LED light source with trailing edge phase cut dimming

• US 9,326,344 B2
• Filed: 01/25/2013
• Issued: 04/26/2016
• 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
• Primary Examiner(s): WHITE, DYLAN C
• Application Number:
  US14/372,846
• Publication Number:
  US 20140354165A1
• Time in Patent Office: 1,187 Days
• Field of Search: 315/200.R
• US Class Current: 1/1
• 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 a first rectifier output terminal and a second rectifier output terminal and rectifier input terminals, wherein the rectifier input terminals are connected to dimmer output terminals of a phase cut dimmer of the trailing edge type, said phase cut dimmer having dimmer input terminals for connection to a mains supply,

a first unidirectional element and first capacitor connected in series between the first and second rectifier output terminals,

a converter circuit having converter input terminals electrically coupled to each terminal of the first capacitor and converter output terminals electrically coupled to a LED load, wherein the converter circuit is configured to generate a current through the LED load, wherein the current is dependent on a dim signal and a voltage present across the first capacitor,

a dim circuit that generates the dim signal based on a voltage present between the first and second rectifier output terminals,

a first switch and a second capacitor electrically coupled between the second rectifier output terminal and a first connection terminal at a connection between the first unidirectional element and the first capacitor,

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

2. The dimmable LED light source according to claim 1, wherein the LED light source further comprises a second unidirectional element shunted across 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 rectifier output terminal and the second rectifier output terminal, the bleeder comprising a second switch and an impedance arranged in series; and

a switch control circuit arranged to control the bleeder 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, the filter comprising a first resistor and a second resistor in series between the first and second rectifier output terminals, and a third 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 and second rectifier output terminals, a first phase angle of the voltage at which the bleeder is switched off, and a second phase angle of the voltage 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 periodic digital signal 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 each 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 capacitor,

providing a converter circuit having a LED load coupled to the converter circuit'"'"'s output terminals and generating a current through said LED load based on a voltage across the first capacitor and a dim signal,

charging a second capacitor when a voltage between the first and second rectifier output terminals is high and discharging the second capacitor into the first capacitor when the voltage between the first and second rectifier output terminals is low, and

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

8. A method according to claim 7, wherein the phase cut dimmer comprises a power supply and a timer, the method further comprising 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.

9. A driver comprising:

a first rectifier output terminal and a second rectifier output terminal that are electrically coupled to a rectifier that provides a voltage to the first and second rectifier output terminals based on outputs of a phase cut dimmer of the trailing edge type,

a first unidirectional element and a first capacitor that are electrically coupled in series between the first and second rectifier output terminals, a voltage across the first capacitor being provided to a converter that supplies a current to an LED based on the voltage and a dim signal, and

a first switch and a second capacitor that are electrically coupled in series, and electrically coupled in parallel to the first capacitor;

wherein;

the first capacitor has a first capacitance that is substantially smaller than a second capacitance of the second capacitor, and

the first switch is configured to provide voltage from the second capacitor to the first capacitor when a voltage between the first and second rectifier output terminals drops below a first reference voltage.

10. The driver of claim 9, including the rectifier.

11. The driver of claim 10, including the phase cut dimmer, the phase cut dimmer including a third capacitor, a second switch, and a timer that controls the second switch to provide at least one of the outputs of a phase cut dimmer.

12. The driver of claim 9, including a low-pass filter electrically coupled to the first and second rectifier output terminals, the low-pass filter providing the dim signal.

13. The driver of claim 9, including a second unidirectional element electrically coupled in parallel to the first unidirectional element and the first switch.

14. The driver of claim 9, including a flip-flop device that controls the first switch to be conductive when the voltage between the first and second rectifier output terminals drops below the first reference voltage.

15. The driver of claim 14, wherein the flip-flop device controls the first switch to be non-conductive when a voltage across the second capacitor drops below a second reference voltage.

16. The driver of claim 14, wherein the flip-flop device controls the first switch to be non-conductive when a voltage across the second capacitor drops below a second reference voltage.

17. The driver of claim 9, including a flip-flop device and a low pass filter that provides the dim signal.

18. The driver of claim 17, wherein the flip-flop device is set when the voltage between the first and second rectifier output terminals rises above a third reference voltage, and reset when the voltage between the first and second rectifier output terminals drops below the first reference voltage.