That is, at a very low amperage (Very small decimal amperage,). Where can I buy them? What sort of price range? What limitations apply?
EDIT: (Very small amperage) previously read as (Less than 3 amps), the current text is the most accurate.
Posted Dec 3, 2012, 4:33 AM UTC · edited
Diodes make great switches. Bias the AC voltage and it's switched on. Television flyback diodes are cheap.
21 kV is going to get through anything silicon though.
… like a red-hot poker through butter…
Television flyback diodes should withstand twice the normal operating voltage of 29KV. Take one of these long cylinders apart and you'll see hundreds of sandwiched diode junctions.
In one direction. You'd still need to bias it off with -30kV DC
I've not heard of this before. How might I do this? Know of any resources I could go over to learn how to do this?
Google "pin diode switch design". Your gonna need one hell of a diode to do 3A at 21Kv though. This I have not seen this method used at such low frequency and high voltage.
The amperage could be far lower than 3A, perhaps even decimal amperage, would that make significant difference in the difficulty?
Well a pin diode would be hard to use because of the low frequency. A normal diode would be hard to use because your gonna need at lest 21KV DC to bias it. Add the fact you will need 42KV capacitors to block the dc bias and the thing starts to look like a lot more hassle then a vac relay to me.
15kHz
...
such low frequency
What kind of frequencies is this method generally used for?!
100MHz and up, typically. The pin diodes I've got laying around are meant for applications in the 2GHz range and I know there's parts meant for microwave applications at 15+ GHz.
In the world of integrated circuits 15kHz is embarrassingly slow.
15 kHz isn't particularly high frequency, you should be fine with any relay rated for more than 25kV
This is true, but most off-the shelf relays have a breakdown voltage of 1-5 kV. 25 kV is enough to sustain an arc several inches long under the right conditions. For example, most Jacob's Ladders are in the 15 kV - 30 kV range.
Know where I can find a small relay rated in that range? Everywhere I've looked I've only found huge relays rated for 50+ amps for quite a price.
Any help is appreciated!
I'm aware that Cynergy3 has 10KV and 15KV relays that you can purchase new.
Look for a reseller that specializes in high voltage parts. I've seen such a site in the past, but can't remember the URL.
3 Amperes is not very low. You are dealing with 63000 watts.
I have edited to reflect the smallness of the amperage, wasn't thinking at 1 AM. If we're in tiny decimal amperage ranges, does that change the answer?
I would suggest a vacuum relay. The price starts at around a hundred bucks and asymptotically approaches infinity.
example:
http://www.ebay.com/itm/Kilovac-KC-20-Vacuum-Relay-25KV-SPST-NO-26-5V-coil-/290822696914?pt=LH_DefaultDomain_0&hash=item43b6622fd2
The main limitation i know of is don't drop it!