Question

Can a transistor be used as a Rectifier?

Answer 1

To describe the conditions and principles as to why a rectifier is used and how it helps. To compare it with the characteristics of the junction diode. To note the conditions for which the transistor may behave like a rectifier. To also mention why a standard rectifier is preferred over a transistor that behaves as a rectifier.

Complete step by step answer:
Transistor is a three-terminal conductor normally used as an amplifier or as a switch. Devices like this always have clear instructions about using AC/DC. However, there are times once you might need an AC electrical outlet but have to connect a tool that needs a DC. This is when a Rectifier steps in. In simple words, a Rectifier converts electrical energy into DC.
The Volt-Ampere characteristics of a junction diode explain how current is passing through the diode only if it's forward biased. Hence, if an alternating voltage is applied across a junction diode, then the current will flow only within the part where it's forward biased. This property of a junction diode is accustomed to rectify alternating voltage/current. The circuit used for this purpose is called a Rectifier. So in order to use a transistor as a rectifier, either the emitter-base segment or the collector-base segment must be used. In every transistor, the bottom is thinner than the emitter, and also the collector is lightly doped so both segments won’t work as a correct rectifier. Example: Germanium diode-connected transistor involves a drop of about $0.13$ volts, rectifier diode about $0.3$ (over $2.5$ times) it’s just that rectifiers are optimized for rectification and are designed to execute at normally higher currents, and it's cheap. A transistor may be used as a rectifier. If we connect the base-emitter or base-collector region and use it as a diode, a transistor will work as an occasional current rectifier. It’s just that standard rectifiers are cheaper and might rectify higher values of current yet, and hence, are preferred for rectification.

Note:
When used as an amplifier, a transistor works in the active region, i.e. its emitter-base junction is always forward biased and collector-base junction is always reverse biased. When used as a switch it works within the saturation zone and cut-off area. This suggests that, by switching between its “top-off” (saturation) and “absolute OFF,” the transistor is employed as a switch to basically overwrite its Q-Point and therefore the voltage dividers circuit that's needed for amplification.