# Diodes in series, 3kV

I want to build voltage multiplier using Cockcroft–Walton scheme.

I've got bunch of 3kV capacitors (2200pF though), and even bigger bunch of 1N5399 1kV diodes.

So, obviously I want 3 diodes in series to match capacitors rating.

I know that one cannot simply do that, and one need balancing resistors to match reverse current, but I see that for reverse current in datasheet (5uA) I need 200MOhm resistors, which seems to be something I can ommit. I know that at elevated temperatures diode reverse current would increase, but I won't work above 30 C.

Getting Higher-voltage diodes is probably not an option - they are ether too expensive or have too high forward drop voltage (like 20V for TV 14kV generators), and tiny current.

Suggestions, can I go without resistors?

PS. I know that I might want bigger caps, but they are not really common stuff. In this case I will have DC stage providing 3000V single polarity pulses @~30kHz or a bit more, so output current should be sufficient even with 2200pF. Target voltage is 15-20kV, so I will have ~ 7 stages.

• I've never used resistors, but admittedly I've only built CW circuits up to a few kV. Do you have a source that shows/recommends these resistors?
– mng
Oct 30 '11 at 21:09
• @mng Hmm.... Probably you right, I've seen this on traning video which probably was outdated. Oct 31 '11 at 9:42

A datasheet I found for the 1N5399 (Vishay) shows variation in the leakage current from $5 \mu A$ to $300 \mu A$ as a function of diode temperature. Be careful with your lower assumption.