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From: Fred Bloggs
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Subject: Re: V regulator input cap size?
References: <0001HW.B9D991AD000C5917163F7590@news.covad.net> <email@example.com> <0001HW.B9D9CD54001A5D15163F7590@news.covad.net> <0001HW.B9DAE8B7003F6E14163F7590@news.covad.net> <3DC1A954.firstname.lastname@example.org> <1%hw9.136243$Q3S.email@example.com> <3DC1AF48.firstname.lastname@example.org> <email@example.com>
Date: Fri, 01 Nov 2002 01:33:02 GMT
NNTP-Posting-Date: Thu, 31 Oct 2002 17:33:02 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
Spehro Pefhany wrote:
> In sci.electronics.design Fred Bloggs wrote:
>>Okay- thnx for replying. I suspected as much. You are aware that the
>>modern relays cannot withstand more than 110% nominal at continuous
> Derate the Ta(max) a bit then, easy without the "Easy Bake Oven" effect
> of wasted power. 85'C -> 60'C would give a lot of margin.
>>That is why I think a current source drive is best given a 30%
>>spread on line voltage.
> Not very often used on relay coils, particuarly with a linear regulator.
> Cost factors and such like. Probably the line voltage range is what drives
> the relay specs rather than the other way around.
You must be thinking of ACV relays, the DC relays don't leave a lot of
room. They have a real bad spread on pull-in voltage and it gets higher
with temperature by quite a high percentage by the time you hit 70C. If
you want save a current source then you could do something like this
where the capacitor guarantees turn-on and then the DC value settles
down to safely below over-voltage:
Please view in a fixed-width
font such as Courier.
| C | |
| | K |
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