Reverse bias rectifier diodes

Thread Starter


Joined May 22, 2020
I've just joined in the hope that someone can explain something that is beginning to really bug me.

I need to produce a negative DC from an AC transformer voltage, and realise I can do this through a half wave rectifier. What I don't understand is how.

This contains a reverse biased diode, which I assume only lets the negative wave of the AC current through.

What I cannot get into my head is how the reverse biased diode allows current through when biased this way.

Surely the whole point of the diode is to only allow flow when positively biased.

I realise I'm being extremely thick, but having endlessly read it up, all I can find is schematics showing rectifier circuits, and articles stating that reversed biased rectifier diode will not let current through.

Any assistance will be much appreciated.


Joined Feb 24, 2006
The diode conducts on the negative half cycle when the transformer secondary goes more than 1 diode drop below ground. You can see the difference between the red peak and the green peak which should be about -- 1 diode drop. It's working perfectly. The diode is ONLY reverse biased on the positive half cycle. Add a separate diode in the other direction to a separate load resistor and see what happens. Does it now make sense?