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7.26V output from a 9V battery

Discussion in 'Electronic Basics' started by [email protected], Feb 11, 2005.

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  1. Guest

    Hello,
    I am new to electronics and I have a project to interface an active
    electrode that need a clean 7.26V (+- 0.02V) supply voltage. I would
    like to use a 9V battery. The active electrode comsumes 0.7mA. Can I
    simply use a series of resistors or do I need a voltage regulator or a
    converter?

    Thanks

    Daniel Jeffrey
     
  2. since the voltage from a 9 volt battery varies from about 9.5 to zero
    over the life of the battery, you will definitely need an active
    regulator of some sort to hold a 0.7 mA load to a 7.24 to 7.28 volts.
    The most common and easy to apply regulators need at least 1.5 volts
    to waste, so they are a bit tight for this spec, but some of the low
    current low drop out (need less voltage to waste) regulators might be
    appropriate.

    For example:
    http://www.fairchildsemi.com/ds/LP/LP2951.pdf
     
  3. Montreal

    Montreal Guest

    Thanks I'll look at your example.

    Much appreciated.

    Daniel
     
  4. Bill Bowden

    Bill Bowden Guest

    Can I simply use a series of resistors or do I need a voltage
    You need a regulator but the input has to be at least a couple volts
    higher than the output, so you might want to use a 9 volt battery
    and a couple AAA cells so you have 12 volts. There is a low
    current 5 volt regulator 78L05 that can be raised to 7.26 volts
    with a couple resistors. Connect a couple resistors in series
    from the output to ground and tie the common pin of the
    regulator to the junction of the 2 resistors. Maybe a 10K
    resistor at the output and something around 5K for the other.
    Then adjust one of the resistors to get the right output.

    But, I'm not sure this will hold the tollerance you want
    of +/- 0.02

    It may also require a minimum load of more than a couple
    mA. In that case you will need to add another resistor
    from output to ground so the regulator operates at
    5 mA, or whatever minimum is required.

    -Bill
     
  5. peterken

    peterken Guest

    that's some *really* weird voltage to use...
    might be easiest to just build a simple transistor regulator, say a straight
    forward emitter follower or possibly a more complex model controlled by a
    rail-to-rail opamp (lm158/258, lm324, or something)
    might even use the output of the opamp directly as supply for that kind of
    low-power
    for reference just use a 5V1 zener @ 10mA, most stable at low cost
     
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