Increasing reliability of operation of light emitting diode arrays at higher operating temperatures and its use in the lamps of automobiles

• US 7,414,370 B2
• Filed: 02/03/2006
• Issued: 08/19/2008
• Est. Priority Date: 02/03/2006
• Status: Expired due to Fees

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Kunjappan, Shanoprasad
• Primary Examiner(s): VO, TUYET THI
• Application Number:
  US11/307,371
• Publication Number:
  US 20070182337A1
• Time in Patent Office: 928 Days
• Field of Search: 315/82, 315/83, 315/77, 315/247, 315/246, 315/225, 315/224, 315/241.S, 315/241.P, 315149-159, 315/312, 315/309
• US Class Current: 315/241.00S
• CPC Class Codes: H05B 45/56 involving measures to prevent abnormal temperature of the LEDs

Abstract

A lamp in which a LED array is coupled to a transistor such that the same amount of current flows through both. The voltage level at the control (e.g., base) terminal of the transistor is controlled such that the current magnitude is reduced when the operating temperature rises. As a result, the heat generated from the junctions of the LEDs in the LED arrays is reduced, thereby compensating for the increase in the operating temperature.

Claims

1. A lamp comprising:

a transistor having a control terminal, said transistor passing a current of a magnitude determined by a voltage at said control terminal;

a LED array coupled to said transistor, and generating light with an intensity proportionate to said magnitude of said current; and

a driver block coupled to said control terminal, wherein said driver block comprises at least one component having a cross voltage which has a negative correlation with said operating temperature, wherein said voltage is derived across said component to generate said voltage with a first level in response to an operating temperature of said lamp being equal to a first value, and with a second level in response to said operating temperature of said lamp being equal to a second value,

wherein said first value is not equal to said second value and said first level is not equal to said second level such that said LED array generates light with a different intensity in response to said operating temperature of said lamp being at said first value compared to when said operating temperature of said lamp being at said second value

wherein said first value is more than said second value, and said first level causes said magnitude to be lesser compared to the magnitude caused by said second level, whereby LEDs in said LED array pass less current in response to an increase in said operating temperature.

2. The lamp of claim 1, wherein said LED array is coupled to said transistor such that the same magnitude of current passes through both of said transistor and said LED array.

3. The lamp of claim 1, wherein said at least one component comprises a diode.

4. The lamp of claim 1, wherein said transistor is turned on when said control terminal has a voltage which exceeds a pre-determined threshold and turned off otherwise.

5. The lamp of claim 1, wherein said lamp is used in an automobile, wherein said driver block receives a first signal indicating that a brake is being applied and a second signal indicating that a tail light is to be present, said driver block receiving said first signal and said second signal and generating said voltage with a third voltage level when said first signal indicates that said brake is applied and with a fourth voltage level when said second signal indicates that said tail light is to be present.

6. The lamp of claim 5, wherein said driver block comprises:

a first resistor, a second resistor and a third resistor;

a first transistor having a control terminal and a pair of terminals having a current channel in between;

a first constant voltage reference and a second constant voltage reference,

wherein said second resistor and a combination of said first transistor and said third resistor are connected in parallel between a first node and a second node, wherein each of said first signal and said second signal is coupled to said first node,

wherein a terminal of said first constant voltage reference is coupled to said first node, another terminal of said first constant voltage reference being coupled to a constant voltage level,

wherein a terminal of said second constant voltage reference is coupled to said control terminal of said first transistor and said first signal, another terminal of said second constant voltage reference being coupled to a constant voltage level,

wherein one of said pair of terminals of said first transistor is coupled to said first node, and the other one of said pair of terminals of said first transistor is coupled to said third resistor,

wherein said first resistor is coupled between said second node and said at least one component.

7. The lamp of claim 6, wherein said at least one component comprises a diode and said first constant voltage reference comprises a zener diode.

8. A lamp comprising:

a transistor having a control terminal, said transistor passing a current of a magnitude determined by a voltage at said control terminal;

a LED array coupled to said transistor, and generating light with an intensity proportionate to said magnitude of said current;

a driver block coupled to said control terminal and generating said voltage with a first level when an operating temperature of said lamp equals a first value, and a with a second level when said operating temperature of said lamp equals a second value, wherein said first value is not equal to said second value and said first level is not equal to said second level, wherein said driver block comprises;

at least one component having a cross_voltage which has a negative correlation with said operating temperature, wherein said voltage is derived across said component;

a first resistor, a second resistor and a third resistor;

a first transistor having a control terminal and a pair of terminals having a current channel in between;

a first constant voltage reference and a second constant voltage reference,

wherein said second resistor and a combination of said first transistor and said third resistor are connected in parallel between a first node and a second node, wherein each of said first signal and said second signal is coupled to said first node,

wherein a terminal of said first constant voltage reference is coupled to said first node, another terminal of said first constant voltage reference being coupled to a constant voltage level,

wherein a terminal of said second constant voltage reference is coupled to said control terminal of said first transistor and said first signal, another terminal of said second constant voltage reference being coupled to a constant voltage level,

wherein one of said pair of terminals of said first transistor is coupled to said first node, and the other one of said pair of terminals of said first transistor is coupled to said third resistor, and

wherein said first resistor is coupled between said second node and said at least one component,

wherein said first value is more than said second value, and said first level causes said magnitude to be lesser compared to the magnitude caused by said second level, whereby LEDs in said LED array pass less current with an increase in operating temperature.

9. The lamp of claim 8, wherein said lamp is used in an automobile.

10. The lamp of claim 8, wherein said at least one component comprises a diode and said first constant voltage reference comprises a zener diode.

11. The lamp of claim 8, wherein said transistor is turned on when said control terminal has a voltage which exceeds a pre-determined threshold and turned off otherwise.

12. The lamp of claim 11, wherein said driver block receives a first signal indicating that a brake is being applied and a second signal indicating that a tail light is to be present, said driver block receiving said first signal and said second signal and generating said voltage with a third voltage level when said first signal indicates that said brake is applied and with a fourth voltage level when said second signal indicates that said tail light is to be present.