INDEX

Pulse Width Modulation

Advantage of pwm is that it is easy for driving analog circuits with digital outputs.

See the above diagram, we can see three pulse having duty cycle(ton/T) of 10%,50%,90%. In all three cases total time , T remains same irrespective of value of t1,t2. This is a PWM signal. A PWM signal is one in which total time always remain same and ton and toff vary. Now you apply this output to a transistor circuit shown below.

Then the transistor continuously switch ON and OFF and the effective voltage across the motor become voltage across motor,V=(Ton/Ttotal) *Vcc In PWM case Ttotal remains same, only Ton will vary which makes a varying voltage across the motor. PWM can be easily generated by any digital circuit(microcontroller used mostly). In PWM switching speed is comparatively slow because we continuously switch ON and OFF motor. A motor is basically an induction, it takes some time to charge and discharge. So if the quality of motor is good, then you can get a good PWM response. The inductance of the motor limits the selection of Ttotal. I used Ttotal=10ms for the 2kgcmsRs.400 motor and it gave a good response.