LED LIGHT SOURCE

摘要

The invention relates to a dimmable LED light source comprising:—a rectifier having rectifier input terminals for connection to respective output terminals of a phase cut dimmer of the trailing edge type, input terminals of the phase cut dimmer being connected to the mains supply, and having rectifier output terminals,—a first bleeder circuit connecting the rectifier output terminals,—a series arrangement comprising a unidirectional element and a capacitive means connecting the rectifier output terminals,—a converter circuit, having input terminals coupled to respective sides of the capacitive means and output terminals coupled to a LED load, for generating a current through the LED load, in dependence on a dim signal, out of a voltage present across the capacitive means,—a dim circuit for generating a dim signal as a function of the adjusted phase angle of the phase cut dimmer and for supplying the dim signal to a dim input of the converter circuit, the dim circuit comprising:—gradient detection circuitry for determining the gradient of the voltage across the capacitive means and for determining as the adjusted phase angle the first value of the phase angle for which the gradient is negative, when the phase angle is less than 90 degrees,—signal generating circuitry for generating a sinusoidal signal that represents the mains supply voltage,—circuitry for activating the first bleeder when the phase angle is 90 degrees and for switching off the first bleeder when the adjusted phase angle has been determined, in case the adjusted phase angle is higher than 90 degrees,—deviation detection circuitry for detecting the deviation of the voltage across the rectifier output terminals from the sinusoidal signal, for comparing the deviation voltage with a reference voltage and for determining as the adjusted phase angle the value of the phase angle for which the deviation voltage is higher than or equal to the reference voltage, when the phase angle is between 90 and 180 degrees.