Stacking Diodes for HV Switching 1

[ILEN]

Question: Can I stack multiple FR304(400V) in series to get a HV (5kv) diode response with a trr<150ns?


Background: This is more of a physics experiment, but it's a EE issue. I've been experimenting with moving charge around. I'm currently using different methods to charge two suspended parallel plates(air dielectric), to a couple thousand volts; using a diode to keep the capacitor from discharging. This time, I thought I'd try using switching transients to charge the plates. I found several books on the topic, but most of them involve the elimination of unwanted transients in communication networks. The only useful book I've currently found is called "theory and calculation of transient electricity", by steinmetz. If you have any reference material with current information, I'd very much appreciate it. I know they use them in pulse forming networks, which is similar.

 

[benta]

"Can I stack multiple FR304(400V) in series to get a HV (5kv) diode response with a trr<150ns?"

Not directly, no.
You cannot be certain that they will "share" the reverse voltage equally.

Two options:

1: match the diodes so they all have the same reverse leakage current. Personally, I don't think this is an option, as the matching will change over temperature etc.

2: Balance the reverse voltage by using a parallel resistor over each diode. I'd select the resistor value so the the resistor will "bleed" around 10 times the worst case reverse leakage current at the operating voltage.

Cheers,

Benta.

 

[VEBill]

Benta's advice matches what I've seen. But I've seen capacitors (as well as the resistors) place in parallel with each diode in the stacks.

None of this is going to help with the switching time requirement... It's probably better to go find a suitable diode in the first place.

 

[Skogsgurra]

There are diodes with controlled avalanche. They divide voltage quite well. But not so sure if you really need 150 ns reverse recovery, I'm not so sure.

Diodes are cheap. Get a bunch of 1N4007 and just do it. That is your best source of knowledge - your own experience.You can also build a cascade, like this one:

http://gke.org/pub/files/Metal-paper capacitor on overvoltage.pdf

Add stages to get the needed voltage. You can use standard diodes and standard capacitors for all stages. Voltae increases and current decreases as you add stages. The configuration shown will deliver tens of milliamps, which is ample if all you want is to charge a plate electrode.

As I said, just do it.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[2dye4]

Start looking for fast recovery diodes with 1000 Volt blocking capacity.

One source

http://www.vishay.com/diodes/rectifiers/fast-recovery-superectifier/

If you are going to stack them in series to obtain higher blocking voltage then you must bypass each diode with a resistor that conducts more steady state current at the maximum voltage than the worst leakage, 3-5 times for safety.

And you must bypass each diode with a high voltage capacitor that is 3-5 times larger than the highest reverse capacitance given the spread of values in a lot.

So look for 3 things, fast recovery, low reverse leakage, low reverse capacitance.

You may be able to sort diodes for ideal properties to obtain better values if you have that kind of time.

What you are making sound like a flyback converter. Search that term.

OR try to find

http://www.edidiodes.com/pdf/diodes/TVR-30.pdf

Good luck

 

[Warpspeed]

A real oldie but still useful.

http://www.r-type.org/pdfs/1b3gt.pdf