Disconnecting L293D bridge for power savings

Discussion in 'General Electronics Chat' started by Hemi, Mar 22, 2012.

  1. Hemi

    Thread Starter New Member

    Mar 17, 2012
    4
    0
    Hello,

    I am looking for ideas on disconnecting an L293D motor driver for power savings. This is my first electronics project and I'm learning as I go so please go easy on me :D

    My project basically consists of a Picaxe14m2, IR sensor, and L293D powered by 4x AA ni-mh batteries. I'm designing this project with maximum power savings in mind since the device will probably remain mostly idle and the L293D driving a motor for a few seconds maybe once or twice a week . When only the picaxe and IR sensor are connected, I measure ~1.5mA draw. With the L293D connected (and all unused inputs grounded and enable pins and used inputs set low by the picaxe), the current draw rises to ~17mA. My plan was to use a PNP transistor to switch on L293D only when needed. After breadboarding this and programming the picaxe to turn on the PNP via the NPN, the motor spins slowly or doesn't start at all. I haven't had a chance to measure the voltage or current between the PNP and the L293, but obviously one or both are suffereing.

    Do I need the NPN to turn on the PNP even though the supply voltage for the L293D is the same as the Picaxe? I was thinking I could eliminate R2, leave R1 in place connect that directly to the picaxe but the switching schematics I've looked at usually show an NPN in there when using an MC.

    Attached is a schematic of how I currently have it wired. Any help would be great. (opps, forgot a pull down resistor on my schematic, linked is a updated copy).

    [​IMG]

    Thanks.
     
    Last edited: Mar 22, 2012
  2. Hemi

    Thread Starter New Member

    Mar 17, 2012
    4
    0
    No suggestions?
     
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