LED LIGHT SOURCE

• US 20140354165A1
• Filed: 01/25/2013
• Published: 12/04/2014
• Est. Priority Date: 02/02/2012
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Malyna, Dmytro Viktorovych, De Bruycker, Patrick Alouisius Martina, Rademacher, Harald Josef Gunther
• Granted Patent: US 9,326,344 B2
• Time in Patent Office: Days
• US Class Current: 315/200.R
• CPC Class Codes: H05B 39/09 in which the lamp is fed by pulses automatic circuit devices built into or on the incandescent lamp H01K1/625; vehicle winking devices B60Q1/38
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3575 by means of dummy loads or bleeder circuits, e.g. for dimmers
• CPC Class Codes: H05B 45/37 Converter circuits

Abstract

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 a first rectifier output terminal and a second rectifier output terminal, —a bleeder circuit connecting the rectifier output terminals, —a series arrangement comprising a first unidirectional element and first capacitive means connecting the rectifier output terminals, —a converter circuit, having input terminals coupled to respective sides of the first 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, —a series arrangement comprising a switching element and second capacitive means coupled between a terminal between the first unidirectional element and the second output terminal of the rectifier, —a control circuit for controlling the switching element in the conductive state when the voltage between the first and second output terminals of the rectifier drops below a first predetermined reference and for controlling the switching element in the non-conductive state when the voltage across the second capacitive means has reached a second predetermined reference, wherein the first capacitive means is dimensioned so that the voltage between the first and the second output terminal of the rectifier equals the sum of the voltage across the first capacitive means and the voltage across the first unidirectional means if the switching element is non-conductive.

Claims

1. 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 and having a first output terminal and a second output terminal, said phase cut dimmer having input terminals for connection to a mains supply,

a series arrangement comprising a first unidirectional element and first capacitive means connecting the first and second output terminals of the rectifier,

a converter circuit, having input terminals coupled to respective sides of the first capacitive means and output terminals coupled to a LED load, configured 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 out of the voltage present between the first output terminal and the second output terminal of the rectifier and for supplying the dim signal to a dim input of the converter circuit,

a series arrangement comprising a first switch and second capacitive means coupled between the second output terminal of the rectifier and a terminal between the first unidirectional element and the first capacitive means,

a control circuit for controlling the first switch in the conductive state when the voltage between the first and second output terminals of the rectifier drops below a first predetermined reference and for controlling the first switch in the non-conductive state when the voltage across the second capacitive means has reached a second predetermined reference,

wherein the first capacitive means is arranged so that the voltage between the first and the second output terminal of the rectifier equals the sum of the voltage across the first capacitive means and the voltage across the first unidirectional means, when the first switch is non-conductive.

2. The dimmable LED light source according to claim 1, wherein the LED light source further comprises a second unidirectional element shunting the first unidirectional element and the first switch.

3. The dimmable LED light source according to claim 1, wherein the phase cut dimmer comprises a power supply and a timer, the dimmable LED light source further comprising:

a bleeder connected between the first output terminal and the second output terminal; and

a series arrangement of a second switch and an impedance and a switch control circuit arranged to charge the power supply and to reset the timer.

4. The dimmable LED light source according to claim 1, wherein the dim circuit comprises a low pass filter comprising a series arrangement of a first resistor and a second resistor coupled between the first output terminal and the second output terminal, and a capacitor shunting the second resistor.

5. The dimmable LED light source according to claim 1, wherein the dim circuit comprises:

detection circuitry arranged for detecting, in each period of the voltage between the first output terminal and the second output terminal, first phase angle at which the bleeder is switched off, and a second phase angle at which the switching element is made conductive; and

difference circuitry for generating a difference signal that represents the difference between the second and the first phase angle.

6. The dimmable LED light source according to claim 5, wherein the difference signal is a digital signal that is periodical with a period of 180 degrees and that is high during a time lapse equal to the difference between the second and the first phase angle and low in the remainder of the period and wherein the dim circuit is further equipped with a low pass filter for filtering the difference signal.

7. A method of dimming a LED light source comprising the steps of:

using a phase cut dimmer to generate a phase cut sinusoidal supply voltage out of a sinusoidal supply voltage,

rectifying the phase cut sinusoidal supply voltage using a rectifier having a first rectifier output terminal and a second rectifier output terminal,

supplying the rectified phase cut sinusoidal supply voltage to a series arrangement of a unidirectional element and first capacitive means,

providing a converter circuit having a LED load coupled to its output terminals and generating a current through said LED load out of a voltage across the first capacitive means,

providing a second capacitive means and charging the second capacitive means when the voltage between the first rectifier output terminal and the second rectifier output terminal is high and discharging the second capacitive means into the first capacitive means when the voltage between the first rectifier output terminal and the second rectifier output terminal is low,

generating a dim signal as a function of the voltage present between the first and second output terminal of the rectifier,

controlling the magnitude of the current through the LED load as a function of the dim signal, and

controlling the voltage across the first capacitive means so that the sum of the voltages across the first capacitive means and the voltage across the first unidirectional element equals the voltage between the first and the second output terminal of the rectifier, when the second capacitive means is not being discharged.

8. A method according to claim 7, wherein the phase cut dimmer comprises a power supply and a timer, the method further comprising the step of bleeding a current from the first rectifier output terminal to the second rectifier output terminal, for charging the power supply and for resetting the timer.