Design voltage divider circuit

1. Mar 22, 2013

ProPatto16

1. The problem statement, all variables and given/known data

The memory components in a personal computer require voltages of -12 V, 4 V and 12 V all with respect to a common reference terminal (you can assume this to be the ground). Design a circuit to achieve this if the total power supplied to the divider circuit is 80 W and the supply voltage is 24 V.

3. The attempt at a solution

its simple to make the voltage divider for the positive terminal voltages, but im not sure, mathematically, how to include a negative terminal.

Ive been placing a resistor between the negative terminal on the source and the ground but whatever resistor i put in there changes the rest.

i suppose my question is
How do you achieve negative voltages from a one sourced voltage divider?

thanks

2. Mar 22, 2013

rude man

Think switching regulators!

3. Mar 24, 2013

CWatters

Is that really the entire question?

You would normally need to know the power required for each rail. It's trivial to make a 4V rail if you only need a few uA from it.

The problem doesn't appear to stop you making the +12 and -12 by "center tapping" the 24V ??