Question

Why a silicon npn junction transistor cannot be used to rectify alternating voltages?

Answer 1

Answer:

Since base is thin one and lightly doped, either of the two segment does not work properly as p-n junction diode, which is required for a rectifier. That is why, a transistor can not be used as a rectifier.

A transistor can be used as a rectifier. When you connect base-emitter or base-collector region and use it as a diode, a transistor can work as a low current rectifier.It is a common practice in precision analog electronics to use Bipolar transistors as diodes. ... For example, a 3904 type transistor will have <1pA of reverse leakage using the Base Emitter junction. However, it turns into a zener diode at around 6.8V. Works great for 5V and lower voltage logic circuits.