Motor Back Emf

Greetings Everyone!

I am trying to control 3 DC motors and a stepper motor. All of them
need to be biderctional. I use a 5 V supply for the motors. However i
am having a problem with the back emf. It burns out the
microcontroller. I tried diodes and H-bridge(L293D). The back emf
generated is close to 10V.

Can anyone please suggest an interphase for the microcontoller-motor?

Thanks in Advance
Devyn

 

I guess the back EMF goes onto the 5V supply which rises. Any TTL logic on
this supply will be damaged then.

What you can do is to seperate the logic supply with the supply for the
motors. If the same supply must be used then put a diode in the + line,
cathode towards the motor driver. This keeps the back EMF energy from
flowing back into the 5V supply. Be carefull that this voltage behind the
diode can/will rise as high as the back EMF, 10V. Of course place some
buffer capacitor on the 5V, after the diode.
Use an active voltage clamp to be sure 5V doesn't rise when back EMF is
generated.

Al

 

Use separate PS for motor drive and Microprocessor. Use optic Isolators from
Micro output to HBridge drive circuits.