You can use a transistor to drive the motor. Use a series resistor on the base of the transistor to limit the base current. You would have to work out the value according to the amount of required base current required. This will isolate the base a little, and thus give the transistor some current limiting.
Put a small capacitor arrangement across the motor. Take care for the polarity of the cap (as normal). You can typically use a 10 uF / 25 V in parallel to a 0.1 uF / 100 V cap. This is done very often in many types of devices using small DC motors. These are very common type voltage ratings at the values indicated. The idea of the smaller cap is to suppress any high frequency noise that the larger cap cannot deal with because of its structure. The larger cap is the main suppressor for the lower frequency noise or spiking factor.
Across the transistor you can put a silicon type rectifier diode. Take regard for the polarity of the diode. You want to have the diode arranged so that it only conducts across the transistor inversely. This will suppress any reverse polarity noise from going across the transistor. Only when the transistor is forward conducting the motor should run.
The PWM effect should still work. The cap arrangement across the motor is not large enough to cause any delay effects, or cause excessive loading.
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Jerry Greenberg GLG Technologies GLG ========================================= WebPage
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I pretend to control a small dc motor (about 5 - 6V) using a microcontroller (PIC) and I think I need some precautions since the motor may be an inductive load...
What I want to do is this : the PIC connects to the base of a transistor working in saturation zone, so that is behaves like a switch turning on and off the motor's power supply (you know, the motor is wired to the power source and connected to the transistor colector, the usual stuff.)
By doing PWM on the signal outputed by the PIC to the transistor's base, it's possible to control the motor speed (the motor is "quickly" beeing turned on and off).
Since the motor is an inductive load (all dc motor are? correct me if i'm worng) each time I power it and "unpower" it, a spike of current is generated so the life of this circuit would be seriously shortened ...
What is the easiest yet functional way to protect it agains these spikes ? Some diodes ? Where and how ? I'm know very little about this matter ... A small schematic or a detailed description of an example circuit is really welcome.
Thanks a lot
Pedro Duarte