Bipolar transistors

A transistor with DC current gain hFE = 100 has a base current of 10 μA. Roughly what is the collector current in the active region?

  1. A100 μA
  2. B1 mA
  3. C10 mA
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Answer: B. 1 mA

In the active region, IC = hFE × IB, so 100 × 10 μA = 1,000 μA = 1 mA. However, if the collector circuit can only supply less current than this, the transistor saturates and IC will not reach hFE times IB.

  • A. 100 μA would correspond to hFE = 10.
  • B. Correct. 100 × 10 μA = 1 mA.
  • C. 10 mA would correspond to hFE = 1000.
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More Bipolar transistors questions

  1. What is the state of the junctions when a bipolar transistor is in the cutoff region (off)?
  2. What is the typical base-emitter voltage VBE of a silicon bipolar transistor operating in the active region?
  3. What is the collector dissipation of a transistor operating at a collector-emitter voltage of 5 V and a collector current of 100 mA?
  4. Which correctly describes the difference in how bipolar transistors and MOSFETs are controlled?
  5. In a common-emitter amplifier with transconductance gm = 40 mS and collector resistor RC = 5 kΩ, roughly what is the magnitude of the voltage gain? (Ignore the load.)