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Inrush surge damage to non-pulse-rated 1210 resistor?

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T

treez

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Hello,
Our contractor has decided that we can save money on our offline 240VAC lighting product by changing the 47R resistor in the attached (partial) schematic to a non-pulse-rated 47R, 1210 resistor.

At the moment, we use a pulse rated 47R, 1210 resistor as follows…..

SG73-RT series pulse rated resistor.
https://www.koaspeer.com/catimages/Products/SG73-RT/SG73-RT.pdf

The Power pulse seen by this 47R is also attached. (..this is worst case, ie , when the mains is applied to the product at the instant of 240VAC mains peak)

Do you think such a general, non-pulse-rated resistor will have reliability problems in this situation?
The product would be switched on once per day
(LT spice simulation of the switch-ON transient attached)
 

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  • Inrush power in 47R resistor.jpg
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  • Inrush in 47R.TXT
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Hi,

your chart shows about 120W for 70us.
This is just a bit above the 2A package (0805) specification of the pulse rated resistors.

contractor has decided that we can save money
Click to expand...
Make him responsible for eventual fails.

Klaus
 

In general I've often been able to dig and find app notes for the general pulse rating of non-pulse rated parts. I'd suggest trying to do that for the part your contractor wants to use.
https://www.vishay.com/docs/28870/pulseloadsmdlimit.pdf

Otherwise I'd consider the type of resistor. Some types are inherently more robust. One last trick: ensure it's a high tolerance like 5% to try and avoid any trimming which hurts power handling (may be hard to verify this however).
 

Any resistor will have a pulse Joule maximum regardless if
rated ot nor. You only get knowledge / confidence with the
rating (you would hope, but are not guaranteed, that a
pulse rated resistor outperforms one that has none stated).

Trimming involves creating a "neck" in the resistor material
slab, which necessarily concentrates power locally and
makes local power-to-blow less than the "bulk" material.

You could of course characterize any resistor you like and
get a power-to-blow vs pulse width curve, margin up for
what you believe is the worst case max pulse and worst
case max amplitude, and go with it. What margin to apply
however is yours to guess.
 

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