These three circuits help illustrate the concept of Pulse-Width Modulation (PWM) and how it can be used to control motor speed and LED intensity. Each circuit has a 5-volt supply voltage and identical LEDs. Note that the simulation is running in slow motion (60 msec/sec or 6% of normal speed). The pulses are set to a frequency of 50 Hz (50 cycles per second, or 20 msec per cycle).
The top circuit has a duty cycle of 100%, so the LED is always on and will appear the brightest of the three.
The center circuit has a duty cycle of 75%. This means that the voltage pulse is on for 75% of the cycle, and off for 25% of the cycle. When viewed at normal speed, this LED will have a lower intensity than the top LED.
The bottom circuit has a duty cycle of 10%, which means that the LED is on for only 10% of the time. When viewed at normal speed, this LED will have a lower intensity than the other two.
