PWM is the most common method of speed control to control DC motor. It is a one fundamental of control system in programming interface or robotics. PWM is the process of switching the power to a device on and off at a given frequency, with varying on and off times. These on and off times are referred to as “duty cycle”. This is a simple design of PWM circuit that using 555 IC. In the figure shows the wave forms of 10%, 50%, and 90% duty cycle signals.
How is this circuit work? When this circuit powers up, the trigger pin is L as capacitor C1 is discharged. It will begin the oscillator cycle, causing the output to go H. If the output is H, capacitor C1 begins to charge through the right side of R1 and diode D2. And then the voltage on C1 reaches 2/3 of +V, the threshold (pin 6) is activated, which in turn causes the output (pin 3), and discharge (pin 7) to go LOW. If the output (pin 3) goes L, capacitor C1 starts to discharge through the left side of R1 and D1. When the voltage on C1 falls below 1/3 of +V, the output (pin 3) and discharge (pin 7) pins go H, and the cycle repeats.
Pin 5 is not used for an external voltage input, so it is bypassed to ground with a 0.01uF capacitor. For note the configuration of R1, D1, and D2. Capacitor C1 charges through one side of R1 and discharges through the other side. The sum of the charge and discharge resistance is always same, therefore the wave length of the output signal is constant. Only the duty cycle varies with R1. The overall frequency of PWM signal in this circuit is determined by the values of R1 and C1. In the schematic above, this has been set to frequency 144 Hz.
How is this circuit work? When this circuit powers up, the trigger pin is L as capacitor C1 is discharged. It will begin the oscillator cycle, causing the output to go H. If the output is H, capacitor C1 begins to charge through the right side of R1 and diode D2. And then the voltage on C1 reaches 2/3 of +V, the threshold (pin 6) is activated, which in turn causes the output (pin 3), and discharge (pin 7) to go LOW. If the output (pin 3) goes L, capacitor C1 starts to discharge through the left side of R1 and D1. When the voltage on C1 falls below 1/3 of +V, the output (pin 3) and discharge (pin 7) pins go H, and the cycle repeats.
Pin 5 is not used for an external voltage input, so it is bypassed to ground with a 0.01uF capacitor. For note the configuration of R1, D1, and D2. Capacitor C1 charges through one side of R1 and discharges through the other side. The sum of the charge and discharge resistance is always same, therefore the wave length of the output signal is constant. Only the duty cycle varies with R1. The overall frequency of PWM signal in this circuit is determined by the values of R1 and C1. In the schematic above, this has been set to frequency 144 Hz.
No comments:
Post a Comment