PWM Controllers for Flyback DC/DC Converters

Pulse Width Modulation (PWM) is widely used in switch mode power supplies that use digital control to provide the switching action. PWM itself is a controlled digital output signal. A pulse is much like a step-function in that it is binary, either fully on or off, and thus digital in nature. The on-time of a pulse is when the DC supply voltage is fully applied to the load. The period during which the voltage supply is switched off is the binary low of the pulse. Thus, PWM is a means of digitally emulating a varying analog signal by generating a train of pulses that vary in frequency.