Stress testing unknown diodes

I've retrieved some diodes I might like to use - Schottky rectifiers with under 0.2 Vf, but can't find any reference to them on the 'net. Any hints or tips on testing to identify maximum current / voltage - is there a method that only destroys one diode?

throbscottle said:

I've retrieved some diodes I might like to use - Schottky rectifiers with under 0.2 Vf, but can't find any reference to them on the 'net. Any hints or tips on testing to identify maximum current / voltage - is there a method that only destroys one diode?

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I'd measure the diameter of the leads and body. Then compare lead diameter to known diodes. Specs for many known diodes are listed on Digikey.

Pictures?

Hello,

You can test for max current by applying a known current and testing for temperature rise. With some diodes though they have to be soldered into a PC board of the right type and has the right pad sizes and possibly heat sink copper.
You can also test the forward voltage vs current this way too.

To test for maximum reverse voltage, you apply a reverse voltage and look for a maximum leakage current. It's nondestructive as long as you do not go too high on the voltage, which means you have to monitor the current.

To test for light sensitivity, you shine a bright light on the body and check the photo current. Clear glass diodes will exhibit more sensitivity than others as they act like a tiny solar cell.

Sometimes you might want to check the capacitance too.

To check the recovery time, you have to push a current through the diode in the forward direction, then suddenly reverse the applied voltage. You can check the time of the short spike of reverse current as the diode recovers. Some diodes have zero recovery time, but it may be just very low.

It depends on what tools you have. Every parameter has non-destructive test methods
and many destructive ones.

Power Supply with digital V,A,W readouts and CC limiter $50 ?
Scope, Generator ?

DMM with diode test mode gives the threshold at low current <= 1mA,

slope of I/V computes 1/
resistance = conductance which is proportional to power dissipation rating.

Vr or PIV can be measured with 1uA using high R value with V and DMM.

Some DMM's measure capacitance which is proportional to conductance. of Ids.

But diodes are only ~ $0.25 (1).
How much are you saving with this?

DMM diode testers can be very low currents too
(100 uA) thus < 200 mV Vf can be a bit misleading.

Measure the forward voltage drop across the diode when a small current (such as 10 mA) is passed through it. This can give you an idea of the diode's characteristics.

It was the fact that I already have them. It's just for an idiot diode - guess who's the idiot? DO-214AA / SMB sized diodes. I connected it via a 100k resistor to test reverse voltage. I hadn't thought about monitoring current - and only just come back to this thread. So anyway 36v is as high as I can go and it didn't start conducting, though I suppose with 100k it might be too much protection! I ran up to 4A through it and it also survived that ok (will only be subjected to 3A max in use anyway).

But it will certainly be interesting to try and characterise it further, especially since I think I have about 10 of them, so will try suggestions. (Case marking is 34 81 if anyone's interested.)

I seem to remember a VERY old magazine project, perhaps Practical Electronics?, where they used a high voltage generator and current limiting to measure the reverse breakdown voltage of rectifiers.

Context from where you retrieved them is important. Were they located on the output of a low voltage power supply? Then it is safe to assume that the peak reverse voltage to be below 30 volts.
The diode package will also give you a clue on the maximum current rating. If the body is plastic and sized like a 1N4000, then you can assume 1 amp.

I used to get PE every month! But that's just the kind of thing I had in mind.
They came from the on-board regulator of a Wi-Fi router. Other diodes of that size that I can identify (but not sbd's unfortunately) seem to be 3 or 4 amp anyway.

But I intend to give Mr Al's and Tony Stewart's methods a try anyway because it's' just plain interesting. And what's life without interesting?

throbscottle said:

I used to get PE every month! But that's just the kind of thing I had in mind.
They came from the on-board regulator of a Wi-Fi router. Other diodes of that size that I can identify (but not sbd's unfortunately) seem to be 3 or 4 amp anyway.

But I intend to give Mr Al's and Tony Stewart's methods a try anyway because it's' just plain interesting. And what's life without interesting?

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Hello again,

You should also try to determine if they are regular silicon diodes or Schottky diodes.
Schottky diodes will have a lot more reverse leakage. If you measure with an Ohmmeter, you might see 20k in reverse, which is low reverse resistance for a diode.
Regular silicon diodes cannot be measured in reverse with an Ohmmeter, their reverse resistance could be 500Megohms.

MrAl said:

You should also try to determine if they are regular silicon diodes or Schottky diodes.

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Read the very first line of the OP's very first post in this thread...

throbscottle said:

Schottky rectifiers with under 0.2 Vf

Click to expand...

ZipZapOuch said:

Read the very first line of the OP's very first post in this thread...

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Oh ok no problem. Then he can expect relatively high reverse current, and even with an Ohmmeter he can measure some resistance in reverse polarity.