Led Lighting Device

• US 20080303452A1
• Filed: 12/12/2006
• Published: 12/11/2008
• Est. Priority Date: 12/13/2005
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Van Erp, Josephus Adrianus Maria
• Granted Patent: US 8,004,211 B2
• Time in Patent Office: Days
• US Class Current: 315/294
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/44 with an active control inside an LED matrix
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

The present invention relates to a multiple LED driver circuit in which each LED (15, 17) is controlled by a bypass switch (19, 21). The LEDs are supplied by a switched mode power supply (8) and are connected to a constant current source to draw a predetermined current through the LEDs. The switched mode power supply is arranged to output different voltages depending on the number of switched-on LEDs. This is carried out by supplying the control signals (sw₁, sw₂) of the bypass switches to the switched mode power supply. In this way, the power dissipation of the constant current source can be kept at a low level.

Claims

1. A LED lighting device comprising at least a first and a second LED (15,17;

33,31) supplied by a switched mode power supply (8;

49), wherein the current through the first LED (15;

33) is controlled by a first bypass switch (19;

41), connected in parallel with the first LED, the current through the second LED (17;

31) is controlled by a second bypass switch (21;

39), connected in parallel with the second LED, the first and second LEDs being connected in series between the switched mode power supply and a first constant current source (25;

47), and wherein the switched mode power supply is arranged to supply a number of different output voltages (Vout) depending on the state of the first and second bypass switches, such that the voltage depends on the number of LEDs emitting light.

2. A LED lighting device according to claim 1, wherein the first and second LEDs are arranged to be controlled by pulse width modulation, such that the first and second LEDs are switched on simultaneously at the beginning of a pulse width modulation period and are switched off during the pulse width modulation period at instants determined by their respective duty cycles.

3. A LED lighting device according to claim 2, wherein the switched mode power supply is arranged to rise towards a maximum voltage before the beginning of the pulse width modulation period.

4. A LED lighting device according to claim 1, comprising means for driving the output voltage to zero or close to zero when all LEDs are switched off.

5. A LED lighting device according to claim 1, wherein the first and second LEDs emit light of a different color.

6. A LED lighting device according to claim 5, wherein the first and second LEDs (33,31) emit light of a green and blue color, respectively, and are connected to the first constant current source (47) via a third LED (35), which is controlled by a third bypass switch (43), wherein the first and second LEDs are connected to a second constant current source (45) via a fourth LED (29), which is controlled by a fourth bypass switch (37), and wherein the third and fourth LEDs emit red or amber-colored light.