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From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: Predictive failures
Date: Wed, 17 Apr 2024 03:46:02 -0000 (UTC)
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John Larkin wrote:
> Don wrote:
>>john larkin wrote:
>>> Don wrote:
>>>>Don Y wrote:
>>>>> Is there a general rule of thumb for signalling the likelihood of
>>>>> an "imminent" (for some value of "imminent") hardware failure?
>>>>>
>>>>> I suspect most would involve *relative* changes that would be
>>>>> suggestive of changing conditions in the components (and not
>>>>> directly related to environmental influences).
>>>>>
>>>>> So, perhaps, a good strategy is to just "watch" everything and
>>>>> notice the sorts of changes you "typically" encounter in the hope
>>>>> that something of greater magnitude would be a harbinger...
>>>>
>>>>A singular speculative spitball - the capacitive marker:
>>>>
>>>>    In-situ Prognostic Method of Power MOSFET Based on Miller Effect
>>>>
>>>>    ... This paper presents a new in-situ prognosis method for
>>>>    MOSFET based on miller effect. According to the theory
>>>>    analysis, simulation and experiment results, the miller
>>>>    platform voltage is identified as a new degradation
>>>>    precursor ...
>>>>
>>>>    (10.1109/PHM.2017.8079139)
>>>
>>> Sounds like they are really measuring gate threshold, or gate transfer
>>> curve, drift with time. That happens and is usually no big deal, in
>>> moderation. Ions and charges drift around. We don't build opamp
>>> front-ends from power mosfets.
>>>
>>> This doesn't sound very useful for "in-situ" diagnostics.
>>>
>>> GaN fets can have a lot of gate threshold and leakage change over time
>>> too. Drive them hard and it doesn't matter.
>>
>>Threshold voltage measurement is indeed one of two parameters. The
>>second parameter is Miller platform voltage measurement.
>>    The Miller plateau is directly related to the gate-drain
>>capacitance, Cgd. It's why "capacitive marker" appears in my
>>original followup.
>>    Long story short, the Miller Plateau length provides a metric
>>principle to measure Tj without a sensor. Some may find this useful.
>
> When we want to measure actual junction temperature of a mosfet, we
> use the substrate diode. Or get lazy and thermal image the top of the
> package.

My son asked me to explain how Government works. So I told him. They
hire a guy, give him a FLIR, and bundle both with their product as an
in-situ prognostic solution.

Danke,

-- 
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.