Yes sir they can fail to a short circuit. And some do it gradually so you can
watch it happen.We were amazed and watched it over and over, having never seen
anything like it before.It started with brief pulses of over voltage in an AC
application, No DC to continue the brief arc. After the initial insult that
started a defect, the normal operation would continue for a spell, enlarging
the defect until the circuit ceased to function. A open fail would have left
the FETS turned off, but a shorted fail turned both FETS on for the dramatic
conclusion.And that folks, explains the ringing in your ears and the lingering
glow of a flash in your eyes.
From: Charlie Blackham <char...@sulisconsultants.com>
To: EMC-PSTC@LISTSERV.IEEE.ORG
Sent: Monday, November 17, 2014 4:40 AM
Subject: [PSES] Surface mount resistors failing short circuit
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Have a discussion with an NRTL regarding fault testing on the charge/discharge
circuit for a 65mAh 3.1V coin cell battery in product being assessed against
60950-1. The NRTL insist on short-circuiting the single 560R current
limiting resistor and I am unable to find any evidence that thick-film or
thin-film surface mount resistors can fail short-circuit as they appear to fail
open-circuit Now, we could add a 2nd series resistor, but that would require
a board change - can SMT resistors fail this way, or are the NRTL being
over-enthusiastic (unreasonable) Thanks Charlie Charlie Blackham Sulis
Consultants Ltd Tel: +44 (0)7946 624317
LinkedIn:uk.linkedin.com/in/charlieblackham/ Web:www.sulisconsultants.com
Registered in England and Wales, number 05466247 -
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