How to know what size diode to use for inductive spiking?

Question

I am making a simple Zener flyback circuit for an inductor.

What current rating should the diodes be sized for? Could I use a 1 watt Zener diode because the voltage spike only lasts a few microseconds, or would I have to use a 666 ampere diode? (I = V/R [666 = 66.6/.1])

I currently have a 10 ampere silicon diode and a 1 watt Zener. I have a feeling they will be damaged very quickly, though. Can Zener diodes be put in parallel to split the current?

Here is the circuit I'm using:

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

You really should look into Transorbs for this, acronym TSB. Although they have a power ratings, they are designed for short duration surge events. Incidentally they are available in both unipolar and bipolar configurations.

Answer 2

The diode needs to be able to handle the current that is flowing through the inductor when the transistor is conducting. This is because the current through an inductor can't change abruptly.

However it's not entirely clear how big that current actually is in your application. Judging from your schematic and the front page RDSon of the transistor alone, the current would be 66.6V/10.5mOhm =~ 6kA, which is way above the rated current of the transistor (and the diodes).