Bipolar transistors

Which correctly relates the emitter current IE, base current IB and collector current IC of a bipolar transistor?

  1. AIE = IC − IB
  2. BIE = IB × IC
  3. CIE = IB + IC
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Answer: C. IE = IB + IC

The current flowing into a transistor equals the current flowing out, so the emitter current is the sum of the base and collector currents, IE = IB + IC. Since IB is much smaller than IC, IE ≈ IC is often a good approximation.

  • A. In an NPN transistor, both the base and collector currents flow into the emitter, so they add rather than subtract.
  • B. The currents add; they do not multiply.
  • C. Correct. By Kirchhoff's current law, IE = IB + IC.
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More Bipolar transistors questions

  1. 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?
  2. What is the state of the junctions when a bipolar transistor is in the cutoff region (off)?
  3. What is the typical base-emitter voltage VBE of a silicon bipolar transistor operating in the active region?
  4. What is the collector dissipation of a transistor operating at a collector-emitter voltage of 5 V and a collector current of 100 mA?
  5. Which correctly describes the difference in how bipolar transistors and MOSFETs are controlled?