I have studied the Navy related materials on pulse width modulation but I'm not clear as to what they really are or what they're supposed to indicate. From what I read, the output of PWM doesn't have a sufficient current carrying capabilities to drive a motor. It's added in a circuit to stabilize the output current.
The textbook is being vague about pulse width modulation that it's frustrating me: "Pulse width modulation is the method by which a fixed frequency and amplitude is varied in duty cycle by an analog signal." The book then describes that inputs to a PWM are a clock pulse and a DC level. I'm not clear where this clock pulse comes from.
What I need to get at before studying PWM circuits is what does a duty cycle indicate? What happens to the pulse width when the load increases? How does a DC voltage get converted into pulse width?