Question

Current is sourced away or sinked from the base of the transistor to ground for operation in

• A. npn transistors
• B. pnp transistors
• C. Both
• D. None

Answer 1

Answer: (B)

pnp transistors

The pnp transistor configuration is shown below. The characteristics of both pnp and npn transistors are similar except that the biasing of the voltage and current directions are reversed for any one of the possible three configurations such as a common base(CB), common emitter(CE) and common collector(CC).

The voltage between the base and emitter terminal $V_{BE}$ is negative at the base terminal and positive at the emitter terminal because for a pnp transistor, the base terminal always biased negative with respect to the emitter. Also, the emitter voltage is positive with respect to the collector ($V_{CE})$.

The voltage sources are connected to a pnp transistor, which is shown in the figure. The emitter is connected to the $V_{CC}$ with the $R_L$; this resistor limits the max current flowing through the device, which is connected to the collector terminal. The base voltage $V_B$ is connected to the base resistor $R_B$, which is biased negative with respect to the emitter. To cause the base current to flow during a pnp transistor, the base terminal must be more negative than the base terminal by approx. $0.7V$ or a Si device.