The construction of a PNP transistor is done as the name suggests by taking an N-type semiconductor material and sandwiching that in between two P-type semiconductor materials. In reality, the P-type material is generally much thicker in width than the N-type material. A transistor has two PN-junctions of which one is forward biased while the other is reversed biased. The path for the carriers through the forward bias has low resistance and the reverse bias has high resistance. A weak signal is fed as input at the low resistance circuit and output is taken from the high input circuit.
Construction of PNP Transistor
Emitter: A transistor has three sections of doped semiconductors. It has an emitter on one side and a collector on another. The middle portion is called the base. Below we have described all three parts of the transistor. The work of the emitter is to supply charge carriers.
Base: The middle section of the transistor, which forms the two PN junctions between the emitter and collector, is called the base. The base-emitter junction is forward biased allowing a low resistance for the emitter circuit.
Collector:
The section on the other side of the emitter that collects the charges is called the collector. The collector is always reverse-biased. Because the transistor has two PN junctions, it is like two diodes. The junction between the emitter and base may be called the emitter-base diode ??or emitter diode.
Working of PNP Transistor
The PNP transistor can be said to be naturally in a Normally Open state. Switching ON the PNP transistor requires us to make the voltage at the base terminal lower than that of the emitter terminal.
When turned ON, the current that is generated from the majority carriers, in this case, the holes, starts flowing from the base-emitter part of the transistor. This flow of current then flows to the base and then finally to the collector.
From the direction of the current flow in the transistor, the PNP transistor’s terminals can be divided into input and output ports. The input terminal is the base, and the output is the emitter and collector.
The base region is the part of the PNP transistor that controls the small currents that in turn control large amounts of current in the emitter to a collector in the transistor. The voltage source is connected to the emitter terminal, and the load is connected to the collector terminal.
The following transistor equation(s) can be used to calculate the PNP transistor’s base, emitter, and collector currents.
- IC = IE – IB
- IB = IE – IC
- IE = IB + IC
Operating Modes of Transistors
- Active Mode
- Cutoff Mode
- Saturation Mode
- Breakdown Mode
Applications
- Used as switches
- Used in amplification circuits
- Used in Darlington Pair Circuits
- Used for Robotics