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*
BL> what a switch-mode doesn't like.

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

 The problem with an SMPS is that it never does start. A series
regulator will struggle on and get things turning in its constant-
current mode.

JB> But this is a DVD player IIRC so the high load should be less

 Yes. I'm surprised it takes 20W! I thought it was a VCR. If the 3A
is real (I doubt it) it will have the same starting surge as a VCR,
opening the drawer, spinning up the disc, etc. All fixed-field DC
motors are the same, and micro-controlled devices are twitchy. If the
voltage takes a sudden dive it's just as likely to reset, eject, or
god knows what!

JB> also something based around this layout _must_ be more effificent than
JB> a series regulator for any non-trivial current needs.
JB> .
JB> .       ____     ________     _____
JB> .           \   /   _|_  WWWWW
JB> .           ~~T~~   /^\
JB> .                   ~T~
JB> .                    |
JB> .      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
JB> .

 I have no idea what that circuit is supposed to show. ~~T~~ defeats
me.

 A shunt resistor works better than one in series, and I suggested a
light bulb because it makes a pretty good constant current, it runs
really hot which makes it small, and it's well insulated. It also
keeps the spiders out.

 Anyway, it's all a bit academic now. David has confessed that he has
6 x 2V lead-acid cells with knobs on. All he has to do is tap into 6V
and he's laughing.

 Lo-tech always works.

Regards,
Bob
   

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