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From: Lizard Blizzard
Subject: Re: V regulator input cap size?
Date: Tue, 22 Oct 2002 09:10:24 -0700
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Thomas C. Sefranek wrote:
> Ahhh Dave,
> Either suggestion generates the same "major" heat!
One other thing that could reduce the heat is to use a reactive element
such as a cap or inductor between the secondary winding of the
transformer and the full wave bridge. However if it's a cap, it might
be somewhat large for a couple hundred mA. And altho it dissipates very
little heat, it still would not limit the max voltage if the current was
to drop to a low level.
> Dave Dahle wrote in message
>>"DaveC" wrote in message
>>>What to do? I'm using 35vac from an HVAC control-voltage transformer.
>>>transformer is used for standard control circuits in the HVAC unit on
>>>roof, so I can't change the transformer.
>>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
>>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
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