Pulse Width Modulation (PWM) is the industry-standard technique used to control the speed, torque, and power delivery of electric motors by rapidly switching the supply voltage on and off. Rather than continuously lowering the voltage—which wastes a massive amount of energy as heat—a PWM drive delivers full-voltage pulses. The motor’s internal inductance acts as a natural filter, smoothing out these rapid pulses into a stable, continuous mechanical response. Core Mechanics of a PWM Drive
A PWM signal is fundamentally defined by three key variables:
Duty Cycle: The percentage of time the voltage is “ON” versus “OFF” within a single cycle.
Switching Frequency: How fast the drive completes an ON-OFF cycle, typically measured in kilohertz (kHz).
Amplitude: The maximum voltage level delivered during the “ON” phase.
The effective power sent to the motor relies entirely on the Duty Cycle calculation:
Average Voltage (Vavg)=Duty Cycle×VmaxAverage Voltage open paren cap V sub avg end-sub close paren equals Duty Cycle cross cap V sub max end-sub
100% Duty Cycle (Full Speed) ▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬ 50% Duty Cycle (Half Speed) ▬▬▬ ▬▬▬ ▬▬▬ ▬▬▬ ▬▬▬ ▬▬▬
If a 12V power supply is modulated at a 50% duty cycle, the motor behaves as if it is receiving a steady 6V supply, reducing its rotational speed accordingly. Key Components of a PWM Control System
A complete guide to any modern PWM drive involves an architectural system split into three distinct stages:
The Controller (The Brain): Microcontrollers (such as an Arduino or specialized industrial ICs) generate low-power, high-precision digital PWM signals based on user inputs or software algorithms.
The Switching Driver (The Muscle): Because a microcontroller cannot handle the high current demands of a motor, the signal is routed to high-speed solid-state switches. MOSFETs are universally preferred over BJTs due to their minimal input current requirements and vastly superior energy efficiency.
The Topology (H-Bridge): For bidirectional control, drivers employ an H-Bridge configuration. By opening and closing specific pairs of transistors across four quadrants, the drive can alter the direction of the current, allowing the motor to spin forward, reverse, or execute a hard brake. Critical Design Considerations 1. Selecting the Ideal PWM Frequency
The basic principle of PWM control How does PWM … – EEWorld
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