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Pulse Width Modulation is one of the most commonly used techniques for controlling semiconductor devices. PWM stands for Pulse Width Modulation.
- It is also known as Pulse Duration Modulation (PDM).
- It is a method of controlling the average power delivered by an electrical signal.
- In pulse width modulation, analog signals are produced by using different types of digital devices.
- The produced signals carry the impulses in the form of square waves. So, it depends on the production and time the level of the wave will be high or low.
- Pulse width modulation decreases the range of power gained by the electrical signal.
- It can be done by turning those PWM signals into different parts.
- This technique is predominantly employed in communication systems.
- Apart from that, many other related topics will be covered.
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Key Terms: Pulse Width Modulation, PWM signals, Non-Sinusoidal Wave, Trail edge Modulation, Lead Edge Modulation, Pulse Center Two Edge Modulation Applications
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What is Pulse Width Modulation?
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In physics, PWM stands for Pulse Width Modulation. Pulse-width modulation is a process in which the power is maintained which is supplied by the various types of digital devices including AC and DC motors.
- In the technique, the energy of signals is distributed in series and not in a continuous form.
- It is used in order to encode the amplitude of the signals produced during the process of modulation.
- In order to control a load smoothly, the PWM switching frequency must be carefully selected.
- The PWM switching frequency can vary greatly depending on application and load.
- Not only in modulation, but they are also used for communication purposes.
- During this process, a very little amount of power is released.
- The pulse width modulation process includes the power to become off
- The process is widely used in controlling DC devices and in dim light.
AC and DC Motor
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How is PWM Generated?
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The pulse width modulation signals are generated by using a comparator. The signals are classified into two types.
- The first one is the input signal whereas the second part is the non-sinusoidal wave.
- The main work of the comparator is to compare both the parts of signals in order to generate the PWM signals in the form of output.
- It works like if the first signal is more than the other modulating signal, then the output signals produced will be very high.
Generating Pulse Width Modulation
Some important parameters associated with the PWM signal
Duty Cycle
For some time intervals, a PWM signal stays “ON” and for some time intervals, a PWM signal stays “OFF”. The percentage of time for which the signal remains “ON” is known as the Duty cycle.
- Duty cycle represented in percentage.
- For fully “ON”, the duty cycle will be 100%.
Frequency of PWM
The frequency of PWM signals determines how fast a PWM completes a period. The frequency of PWM can be expressed as follows:
Frequency = 1/Time Period
Time Period = ON Time + OFF time
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Types of Pulse Width Modulation
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The different types of pulse width modulation are as follows:
- Trail Edge Modulation – It is a type of PWM comparator that controls the power-converter duty cycle (D). In this process, the sawtooth voltage waveform (OSC) is compared with an error voltage, especially known as (ERR).
- Lead Edge Modulation – This is just the opposite of Trail Edge Modulation. In this technique, the OSC signal is compared to the non-inverting comparator input whereas the error voltage is inserted into the inverting pin. Then, (QB) signals are synchronized with the OSC voltage.
- Pulse Center Two Edge Modulation – In this process, the center of the PWM pulse is made fixed and the two lead edge and trail edge are modulated in order to control the cycle. The width of the signal is compressed or expanded when required.
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Applications of Pulse Width Modulation
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The technique is very effective as it controls the power of AC and DC motors. That's why this method is used for various power-related applications. The following are the uses of Pulse Width Modulation:
- The process is used for encoding purposes in telecommunication.
- It maintains the level of voltage and speed of AC and DC motors.
- It also vanishes the amount of heat present in the fan of the CPU of the computer.
- Pulse Width Modulation is used in different audio and video amplifiers.
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Things to Remember
- PWM stands for Pulse Width Modulation. It is an effective technique used to control semiconductor devices such as AC and DC motors.
- Generating PWM signals is done by maintaining the power supplied by the digital devices.
- A pulse modulator is mainly used to produce analog signals from digital devices.
- Trail Edge Modulation controls the power-converter duty cycle (D).
- Lead Edge Modulation uses the comparison of the OSC signal to the non-inverting comparator input whereas the error voltage is inserted into the inverting pin.
- Pulse Centre Two Edge Modulation uses a fixed PWM pulse center and the two edges, lead and trail are modulated to further control the cycle.
- Applications of Pulse Width Modulation- maintaining voltage levels and speeds, telecommunication industry, heat reduction in the fan of a computer CPU, and in amplifiers.
Sample Questions
Ques. Which is pulse modulation? (2 marks)
Ans. Pulse modulation is a modulation type wherein the signal gets transmitted in the form of pulses. A major application is in transmitting analog information. In pulse modulation, the sampling of continuous signals is done at regular intervals.
Ques. What do you mean by pulse width modulation? (2 marks)
Ans. Pulse width modulation is a commonly used control technique that is used for generating analog signals from digital devices such as microcontrollers. These produced signals have a train of pulses and they will be in the form of square waves.
Ques. How do you calculate pulse width modulation? (2 marks)
Ans. For determining the proportional PWM output voltage, use the formula:
(Duty ÷ 256) × 5 V.
For example, if the Duty is 100, then putting the value of Duty in the above equation, we get
(100 ÷ 256) × 5V = 1.953 V. PWM gives the output a train of pulses whose average voltage is 1.953 V.
Ques. Define pulse width modulation and demodulation. (2 marks)
Ans. The PWM and the carrier signals are connected with each other to an input of a product detector and the sequence of pulses has a width that is inversely proportional to the width of PWM pulses present at the output. When the Va signal passes through this low pass filter a demodulated signal will be obtained.
Ques. How many types of pulse width modulations are there? (2 marks)
Ans. Varying the amplitude, polarity, presence, or absence duration or occurrence in terms of the time of pulses gives rise to four basic forms of pulse modulation which are pulse-amplitude modulation (PAM), pulse-code modulation (PCM), pulse-width modulation PWM, and pulse position modulation.
Ques. Define a pulse width modulation inverter. (2 marks)
Ans. The Pulse Width Modulation or PWM technology has been used in inverters for giving a steady output voltage of 230 or 110 V AC irrespective of its load. This inverter is based upon the PWM technology which is superior to the conventional inverters.
Ques. How can Pulse Width Modulation Signals be generated? (2 marks)
Ans. This modulation signal is generated using a comparator. The modulating signal forms one of the parts of the input into a comparator, while the non-sinusoidal wave or a sawtooth waveforms the other part of the input. This comparator compares two signals and generates a PWM signal as its output waveform.
Ques. Write some of the applications of Pulse Width Modulation. (3 marks)
Ans. Because of its high efficiency, low loss of power, and the ability of the PWM technique has been used in a range of power applications.
- It is used in telecommunications for the purpose of encoding.
- It is also used in audio or video amplifiers.
- It assists in the regulation of voltage and therefore is used for controlling the speed of motors.
Ques. List the advantages of PWM. (5 marks)
Ans. The advantages of PWM are as follows:
- Manufacturing of PWM is cheap.
- The power consumption of a PWM is low with a high power handling capability.
- Noise interference is low.
- Parameters like amplitude and frequency can be independently controlled.
- The Pulse Width Modulation technique helps in the prevention of excessive heat present in LEDs.
- The results of the pulse modulator are accurate and it saves time.
- Pulse Modulator results in the production of high input power.
Ques. List the disadvantages of PWM. (5 marks)
Ans. The disadvantages of PWM are as follows:
- PWM circuits are very complex in nature.
- Switching on and off operations require a semiconductor.
- The pulse modulator produces electromagnetic noise.
- For PWM large bandwidth is needed for communication.
- The frequency of the pulse width modulator is high and so its switching losses are.
- The pulse modulator stimulates the Radio Frequency Interference (RFI).
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