Bipolar transistors

What is the main reason for using a current-feedback bias circuit with an emitter resistor in a transistor amplifier?

  1. ATo maximize the voltage gain
  2. BTo stabilize the operating point against temperature changes and hFE variations
  3. CTo make the circuit oscillate
Show answer and explanation

Answer: B. To stabilize the operating point against temperature changes and hFE variations

With an emitter resistor, an increase in collector current raises the emitter voltage, which lowers the base-emitter voltage and applies negative feedback that limits the current increase. The operating point therefore stays stable despite temperature changes and transistor-to-transistor hFE variations.

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More Bipolar transistors questions

  1. In an amplifier, what is the DC voltage and current state of the transistor with no input signal called?
  2. Which distortion tends to occur in a class B push-pull amplifier in which NPN and PNP transistors handle the positive and negative half-cycles?
  3. What is the role of a coupling capacitor placed between amplifier stages?
  4. How does the current gain hFE of a silicon bipolar transistor generally change as temperature rises?
  5. Which condition increases the small-signal input resistance (hie) of a common-emitter amplifier?