Electronic – Two diodes in parallel for over-voltage protection

diodeshigh voltagepower supply

I've got a power supply circuit that needs the input to be protected against some pretty big voltage spikes. To do this, I need a really beefy clamping diode (D1) that will handle the voltage and current associated with those spikes. I also have a second diode in parallel with less current/voltage handling capability, but with a higher breakdown voltage (D2). My thought was that the secondary diode might react faster, but the primary diode would do the real voltage clamping. The circuit below is a simplified version (not including additional bias components).

Simplified Circuit

My hope is that the two diodes will provide the response as shown below. Is this a bad idea? Any cautions or warnings for this type of implementation?

Input Voltage Graphs

Best Answer

It won't work -- if you put 2 diodes in parallel, I can't easily say how they will share current in the forward (conducting) direction, but in blocking, the LOWEST breakdown one will breakdown. The 2nd is useless.

You might put 2 in series, but this has its own problems (they don't split the applied V equally). Best to get a single component rated for what you want to do.