In a PNP transistor, electron flow:
Right Answer is:
Into the transistor the collector and base leads
SOLUTION
PNP TRANSISTOR
If a thin layer of N-type Silicon is sandwiched between two layers of P-type silicon. This transistor is referred to as PNP. Consider a PNP transistor shown in Fig. biased in the forward active mode, that is emitter-base junction is forward biased (VEB is +ive) and the collector-base junction is reverse biased (VCB is —ive). Due to the externally applied voltages VEB and VCB, currents flow in the transistor. In PNP transistor hole is the majority charge carrier.
In a PNP transistor, the P region emitter is biased in forward direction because it emits or injects the charge carriers into the transistor. The collector is biased in the reverse direction because its function is to collect or attract the charge carriers. The middle electrode which has a common region to the two out of electrodes (emitter and collector) is called the base. The forward-biased junction is called the emitter junction. Similarly, the reverse-biased junction is called the collector junction.
As soon as biasing is applied the majority charge carriers (holes) of P region (emitters) flow (i. e. diffuse) to the N region (base) as they are repelled by the positive terminal of the battery. At the same time, the electrons of N region are attracted by the positive electrode. Hence the potential barrier at the emitter junction reduces forward emitter biasing. Thus in PNP transistor with emitter forward biased, the majority of the holes are able to drift across the base (which is made very thin) without combining with the electrons present there. However, a small number of holes (about five percent) are lost in the base (N region) due to the combination with electrons, which results in a small base current.
The remainder (more than 95 percent) cross into the collector region to constitute collector current Ic. In this way, almost the entire emitter current flows in the collector circuit. It may be noted that current conduction within the PNP transistor is by holes. However, in the external connecting wires, the current is still by electrons.