In a voltage mode controller, VOUT is fed to the error amp through a feedback network. The feedback voltage is compared to a reference voltage. The difference between the reference voltage and the feedback voltage creates an error voltage. The error voltage is then compared against a sawtooth waveform by the PWM comparator. The output of the comparator then goes to the high-side FET driver to form the tON time. The two different waveforms of duty cycle show how different error voltages control the duty cycle. It can be seen that the total cycle time does not change, but the tON time and the tOFF time change to adjust the output voltage.