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Switched Capacitor Voltage Halver-Inverter

Discussion in 'Electronic Design' started by Steve Kavanagh, Oct 21, 2003.

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  1. 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 ?

  2. Jim Meyer

    Jim Meyer Guest

    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.

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