Leds driver

• US 20060071614A1
• Filed: 12/11/2003
• Published: 04/06/2006
• Est. Priority Date: 12/19/2002
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Tripathi, Ajay, Clauberg, Bernd, Khetarpal, Rohit, Min, Young-Kee, Narasimhan, Raghuram
• Granted Patent: US 7,262,559 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 45/58 involving end of life detection of LEDs
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

The power supply (20) for LEDs provides power to a LED light source (10) having a variable number of LEDs wired in series and/or in parallel. The power supply (20) uses current and voltage feedback to adjust power to the LEDs and provides protection to the LED light source (10). A feedback controller (27) compares sensed current and sensed voltage to a reference signal and generates a feedback signal, which is processed by a power factor corrector (124) to adjust the current flow through the transformer supplying current to the LEDs. A LED control switch (24) clamps a peak of the current to the LEDs to provide further protection to the LED light source (10). A short/open detection circuit (30) indicates any detection of a “LED outage” of the LED light source (10).

Claims

1. A power supply (20) for a LED light source (10), said power supply (20) comprising:

a power converter (23) operable to provide a regulated power including a LED current and a LED voltage; and

a LED control switch (24) operable to control a flow of the LED current through the LED light source (10),

wherein said LED control switch (24) is further operable to clamp a peak of the LED current during an initial loading stage of the LED light source (10).

2. The power supply (20) of claim 1, wherein said LED control switch (24) includes:

a switch (SW1) operable to establish a current path from the LED light source (10) to said power converter (23) when the LED current is below a peak threshold, said switch (SW1) further operable to eradicate the current path when the LED current is above the peak threshold.

3. The power supply (20) of claim 2, further comprising:

a LED PWM dimmer (29) operable to provide a pulse width modulation signal to said switch (SW1) in response to an external dim command,

wherein said pulse width modulation signal has a target pulse width in response to the dim command exceeding a ramp signal, and

wherein said pulse width modulation signal has a minimum pulse width in response to the ramp signal exceeding the dim command.

4. The power supply (20) of claim 3, wherein said LED PWM dimmer (29) includes:

an astable multivibrator circuit (129) operable to establish the minimum pulse width in a precise and temperature insensitive manner.

5. The power supply (20) of claim 2, wherein said LED PWM dimmer (29) includes:

a comparator (U3) operable to establish the target pulse width in response to a reception of the dim command and the ramp signal.

6. The power supply (20) of claim 5, wherein said LED PWM dimmer (29) further includes:

a ramp generator operable to provide the ramp signal to said comparator (U3) indicative of the minimum pulse width.

7. The power supply (20) of claim 6, wherein said LED PWM dimmer (29) further includes:

an astable multivibrator circuit (129) operable to establish the minimum pulse width in a precise and temperature insensitive manner.

8. The power supply (20) of claim 1, further comprising:

a detection circuit (30) operable to provide a detection signal indicative of an operating condition of the LED light source (10) associated with the LED voltage,

wherein the detection signal has a first level representative of a load condition of the LED light source (10), and

wherein the detection signal has a second level representative of either a short condition or an open condition of the LED light source (10).

9. The power supply (20) of claim 8, wherein the load operating condition indicates a magnitude of a LED voltage drop across the LED light source (10) is between zero volts and the LED voltage.

10. The power supply (20) of claim 8, wherein the short operating condition indicates a magnitude of a LED voltage drop across the LED light source (10) approximates zero volts.

11. The power supply (20) of claim 8, wherein the open operating condition indicates a magnitude of a LED voltage drop across the LED light source (10) approximates the LED voltage.

12. The power supply (20) of claim 1, further comprising:

a current sensor (25) operable to sense the LED current flowing through the LED light source (10), said current sensor (25) including

an operational amplifier (U6), and

means for adjusting a gain of said differential amplifier.

13. The power supply (20) of claim 1, further comprising:

a voltage sensor (26) operable to sense the LED voltage applied to the LED light source (10), said voltage sensor (26) including

an operational amplifier (U6), and

means for adjusting a gain of said differential amplifier.

14. A method of operating a LED light source (10), said method comprising:

providing a regulated power to the LED light source (10), the regulated power including a LED current and a LED voltage;

controlling a flow of the LED current through the LED light source (10); and

clamping a peak of the LED current during an initial loading stage of the LED light source (10).

15. The method of claim 14, further comprising:

generating a detection signal indicative of an operating condition of the LED light source (10) associated with the LED voltage,

wherein the detection signal has a first level representative of a normal operating condition of the LED light source (10), and

wherein the detection signal has a second level representative of either a short operating condition or an open operating condition of the LED light source (10).