NE555PWM pulse width modulation circuit

NE555PWM pulse width modulation circuit

PWM is called pulse width modulation signal, which uses the width of the pulse to adjust the brightness and can also be used to control DC motors. The basic frequency of the PWM pulse width modulation signal is at least about 400HZ-10KHZ. When adjusting the brightness or darkness of the LED, this basic frequency cannot be changed, but the width of the wave above this frequency is changed. The wider the width, the brighter and brighter the width. The narrower it is, the darker it is. PWM controls the lighting time of the LED, rather than changing the output voltage to control the brightness.

Figure 1-5 PWM pulse width modulation picture

The following is the working principle of PWM:

The reset pin is connected to +V, so it has no effect on the circuit.

When the circuit is powered on, Pin2 (trigger point) is low because capacitor C1 begins to discharge. This starts the oscillator cycle, causing pin 3 to go high. When pin 3 reaches a high potential, capacitor C1 begins to charge through R1 and diode D2. When the voltage of C1 reaches 2/3 of +V, pin 6 is activated, causing the output pin (Pin3) and the discharge pin (Pin7) to become low potential.

When pin 3 goes low, capacitor C1 starts to discharge through R1 and D1. When the voltage at C1 drops below 1/3 of +V, the output pin (Pin3) and discharge pin (Pin7) go high and the circuit cycle repeats. Pin5 is not used as an input by external voltage, so it is connected to a 0.01uF capacitor.

Capacitor C1 passes through R1 and the diode, and the diode is discharged and charged at the same time. The sum of the charge and discharge resistors is the same, so the period of the output signal is constant. The working range only changes with R1.

The overall frequency of the PWM signal in this circuit depends on the values ​​of R1 and C1. Formula: Frequency (Hz)=1.44/(R1*C1)