Generating a +/- 3.3V power supply from one 9V battery

Discussion in 'The Projects Forum' started by working_on_EMG, Dec 22, 2010.

  1. working_on_EMG

    Thread Starter New Member

    Dec 4, 2010
    12
    0
    Hello everyone.

    I want to supply a +/- 3.3V to an instrumentation amplifier IC (INA 128) using a single 9V battery. Is there any suitable voltage regulator i can use to achive this task? LM338 perhaps?

    Thanks
     
  2. #12

    Expert

    Nov 30, 2010
    16,247
    6,742
    TC7660 is the first 7660 that came up at www.mouser.com.
    It's a charge pump that can be used as a doubler or an inverter. That's one way to get a negative voltage from a positive supply. There are other ways, but this is the first one that came to mind.

    You could also use a resistive voltage divider to get the proper voltages, amplify the current with op-amps, and use those to power the instrumentation amp.
     
  3. working_on_EMG

    Thread Starter New Member

    Dec 4, 2010
    12
    0
    Thanks no #12! I wanna use these regulators to prevent current oscillations to the Instrumentation amplifer.
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    631
    Power a + 6.6 volt regulator with the 9 volt batter. Connect a 2:1 voltage divider across the regulator output, for example, by using two 100k resistors. Use an opamp voltage follower (unity gain non-inverting configuration) to buffer the output of the divider. The output of the opamp is your ground, the + output of the regulator is +3.3v with respect to your ground and the - terminal of the battery is -3.3 volts with respect to your ground.

    [​IMG]


    The uA741 in the schematic above is particularly poor choice, mainly because of its high quiescent current but it should work in most cases. For more information on this circuit, please see the source of the schematic above at http://www.circuitstoday.com/voltage-splitter-using-op-amp

    For the 6.6 volt power supply, you can use an LM317 set up as a 6.6 volt regulator, or a 7806 regulator with a silicon diode in series with its ground (-) terminal. Use of the diode will add some voltage drift, which might not be important to your application.

    [​IMG]
     
  5. tyblu

    Member

    Nov 29, 2010
    199
    16
    if you need more than 6.6V somewhere else in your circuit, you can buy ICs that will spit out 3.3V and -3.3V from 9V, likely with external components, from DigiKey or Mouser. Note that 9V batteries are plain bad batteries.
     
  6. #12

    Expert

    Nov 30, 2010
    16,247
    6,742
    I don't know why an instrumentation amp would have problems with current oscillations or why a voltage regulator would stop them. If you post a schematic, we might find that you are chasing a non-problem.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,762
    924
    The op amp virtual ground circuit is the best way to make split voltages for IC's that only need a few mA of current.

    The 101 series of op amps (another ancient series)is capable of driving large loads, if you need more than just a few mA.
     
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Dig deeper in Mouser or some of the more popular websites such as National Semiconductor that Mouser doesn't stock. I've never needed one but I'll swear I've seen switching regulators that either natively put out +/- 3.3V or can be designed such that the buck signal can be split half and half between two inductors and rectifiers. It will only regulate on one but if the output circuitry is identical the -3.3V should be very close in following.

    Worst case, since you're using a battery it's an isolated power supply and if you only need a minor amount of current you can divide the voltage into + & - 3.3V with two zeners and a resistor all in series.

    I really need one of those sketch tablets, I can draw stuff like this far easier than firing up my design software.
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
Loading...