Power resistor can handle short , high power pulses?

Hi,

We are using the RSF300JB-91-100R resistor (100R,3W) in an inrush overvoltage damping circuit as attached. (LTspice also attached)
Will this resistor be able to handle these power pulses several times per day for 20 years?
As shown, the power pulse is 1700W peak and lasts for some 35us.

RSF300JB-91-100R resistor datasheet
**broken link removed**

Hi,

I don't think this is a suitable resistor for pulse loads.

Why don't you choose a pulse load rated resistor?
Or at least a carbon resistor?

Klaus

Pulsed power handling is tricky and I'd say you
want to do some test-to-fail and determine how
much safety margin there may be.

There are some resistor familes which bother to
rate pulsed power and many that do not.

Thin and thick film resistors will both have a
power-to-blow curve. There may be a lesser
stress power-to-drift as well, although a finite
drift may be tolerable if it has an acceptable
asymptote (thermal "annealing" of material
would reach a steady state; thermal entrainment
of resistor film into passivation could go on until
fail-open).

I'd worst-case pulse width and peak current by
at least 20% apiece and see what you see. I'd
bring the rep rate up from "couple daily" to maybe
10ms period, figuring <1% is probably close enough
to sparse for the experiment. Then 2X daily * 20 yrs
is 14600 cycles which would get done in 146 seconds.
You could try that and, if it doesn't blow up or hit a
spec temp limit, let it run over the weekend for more
confidence.

Now in this graph (from real bench data, on an IC
thin film resistor) 35uS is looking like it's pretty much
on the asymptote (non-adiabatic) and only 1W/mil2
pulsed power density.

Now if I took an 0804 resistor to have maybe 7x3mm
of resistor film area, and did the arithmetic:

3000um*7000um/(mil/25.4um)**2*1W/mil2

= 32550 W

So you've got maybe a factor of 20 to soak up any
material, size, repetitions & rate, or general
physics-of-failure related discrepancies. Not a
bad position to be in, I guess.

But I'd still be testing (I did this testing for the results
shown about 25 years ago because I needed to
know and nobody could tell me).

Wire-wound resistors are more reliable for this kind of purpose..

My personal painful experience:

If the resistor does not specify a pulse rating, then no amount of test cannot guarantee that you won’t have future issues.

this is some guidance
go to

search on pulse handling in keyword search box on right
click on application notes under documents box on left

there should be four application notes - 3 on resistors and one on power semiconductors

google rwr pulse handling
the first item up (when I did it) is a PDF about wirewound resistors and pulse handling thereof

google wire wound resistor pulse handling
scroll down to resistor pulse handling capability -sandia national ...
this references a PDF report on wire wound resistor pulse handling
there is a short section on how to correct for resistors that are not wire wound

page 8, Appendix 1 has the table from Dale (when it was Dale and not Vishay)
that I used 30 or so years ago to select and ensure the resistor in pulse situations would survive over the long haul

I ran across this today, a Vishay series of high power
density resistors.


in the datasheet is a nice pulse power vs pulse width
graphic.



May or may not be suited to this specific (OP)
application, but there is some thought given to this
problem in certain quarters.

It could be necessary to series / parallel devices to
get a total Pdiss that survives. That's an old trick.

Note the specificity of conditions called out, and the
manufacturer's recommendation to test it yourself.