PWM Generator Circuit

387

07:12:30

PWM signal is very useful in various applications.
This signal is mainly used in motor speed control.
This signal effects in inductive load (Motor) but not in resistive load.
Motor speed is directly proportional to motor supply voltage.
Therefore, by changing motor supply voltage(PWM average output voltage), motor speed can be controlled.
By this circuit,
more wiper% of potentiometer , more duty cycle% , more average output voltage.

Vavg = (Vpwm x Duty cycle) / 100%

If potentiometer wiper is at middle, dutycycle is 50%
Since opamp output voltage called Vpwm is
5V, Vavg is 2.5V.
Therefore, by varying potentiometer, we can vary Vavg and motor speed.

Caution: Since motor draws high current  for opamp, use BJT or MOSFET as a switch.

This PWM speed control method advantage than directly supply to motor is less power dissipation.

I am an electronic engineering student from Myanmar country.
I have only little electronic knowledge.
But I want to share my little knowledge for fresher.
If this operation is not complete ,comment me.
Thank You

published 9 years ago

WTFCircuit

9 years ago

Use a sawtooth or triangular wave for more precision

SoeMyatHtet

9 years ago

Yes, thank you for comment

rodrigovictor

9 years ago

And how these wor in realy

SoeMyatHtet

9 years ago

Op amp operates as comparator circuit and, the potentiometer and DC voltage (1V) operates as voltage divider circuit. If Wiper positon is at middle, half of DC voltage(500mV) is fed to the inverting input of the opamp. For non inverting input, f=1kHz , 0<Amplitude<1V sine wave signal is fed. By comparator circuit formula Vout =Av (V1-V2), due to open loop gain, this circuit provides HIGH and LOW states. If V1 or Vsine is less than V2 or Vpoten , output state is LOW. If V1 is greater than V2, output state is HIGH. Half of sine wave amplitude or V1 is 500mV.Therefore, at Vpoten or V2 is 500mV, duty cycle is 50%. If Vpoten is dropped to 200mV(wiper is at 80%), duty cycle is about 80%(period of HGH state is 8ms and LOW state is 2ms), because V1 range is 0 to 200mV for LOW state and is 200mV to 1V for HIGH state.Thus, HIGH state is more period and LOW state is less period. By this way, HIGH state and LOW state period (or) duty cycle (or) Vavg can be controlled.

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