Pulse Width Modulation (PWM)

In Electronic Engineering, Pulse Width Modulation, or PWM, is a commonly used technique for effectively controlling the power supplied to electrical devices. In order to attain a desired average voltage or power level, the principle of pulse width modulation (PWM) is used for a periodic signal, which is usually a square wave. A key component of pulse width modulation (PWM) is the duty cycle, which is defined as the ratio of the pulse width to the whole time period. An increase in the duty cycle translates into an increase in average power output. Basically, PWM is used to obtain analog signals from digital services- for instance, the microcontrollers and it represents the amplitude of an analog signal input signal.

What is Pulse Width Modulation?

Pulse-width modulation, commonly known as PWM, is a modulation method that changes the pulse signal’s width in electrical systems to regulate the average power supplied to a load. PWM is particularly helpful for effectively regulating the output of audio amplifiers, the speed of motors, and the brightness of light. PWM is an elegant way of referring to a particular kind of digital signal. Applications for pulse width modulation are numerous and include complex control circuits.

Pulse width modulation enables us to adjust the amount of time the signal is high in an analog fashion, allowing us to achieve a range of effects in both applications. Although the signal can only ever be high ( often 5V ) or low (ground) at one point in time, we can alter the ratio of high to low signal times over a regular length of time. PWM is still essential to contemporary electronics as technology develops, and for convenience of use, it is frequently included in microcontrollers and specialist PWM controller integrated circuits (ICs). Because of its versatility and effectiveness, it is a key component in the design and management of a broad range of electronic systems, greatly advancing the fields of power electronics and control engineering.

How is a Pulse Width Modulation Generated ?

A comparator is used to create a signal that modulates pulse width. One component of the comparator’s input is the modulating signal, while the other component is either a sawtooth wave or a non-sinusoidal wave. The comparator creates an output waveform of a PWM signal after comparing two signals.

One possible output of a monostable multivibrator is a PWM signal. When an external trigger is applied, a monostable multivibrator will only produce one output pulse and have one stable state. An operational amplifier comparator can be used to build a monostable multivibrator circuit. One portion of the input to the comparator is structured by the modulating signal, and the other portion is wave formed non-sinusoidally. After analyzing two signals, the comparator generates a PWM signal as the output waveform. The output is in a “High” condition when the sawtooth or non-sinusoidal signal exceeds the modulating signal.

PWM Signal Generator

The output signal is in a “High” condition if the sawtooth signal exceeds the modulating signal. The comparator output, which establishes the pulse width produced at the output, is determined by the magnitude value.

Important Parameters of PWM signal

An analog circuit can be controlled using digital pulses produced by a PWM signal. The behavior of a PWM signal is determined by two main factors:

• Duty cycle: The fraction of a second that a signal or system is operational is called a duty cycle. A duty cycle is usually expressed as a percentage or ratio. The amount of time a signal takes to complete an ON-OFF cycle is called a period.
• Frequency: The pace at which something recurs or occurs over a specific time period is known as its frequency. Put another way, the rate at which a vibration occurs that results in a wave, such as radio, light, or sound waves; this rate is usually measured in seconds.
• Output Voltage of PWM signal: It is the percentage of the duty cycle and can be calculated in that way only by calculating its percentage also. Let’s say the duty cycle is 100% then the output voltage will be 5V.

About the duty cycle, we call a signal “ON” when it is high, and it indicates how long a signal stays in its ON state. A duty cycle is quantified or measured as a percentage. This percentage indicates the precise amount of time, expressed as the inverse of the waveform frequency, that a digital signal is ON during a period (interval).

A digital signal with a 50% duty cycle, or a perfect square wave, would, for instance, be half in the ON state and half in the OFF state. A digital signal with a duty cycle of 75% will be in an ON state for three quarters of the time and an OFF state for one quarter of the time.

Duty Cycle of PWM

We refer to this as “on time” when the signal is high. We employ the idea of duty cycle to define the quantity of “on time”. A duty cycle’s percentage is expressed. The proportion of time a digital signal is on throughout a period of time or interval is precisely described by the percentage duty cycle. The waveform’s time is equal to its inverse frequency.

Duty Cycle : On Time / On Time + Off Time

We would say a digital signal has a 50% duty cycle and looks like a perfect square wave if it is on for half of the time and off for the other half. The digital signal spends more time in the high state than the low state if the percentage is greater than 50%, and vice versa if the duty cycle is lower than 50%. Here is a graph depicting the three scenarios.:

Duty Cycle of PWM

A 100% duty cycle is equivalent to a 5 volt (high) voltage setting. Grounding the signal would be equivalent to 0% duty cycle.

Frequency of PWM

It is easy to define a frequency or period for regulating a particular servo. A servo engine routinely anticipates an update every 20 ms with a pulse lasting between 1 and 2 ms. This is equivalent to a 5%–10% obligation pattern at 50 Hz. Currently, the servo engine will be at 90 degrees, 0 degrees, and 180 degrees at 1 ms, assuming the pulse is at 1.5 ms. In outline, we may obtain the entire range of motion by refreshing the servo with a value between 1 and 2 milliseconds.

Data is currently transferred over communication channels using PWM’s duty cycle in an unambiguous communication system as well. PWM, then, is a method for converting high-frequency pulses into low-frequency output signals.

Frequency : 1 / Time Period

Frequency of PWM

Types of PWM

There are seven types of Pulse Width Modulation, such as

• Single-pulse width modulation
• Multiple-pulse width modulation
• Sinusoidal pulse width modulation
• Hysteresis band pulse width modulation
• Trail Edge pulse width modulation
• Lead Edge pulse width modulation
• Pulse Centre Two Edge pulse width modulation

Single-Pulse Width Modulation (PWM)

A single pulse is produced at each switching cycle in single-pulse width modulation. The average power applied to the load is controlled by varying the pulse’s width. Single-PWM is straightforward and simple to use, although it could have a larger harmonic content and be unsuitable for applications that need precision control at low power levels.

Single-pulse width modulation

Multiple-Pulse Width Modulation (MPWM)

Multiple pulses are generated during each switching cycle in multiple-pulse width modulation. This method seeks to lower harmonic distortion while raising the output waveform’s general quality. Two-level and three-level MPWM are frequently used; in these implementations, the number of pulses in each cycle is increased to improve waveform fidelity, which makes MPWM especially helpful in high-power applications.

Multiple-pulse width modulation

Sinusoidal Pulse Width Modulation (SPWM)

The process of altering pulse width to resemble a sinusoidal waveform is known as sinusoidal pulse width modulation. Through the use of a sine wave reference to alter the pulse widths, SPWM minimizes harmonic distortion and yields a smoother output. Inverters and motor control systems, where a high-quality output waveform is crucial for lowering harmonic interference and raising system efficiency, are two common applications for this technology.

Sinusoidal pulse width modulation

Hysteresis Band Pulse Width Modulation

Hysteresis Band Pulse Width Modulation is the comparison of the erroneous signal with a predetermined band, called hysteresis. The pulse width is changed to put the system back into balance when the erroneous signal rises above the hysteresis range. This approach provides a straightforward and reliable control strategy, especially in applications where sudden variations in load or disturbances are frequent. Power converters and voltage regulators frequently use hysteresis band PWM because to its built-in noise immunity and simplicity of use.

Hysteresis band pulse width modulation

Trail Edge Pulse Width Modulation

A typical modulation method in digital communication systems is called “trail edge modulation.” With this technique, the signal waveform’s trailing or falling edge is where the modulation happens. This indicates that when a signal moves from a higher voltage level to a lower voltage level, its amplitude or frequency changes.

Applications for trail edge modulation include data transmission and modulation techniques including pulse width modulation (PWM) and pulse amplitude modulation (PAM). Trail Edge modulation is one of the modulation techniques that can be chosen, according on the needs of the system, bandwidth constraints, and noise robustness, among other things.

Lead Edge Pulse Width Modulation

It is also known as the rising edge, of the signal waveform is where the modulation process takes place in lead edge modulation. This suggests that when the signal moves from a lower voltage level to a higher voltage level, modulation changes occur. Lead Edge modulation offers flexibility in adjusting to particular application requirements and is employed in various communication systems and modulation schemes. It is frequently used in a variety of digital communication protocols, where it modulates signals near the beginning of their waveform to facilitate the effective transfer of information.

Pulse Centre Two Edge Pulse Width Modulation

A particular kind of modulation called “Pulse Center Two Edge Modulation” entails modifying a signal at the pulse waveform’s leading and trailing edges. This method is frequently used in pulse modulation schemes, in which the data to be sent is represented by pulses. Pulse Center Two Edge modulation increases the capacity for encoding information and provides greater flexibility in signal representation by modulating at both edges. In situations where exact time and effective bandwidth utilization are critical, this approach may prove beneficial. Particularly in pulse modulation techniques like pulse width modulation (PWM) or pulse position modulation (PPM), it finds use in digital communication systems.

Difference Between PPM (Pulse Position Modulation) And PWM (Pulse Width Modulation)

Pulse Position Modulation	Pulse Width Modulation
Changes the position of pulses to encode information.	Changes the pulse width to encode information.
Adjusts the pulse’s location within a time interval.	Alters the pulse’s breadth or duration
It is highly sensitive to timing variations	It is less sensitive to timing variations
It is usually calls for more bandwidth than PWM	It can required more bandwidth-efficient in certain scenarios
Example : Optical communication systems	Example : Motor Control System, Audio System

Applications of PWM

• Modulation in electronics refers to the application of a regulating or shifting force on an object. Similar to the human voice, we also refer to it as a variation in the pitch, intensity, or tone of a frequency.
• We frequently witness the usage of modulation techniques to operate devices such as LEDs or DC motors.
• Maximum power point tracking (MPPT) in conjunction with PWM is a crucial technique for reducing a solar panel’s output in order to align it with a battery’s use.
• By adjusting the duty cycle, an LED’s brightness can be somewhat controlled. By diluting each of the three hues with varying amounts, an RGB (red, green, and blue) LED allows you to regulate the quantity of each color you require in the blend of variety.
• The PWM process regulates the fan within the PC’s CPU, which effectively disperses heat.

Advantages and Disadvantages of PWM

Given Below are Advantages and Disadvantages of PWM :

Advantages

• PWM technology keeps LEDs from overheating while preserving their brightness.
• PWM technology responds quickly and with accuracy.
• A high input power factor is provided by the PWM technique.
• Motors may provide their full torque even at lower speeds thanks to the PWM technology

Disadvantages

• The significant switching losses are a result of the high PWM frequency.
• Radio Frequency Interference is caused by it (RFI).

Conclusion

In conclusion, Pulse Width Modulation, or PWM, is an incredibly useful and adaptable method in the field of electronics and control systems. Its versatility in modifying duty cycles and frequencies, combined with its effective control over power delivery via pulse width modulation, has made it an essential part of many applications. PWM is essential for obtaining accurate and energy-efficient control in a variety of applications, including audio amplification, lighting systems, motor control, and power regulation. Applications for pulse width modulation (PWM) are numerous and include lighting systems, motor control, audio signal modulation, and electronic device power management.

PWM has become especially useful in areas where precise control over power delivery is crucial due to its energy-efficient capabilities. PWM is used in many different industries, including robots, LED lighting, and renewable energy systems, in situations up to 250. Its adaptability makes it a key technology for ensuring optimal performance and energy conservation in these fields.

FAQs on PWM

What is the technique of Pulse Width Modulation (PWM) ?

Pulse-width modulation is a modulation technique used to change the average power delivered to a load.

It makes use of a square wave, and the average power is determined by the duty cycle, which is the ratio of the pulse width to the whole period.

Explain duty cycle in PWM ?

The percentage of a full cycle that the PWM signal spends in the high state, or on, is known as the duty cycle.

It is an important metric because it establishes the average voltage or power applied to the load.

Why does one utilize pulse width modulation ?

A useful technique for regulating the amount of power supplied to a load without releasing any extra energy is pulse width modulation.

Which applications does pulse width modulation have ?

The PWM technique is employed in many different power applications because to its great efficiency, low power loss, and accurate power control:

They are employed for encoding in communications and Amplifiers for audio and video use them.