Switching Power to Op Amps

Discussion in 'General Electronics Chat' started by DanRilley, Nov 22, 2009.

  1. DanRilley

    Thread Starter Senior Member

    Jan 13, 2008
    107
    0
    Hi, I am wondering if it is more efficient to switch off power to an Op Amp if it is not being used. Also, if this is done, would it cause any voltage spikes?

    I wonder this because I have a circuit that allows the user to choose between three different oscillators. The normal way would be to just switch the signal path, but I was wondering if also switching power off on the op amps would provide better efficiency in power consumption.

    A final side-note question. Circuits often have a 104 capacitor between +V and GND to prevent voltage spikes (I've never noticed/experienced these, but like most people like to play it safe), should this be done to every op amp no matter what?

    Thanks for the info,
    Dan
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You will need to review the datasheet for the particular opamp(s) in question.

    Most opamps have pretty low idle current.
    If you DO decide to disconnect power to the opamps that are not being used, you will need to follow a certain procedure to ensure that the opamp is not damaged.
    1) Disconnect the inputs and outputs from any signal sources/destinations. If the opamps have CMOS/FET inputs, they should be connected to a resistive divider connected between Vcc/Vee.
    2) Remove power to Vcc/Vee.

    You need to power it up in the reverse order:
    1) Apply power to Vcc/Vee
    2) Connect the inputs/outputs to signal sources/destinations.

    Failure to follow do so will likely result in permanent damage to the opamp.

    The 104 marking denotes a capacitor that has a value of 0.1uF (equivalent to 100nF, or 100,000pF - basically, a 10 with 4 zeros after it.)

    These are power supply bypass capacitors. They are an absolute necessity across the power/ground pins of any IC, whether analog or digital; when designing a PCB, they should be liberally sprinkled around the board.

    Many IC's may require additional capacitors across the supply pins.
     
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