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Introduction of Advanced Analog Circuit
Published in Arjuna Marzuki, CMOS Analog and Mixed-Signal Circuit Design, 2020
A pulse width modulator is used to realize the feedback control. The pulse width modulator is operable to control the pulse width of the modulation (PWM) applied to the buck converter circuit that controls the LED voltage depending upon the LED current as it is detected by the feedback signal. In achieving high-power efficiency and constant current, the PWM technique is often employed in the LED driver. PWM is a technique in which a series of digital pulses is used to control an analog circuit. The length and frequency of these pulses determine the total power delivered to the circuit. PWM signals are most commonly used to control DC motors, but have many other applications including controlling the brightness of an LED. The PWM strategy switches modes between PWM and pulse frequency modulation to reduce the working frequency and improve the power efficiency simultaneously when the load is changing. The control technique of PWM can achieve a constant output current and high-power efficiency, while reducing the complexity and cost.
Real-World Control Device Interfacing
Published in A. Arockia Bazil Raj, FPGA-Based Embedded System Developer's Guide, 2018
The simplest method to control the rotation speed of a DC motor is to control its driving voltage, that is, the higher the supply voltage, the higher the speed of the motor. The PWM method is also used in many DC motor speed control applications. In the basic PWM method, the operating power to the motor is turned on and off to modulate the current to the motor, as shown in Figure 9.7a. The duty cycle, that is, ratio of on time to total time, determines the speed of the motor. Since the DC motor mainly consists of a large inductor, it is basically a low-pass device; hence, we need to take care when generating the PWM control signal. It is not capable of working at a high-frequency PWM control signal. The speed can be controlled just by varying the duty cycle, that is, (Ton/(Ton+Toff)), between 0% and 100%, for example 90%, 50%, and 10%, as shown in Figure 9.7a. The PWM control signal can be generated from any standard timer circuit or from any programmable digital device. An application circuit for controlling the speed of a DC motor is shown in Figure 9.7b. The PWM control signal generated from FPGA is applied to the base of an NPN transistor, which results in current flow from collector to emitter through the DC motor. Since the internal resistance of the transistor becomes small, the voltage drop is across the motor and drives it. The average power available across the motor depends on the on period and frequency of the PWM input. The speed can be controlled by giving the appropriate PWM signal to the base of the transistor. A 0.1 μF capacitor is used to remove the repels/spikes in the voltage across the motor.
Advanced Motor Controls
Published in Julio Sanchez, Maria P. Canton, Embedded Systems Circuits and Programming, 2017
Julio Sanchez, Maria P. Canton
The basic idea of pulse width modulation is to control the average value of a current fed to a load by rapidly turning on and off the power source. In this context, a duty cycle is defined as the percentage of the PWM control period during which the signal is held high. For example, a 10V signal that is held on 50 percent of the time (50 percent duty cycle) results in an average voltage of 5V. Figure 19-11 shows the fundamental elements in the concept of pulse width modulation.
Design and Development of SECU Converter Cascaded Control for EV Applications
Published in Electric Power Components and Systems, 2023
Jenifer Arockia Raj, Sukhi Yesuraj
The average voltage across the energy transfer capacitors and output capacitors is obtained as The average current in the input inductors is and The switching design of a power converter determines the switching sequence and timing of the semiconductor devices to regulate the output voltage or current. The Pulse Width Modulation (PWM) pattern is a technique used in switching converters to control the duty cycle of the pulse train applied to the switch, which regulates the output voltage. It involves comparing a reference signal with a triangular waveform to generate a modulated waveform that controls the switch.