Al salaam a'alaykum Brenton

17 Nov 03 08:48, Brenton wrote to All:

 B> David has a DVD player, not a VCR.  The DVD player has a plug-pack 
 B> power-supply which normally plugs into a 240v GPO and has an output rated 
 B> at 6.3v 3A  His country pigeon coop has a battery powered DC supply where 
 B> the output can vary from 11.5v to 14v.

That's what I've been trying to tell him. He seems to have something else
stuck in his mind.....

 B> He does NOT have a 6.3v to 240v inverter.  The plug-pack which was 
 B> supplied with the DVD player is the reverse of that.  It is a 240v AC to 
 B> 6.3v DC switched-mode supply which is rated at 3A

Exactly!

 B> David, the one smart thing Bob suggested was to look at how your 
 B> batteries are wired.  It is not uncommon for large DC battery banks as used 
 B> in outback situations to consist of half a dozen 2v cells hooked up in 
 B> series.  I have seen a few setups like this in the north west corner of 
 B> South Australia and 2v cells seem to be the go.  

That is exactly how the cells are configured.

 B> If your battery pack does indeed consist of 2v cells, then you could just 
 B> take a tap off of the third one which would provide you with an output 
 B> voltage close enough to power your little DVD player with 100% efficiency.  
 B> My bet is that the DVD player itself will have some sort of regulator 
 B> internally and the plug-pack is just a primary step-down so 
 B> it doesn't have to work to hard.  If you plug it in and it blows up, you 
 B> will have discovered why God invented the term Warranty Claim. Just take it 
 B> back and look surprised that it failed.  They won't be able to prove 
 B> anything.

I guess I should use the centre tap as +6V with the 0V being common to the
DVD and the 12V TV?

 B> If John can't supply you with the part numbers from Jaycar for the 
 B> components you need to build the switcher, I will have a look for you in 
 B> the next few days. I may even have a PCB here that could be used to build 
 B> it on, as I do have a small board in my product which contains a LM2595 
 B> switcher and a single MAX202 chip.  The only issue may be that I use a 
 B> fixed output switcher and for your supply there will need to be two 
 B> resistors which the board won't have space for, but it should still be 
 B> easier than trying to bread-board it.

I too want a fixed output - fixed at 6.3V not 5 or 9 or whatever those
things seem to come at.

I've been considering Bob's idea of the series regulator - the LM350 looks
like it would do, and the component count is lower than the switch-mode,
with a simpler circuit.

What do you think (assuming the 6V ida doesn't work......)?

Regards,
David

--- Msged/LNX TE 06 (pre)