The various Current components which flow across a PNP Transistor are as shown in the figure.
For Normal operation
- Emitter Junction is Forward Biased.
- collector Junction is Reverse Biased.
The current flows into Emitter is Emitter current , .
This current consists of two components
- or – Current due to majority carriers(holes).
- or – Current due to minority carriers(electrons).
since is very small
All the holes crossing the Emitter junction do not reach the Collector junction because some of them combine with the electrons in the N-type Base.
– is the hole current in the Collector.
∴ Base current = Total hole current in Emitter – hole current in Collector.
If emitter were open circuited Amperes which implies from Equation(1) Amperes.
Under these conditions, Base-Collector junction acts as Reverse-Biased Diode and gives rise to a small reverse-Saturation current known as .
when , Total Collector current is the sum of current due to holes in the Collector and Reverse Saturation current .
i.e, In a PNP Transistor consists of holes moving across (from Base to Collector) that is and electrons crossing the junction (from Collector to Base) constitutes .
Total current in the transistor is given by .
The general expression for Collector current is