Switch mode power transformers (and supplies) get their name from the switching action needed to sustain transformer operation. By controlling the amount of on time and off time of the switches, one can also control the amount of power delivered to the transformer’s load (or load circuit). The voltage can be fed to the switch mode power transformer in voltage pulses. The pulse duration is a portion of an overall cycle time. The cycle time is equal to the inverse of the operating frequency. The terms duty cycle and pulse width modulation arise from the control of the switching on time and off time.