# Early effect in Common Base Configuration

Early effect (or) Base-width modulation:-

In Common Base configuration in the Reverse Bias, As the voltage $V_{CC}$ increases, the space-charge width between collector and base tends to increase,  with the result that the effective width of the base decreases. This dependency of Base-width on the Collector to emitter voltage is known as the early effect.

The early effect has three consequences:-

1. There is less chance for recombination with in the base region. Hence $\alpha$ increases with increasing $\left&space;|&space;V_{CB}&space;\right&space;|$.
2. The charge gradient is increased with in the base and consequently, the current of minority carriers injected across the emitter junction increases.
3. For extremely large voltages, the effective Base-width may be reduced to zero, causing voltage break-down in the transistor. This phenomenon is called the Punch-through.

For higher values of $V_{CB}$, due to early effect the value of $\alpha$ increases, for example $\alpha$ changes say from 0.98 to 0.985. Hence there is a very small positive slope in the CB output characteristics and hence the output resistance is not zero.

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