+ - 15 volt supply

[Harry Bissell]

I'd have to differ...
Half wave supplies suffer from major problems. One is the ripple is usually much
worse than a full wave supply. This is because the rectifier diode can "recharge"
the capacitor only once every 16.6mS. So you need twice as much capacitor for a
given load current.
There is also no "hard" DC ground... ground is the center tap of the two filter
caps. So unequal loading can pull the ground away from center... and you have to
rely on the regulators to compensate. Half wave supplies are suitable only for
low and "well known" currents. If the current draw will vary much, avoid them.

OTOH if you have a circuit that can survive on (essentially) a couple of 9V
batteries than the circuit can benefit from the simplicity of the half-wave
supply.

Full-Wave supples refresh the cap every 8.33mS. The ripple frequency is twice as
high (120Hz) so it is much easier to filter out ripple. The Full Wave Bridge uses
four diodes and a center tapped transformer. Check out www.signaltransformer.com
for some small transformers that can be used. There used to be an excellent
tutorial but I didn't find it. I will bitch at them for sure as soon as I'm done
here.

Half-wave or Full-wave the choice is yours. If you need a lot of current use the
full wave or else the caps will have to be really BIG.

:^) Harry


Antti Huovilainen wrote:

> On Mon, 20 Dec 1999, Gerry Dahl wrote:
>
> > Hi,
> > I'm looking for a very good +15 - 15 power supply project, I had on in mind
> > but the IC in it is obsolete (MC1468) and I need to build 2 of them.
>
> If you don't need the utmost in precision, a 15V AC transformer (get a
> wallmart and you don't have to worry about high voltages or grounding),
> simple half-wave rectifier and a pair of 7815/7915 will do. I use one in
> the modular I'm building.
>
> Antti
>
> "I'm just gonna go home, lie down and listen to country music.
>  The music of pain" - Xander