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 Post subject: Testing Diodes for PRV - Semiconductor Guys?
PostPosted: Dec Wed 04, 2019 10:41 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 3912
Location: Florida
I have rectifier diodes that have been pulled from all sorts of things over the years. Most of these are either not marked or marked with numbers unknown to Google.

I tested them for PRV (peak reverse voltage) by applying DC through a resistor (1 meg) to limit the current. So far, all except one or two have withstood 500 volts with no sign of breakdown. The tests lasted maybe 15 seconds to a minute.

My guess is that if a diode doesn't break down immediately it isn't going to. Is this generally true or is there any need to let them "cook" a while at high voltage, cycle them or what?

My uses will be for 60 Hz so there won't be any fast rise times involved.

RRM

p.s. If anybody wonders why bother checking them, it's because I don't like throwing parts away if they might be useful some day, no matter how cheap the replacements might be.


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 Post subject: Re: Testing Diodes for PRV - Semiconductor Guys?
PostPosted: Dec Wed 04, 2019 3:34 pm 
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Joined: Sep Tue 30, 2014 6:08 am
Posts: 4877
Location: Norfolk, VA
I've used a Duoyi DY294 for 3 years now - it does breakdown (PRV/PIV) testing of diodes, transistors, MOVs and capacitors. Quick, 1 second, accurate results. It also will characterize zeners, It'll let you know if that Vce=400V transistor is genuine or not..

Image

Jestine Yong has by far the best tutorial on the DY294's use:
http://jestineyong.com/review-of-the-dy ... er-part-1/
It's a 3-parter, and I summarized the tests using a label placed inside the top cover of mine. The DY294 is available on eBay and at Banggood.

I salvage power diodes (>3A) and the TO-220/TO-247 duals, but for the small current axial stuff, I don't bother. 1 reel of 1N4007s off eBay has lasted about 11 years, and I have a huge stash of fast rectifiers thanks to TV shop surplus.

My "go to" diodes:

1N276 and 1n295 for germanium
1n4148 for signal switching, and the occasional 1N645 (military surplus stuff)
1N4007 and 1N5408 for rectifiers.
1N5817 and 1N5820 for Schottky
1N47XX(A) series for zeners - i don't bother with the 500mw stuff, except for the exceptional voltages not covered by the 1n47XX series.
KBPC series bridge rectifiers - 6, 12, and 25A stuff. Allied had some on their excess inventory list, so they were cheap and genuine. I've used exactly 4 of the 108 I ordered.... :x
For fast recovery or HV "fast diodes", I have a stash of old RCA, GE and Zenith OEM parts that serve me well, and a handful of MR856 fast high-current diodes.
All other diodes, I have to order, as the esoteric nature (TVS diodes, stud mount zeners, stud rectifiers, HV stacks) doesn't serve well in stocking.
Tube wise, I've got dozens of rectifiers, nearly all but the 5R4.

_________________
Brian
"Capacitor Cosmetologist since 1979"
USN Retired 1984-2006 (Avionics/Cal)


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 Post subject: Re: Testing Diodes for PRV - Semiconductor Guys?
PostPosted: Dec Wed 04, 2019 8:37 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8923
Location: Long Island
PRV testing is typically done with pulse voltages, not steady state DC, since the characteristic you are after is a dynamic one. A diode may suffer reverse breakdown more easily with a rapid voltage increase than a gradually applied, steady state voltage. Here's a good paper that lays out a simple, inexpensive way of testing diodes using an inductor and a switching FET to give you high voltage pulses from a basic pulse source. https://meettechniek.info/active/diode-dc.html You might get some use out of that x100 scope probe after all!

The author makes note of the importance of considering junction temperature in diode measurements, but this can be neglected if you just want a quick idea of a diode's PRV at room temperature. The paper doesn't go into it, but there is also a difference between the PRV a diode can withstand in just one single shot, and the peak repetitive pulse voltage that can be tolerated continuously.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


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 Post subject: Re: Testing Diodes for PRV - Semiconductor Guys?
PostPosted: Dec Thu 05, 2019 4:50 am 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 10009
Location: Santa Rosa, CA
Production testing on rectifiers is done by measuring the voltage at the rated maximum leakage current.

Diodes are not usually stressed to the breakover point.

Leakage testing is done 100% at 25C and sampled at 150C or higher depending on the specs.

You can test PRV on a curve tracer with 1% duty cycle.

A 1N4007 has to have less than 5 uA reverse leakage at 1000 V. Typically, they won't breakover until well above that... maybe 1400V or more. But that is not the applicable spec. Too risky to test for maximum voltage in a production line test.

Rich


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 Post subject: Re: Testing Diodes for PRV - Semiconductor Guys?
PostPosted: Dec Thu 05, 2019 1:22 pm 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8923
Location: Long Island
Measuring the PRV of a diode to find out the actual number is a different process than just ensuring it meets some minimum criteria in production. Diodes would cost a lot more than a few cents each if they had to be individually tested to determine the precise voltage at which reverse conduction begins.

It might also be mentioned that most rectifier type diodes can safely tolerate reverse breakdown safely as long as the current is limited enough to prevent heating of the diode junction, so they could be tested that way in production if necessary. But there are very few places where it would matter; usually it is sufficient to know the breakdown voltage will meet or exceed the published specification. The question here is what to do when there are no specifications that can be referenced.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


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