I am doing a project which required to use the pwm output to drive some motors, the motors needs quite a lot of current hence i decided to use some opamps as voltage buffer. However this is not working well as when the signal hits the -ve rail (GND),the opamp behave strangely , i am thinking of adding a 3v rail and set it as GND, my question is will i fry mbed if i connect 9v to Vin and 3v to GND.

many thanks

How much current? Op-amps aren't made to drive anything. You can get some power op-amps that might do what you want, but these aren't made to drive motors either. You can get some small motor driver IC's that are made specifically for your application. Tell us more about your project and someone will point you in the right direction :)

I was confused by Wikipedia and though a opamp voltage buffer will do the job :P

thanks for pointing out the mistake!

My project is to build a haptics feed-back device that can help blind people to understand the surrounding environment, the device will produce vibration base on the direction of obstacle detected by sensor.

the vibration motors i found is rated at 3v 130mA, i am trying to drive them with the pwm signal from mbed.

i am now trying to use FET in common collector mode instead, please let me know if there are better solutions.

Great project, Patrick.

Here's something you could try.

The NPN transistor can be any garden-variety device that is rated for a few hundred mA. Even a 2N3904 would work in a pinch.

The diode catches the inductive spike when the motor turns off. Mount it right across the motor terminals.

The capacitor will help keep noise out of the rest of your circuit.

Good luck.