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would this work?

Discussion in 'Electronic Basics' started by Dan, Feb 3, 2004.

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  1. Dan

    Dan Guest

    I need to regulate a dc voltage to +24V.

    Would this work? the ICs are LM2937IMP-12 from National
    Input voltage say 25-30 volts but coming from an unregulated power supply.

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    created by Andy´s ASCII-Circuit v1.24.140803 Beta

    Daniele Malleo
  2. Beau Schwabe

    Beau Schwabe Guest

    I have done this before with stacking two 5V regulators from a 12V
    power source to supply a +5/-5 without any problems, however I would
    preload the regulators with a voltage divider. Especially the lower
    regulator in your schematic.

    1K 1K
    24V output(top regulator) <----/\/\----o----/\/\----> GND
    12V output(bottom regulator) <---------o

    -Beau Schwabe
  3. You are onto an idea that can work, but you don't have the connections
    quite right. Both regulators need to have the unregulated voltage
    applied to their inputs, but the output of one has to be connected to
    the reference terminal (the one normally grounded) to elevate its
    reference to 12 volts. You should also load the 12 volt output to
    ground with a resistor to make sure it always has some minimum load
    (see the data sheet). Be warned that this method may screw up the
    current limit and have other problems during start up and shut down
    when voltages may be momentarily reversed. Finding a single 24 volt
    regulator (or an adjustable that can be set to 24 volts) is probably
    simpler. Low drop out regulators are harder to set up as adjustable
    units because of the variable current that passes through the
    reference pin as output load current changes.
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