The feature set of the L6566 is quite rich. Most of the features seen in the VIPer Plus family are present and enhanced, such as OVP set as either latched or auto-restart, over-current protection with delayed shutdown, brown-out protection with hysteresis, and a programmable soft-start. The most powerful feature of the L6566 however is its ability to be used as either a fixed-frequency flyback controller or as a quasi-resonant controller. Other useful features include an adaptive UVLO, input voltage feed forward to adapt current limit to constant power output, internal gate driver for the external switch, and options for both 700 V and 840 V tolerant high voltage startup circuitry that extends the input voltage range capability of the device.