From: email@example.com (Bob Wilson)
Subject: Re: Difference between Switching and Linear regulator
Date: Thu, 26 Sep 2002 02:57:38 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
In article <firstname.lastname@example.org>, email@example.com says...
>I know that a switching regulator has more efficiency than a linear
>regulator. Let's explain:
>I have 36V AC output from a transformer (after the rectifier bridge).
>I need 12VDC and 5VDC rails.
>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.
>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
>Has anyone ever designed a similar switching power supply? Is the
>schematics available? As I understand it's pretty difficult to design
>a switching power supply.
First, you should forget about trying to build something yourself (a
switcher, in this case) that you do not understand the details of.
In your case, however, the most sensible approach would probably be to use a
switcher to supply the 12V output, which seems to be the big current
consumer, then use a linear to drop some of the 12V output to 5V.
This will make a huge improvement in efficiency over using linear conversion
for the whole shebang, and still involve only one switcher. Another
possibility is a dual output switcher, but these are DEFINITELY not for
someone who hasn't got a lot of experience. This is because only one output
will be properly regulated, and the other will be only passively regulated.
Done incorrectly, the passively regulated output voltage will wander all
over the map depending on load and other factors.