# Average or RMS values for Pulses?

Discussion in 'General Electronics Chat' started by masa6614, Jul 26, 2010.

1. ### masa6614 Thread Starter Active Member

Nov 9, 2008
49
0
Hello everyone,
I'm hoping i can get some help on this. I plan to use a diode, 1N4148, but it will only see a single, very short pulse. Looking at the diode's datasheet, it says it is capable of handling a 1A square wave pulse for 1ms.
I modeled the pulse it will be seeing using ltspice, and as you can see from the attachment, the pulse peaks at around 7A, but quickly dies down in about 100usecs. So i change the range of the graph to a 1ms window, and want to know if I should use the Average (214mA) or RMS (841mA) calculated value from the curve, or neither, in determining if this diode can handle this pulse? Thanks!

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2. ### tom66 Senior Member

May 9, 2009
2,613
214
I thought the surge limit was 5A?

3. ### Ghar Active Member

Mar 8, 2010
655
73
That rms and average value is based on the length of your simulation.

If you wait longer those values will drop to 0.

I think an energy calculation like I^2t would be representative but I don't know what the best practice is.

Edit: Guess not...

This datasheet lists 4A for 1us or 1A for 1ms.
Waaaay different energy.

4. ### masa6614 Thread Starter Active Member

Nov 9, 2008
49
0
this is what the datasheet says -
Ratings:
4A for 1usec
1A for 1msec
0.5A for 0.5sec

5. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
Failure of a semiconductor junction is dependant on the temperature of the junction.

The temperature depends on the cooling characteristics, the turn on and particularly the turn off times as well as the energy input.

The pulse ratings are for non repetetive wave forms ie the occasional pulse. The IN4148 would soon die if fed a 4A pulse of 1μs as part of every 50 Hz cycle of say 10mA.