Switched Capacitor Voltage Halver-Inverter

I have a piece of equipment that runs from a -24V (nominal) supply. I
would like to add to it a circuit that requires +8V regulated at about
250mA. I am concerned that the magnetic field from a regular switcher
(with inductor) could upset (modulate) a couple of oscillators in the
equipment. So I'm wondering about using a switched capacitor circuit,
followed by an LDO regulator.

I've convinced myself that both voltage-halving (as can be done with
the 7660 at lower V/I) and voltage inversion can be done in the same
circuit. But I am concerned that voltage drops in the bipolar/diode
circuit I have in mind could be excessive. I haven't found any sign
of monolithic devices that can handle this voltage/current
combination. Are there any readily available rail-to-rail-output
op-amps or drivers that will work at -24V supply ?

Has anyone any clever suggestions for an efficient, simple, economical
(in Qty.1) circuit ?

Steve

 

My suggestion is to build a simple switching DC-DC power supply
*with* an inductor or transformer but pick a controller that will
operate at over 500 KHz. Some switchers go up to 1 MHz now days.

When the frequency gets that high, shielding and filtering
becomes much easier. A small six-sided copper box with some
feed-through capacitors and ferrite beads will assure you that any
conducted or radiated noise will be attenuated to levels that
shouldn't polute anything short of a superconducting SQUID device.

Jim