Pulse Width Modulator - Embedded System Design - Lecture Slides, Slides of Computer Science

Download Pulse Width Modulator - Embedded System Design - Lecture Slides and more Slides Computer Science in PDF only on Docsity! Pulse width modulator • Generates pulses with specific high/low times • Duty cycle: % time high – Square wave: 50% duty cycle • Common use: control average voltage to electric device – Simpler than DC-DC converter or digital-analog converter – DC motor speed, dimmer lights • Another use: encode commands, receiver uses timer to decode 1 clk pwm_o 25% duty cycle – average pwm_o is 1.25V clk pwm_o 50% duty cycle – average pwm_o is 2.5V. clk pwm_o 75% duty cycle – average pwm_o is 3.75V. Docsity.com Controlling a DC motor with a PWM 2 void main(void){ /* controls period */ PWMP = 0xff; /* controls duty cycle */ PWM1 = 0x7f; while(1){}; } The PWM alone cannot drive the DC motor, a possible way to implement a driver is shown below using an MJE3055T NPN transistor. 5V B A Internal Structure of PWM clk_div cycle_high counter ( 0 – 254) 8-bit comparator controls how fast the counter increments counter < cycle_high, pwm_o = 1 counter >= cycle_high, pwm_o = 0 pwm_o clk Input Voltage % of Maximum Voltage Applied RPM of DC Motor 0 0 0 2.5 50 1840 3.75 75 6900 5.0 100 9200 Relationship between applied voltage and speed of the DC Motor DC MOTOR 5V From process or Docsity.com