FAA Aviation Mechanic General (AMG)Fundamentals of Electricity and ElectronicsHard
A technician is troubleshooting a transistor circuit and determines that the transistor is an NPN type. For the transistor to be properly biased in the active region for amplification, what should be the polarity of the voltage applied to the base-emitter and base-collector junctions, respectively?
- AForward-biased base-emitter, reverse-biased base-collector
- BReverse-biased base-emitter, reverse-biased base-collector
- CReverse-biased base-emitter, forward-biased base-collector
- DForward-biased base-emitter, forward-biased base-collector
Show answer & explanationAnswer & explanation
Correct answer: A. Forward-biased base-emitter, reverse-biased base-collector
For an NPN transistor to operate in the active region (for amplification), the base-emitter junction must be forward-biased to allow current injection into the base, and the base-collector junction must be reverse-biased to collect these injected carriers and create a large output impedance.
Why the other options are wrong
- B. This configuration (both reverse-biased) would put the transistor in the cutoff region, effectively turning it off.
- C. Reverse-biasing the base-emitter junction would turn the transistor off (cutoff region).
- D. This configuration (both forward-biased) would put the transistor in saturation, not the active region.
NPN Transistor Active Region Biasing
To operate an NPN transistor in the active region for signal amplification, the base-emitter junction must be forward-biased and the base-collector junction must be reverse-biased.
- Forward-bias allows base current to flow.
- Reverse-bias allows collector current to be controlled by base current.
- Essential for linear amplification.
Memory trick: Cut it, Act it, Sat it: Three ways a transistor can be lit.