Purpose of Logic supply in motor controller

Dear all,

I am currently using the micro dual serial motor controller. I wish to find out what is the purpose of the logic supply pin which is pin 3 of the controller.

Why must we supply 5V to it?

Kindly advise

The logic supply pin provides power to run the electronic components (the microcontroller and the dual H-bridge) on the motor controller, while the motor supply pin provides power for the motors. Keeping these supplies separate lets you power your motors with a wider range of voltages (1.8V-9.0V) than the electronic components can use (2.5V-5.5V), and protects the components from interference and electronic noise from the motors.

If your motor power supply is already between 2.5V and 5.5V you can connect it to both the logic and motor supply pins, but you might run into trouble if noise from your motor interferes with the controller’s operation. One way to protect against this is to use a higher voltage power supply to run the motors directly, and to connect that supply to a voltage regulator which will provide cleaner power at a lower voltage to connect to the logic supply pin.


P.S. In any setup, or with completely separate power supplies, motor noise can still be an issue, so it’s always good to use noise filtering capacitors on your DC motors!

Thanks Adam.
That was a very clear explanation, really appreciate it!!

Thanks once again…

Sorry, I have another doubt.

You mentioned about using capacitors to filter off the electrical noise.

Why are capacitors capable of doing that?

Also I found one article which writes “A capacitor is an electronic component that will conduct only currents that are changing at a high frequency”

May I know what is the meaning of this line?

Kindly advise…

I’m not sure what that quote is referring to, capacitors don’t really conduct current through themselves.

Capacitors are like little rechargeable batteries. If you put one in parallel with a power supply it will quickly charge itself up to the same voltage. If the power supply voltage changes slowly, the capacitor will charge or discharge itself to follow, but if the voltage on the power lines fluctuates quickly (like with noisy interference) the capacitor will smooth out the voltage by absorbing power from the voltage spikes and releasing power during voltage dips.

A recommendation for motor capacitors can be found on page 4 of the Low Voltage Dual Serial Motor Controller user’s guide here. These recommendations also apply to the micro dual motor controller, but were not included in its manual.


Thanks alot! Adam :slight_smile: