Author Topic: Testing 1N4007 with a megger  (Read 8943 times)

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Offline taydinTopic starter

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Re: Testing 1N4007 with a megger
« Reply #25 on: November 02, 2019, 10:15:14 am »
Yesterday I have also tested a 1N4001. Same behavior as the 1N4007. Broke down at about 1800V, measures ok with a multimeter. So indeed, the 1N4001 is a 1N4007 in disguise.

This begs the quesion. In the old days, when they were classifying the diodes according to their voltage rating, how did they determine the breakdown voltage? I guess there's gotta be a way to detect the onset of avalance without damaging the diode.
« Last Edit: November 02, 2019, 10:26:36 am by taydin »
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Offline T3sl4co1l

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Re: Testing 1N4007 with a megger
« Reply #26 on: November 02, 2019, 11:13:27 am »
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Offline jaromir

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Re: Testing 1N4007 with a megger
« Reply #27 on: November 02, 2019, 11:23:07 am »
This begs the quesion. In the old days, when they were classifying the diodes according to their voltage rating, how did they determine the breakdown voltage? I guess there's gotta be a way to detect the onset of avalance without damaging the diode.

They are measuring Vbr even today, not just in old days. Breakdown voltage is measured at few orders of magnitude lower current than your limit, for example Vishay declares Vbr at 5uA - see https://www.vishay.com/docs/88503/1n4001.pdf
You mentioned 3mA before (I don't know how well is the current limited in your Megger, it's not designed to test semiconductors, after all) - that is quite a lot for a small diode at 1,8kV, no wonder they got damaged, especially on repeated measurements.

The Vbr parameter is measured using current source with high compliance voltage, measuring voltage on the diode.
 
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Offline mzzj

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Re: Testing 1N4007 with a megger
« Reply #28 on: November 02, 2019, 09:29:49 pm »

This begs the quesion. In the old days, when they were classifying the diodes according to their voltage rating, how did they determine the breakdown voltage? I guess there's gotta be a way to detect the onset of avalance without damaging the diode.

Read somewhere (usenet?) that back in the day silicon diodes would fail catastrophically at overvoltage. Controlled avalanche diodes are bit later improvement.
https://groups.google.com/forum/#!search/controlled$20avalanche$20diode$20series/rec.radio.amateur.homebrew/XLRgaCb7XQE/tO2M_k_fleYJ
 

Offline taydinTopic starter

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Re: Testing 1N4007 with a megger
« Reply #29 on: March 06, 2020, 07:38:04 pm »
I just wanted to revisit this with new information.

Earlier, I had done a ramp test to 2.5 kV on a 1N4007 diode with a series 10 MΩ resistor. The diode had failed at a voltage about 2 kV and later measurements showed that the diode had permanently degraded. So my conclusion at that time was that, even with a series resistor, a high enough voltage causes the diode to fail.

But there is more to this story and that statement isn't correct. When looking at the datasheet of 1N4007, the worst case leakage current is specified to be 50 uA (at rated voltage and 100 degrees celsius temperature). This means that the manufacturer guarantees that the diode will NOT GET damaged under these conditions.

But when I made the ramp test, at 2 kV, with a 10 MΩ resistor, the resultant current is 200 uA, well beyond the 50 uA that the manufacturer specifies. If I had used a 40 MΩ resistor, the diode would not have failed at 2 kV.
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Offline taydinTopic starter

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Re: Testing 1N4007 with a megger
« Reply #30 on: March 06, 2020, 07:45:41 pm »
So I did another test, but now using a lower voltage BAW27 diode (rated reverse voltage is 60V). The worst case leakage current is specified to be 50 uA (rated voltage, 100 degrees celsius temperature).

I used my 2450 SMU to source 60V and measured the leakage current. I waited until the current settled at about 20 nA. Then I configured a 50 uA current limit and started to increase the reverse voltage. The leakage current increased to about 100 nA at 100V. And finally at 110V, the current hit the 50 uA limit.

Then I reduced the voltage back to 60V, and indeed, the leakage current returned back to 20 nA.

So the conclusion is that an avalanche is not harmful to the diode if the current stays below the worst case leakage current specification.
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Offline zitt

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Re: Testing 1N4007 with a megger
« Reply #31 on: March 06, 2020, 08:11:25 pm »
Wonders to self; how this breakdown "knee" is temperature related.... If running at 120C; is the breakdown voltage higher or lower. what about -40 C?
 

Offline taydinTopic starter

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Re: Testing 1N4007 with a megger
« Reply #32 on: March 06, 2020, 09:11:52 pm »
Wonders to self; how this breakdown "knee" is temperature related.... If running at 120C; is the breakdown voltage higher or lower. what about -40 C?

Don't know. But the reverse leakage is temperature dependent. For the BAW27, the reverse leakage current is 100 nA at 25 degrees and 50 uA at 100 degrees.
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Offline mikerj

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Re: Testing 1N4007 with a megger
« Reply #33 on: March 06, 2020, 10:29:02 pm »
After the above  test, I did another ramp, this time 5 kV. But the test stopped at 4.8 kV, because either the resistor broke down or the diode. Not sure which, will find out

I measured the resistor, it is still 10 MOhms. And just to make sure the diode is OK, I ramped it up to like 800V and it didn't breakdown. So I suppse the resistor arced internally, but the megger shut off the voltage before the diode would get killed. The resistor is 1/4W metalfilm.

So can we conclude that limiting the current prevents the junction from sustaining permanent damage under avalanche?

Nope, we can't ...

If the resistor broke down then you didn't limit the diode avalanche current to the expected value.
 

Offline taydinTopic starter

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Re: Testing 1N4007 with a megger
« Reply #34 on: March 07, 2020, 09:32:05 am »
If the resistor broke down then you didn't limit the diode avalanche current to the expected value.

The resistor broke down at 4.8 kV, which is way past the 2 kV point where the diode avalanched.
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Online Zero999

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Re: Testing 1N4007 with a megger
« Reply #35 on: March 07, 2020, 10:35:28 pm »
If the resistor broke down then you didn't limit the diode avalanche current to the expected value.

The resistor broke down at 4.8 kV, which is way past the 2 kV point where the diode avalanched.
250µA might have been too high for the diode though.
 

Offline Vovk_Z

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Re: Testing 1N4007 with a megger
« Reply #36 on: March 09, 2020, 09:38:17 am »
To resistor worked as resistor (but not as air gap) you have to obey it rated voltage.
1/4W resistor usually is something about 250V rated (300V peak).
So for your tests you need to use 4-10 series connected at least 1 W rated resistors.
 

Online rodpp

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Re: Testing 1N4007 with a megger
« Reply #37 on: March 09, 2020, 11:30:17 pm »
I did the reverse breakdown voltage test on a 1N4007. My sample knee was around -1600V:



And the forward IV curve before and after the test was the same, so no damage:



If the reverse current is lower than the datasheet specification, no damage should occur with the diode.
 
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Online Zero999

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Re: Testing 1N4007 with a megger
« Reply #38 on: March 10, 2020, 08:42:07 am »
I did the reverse breakdown voltage test on a 1N4007. My sample knee was around -1600V:

(Attachment Link)

And the forward IV curve before and after the test was the same, so no damage:

(Attachment Link)

If the reverse current is lower than the datasheet specification, no damage should occur with the diode.
Firstly, please consider those using a lower resolution by not posting such large images and PNG is much better suited to charts, than JPG, which is meant for photographs.

Yes, you tested it at a much lower current than the original poster and just because the forward VI curve is unchanged, it doesn't mean it's not damaged. The only way of knowing that is to test the reverse breakdown voltage again.
 

Online rodpp

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Re: Testing 1N4007 with a megger
« Reply #39 on: March 10, 2020, 10:14:14 am »
Thanks for the tip about the figures.

Regarding the diode test, I did both (forward and reverse) using a curve tracer that apply a retified sin wave repeatedly. Each graph has around five half waves, but during the test was applied much more repetitions. It is clear in the reverse breakdown test graph, where it is possible to see various traces at the knee.
 


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