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From: Lizard Blizzard
Subject: Re: V regulator input cap size?
Date: Thu, 24 Oct 2002 12:39:36 -0700
References: <0001HW.B9D991AD000C5917163F7590@news.covad.net> <email@example.com> <0001HW.B9D9CD54001A5D15163F7590@news.covad.net> <0001HW.B9DAE8B7003F6E14163F7590@news.covad.net> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
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Frank Bemelman wrote:
> "Watson 'Atto Parsec' Name" schreef in bericht
>>In article <email@example.com>,
>>firstname.lastname@example.org talked about...
>>>>>The easiest way is a 7824 followed by 7812. Both should be
>>>>>on a heatsink, you can use a single heatsink for this.
>>>>I searched National's web site and they didn't have a 7824. But
>>>>assuming that the 7824 has the same 35V maximum limit on input
>>>>he would still have the same problem, the unreg'd voltage would still
>>>>exceed its limits.
>>>It can handle 40V.
>>That's still 9 or 10V short of what the unreg'd supply voltage will be at
>>the filter cap.
> You accidently snipped away the part were the OP mentioned the *new* values:
I didn't snip it, perhaps someone else did previously. But I have used
transformers similar to these control transformers, and they put out
about 42 volts at the filter capacitor. You have to remember that the
transformer gives 28VAC at full load, so at much lower load, the
secondary AC voltage will be substantially higher. And after
rectification, it can go as high as 44 or so VDC which is about 31 to
32VAC times 1.414. If a regulator with 40V max is used, it will still
have an input voltage that exceeds its maximum.
>>>>Supply voltage measures at 28vac rms. (for some reason it's running
>>>>lower than normal for HVAC) which will give ~ 37vdc(?). The max input for
>>>>7812 is 35v.
> Frank Bemelman
> (remove 'x' & .invalid when sending email)
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