Which transistor terminal is the source of charge carriers in an NPN transistor?

Which transistor terminal is the source of charge carriers in an NPN transistor?

• A. Base
• B. Emitter
• C. Collector
• D. Gate

Answer: (B)

In an NPN transistor, the source of charge carriers is the emitter. The emitter is heavily doped n-type and is forward-biased with respect to the base, so electrons are injected from the emitter into the base. The base is thin and p-type, so most of these electrons diffuse across the base and are swept into the collector by the reverse-biased collector-base junction, creating the collector current. Because the emitter supplies the majority of carriers, it acts as the source. The base mainly controls the flow (through its current) and the collector serves as the sink for the carriers. The gate term isn’t used for a BJT.

In an NPN transistor, the source of charge carriers is the emitter. The emitter is heavily doped n-type and is forward-biased with respect to the base, so electrons are injected from the emitter into the base. The base is thin and p-type, so most of these electrons diffuse across the base and are swept into the collector by the reverse-biased collector-base junction, creating the collector current. Because the emitter supplies the majority of carriers, it acts as the source. The base mainly controls the flow (through its current) and the collector serves as the sink for the carriers. The gate term isn’t used for a BJT.