723

Matthew S. Padden m.s.padden at hud.ac.uk
Tue Jan 20 16:43:42 CET 1998


Hi..

>
>        I wonder if anyone could point me to some 723 regulator circuits. Ok
>so I decided. Whilst I'm waiting for a solution to making some mixer boards,
>I'd get to and build another bench power supply. Since ever damn one of my
>original supplies has blown up for one reason or another.
>
>So I started building them up from the circuses in the NSC data book.
>Firstly to find that the negative regulator has no current limiting.
>Secondly, that I'd used a 10 pin TO5 can version which has no "Vz" pin on it
>and can't be used as a negative regulator. Dool! So I went out on the web
>and did a bit of a search and didn't uncover much. 
>
>I basically want a split supply. Each half, positive and negative to have
>independent voltage adjustment. Ideally they'd each have an adjustment for
>current sensing. So that I could set the maximum current before they tripped
>off.
>
>Which brings me to the next problem. The current limiting/sensing resistor
>is so damn low in value that I have trouble comprehending the value pot I'd
>have to use. Perhaps I could shunt it with a pot or something. But then I
>realized that the current limiting is a function of output voltage. Is there
>anyway of adjusting the voltage and current limit independently?
>
>And of course then doing it for a negative going regulator.
>
>Damn this would be so much easier if I had two separate transformers instead
>of a centre tapped one. :(
>
>So if anyone knows where I might find what I'm looking for "OUT THERE"
>somewhere. I would most appreciate it.
>

Well, I'd suggest something based on the Digisound 80-1 PSU. It features the following:

+/- 15V outputs (though you could invent whatever voltage you wanted), each independently 
trimmable.

current limiting on each output. Don't know how you'd overcome the low value pot though.


Basically the PSU is two identical positive supplies, each using a 723 and a pass 
transistor as current source. Each is fed from one of two (independently wound) secondary 
windings on the mains transformer, so both supplies float. The positive rail of the 
'negative' supply is hooked to the ground of the 'positive supply to achieve the +/- 
difference. Then use the centre rail as your 0V.

I can post you a schematic if you want, unless somebody (anybody?) has a scanned version in 
webworld somewhere.

Hope this helps
--
Matthew S. Padden
Computer Music Research Group
Room M5/14
Music Dept.
Huddersfield University
Queensgate
Huddersfield
England HD1 3DH
p: +44 1484 422288 x2402
f: +44 1484 472656
e: mattp at mindless.com
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