PIC + L293D

[Timmymna]

I am designing a speed controller circuit for a cordless drill and have circuit but not sure if my circuit is correct.

The PIC provides PWM to the L293D which can be in forward or reverse (I haven't added the switch for that to the circuit yet)
Would this circuit work for a 12v motor in a drill or would it require transistors / MOSFETs due to the L293D only being able to output 600mA?
If this wouldn't work can anyone suggest would the L293D could be replaced with / added to the circuit?

Thanks for any help given.

 

[Nigel Goodwin]

For a start you need to measure the current the motor takes, under a variety of conditions - including stall conditions with the battery pack you intend to use. The stall condition current will probably be limited as much by the battery pack as the motor, and will certainly be well into double figures.

A 600mA IC is way too puny, you need to be looking at fairly hefty FET's, the reversing in cordless drills is usually done by a DPDT switch, rather than an H bridge - which would cost a lot more to do, and lose extra power in the extra FET's.

 

[Oznog]

Yeah, you need a heavy MOSFET output stage. Drills take something like tens of amps under load.

The L293D isn't appropriate for this circuit. With a reversal switch, you only need a single N-channel MOSFET, you'd just hook the PIC's PWM pin to the gate and you're done. If you're doing an H-bridge, you need 2 P-channels & 2 N-channels. You generally turn on one of the P's with a fixed voltage and feed PWM to one of the N's.

 

[Timmymna]

Thanks for the help , I'll start redesigning my circuit later today and let you know what I come up with. :lol:

 

[falleafd]

you can make L293D to parallel to work with 1A motor.

However, it's cheaper to use L298.

Look in the datasheet of L293D, they have a typical design, so clear!!

Don't have to use external diode with L293D but it's needed with L293.