I am building a project in which I am controlling an SN754410 motor driver driving a small brushed motor with a 2 cell LiPo (8.4v at full charge). The motor is only on a small time, and the rest of the time the 20x2 Picaxe sits in sleep mode, awaiting an interrupt, to conserve the 1000 mAh LiPo battery powering it. Foolishly, I assumed that by driving the enable pin low on the SN754410 it would not have a quiescent current while it sat there all the time, but I was wrong, and the SN754410 is drawing about 30mA all day and night, which, along with the motor usage ended up giving me less than 30 hours of use. I was hoping for 20 days.
My desire is to turn off the SN754410's 5v supply with a transistor when it's not being used, driven by the existing enable pin with no code changes. The quiescent current and motor together draw about 120mA. Unfortunately my regulated power supply gives me 5v, so a transistor will drop the voltage to less than the SN754410's required logic voltage. Is this an appropriate use of a mosfet transistor? I've used mosfets once before, but for driving a high voltage with a logic voltage. Does anybody have a light duty unit that they like for this type of thing? Especially in a TO-92 package?
My desire is to turn off the SN754410's 5v supply with a transistor when it's not being used, driven by the existing enable pin with no code changes. The quiescent current and motor together draw about 120mA. Unfortunately my regulated power supply gives me 5v, so a transistor will drop the voltage to less than the SN754410's required logic voltage. Is this an appropriate use of a mosfet transistor? I've used mosfets once before, but for driving a high voltage with a logic voltage. Does anybody have a light duty unit that they like for this type of thing? Especially in a TO-92 package?