[sdiy] DC-DC inverter

[Heitor Alves]

Hello all!

i'm looking for help in this inverter i need to build, i've been able
to use some maxim IC's to invert +5v to -5v but i need to have -28v...
i've seen some schematics using the 555 giving -12v but its less then
my needs, so i was wandering if i put up two of them (-12v) together
i'm going to be able to get -24v? does anyone knows a better way to
build a stright -28v? the input will be 12v and the current
consumption will be around 150mA.

Thank you all in advance

Heitor