How to test Chinese 10A10 diodes?

[Chris Wilson]

I bought a small job lot of Chinese 10A10 diodes off an auction site. Rated 10 amps at 1000V they are for a couple of HV power supplies for valved amplifiers. In hindsight I might have been better being less impulsive and buying branded from the likes of Digi-Key. But I have 100 of them now, so I am wondering if a home brew test is possible, even if it's destructive? I have an adjustable Hi-Pot tester that'll go way beyond 1000V, but at micro amps. Short of building the diodes into the power supply and loading it up on a real amp, I am not sure how I could check two or three out. Any ideas? Thanks.

[houdini]

test the stats separately the 10 amps can be tested at just over the forward drop of the diode and the voltage can be tested at alot less than 10 amps.

[Balaur]

test the stats separately the 10 amps can be tested at just over the forward drop of the diode and the voltage can be tested at alot less than 10 amps.

While useful to discover obvious manufacturing issues or downright lies, independent parameter testing is not enough. Particularly, the Safe Operating Area (SOA) is difficult to find this way.

Maybe some ideas can be found here.

[Paul Price]

The reverse voltage rating is the critical factor for these diodes.  Apply at least 1000V to those you might want to test though a current limiting resistor and heat them up to the their spec'd max temp and monitor the current with a sense resistor to ground. Check the reverse leakage spec and the threshold voltage of observed avalanche with a high val limiting resistor.
You can do this with by building a simple flyback circuit using a pulsed relay, a makeshift 1000/1 probe and a HV inductor.

You can test the forward voltage characteristics at very safe low voltages, <12V and see if their Vf meets spec at the rated continuous operation current and temp.

 If these diodes are for low freq. rectifier use, these two tests will quickly tell you if the diodes are real or bogus.

The problem is that among a batch of diodes like this, they may be all good, only a few good, mostly all good, or mostly all bad. You may have to test a good portion of them all to be statistically sure.

[fpliuzzi]

This won't tell you all you need to know about your diodes in question, but this easy to build, low cost non-destructive high voltage breakdown tester by Charles Wenzel is a handy thing to have around. It tests semiconductor junctions using a test current range of 1-100uA (set by a pot on the front panel).

www.techlib.com/electronics/highvolts.html

For the version that I built for my bench (photo below) I incorporated a digital panel meter to display the breakdown voltage readout instead of the analog meter shown in the above link. I also added a slide switch so I could set the test voltage applied to the components to either 500V or 1000V.

Regards,
Frank

EDIT: Thanks SeanB for the reminder about the need for a DC supply of closer to 2KV to properly test 1000V diodes. Luckily, most of the 1000V diodes that I do use end up in vacuum tube guitar amps or HIFI gear, such as those made by Dynaco, that generally tend to have a B+ value of under 500Vdc.

[SeanB]

I bought a transistor/diode/capacitor/regulator tester from Frankie, it does the high voltage nicely, gives up to 1400V to test with.  Though with 1000V diodes I would regard a safe point for breakdown to be the voltage half of which is needed to avalanche it or where the leakage is over 100uA. So for a 1kV nominal diode you need to have at least 2kV test voltage.

Forward current is easy, a 12V car battery and a car headlamp, 55/65W, with both filaments in parallel, and check forward voltage of each diode in a quick test. Use a DVM on the 20V range and check with each one that Vf is below the rated max, probably between 0.6-1V. Quick and easy to do, 3 seconds per diode will be an easy way to check for each one.

[Chris Wilson]

I borrowed an HV supply off a friend and they tested out OK, with actually a higher breakdown than the few "branded" ones I had Thanks for the tips, and sorry for the late reply, was awaiting meeting up to borrow his gear. Cheers everyone!