From: John Woodgate
Subject: Re: Difference between Switching and Linear regulator
Date: Wed, 25 Sep 2002 13:58:14 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Wed, 25 Sep 2002 13:47:54 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Peet Grobler
wrote (in <firstname.lastname@example.org>) about 'Difference between
Switching and Linear regulator', on Wed, 25 Sep 2002:
>I have 36V AC output from a transformer (after the rectifier bridge).
>I need 12VDC and 5VDC rails.
If you have 36 V AC after the rectifier, something is very wrong!
>I can either have two swtiching regulators to bring this down to 12V
>and 5V, or have, e.g., an 7812 (for 12V), and on the 12V rail, a 7805.
The liner regulators will indeed waste a lot of power and you have a
problem to get rid of the heat.
>What would the implications be for me? The 12V is used to charge a
>battery (for backup if mains fails). This whole thing will be plugged
>into a mains plug.
>Will I notice the difference in electricity usage, when using linear
>regulators rather than switching regulators? This power supply will be
Why start with 36 V? That's the source of your problem. You need about
17.5 V DC (design-centre value) at the input of your 7812 to allow for
operation with 10% low mains voltage.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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