I have an mbed project with firmware that controls some PwmOut switches. All works fine firmware opens and closes switches as expected. I tested this with a LED (and resistor).
Now my goal is that instead of a light coming on, a electric brush motor (with a simple +/-) 3v-5v should run. I understand that the PwmOut from the mbed will not provide enough current to run the motor.
Will I need a transistor that connects the PwmOut port with the motor?
If yes:
- how do I know what type I need?
- these three legged guys - how are they hooked up?
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\$\begingroup\$ It's worth adding how much current the motor draws (or a datasheet if you're not sure). If it's a small motor you could probably use the circuit from the answer to electronics.stackexchange.com/questions/7235/… \$\endgroup\$PeterJ– PeterJ2013年11月15日 10:20:29 +00:00Commented Nov 15, 2013 at 10:20
1 Answer 1
You can follow the recipe at http://mbed.org/cookbook/Motor which uses the Motor interface for driving a standard DC motor with PWM and an H-Bridge.
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If, instead of using the L293D dual H bridge driver, you want to use a transistor to drive the motor. You choose the transistor mainly by looking for a switching transistor which has a current and voltage rating that exceed the current and voltage ratings of the motor (so it depends on the motor) - for high currents you may need a heatsink for the transistor.
For a bipolar junction transistor (BJT) you'll need a resistor to limit base current. Most driver circuits incorporate a diode to prevent harm to the transistor from back-EMF from the motor windings.
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The connections to a BJT are base, emitter, and collector
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You can find out which leg is which by looking at the data sheet for the specific transistor you have chosen. For example
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You can instead use a MOSFET, these can be more efficient (lower voltage drop when 'on')
Some rather good instructions can be found here