On Fri, 03 Nov 2006 21:09:20 -0000, (Chris
Lewis) wrote:

According to Mark Lloyd :
I have one 12VDC 1A power supply that is connected to 2 separate
cameras. This is a regulated supply, which was needed to reduce noise
in the video output of the cameras.

If one of them needed a different voltage, it would be possible to use
diodes (consider current here too, diodes have current as well as
voltage ratings) to drop the voltage (2 diodes in series give about
1.5V drop). If the devices have a common ground (as those cameras do),
that needs to be considered when powering multiple devices with 1
adapter.

Diodes in series is a reasonable regulator, but it might not
be good enough if the current through them varies a lot.


2 diodes in series is exactly what you have with a full-wave bridge
rectifier. I haven't heard of voltage drop varying with current.
Perhaps you could explain.

In which case, something like a three lead regulator would be
better. But, they usually need more than 1.2V of headroom to
operate.


A 78Lxx would be good if you don't need much current. Those are no
bigger than transistors.

BTW, I'm using a 78L05 to power a MAX233 (RS232 interface) to control
holiday lights (it worked fine for Halloween). The input to it is a
9VDC wall-wart. I can give more information on this if anybody cares.

It could be easier to use the regulator if you had to drop the voltage
a lot (too many diodes).

[That was what I was envisaging for my "universal wallwart strip".
A series of jacks at, say, 20VAC, with things that plug in that have
combinations of bridge rectifiers and regulator chips.]

Don't forget the filter capacitors (for DC).
--
52 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy