Split Rail Power Supply


Joined Aug 1, 2013
I recently discovered an old furnace motor tucked away in a corner. Brushless DC, continuously variable speed, three phase drive (three transistor pairs), 18 poles. Very smooth ramp up and down, very quiet running. Hundreds of watts, 5 A internal fuse.

It was replaced under warranty and they didn't take the dead one away. Tore it apart. 240 Vac input, bridge, two 1000 uF / 200 Vdc caps in series, and one of them blew after about 2 years. The replacement has run for about 15. GE developed the motor for Carrier, for $5 million development cost.


Thread Starter


Joined Feb 25, 2008
No, you can't.

That's twice you've said/shown a AC/DC power supply without filter capacitors. That is fine for charging NICAD or SLA betteries, but for almost all electronic circuits you need to at least filter the pulsating DC to remove the majority of the ripple, or add a regulator circuit it to remove all of it. Whatever the opamp in post #1 is intended for, it will not work with unfiltered, rectified AC.

ah, my schematic was only using oa to show as example for split rail ps.
i can use that ps w/o caps for push-pull, but for something else
two air core coils mounted physically in same axial but amps in opposite direction thus creating a push-pull mag field for anything next to the coils.

have a low voltage 600A transformer, but the voltage is too low to fwd bias diodes, so i need to re-wrap secondary to get v above fwd bias of diode. the i play with the ckt using some large screw in diodes and some fans.