snubber resistor power rating?

In article , Terry Given wrote: [...]

IRC person: Hello, how may I help you?

Ken: I need some pulse rated resistors.

IRC person: Good how many box cars full, and where the siding.

Ken: I only need about 100

IRC: 100 Box cars full is a small order but I think we can do it.

Ken: No, I need 100 resistors

IRC: Ha-ha-ha (Craching sound as he falls out of chair)

Phone: Click Buzzzzzzzzzzzzzzzz

Also IIRC, their spec was weirdly written. It was some time ago but I remember talking to the technical help from some resistor company and pointing out that according to the specs, the part could handle less power for 16mS than it could handle forever.

Caddock is a perfect example of a poor surge (Pulse) power resistor. They are thin film and X1.5 rated peak power. A good surge rated resistor is X5000 or maybe 5 Joules. Call Richard Caddock and see if they speak in Joules.

Cheers, Harry

A-huh, assuming. Harry

No, X1.5 applies to 0.1 attoseconds to 1.5 seconds. 1.500001 applies below

(or something like that)

Thermally the situation looks a lt like this:

Power in = I in R1 R2 R3 R4 R5 -> ---///------///----///----//----//--- GND ! ! ! ! ! --- --- --- --- --- --- C1 ---C2 --- C3 --- C4 --- C5 ! ! ! ! ! GND GND GND GND GND

C1 is the thermal mass of the actual resistive material.

R1 is the thermal conductivity of the resistive material

C2 is the thermal mass of the substrate the resistive material is on.

R2, R3 with C3, C4 are a lumped constant representation of the substrates bulk.

C5 and R5 are for the outer package to the air.

Unless you have some feel for R1 and C1 you really can't extrapolate from

IRC (the company, I do Recall Correctly) make some great smt resistors. And have peak pulse power curves.

Cheers Terry

Yep. A good data sheet is much better than an assumption:

Philips (or whatever the hell they are called now) have nice peak pulse power curves in their discretes book. an 0603 RC21 5% resistor has an average power rating of 63mW, and can take a repetitive 1ns 2W pulse every 1us.

It would be nice if they just gave us the damn RC thermal model, instead of maybe giving us peak pulse power curves. I got a nice surprise the other day when looking at an Infineon FET - a complete thermal model, as part of the datasheet. yay.

Cheers Terry

Now, find me someone who stocks them.

Wow, thats GREAT! pisses all over the CHP series!

I'll remember that part, thanks John.

Cheers Terry

doh.

Cheers Terry