from Bipolar Junction Transistors

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