Problem:
There is a 1.5 Ohm 2512 conventional carbon film resistor which occasionally has to take the current spike of up to 25A for several hundred microseconds. Result: puff, spark, and a small hole in the middle of the resistive layer.
What should be the right part to survive the spikes? It should be small, cheap, low inductance. The tolerance of R up to +/-10% is fine.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
"Vladimir Vassilevsky" schrieb im Newsbeitrag news:4PDRk.4031$ snipped-for-privacy@flpi149.ffdc.sbc.com...
Hello Vladimir,
The keyword for web search is "surge resistor".
Their 1W resistors come close, but they will withstand only for a very few
100us.Another hit from Google: surge resistor
Best regards, Helmut
On a sunny day (Sun, 09 Nov 2008 09:57:14 -0600) it happened Vladimir Vassilevsky wrote in :
Cannot you use a piece of resistance wire and zig-zag it (not coil it) to avoid L?
Jan Panteltje wrote:
I think you mean
...and to expand on Helmut's search terms:
That is a tuff one. You say "There is a 1.5 Ohm 2512 conventional carbon film resistor." Where do you find a surface mount sm2512 carbon resistor. As you know carbon comp is great for surge current, much better than wire wound or thin film so that leaves us with thick film surface mount. You have >900W peak power, time to fix the real problem. I presently use the RHC series from Stackpole in SM2520 which is rated
2W. They can do a 10X rating for 5 sec (20W*5=100J). Then put about 5 thermal vias in each mounting pad to a large heat spreader. At 500uS, heat spreading may be too slow but may help. You need about a 1 joule rated part but I have never seen a SM 2512 rated in Joules. YMMV. Cheers, Harry
If you can't find a suitable part, then try this one.
-- Mark
Probably cermet, actually.
How low inductance? A 1.5 ohm wirewound won't have enough inductance to seriously wreck a several-hundred-us pulse.
You're taking about a quarter of a joule here.
John
If the surge is not within the intended linear function, shunting the current through a diode, zener or tvs, to reduce the energy developed in the circuit is advised. This allows survivability or safer failure modes under singlr fault abnormals, as well.
RL
If I remember correctly I^2*R, a 2512 smt isn't going to last ;D Even if you clamp it, thats a pretty big clamp (TVS). Not SMT.
Cheers
Originally i would have said metal foil, but you could parallel about
8 or 10 of these RM/RO in not much more space to get desired R. It seems that they will take the pounding.ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.