Breakdown voltage

antispam · 2019-12-04T17:14:47+00:00

I have set up simple circuit to test breakdown voltage: transformer + voltage doubler (with 22uF filterging capacitors) delivers about 156V. 156V goes trough 2.2M resistor to part under test. Paralel to the part is voltmeter. This seems to give reasonable results on most parts. However on some mosfets I see curious fenomenon: reading on voltmeter slowly increase and then stabilize at higher value. For example on one part fist reading may be 99V, but than climb slowly to 103. On another part starting at 66V result grows to 74V. AFAICS this is to slow to be purely electronic efect, rather looks like thermal thing. However power going to mosfets is too small to get substantial heating of the whole part. I wonder if this is selective heating of weak spots? Have anybody seen something similar? -- Waldek Hebisch

Dec 04, 2019 21 Replies

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jlarkin 6 years ago

First time I saw this, it was a power-on reset circuit. RC from the supply, emitter follower, schmitt trigger TTL gate. It oscillated so hard it never pulled the gate input up. Looked like a pretty good 100 MHz sine wave. We added a 39 ohm gate resistor, because I always liked the color codes on a 39 ohm resistor.

John Larkin Highland Technology, Inc lunatic fringe electronics

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Joerg 6 years ago

That is a feature, it's called VHF-Thevenin :-)

This can also happen when people place 74AUP and similar logic but use

70's style layout techniques with two-layer and GND islands.

Regards, Joerg http://www.analogconsultants.com/

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