Question

Why is n-p-n preferred over p-n-p?

Answer 1

Explanation:

1. The majority carriers of charge in an n-p-n transistor are electrons, whereas, in a p-n-p transistor majority of charge carriers are holes. The mobility of electrons is more than that of holes because the holes have more effective mass than the effective mass of electrons.
2. Thus n-p-n is preferred as in this electrons have higher mobility than holes, which results in high mobility of energy.
3. In a p-n-p transistor, the positive supply line becomes a common point of input and output current, due to which the ground current is positive. This is inconvenient for design and maintenance.
4. In an n-p-n transistor, the negative supply line becomes a common point of input and output current, due to which the ground current is negative. This is suitable for design and maintenance.
5. Thus, n-p-n is suitable for negative ground current.

Hence, n-p-n is preferred over p-n-p.