LIGHTING SYSTEMS WITH UNIFORM LED BRIGHTNESS

• US 20140361696A1
• Filed: 01/22/2013
• Published: 12/11/2014
• Est. Priority Date: 01/20/2012
• Status: Active Grant

• Current Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Original Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Inventors: Siessegger, Bernhard, Kostrun, Marijan
• Granted Patent: US 9,246,403 B2
• Time in Patent Office: Days
• US Class Current: 315/186
• CPC Class Codes: G01R 31/2635 Testing light-emitting diodes, laser diodes or photodiodes
• CPC Class Codes: G01R 31/40 Testing power supplies testing photovoltaic devices H02S50/10
• CPC Class Codes: G01R 31/44 Testing lamps
• CPC Class Codes: G01R 31/64 Testing of capacitors
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 25/0753 the devices being arranged next to each other
• CPC Class Codes: H01L 25/167 comprising optoelectronic devices, e.g. LED, photodiodes
• CPC Class Codes: H01L 27/156 two-dimensional arrays
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/12032 Schottky diode
• CPC Class Codes: H01L 2924/12044 OLED
• CPC Class Codes: H01L 2924/1301 Thyristor
• CPC Class Codes: H01L 2924/13033 TRIAC - Triode for Alternating Current - A bidirectional switching device containing two thyristor structures with common gate contact
• CPC Class Codes: H01L 2924/1305 Bipolar Junction Transistor [BJT]
• CPC Class Codes: H01L 2924/13091 Metal-Oxide-Semiconductor Field-Effect Transistor [MOSFET]
• CPC Class Codes: H01L 33/62 Arrangements for conducting electric current to or from the semiconductor body, e.g. lead-frames, wire-bonds or solder balls
• CPC Class Codes: H02M 1/4258 using a single converter stage both for correction of AC input power factor and generation of a regulated and galvanically isolated DC output voltage H02M1/4241 takes precedence
• CPC Class Codes: H02M 3/335 : using semiconductor devices only
• CPC Class Codes: H02M 7/06 : using discharge tubes without control electrode or semiconductor devices without control electrode
• CPC Class Codes: H02M 7/2176 : comprising a passive stage to generate a rectified sinusoidal voltage and a controlled switching element in series between such stage and the output
• CPC Class Codes: H05B 45/00 : Circuit arrangements for operating light-emitting diodes [LED]
• CPC Class Codes: H05B 45/10 : Controlling the intensity of the light
• CPC Class Codes: H05B 45/20 : Controlling the colour of the light
• CPC Class Codes: H05B 45/37 : Converter circuits
• CPC Class Codes: H05B 45/395 : Linear regulators
• CPC Class Codes: H05B 45/40 : Details of LED load circuits
• 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: 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

Solid state lighting systems are disclosed for providing uniform brightness of LEDs serially connected in a string. In some embodiments, the LEDs can be powered directly from the mains such that no switch-mode power supply or the output storage elements associated therewith are needed. In some such cases, a linear regulator and switches can be used to control the current through the LEDs to provide uniform brightness. Other embodiments can be used with a switch-mode based driver topology and/or storage elements coupled in parallel with clusters of the LEDs. In any such cases, control logic (e.g., microcontroller or other suitable controller) can be used to control the switches accordingly to provide uniform brightness, and in some cases, to mitigate the implications of having no SMPS output storage element. In some embodiments, the switching pattern provided by the control logic is random, although other switching patterns can be used.

Claims

1. A lighting system, comprising:

a plurality of light emitting diodes (LEDs) serially connected in a string;

a plurality of switches, each switch connected across a different set of the LEDs in the string; and

a controller configured to selectively activate the switches in effort to provide a brightness that appears uniform to a human.

2. The system of claim 1 wherein the controller selectively activates the switches so that the LED string has a forward voltage drop that is within 5% or less of a line voltage powering the system.

3. The system of claim 1 wherein the controller selectively activates the switches so that the LED string has a forward voltage drop that is within 2% or less of a line voltage powering the system.

4. The system of claim 1 wherein the controller is configured to selectively activate the switches using a random switching pattern.

5. The system of claim 1 wherein the controller is configured to selectively activate the switches using a periodic switching pattern.

6. The system of claim 1 wherein the controller is configured to measure forward voltage drop across the LED string, and switching decisions by the controller are based at least in part on the forward voltage drop.

7. The system of claim 1 wherein each of the switches is associated with one or more of the LEDs to provide a switchable LED cluster, and the controller is configured to turn on as many clusters as possible so as to reduce losses in a current source in series with the LED string.

8. The system of claim 1 wherein at any one moment in time, brightness of the brightest activated LED in the string is within 10% or less of brightness of dimmest activated LED in the string.

9. The system of claim 1 further comprising a rectifier circuit configured to receive a voltage source and to provide a rectified voltage across the LED.

10. The system of claim 1 further comprising a current source in series with the LEDs.

11. The system of claim 1 wherein the LEDs can be powered directly from an AC or DC power source such that no switch-mode power supply output storage element is needed.

12. The system of claim 1 further comprising one or more storage elements, each coupled in parallel with a corresponding cluster of a different one or more of the LEDs.

13. The system of claim 1 wherein forward voltage drop across the LEDs is used to generate an auxiliary voltage that powers at least one of the switches and/or controller.

14. The system of claim 1 further comprising a linear regulator configured to receive a line voltage, wherein the linear regulator is operated intermittently based on the received line voltage and is used to generate an auxiliary voltage that powers at least one of the switches and/or controller.

15. An integrated circuit comprising the system of claim 1.

16. A light engine comprising the system of claim 1

17. A lighting system, comprising:

a plurality of light emitting diodes (LEDs) serially connected in a string;

a plurality of switches, each switch connected across a different set of the LEDs in the string; and

a microcontroller configured to selectively activate the switches in effort to provide a brightness that appears uniform to a human, and wherein the microcontroller selectively activates the switches so that the LED string has a forward voltage drop that is within 20% or less of a line voltage powering the system.

18. The system of claim 17 wherein the controller is configured to selectively activate the switches using at least one of a random switching pattern and/or a periodic switching pattern.

19. The system of claim 17 wherein the controller is configured to measure forward voltage drop across the LED string, and switching decisions by the controller are based at least in part on the forward voltage drop.

20. A lighting system, comprising:

a plurality of light emitting diodes (LEDs) serially connected in a string;

a plurality of switches, each switch connected across a different set of the LEDs in the string;

a linear regulator in series with the LEDs; and

a microcontroller configured to selectively activate the switches in effort to provide a brightness that appears uniform to a human, wherein each of the switches is associated with one or more of the LEDs to provide a switchable LED cluster, and the controller is further configured to turn on as many clusters as possible so as to reduce losses in the linear regulator.

21-23. -23. (canceled)