Abdullah M Al-Dossary %166.87.109.11% wrote:
>
> i know from list about PWM the following :
>
> PWM : PULSE WIDTH MODULATION;
> PWM IS USED FOR SERVO MOTOR CONTROL;
> PWM IS USED IN H-BRIDGE CONNECTING POWER SOURCE WITH PIC AND MOTOR AND
> TRANSISTOR ;
>
> BUT
>
> WHAT IS THE CONCEPT BEHINED IT ?
> WHAT IS THE DUTY CYCLE ?
> AND HOW DOES IT LET THE PIC CONTROL THE MOTOR ?
>
> COULD ANYONE PLEASE GIVE AN ANSWER OR EVEN JUST POINT TO MORE INFO.
> AVAILABLE ON A WEB PAGE.
>
> THANK YOU IN ADVANCE.

Simple answer to eccessivly capitalised question:
[P]ulse [W]idth [M]odulation:

On pulse, off pulse....(repeated)

On time versus off time (width) is dynamically alterable (modulation)

On time powers motor, off time does not.

(On time ratio to off time) x 100 = %modulation or power

Off time consumes NO power.

Resistive motor control reduces motor speed from full by wasting (heat
energy) unused series circuit power: ie- current 12 amps, supply 12
volts, resistor 0.5 ohm, motor voltage 6 volts, resistor power
wastage=12amps x 6 volts= 60 watts heat energy.

Thats the basics, further theory deals with improving efficiency in
transformer type situations by modulating to simulate sinewave energy
levels.

regards,
Graham Daniel