PWM modulation

How pulse width modulation works PWM




Very good this video but a complete circuit   is the next.




PWM with 555

IMG_1655 (Custom)









And here is double version for controlling two motors 100mA.

IMG_2001 (Custom)


An a nice tip. Changing the potensiometer R3 , we can change the out frequency of the 555. After some tests  in practise i found

10 KOhm  —>900-1.16 KHz

20 KOhm  —>500-700 Hz

50 KOhm —> 200-300 Hz

100KOhm—> 100Hz

Power is 12V and we can connect a motor 12 V or led array 12 V. We can take the out of 555 at pin 3 ,before R3 there is a pinheader and connect a bigger transistor or a mosfet or an optocoupler and drive even bigger loads in current.


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Pulse Duration Modulation or Pulse Width Modulation is a powerful technique used to control analog circuits using digital outputs. Nowadays PWM has a wide variety of applications such as to create analog voltage level, waveform generation, motor speed control, power control and conversion, measurements and communication etc.

PWM uses a rectangular pulse wave as shown in the figure below whose pulse width is modulated, which results in the variation in the average voltage of the waveform.



PWM Period

The PWM Period is the time duration in which the Pulse Width Modulation takes place. In the diagram shown below PWM Period is marked as T. PWM Period should be chosen to give best results for a particular application.

PWM Resolution

Resolution of a PWM is the number of different steps you can have from zero power to full power. That is a 10 bit resolution means that you can have 1024  steps from zero to full power. Consider the example in which PWM is used to control the speed of a DC Motor. Using a PWM of 10 bit resolution we can have 1024 different speed for DC Motor.

PWM to Generate an Analog Voltage Level

In Switched Mode Power Supplies (SMPS) PWM is used to generate voltage levels. By changing the duty cycle of the PWM we can adjust the average voltage of the waveform. The PWM resolution should be selected to be greater than or equal to the required resolution of the Power Supply. For example a 5V power supply that can be adjusted to 1mV should use a PWM of resolution equal to or greater than 5000.

5/5000 = 1mV



The above figure shows a PIC Microcontroller generating PWM wave at a frequency of 5KHz and 50% Duty Cycle. Two sections of Low Pass Filter are provided to filter out the ripples. The Output voltage will be the average value of the waveform, i.e 2.5V.


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