CIRCUIT IDEAS ELECTRONICS FOR YOU • AUGUST 2006 • 97 WWW.EFYMAG.COM Fig. 2: DC motor speed control using PWM method Fig. 3: Pin configuration of BC337A ± EFY LAB SPEED CONTROL OF DC MOTOR USING PULSE-WIDTH MODULATION SUNIL KUMAR P ulse-width modulation (PWM) or duty-cycle variation methods are commonly used in speed control of DC motors. The duty cycle is defined as the percentage of digital ‘high’ to digital ‘low’ plus digital ‘high’ pulse-width during a PWM period. Fig. 1 shows the 5V pulses with 0% through 50% duty cycle. The average DC voltage value for 0% duty cycle is zero; with 25% duty cycle the average value is 1.25V (25% of 5V). With 50% duty cycle the aver-age value is 2.5V, and if the duty cycle is 75%, the average voltage is 3.75V and so on. The maximum duty cycle can be 100%, which is equivalent to a DC waveform. Thus by varying the pulse-width, we can vary the average voltage across a DC motor and hence its speed. The circuit of a simple speed con-
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DC Motor, Pulse-width modulation, duty cycle