Hi Bob.

16-Nov-03 09:41:02, Bob Lawrence wrote to David Drummond


 BL>> You can buy switch mode regulator ICs, but you have to wind your
 BL>> own switching coil and stuff around with fast diodes. If you're
 BL>> not worried about battery life, I'd use a simple series regulator
 BL>> with a nice big transistor on a nice big heatsink. If you need a
 BL>> dropping resistor, use a 12V light bulb across the regulator.

 DD>> I had thought of using a "simple series regualtor" but this is
 DD>> intended to be used at my "country weekender" where I
don't have
 DD>> mains. Battery life _is_ a consideration.

 BL> I haven't got the data sheets, but those little low-voltage IC
 BL> switch-modes struggle to get 50% efficiency, and at 50% to get 6.3
 BL> at 3A you'll put in 12.6 at 3A... so what's the difference with a
 BL> series regulator? Even if you got 70% (a miracle, IMO) you'd put
 BL> in 2.2A...

 BL> The series regulator has other advantages (besides keeping your
 BL> feet warm on a cold night). The VCR motors take a high starting
 BL> current before they get the wheels turning, and that's *just* what
 BL> a switch-mode doesn't like.

But this is a DVD player IIRC so the high load should be less,
also having a series regular go into overload "foldback" mode
due to too much current would be equally pointless.

also something based around this layout _must_ be more effificent than a
series regulator for any non-trivial current needs.
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 BL> Regards, Bob



 -=> Bye <=-

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