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power supply

Discussion in 'Electronic Basics' started by Peyter, Nov 14, 2003.

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  1. Peyter

    Peyter Guest

    I have a variable voltage, variable current power supply.
    Had a quick look inside hoping to find the L200C, but
    no, it's not there. Instead there is a bunch of op amps,
    a variable zener diode and some fixed voltage ic's, such
    as L7809 and L7812. I am trying to figure out why fixed
    voltages are used, as the output voltage is variable. It
    could be that they are used to power up the lcd displays
    and are not used for the output at all, but I don't know.
    Is it at all possible to do all this just with a few op amps?
    (there are a few other active components as well but they
    seem to be auxiliary items, not the heart of the system,
    such as two bipolar transistors and just diodes.)
  2. It is very possible to build a lab supply without using integrated
    regulators (except for ancillary functions). Most good
    (indestructible) designs are discrete.
  3. Can you see any reason why fixed voltage regulaors would be used
    in a variable voltage power supply, or would that probably be for
    the lcd displays, which I assume must have some fixed Vdd ?
  4. The opamps that operate the supply need stable bias voltages. One of
    the fixed regulators may even be used as a voltage reference for the
    adjustable circuit.
  5. Peyter

    Peyter Guest

    I think you are right, because all of them have heat sinks. If they where just
    for the lcd's they wouldn't need heat sinks. Thanks.
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