Integrated Device and Method for Driving Lighting Loads with a Brightness Compensation

• US 20170188419A1
• Filed: 07/21/2016
• Published: 06/29/2017
• Est. Priority Date: 12/23/2015
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Application GmbH (STMicroelectronics NV), STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Torrisi, Giovanni Luca, Gaertner, Manuel, Lecce, Sergio
• Granted Patent: US 10,375,774 B2
• Time in Patent Office: Days
• CPC Class Codes: B60Q 1/1407 General lighting circuits comprising dimming circuits
• CPC Class Codes: B60Q 11/005 for lighting devices, e.g. indicating if lamps are burning or not
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices

Abstract

An integrated device for driving a lighting load, such as a LED, has a first memory element, configured to store a nominal duty-cycle at a nominal supply voltage. An actual voltage acquisition element is configured to detect an actual supply voltage. A processing unit is coupled to the first memory element and to the actual voltage acquisition element and configured to calculate a voltage compensated duty-cycle. A driver unit is coupled to the processing unit and is configured to be supplied according to the voltage compensated duty-cycle.

Claims

1. An integrated device for driving a lighting load, the integrated device comprising:

a first memory element, configured to store a nominal duty-cycle at a nominal supply voltage;

an actual voltage acquisition element, configured to detect an actual supply voltage;

a processing unit, coupled to the first memory element and to the actual voltage acquisition element, configured to calculate a voltage compensated duty-cycle; and

a driver unit, coupled to the processing unit and configured to be supplied according to the voltage compensated duty-cycle.

2. The integrated device according to claim 1, further comprising a second memory element coupled to the processing unit and configured to store the voltage compensated duty-cycle.

3. The integrated device according to claim 1, further comprising a third memory element coupled to the processing unit, the third memory element configured to store a load characteristic value.

4. The integrated device according to claim 3, wherein the load characteristic value comprises a load voltage drop.

5. The integrated device according to claim 3, wherein the processing unit is configured to calculate a voltage compensated duty-cycle DC_C according to equation:

6. The integrated device according to claim 3, further comprising a plurality of load terminals coupled to the driver unit and configured to be coupled to a plurality of lighting loads, the driver unit comprising a plurality of driver elements, each driver element being coupled to a respective load terminal.

7. The integrated device according to claim 6, wherein the first memory element comprises a plurality of nominal duty-cycle registers, each nominal duty-cycle register being associated to a respective drive element and a respective load terminal.

8. The integrated device according to claim 6, further comprising a plurality of characteristics registers, each characteristics register being associated to a respective drive element and a respective load terminal.

9. The integrated device according to claim 6, further comprising an adjustment activation memory configured to store an activation bit indicative of whether brightness of the lighting load is to be compensated for supply voltage.

10. The integrated device according to claim 9, wherein the adjustment activation memory comprises a plurality of adjustment activation memory elements, each adjustment activation memory element being associated to a respective driver and a respective load terminal.

11. The integrated device according to claim 3, wherein the integrated device further comprises a plurality of load terminals coupled to the driver unit and configured to be coupled to a plurality of lighting loads, the driver unit comprising a plurality of driver elements, each driver element being coupled to a respective load terminal;

wherein the first memory element comprises a plurality of nominal duty-cycle registers, each nominal duty-cycle register being associated to a respective drive element and a respective load terminal;

wherein the integrated device further comprises a plurality of characteristics registers, each characteristics register being associated to a respective drive element and a respective load terminal;

wherein the integrated device further comprises an adjustment activation memory configured to store an activation bit indicative of whether brightness of the lighting load is to be compensated for supply voltage; and

wherein the adjustment activation memory comprises a plurality of adjustment activation memory elements, each adjustment activation memory element being associated to a respective driver and a respective load terminal.

12. The integrated device according to claim 3, wherein the first memory element and the third memory element are configured to be coupled to a microcontroller through an SPI bus.

13. The integrated device according to claim 1, wherein the actual voltage acquisition element comprises an AD converter configured to be coupled to a power supply.

14. The integrated device according to claim 1, wherein the processing unit comprises a state machine implemented as hardwired logic.

15. An integrated device for driving a lighting load, the integrated device comprising:

a supply voltage node;

an analog-to-digital converter with an analog input coupled to the supply voltage node;

a nominal duty cycle register that stores a nominal duty-cycle at a nominal supply voltage;

a hardwired logic circuit coupled to a digital output of the analog-to-digital converter and to the nominal duty cycle register, the hardwired logic circuit configured to implement a state machine to calculate a voltage compensated duty-cycle;

a compensated duty-cycle register coupled to the hardwired logic circuit to store the voltage compensated duty-cycle;

a driver element coupled to the supply voltage node and the compensated duty-cycle register; and

a load terminal configured to connected to a lighting load.

16. The integrated device according to claim 15, further comprising a characteristic register coupled to the hardwired logic circuit and configured to store a load voltage drop.

17. The integrated device according to claim 16, wherein the integrated device comprises a plurality of load terminals and a plurality of driver elements, each driver element configured to be coupled to an associated lighting load via a respective load terminal.

18. The integrated device according to claim 17, wherein the integrated device comprises a plurality of nominal duty-cycle registers, each nominal duty-cycle register being associated with a respective drive element and a respective load terminal.

19. The integrated device according to claim 17, wherein the integrated device comprises a plurality of characteristics registers, each characteristics register being associated with a respective drive element and a respective load terminal and being configured to store a load voltage drop for the respective drive element.

20. The integrated device according to claim 17, further comprising a plurality of adjustment activation registers, each adjustment activation register being associated to a respective driver and a respective load terminal and configured to store an activation bit indicative of whether brightness of an associated lighting load is to be compensated for supply voltage.

21. A method for driving a lighting load, the comprising:

reading a nominal duty-cycle at a nominal supply voltage;

detecting an actual supply voltage;

calculating a voltage compensated duty-cycle based on the nominal duty-cycle and the actual supply voltage; and

controlling switching of a lighting load with a PW modulation according the voltage compensated duty-cycle.

22. The method according to claim 21, further comprising reading a load voltage drop, wherein the voltage compensated duty-cycle is calculated according to equation:

23. The method according to claim 21, further comprising storing the voltage compensated duty-cycle and a load characteristic value indicative of a load voltage drop.

24. The method according to claim 21, further comprising storing an activation bit indicative of whether brightness of the lighting load is to be compensated for supply voltage.

25. The method according to claim 21, wherein detecting the actual supply voltage comprises determining an analog voltage value, the method further comprising converting the analog voltage value to a digital value.