From: Don Pearce
Subject: Re: Difference between Switching and Linear regulator
Date: Wed, 25 Sep 2002 11:46:19 +0430
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On Wed, 25 Sep 2002 07:02:56 GMT, email@example.com (Peet Grobler)
>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.
Assuming the battery charging is merely a trickle, and not substantial
(after the initial charge) don't worry about it.
Multiply 5V by the current to get switched mode consumption. Multiply
36 volts by the current to get linear consumption.
Multiply both of these powers by the number of hours the unit will be
switched on during your electricity billing period. Multiply those
figures by the unit price for electricity, and you will have two costs
- one for switched and one for linear.
The actual numbers, only you have the information to work out.
As for designing a switching supply, the schematic is just the start
of many long hours of sweat, and many iterations of circuit layout.
Don't go there unless you are designing for production.