On Mon, March 21, 2011 12:02 am, Forrest W Christian wrote:
> I have an application which will be dissipating a significant amount of
> power through a resistor - for a very short period.  Say a dozen or so
> microseconds.
>
> Assuming I don't exceed the current specification, how long of a period
> can I average the power dissipation over?  Is there a way to calculate
> this?  I realize that it will probably depend on the amount of
> 'overpowering' I'm doing...
>
> Mainly I want to be sure I'm not going to cook a resistor by dissipating
> quite a bit of power through it for 20-30us - and have no idea where
> even to start to validate this from a mathematical/engineering standpoint=
..

This varies a lot depending on the type of resistor you are using.  Most
through hole and SMT resistors you find will be thin film or metal film
resistors- where there is a layer of resistive material that is laser
trimmed to the proper value.  I've had the best luck with carbon
composition resistors in a pulsed power application, but they are a lot
more expensive. The trimmed resistors usually include a very small gap
that, in high voltage pulse, has a high potential difference and makes the
resistor prone to arcing. This is one of the places where you will need to
carefully read the datasheets and look for peak current ratings. Most
resistors are designed/tested for just plain dissipation of power over
time with a DC-ish load without really pushing the voltage.

Regards,

Matt



Matt Bennett
Just outside of Austin, TX
30.5,-97.9

The views I express are my own, not that of my employer, a large
multinational corporation that you are familiar with.
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