Re: High Voltage Resistors
- From: "Tom Bruhns" <k7itm@xxxxxxx>
- Date: 12 Jun 2006 10:32:27 -0700
Juan wrote:
Hi all,
I'm looking for high voltage resistors for electrostatic discharge tests,
470 kohm. The pulse discharge has a rise time of 1 ns, it's about 60 ns
long, and the voltage discharge it is up tu 8 kV.
What kind of resistor would I need?
Well, um, high voltage resistors, actually. Check out Ohmite (acquired
and assimilated Victoreen, a pioneer of high voltage/high value
resistors) at (for example)
http://www.ohmite.com/cgi-bin/showpage.cgi?product=supermox&kw=Super-Mox-Series-High-Voltage-Resistors,
and Caddock at http://www.caddock.com/ (many different kinds that can
handle what you want).
But be aware that with a 1ns rise time to 8kV, making a circuit that
actually looks resistive will be practically impossible. Note that at
250MHz (1/4 cycle = 1ns), 470kohms reactance is about 1.35fF of
capacitance. I suppose that even the Caddock MG745 series, at 6mm
diameter and 76mm long, will have well over twice that capacitance from
end cap to end cap, and that doesn't count any of the rest of your
circuit. So how you actually build things will matter a lot: you can
perhaps put the resistor through some sort of shield plate with a hole
in it if you need to reduce capacitance. Be sure the hole is large
enough to not allow arcing! It's up to you to get all that right, to
do whatever it is that you need to do. If you really understand what
it is you are trying to accomplish, you might do well to contact the
resistor manufacturers directly, for their recommendations.
Cheers,
Tom
.
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