An LED driver with open loop dimming including a full wave rectifier circuit, a DC/DC converter, and an oscillator circuit. The rectifier is configured to receive an input voltage in the form of an AC conductive angle modulated voltage and to provide a rectified voltage. The DC/DC converter converts the rectified voltage to an output voltage and an output current, where the output current has a magnitude which varies proportionately with a square of a quadratic mean of the input voltage. The oscillator circuit controls switching of the DC/DC converter with constant frequency and constant duty cycle. The DC/DC converter may be a flyback converter and may include a transformer operated in DCM. The driver may include output voltage and/or output current limit. The output current may be limited when the input voltage is within normal operating range of an AC line voltage from which the input voltage is derived.