What is the difference between rectifier diode and zener diode?

A: They are both diodes. The difference lies in the application. A rectifier is used to rectify AC current into pulsating current. The zener diode is used to regulate a voltage source to the zener voltage when connected in the reverse direction.

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If you look at the characteristic curves of a rectifier diode and a zener diode, you will see that they are similar, but the reverse curve of the zener has a much sharper bend at what is called the "knee".

It is at this point on the zener's curve at which it operates.