723 the final insult.

The Dark force of dance batzman at gist.net.au
Thu Jan 29 10:01:19 CET 1998


Y-ellow Paul 'n' y'all.
        I lost my poetic license. Got done for Rhyming under the influence.

Oh yea I agree. The old 723 is an excellent reg. I'm not saying it isn't.
I'm actually using three in this mixer I'm building because I can get some
odd voltages and still have good regulation.

Since this is the second time I've been pulled up on this I should have
clarified what I mean.

You can regulate an output voltage down to 2.5 volts but the input voltage
must be above 7. Actually I think it's something like 7.42. From the
measurements I've been getting. And yes. If you added your own op-amp pumped
zener reference you could do almost anything. But then why not just do
everything with a couple of op-amps and some transistors. It kinda defeats
the purpose of using a 723. Which in effect is exactly that. An op-amp
buffered reference and a pre configured op-amp. Plus a transistor and
another zener. (The zener doesn't exist in the case of the 10 pin TO5 package.)

So what I was trying to say was. Because the reference zener is about 7
volts, any input voltage below that will not allow proper regulation.

I hope I've put that one to bed.

But here's another quirky thing. I didn't know the above when I started out.
The data sheet may or may not have mentioned the reference voltage but none
of the calculations do. So My original app was for 3 votls to run both my
walkperson and a 3 volt halogen headlight for sk8ing at night. Nice and
bright from a 14 volt Magnesium battery. (Anyone know anything about
mil-spec Magnesium batteries please do tell...) Anyway one of the batteries
was rather dead. At least it doesn't deliver any current. So I thought I'd
try a 6 volt battery and that's when I discovered the regulation problem.

That asside I decided that when my source of these weird batteries ran out,
I'd swap to a small 12 volt SLA battery. So I'm now running the thing of my
brand spanking new power supply. No sag here. A good clean 3 amps available
to me. Now someone mentioned the use of a series pass transistor with a 723.
I'm using a TIP32 PNP transistor. According to what rough information I have
on the TIP32, I should be able to draw 3 amps across it given adequate
heatsinking. (Cooling whatever) This bike-headlight draws just over half an
amp @ 3 volts. But much to my surprise, even when mounted to a huge
heatsink, as the TIP 32 gets hotter, the voltage climbs as much as 100
milivolts. Now I haven't gotten to the bottom of this (There I go again with
the Rhymes) but it might be something to look out for.

Hope this helps.

be absolutely Icebox.
 _ __        _                              
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