That's possible, I've had that happen before where the leads pulled out enough to loss connection. it was a batch of diodes with bad bonding on the leads
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
Jamie wrote in news:Mxk8i.295$ snipped-for-privacy@newsfe06.lga:
You're mother is a retard.
1N4148s have a maximum reverse recovery time of 4ns. 1N400x diodes are around 1,000 times longer.
Do tell.. how would that work?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
I think you mean this one:
-- Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
------------------------------------------------------------------ In theory, practice and theory are the same, but in practice they are different -- Larry McVoy
I've seen 1n4148s fail across small relays, the 'off hook' relay in a modem. The cause? Surges in the switched circuit. Big ones. The loop area of the relays' contacts and connections--as laid out on the PCB--was sufficient to couple said surges into their coils & pop
1n4148s. A transformer, it was.This modem was in my PC. After losing several diodes in succession, I fixed the problem by 'improving' the layout to reduce the loop area & proximity to the coil.
Designing industrial stuff, we picked relays wired such that the one- turn switched loop wouldn't couple back to the coil, and laid out traces carefully on both sides exactly to avoid this problem. Otherwise, lightning-induced surges can make quite a mess of things as they propagate backward from the relays and onto your board.
Cheers, James Arthur
That's further off track than I'd expect from you Paul. What has this to do with suppression diodes?
Robert
-- Posted via a free Usenet account from http://www.teranews.com
last I checked 1N4148 was rated for 200 mA continuous.
Bye. Jasen
you get contact bounce on the relay.
Was that suppose to be a joke?
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
Not really, I really have no idea what s/he is talking about in terms of potentially harmful heating. Do you?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
And?
Robert
-- Posted via a free Usenet account from http://www.teranews.com
The person you need to blame this on is "Lamey The Cable Guy" or whatever f****ng stupid nym he is going by now.
The posts is a forgery/clone or whatever you want to call it. I did not write it. That goes for the next one you read as well. I was never in this thread.
Backspacing the URL to "appnotes/" presents a selection of pdf's.
-- Really? How about some facts? Like which relays are you talking about? Do you have some part numbers and some circuits or is this just some more of your pretense at knowledge bullshit?
Thanks for all the helpful replies.
It seems that the overall reliability of the device is best served not by a single diode, but by a transient voltage suppressor. The diode is a little better at protecting the transistor that switches the coil, but apparently it can cause a not-so-clean unmaking of the relay, leading to welding or erosion of the contacts in the case of a heavily-loaded normally-open relay. This is described in
If the contacts operating the relay become dirty or the control transistor begins to oscillate, then you will get repetitive surges at quite frequent intervals. It is better not to rely upon the single-pulse surge current rating of the diode.
A diode with a continuous rating equal to (or greater than) the maximum coil current will give peace of mind under all possible conditions of operation and mis-operation.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
I did not mention the single pulse surge current rating, but the repetitive surge surge current rating. But as with any limiting case, it is a good idea to include some safety factor. By the way, if the coil is driven by rapid pulses, its current will not reach the full, DC, steady state value, but will bounce between some lower limits.
Agreed. Especially if the diode is in a good thermal situation.
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