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From: Lizard Blizzard
Subject: Re: V regulator input cap size?
Date: Tue, 22 Oct 2002 08:13:35 -0700
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Dave Dahle wrote:
> "DaveC" wrote in message
>>What to do? I'm using 35vac from an HVAC control-voltage transformer. The
>>transformer is used for standard control circuits in the HVAC unit on the
>>roof, so I can't change the transformer.
>>Short of getting a 35v/20v transformer (or such unavailable combination),
>>suggestions how I can make this voltage useable for my 12vdc circuit?
>>Two-diode rectification? Single diode?
> How about a two-stage approach? Find a regulator that'll accept a higher
> input voltage to knock the supply voltage down to a more acceptable level to
> feed the 7812 (Correct me if I'm wrong, people, but isn't there a way to
> "float" an LM317 to accomplish this)?
> Unless you want to throw major heat and install a honking big series
Probably the best idea as long as there is enough current to guarantee a
minimum voltage drop, of say 15V. But it could be done cheaply with 18
to 24 1N4002s in series in the input. They will drop about .8V each at
300 mA or so.
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