To control the speed of a motor, there are different ways. But in this tutorial, we are explaining simple and easy way by using the pulse width modulation (PWM). The modulation is a process of varying the parameter of a carrier signal in accordance with the instantaneous value of the message signal. The modulation process is used to reduce the size of the antenna and increases its efficiency. PWM is a technique used to generate the analog signals from the digital devices like MCU. All the modern MCU’s have dedicated hardware for PWM signal generator.
What is a Pulse Width Modulation?
Modulation technique is used to encode the message into a pulsing signal.Even though this technique is used to encode the information for transmission and, the main use of the PWM is to control of power supplies to an electrical device, particularly to control the load in the motor. The PWM is also known as a pulse duration modulation.
Pulse Width Modulation Circuit
The following simple circuit shows the PWM circuit which is based on the NE555 or 7555 chip and it is used to produce the signals of PWM at a fixed frequency output. The timing capacitor is used to charge & discharge using the current flow through the timing network RA and RB. Io the 555 timer circuit, the pin 3 of the output signal is equal to the supply voltage switching and the transistor is fully in ON state. The time is taken for the capacitance to charging & discharging depends upon the values of RA & RB.
The capacitor is charged with the network RA but, it is unfocused around the resistive network RB through the diode D1. When the capacitor is charged, it is discharged immediately through the diode D2 and network RB into pin 7. The pin 3 is at 0V during the discharging process and the transistor is in the OFF state. The time taken for capacitor C to go through one complete charge & discharge cycles depends upon the values of RA, RB and C with the time T for one complete rotation is given as a
- If the output is ON the time TH is equal to 0.693(RA) C
- If the output is OFF the time TL is equal to the 0.693(RB) C
- Therefore the total ON & OFF cycle is calculated by T = TH + TL and the output frequency is by f = 1/T
Using the shown component values the duty cycle of the waveform can be adjusted from 8.3% to 91% using the 6V power supply. The Astable frequency is constant at 256Hz and at this rate the motor is switched ON and OFF. The top part of the potentiometer is resistance R1 plus, the resistive network of RA represents the VR1. The bottom part of the potentiometer plus R2 represents the resistive network of RB. The values are differing to suit the different applications and a DC motor. The 555 timer astable circuit runs faster in hundred hertz minimum and there are no junkies in the rotation of the motor.
The D3 diode is the flywheel diode and it is used to protect the electronic circuit from the motor of inductive loading. If the motor load is high, then the heatsink is used on the switching transistor or MOSFET. The PWM method is a great method to control the amount of power delivered to a load without initiating the waste power.
Pulse Width Modulation Circuit Using 555 Timer
In this circuit 555 timer integrated circuit is used to operate the DC motor and 555 timer is in the astable mode. In the astable mode of operation, the circuit is used as a PWM with a small change in the circuit. With the help of the passive parameters of resistance and capacitance, the frequency of this circuit is operated. The resistance between pin-7 and pin-8, the resistance between pin-6 and pin-7 and the capacitance between pin-2 and the ground govern the frequency of operation and the duty cycle of the IC 555 in astable mode.
The duty cycle is governed by the resistor and it is in between the pins of 6 & 7 of the IC timer. Hence, by using the circuit working we can change the 555 astable multivibrators into PWM by using a variable resistor instead of a constant resistor in between pin-6 and pin-7.
In this circuit, the best thing is that we can make it work as an astable multivibrator with a requirement of hardware with low cost. It can save the cost of making and the space on the printed circuit board is saved. If we want to use the sophisticated pulse width modulated pulse width modulator which will work more perfectly and it has more adjusting capabilities than you can use the microcontroller based pulse width modulator.
The circuit which we are using the pulse width modulator is not so sensitive, therefore it does not demand more accuracy. The duty cycle of the circuit is changed by changing the resistance between the pin of 7 & 6. If we increase the duty cycle, then the speed of the motor also increases and if we decrease the duty cycle than the speed of the motor decreases.
Application of Pulse Width Modulation
- By using the 555 timer circuit it can generate the ramp & square wave generator
- The PWM is used as an ADC ‘
- The pulse width modulation is used in the telecommunication purpose
- Voltage regulator
Advantages of the PWM
The following are the advantages and disadvantages of controlling the speed of a DC motor with PWM are
- The consumption of power to the motor is very less
- Due to heat there is a less amount of energy is decreased
- It will allow the fine motor control
- The efficiency is up to 90%
Disadvantages of PWM
- The pulse width modulation circuit is complex
- Radio frequency interface
- Voltage spikes
This article will describe controlling the motor using the pulse width modulation. I hope by reading this article you have gained some basic information on controlling of a DC motor using the PWM. If you have any queries about this article or about the implementation of electronics & electrical mini projects in the engineering, please feel free to comment in the below section and here is the question for you what are the functions of the pulse width modulation?