What does the Ifsm rating of an scr mean?
- posted
17 years ago
What does the Ifsm rating of an scr mean?
"Peter"
** I = current, f = forward, s = single, m = maximum.Generally it refers to the largest, once in a while, *half cycle 50/60 Hz * current pulse allowable.
........ Phil
Thanks So I have a power supply that has a zener diode across the output to trigger an SCR in the event of over voltage....... The power supply's fuse is , say 10 amp. Does the SCR's rating have to be at least 10 amp or will a lower rating one do given that the fuse in the event of a short to ground through the SCR will fail pretty quickly
Peter
"Peter"
** Knew there was a catch to this.Post the full schematic and all the details an ABSE.
Or else piss off .
....... Phil
Ifsm is defined as "non-repetitive peak forward surge current 8.3ms half-sine-wave"
If you know something about your fuse, you *can* determine whether or not the SCR will clear the fuse without failing, clear the fuse but short-circuit in the process, or just plain old explode.
A fuse is characterised by the amount of energy it takes to melt it; the term used is "I-squared-t" or I^2t. If you have an I^2t figure for your fuse, you can compare it with the SCR's I^2t rating to see which one wins.
If SCR I^2t >> fuse I^2t, the SCR will happily blow the fuse, and keep on ticking. This is what you really want to have happen.
If SCR I^2t
^^^^^ or 10ms, but they will tell you in the datasheet.
Semiconductors are well known for being great fuse protectors !
So in your sentence above you are speculating a lower rated SCR will not fail (or presumably encounter any harm) whilst the fuse will, by maybe restating the question and critiquing your own logic you may well have answered it.
-- Regards Mike
Yeah OK, but what's with the piss off bit? Is there some unwritten rule about posting to this NG that I've missed somewhere?
"Peter"
** Cos YOU are bloody TROLLING !!!!!...... Phil
How is a request for information trolling? The power supply in question is a Johnson Unit that I've repaired for a friend.
Peter, Is that Phil Allison you are having a discussion with? If so, you are wasting your time trying to reason with him. Just killfile the graceless prick. I did, six months ago and have not missed him. His technical knowledge is quite good but he turns to psychotic abuse for no reason. Or maybe his reason is the gratification of getting a shocked reaction. Whatever. He is a troll and is not worth your trouble.
PH
"Peter Howard"
** Piss off - you know nothing IDIOT....... Phil
"Peter"
** Bloody TROLLs like Peter always squeal like stuck pigs when they are OUTED !....... Phil
Very true, and you have never stopped squealing, have you, troll?
-- Service to my country? Been there, Done that, and I've got my DD214 to prove it.
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