LED LIGHT SOURCE

摘要

LED light source suitable for use with a phase cut dimmer (III), comprising •input terminals (K1, K2) for connection to an AC supply voltage, •a rectifier (I) coupled to the input terminals, 108 a series arrangement comprising N LEDs (LL1, LL2, LL3) coupled to the rectifier, •control circuitry (EX) for sequentially activating (deactivating) the LEDs as the supply voltage increases (decreases), wherein the control circuitry comprises: •N controllable current regulators, each regulator being coupled between the cathode of a LED and ground and comprising a transistor and one impedance in series, •a global current control circuit (X) coupled to the control electrodes of said transistors and comprising circuitry for adjusting the voltage at said control electrodes in dependency of the phase angle, •a series arrangement of a switch (S) and a capacitor (C1) coupled- to the rectifier and •means (VIII) for rendering said switch conductive in case the AC supply voltage drops below a reference value.

主权项

1. A LED light source, for use with a phase cut dimmer comprising:
a first input terminal and a second input terminal for connection to a supply voltage source supplying a low frequency AC supply voltage with frequency f, a rectifier coupled to the input terminals for rectifying the low frequency AC supply voltage, a series arrangement comprising N LED loads, a first and second end of said series arrangement being coupled to a first output terminal and a second output terminal of the rectifier, control circuitry for subsequently making the LED loads conduct a current, one by one, in dependence on the instantaneous value of the low frequency AC supply voltage when the instantaneous value increases and for subsequently making the LED loads stop conducting a current, one by one, in dependence on the instantaneous value of the low frequency AC supply voltage when the instantaneous value decreases,wherein the control circuitry comprises
each N control strings comprising a controllable current regulator and being coupled between the cathode of a respective LED load and the second output terminal of the rectifier, and a global current control circuit coupled to the controllable current regulators for controlling the instantaneous value of the current through the control strings, wherein the controllable current regulators each comprise a series arrangement of a transistor and at least one impedance, and wherein the global current control circuit is coupled to the control electrodes of the transistors comprised in the controllable current regulators and comprises circuitry for adjusting the voltage present at the control electrodes of the transistors comprised in the control strings, in dependency of the adjusted phase angle of the phase cut dimmer, wherein a series arrangement of a switch and a capacitor coupled between the output terminals of the rectifier and control circuitry for rendering the switch conductive in case the instantaneous value of the low frequency AC supply voltage drops below a reference value; and wherein the phase cut dimmer is a TRIAC dimmer and the LED light source comprises an RC shunt circuit for providing reliable latching of the TRIAC dimmer.