Bipolar transistors

Which correctly describes thermal runaway in a bipolar transistor?

  1. AOperation stops because the temperature drops too much
  2. BThe current suddenly becomes zero
  3. CRising temperature increases the collector current, which generates more heat, and this positive feedback leads to destruction
Show answer and explanation

Answer: C. Rising temperature increases the collector current, which generates more heat, and this positive feedback leads to destruction

In a bipolar transistor, the collector current increases with temperature even at the same base-emitter voltage. If more current produces more heat, raising the temperature further, positive feedback drives the current up without limit until the device is destroyed. It is prevented by negative feedback from an emitter resistor and adequate heat sinking.

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More Bipolar transistors questions

  1. Which is a characteristic of a SiGe HBT (heterojunction bipolar transistor)?
  2. What is the typical collector-emitter voltage of a silicon bipolar transistor in the saturation region?
  3. Which circuit uses two matched transistors to make the current in one transistor equal to the current in the other?
  4. What does a differential pair, with the emitters of two transistors connected to a common current source, do?
  5. What is the approximate transconductance gm of a bipolar transistor operating at a collector current of 1 mA? (Room temperature, thermal voltage VT ≈ 26 mV)