LED DRIVER WITH END-OF-LIFE DETECTION CIRCUITRY

• US 20120187847A1
• Filed: 12/20/2011
• Published: 07/26/2012
• Est. Priority Date: 12/20/2010
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Hamamoto, Katsunobu, Yamamoto, Masafumi, Ueda, Keisuke, Takikita, Hisaya
• Granted Patent: US 8,853,949 B2
• Time in Patent Office: Days
• US Class Current: 315/125
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges
• 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

An LED lighting device includes a DC/DC power converter having output terminals coupled to respective lamp sockets. A controller receives signals from a current sensor and a voltage sensor, and controls the DC/DC power converter to increase/decrease an output voltage based on a sensed output current with respect to a target value. A sensed output voltage is compared to predetermined upper and lower limit values, and the DC/DC power converter is disabled when the output voltage exceeds the predetermined upper limit value or falls below the predetermined lower limit. The controller further measures an accumulated lighting time of the device, and after the accumulated lighting time has exceeded a predetermined switching time, decreases the upper limit value monotonously or in increments as the accumulated lighting time passes.

Claims

1. An LED lighting device comprising:

a DC/DC power converter having first and second converter output terminals and effective to supply an output voltage across the converter output terminals;

first and second lighting device output terminals coupled to the first and second converter output terminals, respectively, and effective to receive an LED lamp;

a current sensor coupled between one of the converter output terminals and a corresponding device output terminal, and effective to detect an output current;

a voltage sensor coupled across the converter output terminals and effective to detect the output voltage; and

a control circuit effective

to control the DC/DC power converter to adjust the output voltage based on the output current detected by the current sensor with respect to a target value,

to compare the output voltage detected by the voltage sensor to a predetermined upper limit value, and upon the output voltage exceeding the predetermined upper limit value, to disable the DC/DC power converter,

to measure an accumulated lighting time of the device, and

after the accumulated lighting time has exceeded a predetermined switching time, to decrease the upper limit value as the accumulated lighting time passes.

2. The LED lighting device of claim 1, the control circuit further effective to identify a predetermined reset condition being met, and upon identifying the predetermined reset condition as having been met, to reset the accumulated lighting time to zero.

3. The LED lighting device of claim 2, the control circuit further effective to identify when the accumulated lighting time has exceeded a predetermined reset disabling time subsequent to the predetermined switching time, wherein the control circuit does not reset the accumulated lighting time even upon the reset condition being met.

4. The LED lighting device of claim 3, wherein the predetermined reset disabling time corresponds to a point at which the upper limit value is equal to or below a rated voltage.

5. The LED lighting device of claim 1, the control circuit effective after the accumulated lighting time has exceeded a predetermined switching time to decrease the upper limit value linearly over time.

6. The LED lighting device of claim 1, the control circuit effective after the accumulated lighting time has exceeded a predetermined switching time to decrease the upper limit value in stepped increments over time.

7. The LED lighting device of claim 1, the control circuit effective after the accumulated lighting time has exceeded a predetermined switching time to decrease the upper limit value exponentially over time.

8. The LED lighting device of claim 1, further comprising

an AC/DC power converter coupled to first and second input terminals of the DC/DC power converter;

a constant voltage source coupled to a node between the AC/DC converter and the first input terminal of the DC/DC converter and effective to provide a constant output voltage less than a rated voltage across the device output terminals; and

a lamp connection determining circuit effective to generate an output signal representative of a loaded state or an unloaded state for the first and second device output terminals,

the control circuit further effective, upon receiving an output signal representative of a loaded state, to enable the DC/DC converter.

9. The LED lighting device of claim 8, the control circuit further effective during a loaded state

to compare the detected output voltage from the voltage sensor to the predetermined upper limit and a predetermined lower limit,

to enable the DC/DC converter when the detected output voltage is between the predetermined upper and lower limits, and

to disable the DC/DC converter when the detected output voltage is greater than the predetermined upper limit or less than the predetermined lower limit,

the control circuit further effective upon receiving an output signal representative of an unloaded state to disable the DC/DC converter.

10. The LED lighting device of claim 9, further comprising a zener diode coupled between the voltage sensor and a positive output terminal, the zener diode having a breakdown voltage greater than the constant voltage output from the constant voltage source.

11. The LED lighting device of claim 8, the control circuit further effective during a loaded state

to compare the detected output voltage from the voltage sensor to the predetermined upper limit and a predetermined lower limit,

to enable the DC/DC converter when the detected output voltage is between the predetermined upper and lower limits, and

to disable the DC/DC converter when the detected output voltage is greater than the predetermined upper limit or less than the predetermined lower limit,

the control circuit further effective upon receiving an output signal representative of an unloaded state to control the DC/DC converter to decrease the output voltage to less than the predetermined lower limit.

12. The LED lighting device of claim 11, further comprising a zener diode coupled between the voltage sensor and a positive output terminal, the zener diode comprising a breakdown voltage greater than the constant voltage output from the constant voltage source.

13. A method of operating an LED lighting device that includes a DC/DC power converter effective to supply an output voltage to an LED lamp, the method comprising:

sensing the output voltage and comparing the output voltage to both of a predetermined upper limit value and a predetermined lower limit value;

upon the output voltage exceeding the predetermined upper limit value, disabling the DC/DC power converter;

sensing an output current and comparing the output current to a target value;

controlling the DC/DC power converter to increase/decrease the output voltage when the output current is less than/ greater than the target value, respectively;

measuring an accumulated lighting time of the device with respect to an LED lamp; and

after the accumulated lighting time has exceeded a predetermined switching time, decreasing the upper limit value as the accumulated lighting time passes.

14. The method of claim 13, further comprising the steps of:

identifying a predetermined reset condition being met, and

upon identifying the predetermined reset condition as having been met, resetting the accumulated lighting time to zero.

15. The method of claim 14, further comprising the steps of:

identifying when the accumulated lighting time has exceeded a predetermined reset disabling time subsequent to the predetermined switching time, wherein the control circuit does not reset the accumulated lighting time even upon the reset condition being met.

16. The method of claim 15, wherein the predetermined reset disabling time corresponds to a point at which the upper limit value is equal to or below a rated voltage.

17. The method of claim 13, the LED lighting device further including a constant voltage source, the method further comprising the steps of:

upon initially receiving mains input power to the LED lighting device, while the DC/DC converter is disabled, providing a constant output voltage less than a rated voltage from the constant voltage source;

determining a lamp connection state comprising a loaded state or an unloaded state with respect to the LED lighting device; and

upon determining a loaded state, enabling the DC/DC converter.

18. The method of claim 17, further comprising the steps of:

comparing the output voltage to the predetermined upper limit and a predetermined lower limit;

in a loaded state, disabling the DC/DC converter when the detected output voltage is greater than the predetermined upper limit or less than the predetermined lower limit; and

upon determining an unloaded state, disabling the DC/DC converter.

19. An illumination fixture comprising:

a housing defining an interior and having a substantially planar upper surface and first and second lamp sockets at opposite ends of a lower surface; and

an LED lighting device disposed within the interior of the housing and further comprising

a DC/DC power converter having first and second output terminals and effective to supply an output voltage across said first and second lamp sockets,

a current sensor coupled between a converter output terminal and a corresponding lamp socket, and effective to detect an output current,

a voltage sensor coupled across the converter output terminals and effective to detect the output voltage, and

a control circuit effective

to control the DC/DC power converter to increase/decrease the output voltage based on the output current detected by the current sensor with respect to a target value,

to compare the output voltage detected by the voltage sensor to a predetermined upper limit value, and upon the output voltage exceeding the predetermined upper limit value, to disable the DC/DC power converter,

to measure an accumulated lighting time of the device, and

after the accumulated lighting time has exceeded a predetermined switching time, to decrease the upper limit value as the accumulated lighting time passes.

20. The illumination fixture of claim 19, the control circuit further effective to

identify a predetermined reset condition being met, and upon identifying the predetermined reset condition as having been met to reset the accumulated lighting time to zero, and

to identify when the accumulated lighting time has exceeded a predetermined reset disabling time subsequent to the predetermined switching time, wherein the control circuit does not reset the accumulated lighting time even upon the reset condition being met.