The NCP4355 is a secondary side SMPS controller designed for use in applications which require extremely low no load power consumption. The device is capable of detecting no load conditions and entering the power supply into a low consumption OFF mode. During OFF mode, the primary side controller is turned off and energy is provided by the output capacitors thus eliminating the power consumption required to maintain regulation. During OFF mode, the output voltage relaxes and is allowed to decrease to an adjustable level. Once more energy is required, the NCP4355 automatically restarts the primary side controller by ONOFF current that flows through ONOFF optocoupler. The NCP4355 controls the primary controller with an Active ON signal, meaning that it only drives optocoupler current during ON mode to minimize consumption during OFF mode.