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low drop out regulator

Discussion in 'Electronic Basics' started by aman, Feb 28, 2005.

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  1. aman

    aman Guest

    When I am looking at voltage regulator I come across a term "low drop
    out regulator". Can somebody tell me how it is different from a "linear
    voltage regulator".
  2. John Fields

    John Fields Guest

  3. aman

    aman Guest

    That answers my question. Thanks John.
  4. With "normal" three-terminal voltage regulators, you need the input
    voltage to be 2 volts or more above the regulated voltage - otherwise
    the regulator doesn't have room to work correctly, and the output
    voltage will drop.

    A low dropout regulator will continue to operate with as little as 0.5
    volts (or so) difference between input and output.
  5. Low drop out regulators are a variant of linear regulators. Most
    linears are based on an emitter follower output stage, and usually an
    emitter follower driving a bigger emitter follower. This implies a
    significant voltage across the regulator to make it function (usually
    1.5 to 2 volts). If the pass transistor is connected as a common
    emitter (output on the collector) the device may operate below one
    diode drop (less than .6 volts) across the regulator. This
    configuration is harder to stabilize against oscillations under varied
    conditions than the emitter follower configuration is. The base
    current for the pass transistor must also go through the reference pin
    of the regulator, which makes the current in that pin related to the
    load current. The follower configuration has a more stable reference
    pin current, making it easier to connect that kind of regulator in an
    adjustable output voltage arrangement.
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