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Fast (+cheap!) diodes for 6kv+/0.5A/40khz?

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benryanau

Fri Jan 11 2013, 08:13AM

Registered Member #9445 Joined: Thu Jan 10 2013, 04:16AM
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Posts: 5

Hi all.. first post after a long time lurking!
I'm trying to find a HV diode (qty ~20) with a PIV of 6-12kv, running a max of 500mA.
I've tried microwave oven diodes but their recovery time is just too slow, they can't switch beyond a few khz.

Strings of UFxxx or FRxxx 1kv diodes is just too unwieldy and some projects don't have the power budget for the corona loss. Of course I could just go to Element14, RadioSpares, Mouser etc, but I simply don't have the cash to spend on that option. I'm in Australia, in a country town, so surplus isn't an option locally. I use a mob called Futurlec a lot but they only have 1.5kv UF-style parts.

So does anyone have any suggestions on a cheap online source of suitable diodes (that won't kill me with shipping)?

Sulaiman

Fri Jan 11 2013, 01:31PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I buy most of my fast high voltage diodes from China via eBay,
6 to 12 kV 500 mA fast diodes are not cheap, are you sure that you need 500 mA (dc) rated?
Decide what are the MINIMUM voltage and current ratings that you need before buying.
e.g. 12 kV x 500 mA = 6 kW ! .... is this the intended power level?

benryanau

Fri Jan 11 2013, 01:45PM

Registered Member #9445 Joined: Thu Jan 10 2013, 04:16AM
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Posts: 5

Ahh righto. I could get away with 100ma I spose, limits the application a bit (hipo CW multiplier for example). It's not 6kw continuous ofc but peak currents (parallelled transformers, coils) have me worried, wouldn't want to blow the string. But if it makes them affordable I'd be happy with 0.1A,,
Would you be able to rattle off a few part numbers for me that you've ordered? Finding them on Aliexpress/ebay is like a needle in a haystack..

cheers

HV Enthusiast

Fri Jan 11 2013, 02:36PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Actually all high voltage diodes are merely strings of smaller diodes, usually in potted enclosures or bricks.

There are some STPS shchottky diodes rated for 1000V and high frequency use that could be series'd for higher voltage diodes.

benryanau

Fri Jan 11 2013, 02:56PM

Registered Member #9445 Joined: Thu Jan 10 2013, 04:16AM
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Posts: 5

Yeah I know they're just a string of junctions in a single package, hence their high forward voltage (>10v usually).
I'm not against "strings" in any theoretical/technical sense, just the physical impracticality (and labour) of making strings from discrete diodes.
Some of the projects are challenging enough without spending hours on intricate dozen-plus diode spiral-helixes.. and only to find at the end your circuit won't work or runs crosseyed from the sheer corona loss of those bloody strings..

There's gotta be a commonly available 10-15kv high-speed rectifier capable of 100ma out there. What do the inverter microwave ovens run? And TV EHT diodes, maybe they're only 5ma but they're a start..

Haven't seen the STPS series, but I've seen a number of 1.5kv high-speed (and avalanche-capable) diodes around but they tend to be pricey and not always avail from convenient suppliers. Plus it means discrete strings.. not going there :)

Proud Mary

Fri Jan 11 2013, 03:17PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I bought two dozen 50VA 1kV 35 kHz electronic neon PSU for next to nothing, and found myself needing some fast recitifiers to put them to use.

I couldn't find very much that was good for 35 kHz - that was also affordable by my modest lights - until I stumbled on these RGP02-20E 2000V 0.5A Fast Switching Rectifier Diode. They are 300nS.

Obviously, you'd still have to string em together, but only half as many as with the UF4007s.

Pinky's Brain

Fri Jan 11 2013, 03:56PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Never bought them but I have looked before. Found 2CL2FX, hv37-XX (with X depending on the voltage) and UX-FOB diodes meet your specs ... doubt the ones here are original HVCA parts though, so the specs might be a bit dodgy.

Caveat emptor.

benryanau

Sat Jan 12 2013, 01:05PM

Registered Member #9445 Joined: Thu Jan 10 2013, 04:16AM
Location:
Posts: 5

Thanks lads, with your help I've compiled a list of likely diodes.
Though I didn't find the bargain I was looking for (qty 10-20 at low unit price with free/low shipping) I'll keep an eye out.
Here's a table (from OneNote, had to reformat as text) of candidates. Prices are rough per-unit, in Aussie Dollars (close to the greenback).
[b]

TVR30 ------- 30kv -- 10ma -------- 100ns -- $1.00
2CL2FH ------ 12kv -- 60-120ma ---- 150ns -- $1.70
2CLFL ------- 15kv -- 100-220ma --- 100ns -- $2.40
2CLFJ ------- 15kv -- 60-120ma ---- 150ns -- $1.80
RGP02-20E ---- 2kv ---- 500ma ----- 300ns -- $0.50

[/b]

I might pop this on the wiki since I've seen the question asked before..

Patrick

Sat Jan 12 2013, 07:53PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

will you be operating your rectified frequency at 5 to 10 times your Trr?

benryanau

Sun Jan 13 2013, 05:39AM

Registered Member #9445 Joined: Thu Jan 10 2013, 04:16AM
Location:
Posts: 5

Patrick wrote ...

will you be operating your rectified frequency at 5 to 10 times your Trr?

I don't get you.. do you mean will I be working within the calculated max freq of the diode based on its Trr?

TBH I don't know how to easily relate Trr to max frequency. Wish I had a reference table.
Something I do remember, the freq time period is 10 x Trr,.. I read somewhere 10ns = 10Mhz, perhaps it will scale from there.

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