Operation of N-P-N Transistor:
The operation of N-P-N transistor discussed earlier can be simplified as follow :
The operation of N-P-N transistor discussed earlier can be simplified as follow :
- The forward bias at the B-E junction reduces the barrier potential and causes the electrons to flow from n-type emitter to p-type base.
- Holes also will flow from p-type base to n-type emitter.But as the base is more lightly doped than the emitter, almost all the current flowing across the B-E junction consists of electrons entering the base from the emitter. Hence electrons are the majority carriers in an n-p-n transistor.
- Some of the electrons entering into the base region do not reach the collector region. Instead they flow out of the base terminal via the base connection as shown in fig. due to recombination.
- As the base region is very thin and lightly doped, there are very few holes available in the base region for recombination.
Fig.Operation of an n-p-n transistor
- Hence about 2% electrons will flow out of base due to recombination.
- The remaining 98% electrons cross the reverse biasing collector junction to constitute the collector current. They cross the collector region and are collected by the supply Vcc.
- The emitter current is equal to the sum of collector and base currents.
there for.. IE = IC+IB
Operation of P-N-P Transistor in the Active Region:
- The p-n-p transistor behaves exactly in the same way as the n-p-n device.
- The only difference is, the majority charge carriers and holes instead of electrons.
- As shown in the fig. holes are emitted from the p-type emitter across the forward biased EB junction, into the base.
Fig.Operation of a p-n-p transistor
- In the lightly doped base there are very few number of electrons available for recombination.
- Therefore about 2% of total emitted holes will flow out via the base terminal and the remaining are drawn across the collector by the electric field at the reverse biased collector junction.
- As in case of n-p-n transistor, the forward bias at the EB junction controls the collector and emitter currents.