wrote in message
...
On Wednesday, January 20, 2016 at 9:13:52 PM UTC-8,
wrote:
l wish to know the difference between negative 48 volts and the normal 48
volts.
Also l will be glad if a could have a circuit for a regulated -ve 48
volts power supply at 3A. thanks

Thanks a lot Jeff you've actually given me a good understanding. so I can
build a normal 48 volts supply and ground the positive terminal instead.

That is right. Just build any power supply that will meet your needs and do
not ground any of the components in it. That isolates it from the chassies.
The ground the positive output instead of the negative output.

While not usually as high as 48 volts the 3 terminal regulators are made for
the negative as well as the positive output. The leads are sometimes in
different places and most of the diodes and capacitors are just reversed.
That is often the way unregulated supplies are made.