DIMMING MULTIPLE LIGHTING DEVICES BY ALTERNATING ENERGY TRANSFER FROM A MAGNETIC STORAGE ELEMENT

• US 20120025733A1
• Filed: 09/30/2010
• Published: 02/02/2012
• Est. Priority Date: 07/30/2010
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John L.
• Granted Patent: US 8,729,811 B2
• Time in Patent Office: Days
• US Class Current: 315/287
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/22 with intermediate conversion into ac
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 7/06 using discharge tubes without control electrode or semiconductor devices without control electrode
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A single magnetic storage element is used to provide power to multiple lighting devices, which may be strings of light-emitting diodes (LEDs) of different color. A switching circuit controls alternating application of energy among the multiple lighting devices and another switching circuit may charge the primary winding to different energy levels to control the intensity of the multiple lighting devices. In particular, the multiple lighting devices may be controlled to provide a desired color profile while dimming the lighting devices, while requiring only a single magnetic storage element for supplying energy to the lighting devices.

Claims

1. A circuit for powering two or more lighting devices, the circuit comprising:

a first output terminal for providing a first output current or voltage to a first one of the lighting devices;

a second output terminal for providing a second output current or voltage to a second one of the lighting devices;

a first switching circuit coupled to an input power source;

a magnetic storage element coupled to the first switching circuit and having at least one winding, wherein the first switching circuit charges the magnetic storage element from the input power source during charging intervals; and

a second switching circuit coupled to the magnetic storage element for providing the first output current or voltage to the first output terminal and the second output current or voltage to the second output terminal during alternating flyback intervals following the charging intervals.

2. The circuit of claim 1, wherein the magnetic storage element is a transformer having a primary winding coupled to the first switching circuit, wherein the first switching circuit charges the primary winding during charging intervals, and having a secondary winding coupled to the second switching circuit.

3. The circuit of claim 1, further comprising a first control circuit for controlling the first switching circuit, wherein the first control circuit controls the first switching circuit to control charging of the magnetic storage element to different energy storage levels during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby different amounts of energy are transferred to the individual lighting devices.

4. The circuit of claim 3, further comprising a second control circuit for controlling the second switching circuit, and wherein the second switching circuit has an input coupled to an output of the first switching circuit for synchronizing the alternating charging intervals and the alternating flyback intervals.

5. The circuit of claim 3, wherein the first control circuit receives multiple dimming values corresponding to different levels of intensity of the first one of the lighting devices and the second one of the lighting devices, and wherein the first control circuit sets the different energy storage levels according to corresponding ones of the multiple dimming values.

6. The circuit of claim 1, further comprising at least one additional output terminal for providing at least one additional output current or voltage to at least one additional corresponding one of the lighting devices, and wherein the second switching circuit alternatively couples the magnetic storage element to the first output terminal, the second output terminal, and the at least one additional output terminal during the alternating flyback intervals.

7. The circuit of claim 1, wherein the two or more lighting devices are two or more light-emitting diode circuits each having one or more light-emitting diodes connected in series.

8. The circuit of claim 7, wherein the corresponding total forward bias voltages of the two or more light-emitting diode circuits have different values, and wherein the second switching circuit comprises a switching device coupling the first terminal to the second terminal, wherein the magnetic storage element is statically coupled to the first terminal, wherein the first lighting element has a higher total forward bias voltage value than a lower total forward bias voltage value of the second lighting element, whereby when the switching device is disabled the first output current is conducted through the first lighting element, but when the switching device is enabled, the second output current is conducted through the second lighting element.

9. The circuit of claim 8, wherein the magnetic storage element is a transformer, wherein the two or more light-emitting diode circuits are coupled to a secondary winding of the transformer, and further comprising a first control circuit for controlling the first switching circuit, wherein the first control circuit controls the first switching circuit to control charging of a primary winding of the transformer to different volt-second product values during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby the first output current differs from the second output current and wherein the first control circuit comprises a voltage sensing circuit for sensing differing reflected voltages across the primary winding of the transformer during the alternating flyback intervals and determining whether the alternating flyback intervals are following the correct corresponding charging intervals, and changing the order of the charging intervals according to a result of the determining.

10. The circuit of claim 7, wherein the magnetic storage element is a transformer, wherein the two or more light-emitting diode circuits are coupled to a secondary winding of the transformer, wherein the corresponding total forward bias voltages of the two or more light-emitting diode circuits have different values, wherein the first lighting element has a higher total forward bias voltage value than a lower total forward bias voltage value of the second lighting element, and further comprising a first control circuit for controlling the first switching circuit, wherein the first control circuit controls the first switching circuit to control charging of the primary winding of the transformer to different volt-second product values during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby the first output current differs from the second output current and wherein the first control circuit comprises a voltage sensing circuit for sensing differing reflected voltages across the primary winding of the transformer during the alternating flyback intervals and determining whether the alternating flyback intervals are following the correct corresponding charging intervals, and changing the order of the charging intervals according to a result of the determining.

11. The circuit of claim 7, wherein the magnetic storage element is a transformer, wherein the two or more light-emitting diode circuits are coupled to a secondary winding of the transformer, wherein the corresponding total forward bias voltages of the two or more light-emitting diode circuits have different values, wherein the first lighting element has a higher total forward bias voltage value than a lower total forward bias voltage value of the second lighting element, and further comprising a first control circuit for controlling the first switching circuit, wherein the first control circuit controls the first switching circuit to control charging of the primary winding of the transformer to different volt-second product values during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby the first output current differs from the second output current and wherein the first control circuit comprises a circuit for sensing differing durations of the alternating flyback intervals and determining whether the alternating flyback intervals are following the correct corresponding charging intervals, and changing the order of the charging intervals according to a result of the determining.

12. An integrated circuit, comprising:

an output terminal for supplying charging current to a magnetic storage element for supplying energy to two or more lighting devices coupled to the magnetic storage element; and

a first switching circuit having an input coupled to an input power source and an output coupled to the output terminal for charging the magnetic storage element during charging intervals, wherein the energy is supplied to the two or more lighting devices during corresponding non-overlapping and alternating flyback intervals following the charging intervals, whereby application of the energy to the two or more lighting devices is alternated between the corresponding lighting devices.

13. The integrated circuit of claim 12, further comprising a first control circuit for controlling the first switching circuit, wherein the first control circuit controls the first switching circuit to control charging of the magnetic storage element to different energy storage levels during alternating ones of the charging intervals corresponding to the alternating flyback intervals, to supply different amounts of energy to the two or more lighting devices during flyback intervals following the charging intervals.

14. The integrated circuit of claim 12, wherein the magnetic storage element is a transformer and wherein the output terminal supplies the charging current to a primary winding of the transformer, and wherein the two or more lighting devices are coupled to a secondary winding of the transformer.

15. The integrated circuit of claim 14, wherein the two or more lighting devices are two or more light-emitting diode circuits each having one or more light-emitting diodes connected in series, wherein the total forward bias voltage of the two or more light-emitting diode circuits have different total forward bias voltage values, wherein the first lighting element has a higher total forward bias voltage value than a lower total forward bias voltage value of the second lighting element, and further comprising a first control circuit for controlling the first switching circuit, wherein the first control circuit controls the first switching circuit to control charging of the primary winding of the transformer to the different energy storage levels during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby the first output current or voltage differs from the second output current or voltage and wherein the first control circuit comprises a voltage sensing circuit for sensing differing reflected voltages across the primary winding of the transformer during the alternating flyback intervals and determining whether the alternating flyback intervals are following the correct corresponding charging intervals, and changing the order of the charging intervals according to a result of the determining.

16. The integrated circuit of claim 14, wherein the two or more lighting devices are two or more light-emitting diode circuits each having one or more light-emitting diodes connected in series, wherein the total forward bias voltage of the two or more light-emitting diode circuits have different total forward bias voltage values, wherein the first lighting element has a higher total forward bias voltage value than a lower total forward bias voltage value of the second lighting element, and further comprising a first control circuit for controlling the first switching circuit, wherein the first control circuit controls the first switching circuit to control charging of the primary winding of the transformer to the different energy storage levels during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby the first output current or voltage differs from the second output current or voltage and wherein the first control circuit comprises a circuit for sensing differing durations of the alternating flyback intervals and determining whether the alternating flyback intervals are following the correct corresponding charging intervals, and changing the order of the charging intervals according to a result of the determining.

17. A circuit comprising:

a first output terminal for providing a first output current to a first string of light-emitting diodes having a first color;

a second output terminal for providing a second output current to a second string of light-emitting diodes having a second color; and

a power switching circuit having a magnetic storage element from which energy is alternatively supplied to the first output terminal during a first period and to the second output terminal during a second period not substantially overlapping the first period, whereby different current or voltages may be applied to the first output terminal and the second output terminal to control the relative intensity of light provided by the first string of light-emitting diodes and the second string of light-emitting diodes.

18. The circuit of claim 17, further comprising a dimming control circuit that controls charging of the magnetic storage element during a third period preceding the first period and during a fourth period preceding the second period, whereby the energy supplied to the first terminal during the first period and the energy supplied to the second terminal during the second period are controlled in conformity with a dimming control input provided to the dimming control circuit.

19. A method of supplying power to multiple lighting devices, comprising:

first controlling charging of a magnetic storage element during charging intervals;

second controlling discharging of the magnetic storage element to alternate application of energy stored in the magnetic storage element between the multiple lighting devices during alternating flyback intervals following the charging intervals;

first providing a first output current or voltage to a first one of the lighting devices during a first one of the flyback intervals; and

second providing a second output current or voltage to a second one of the lighting devices during a second one of the flyback intervals.

20. The method of claim 19, further comprising controlling the first switching circuit to control charging of the magnetic storage element to different energy storage levels during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby different amounts of energy are transferred to the individual lighting devices.

21. The method of claim 20, further comprising synchronizing the first and second controlling.

22. The method of claim 20, further comprising receiving multiple dimming values corresponding to different levels of intensity of the first one of the lighting devices and the second one of the lighting devices, and wherein the first controlling sets the different energy storage levels according to corresponding ones of the multiple dimming values.

23. The method of claim 19, providing at least one additional output current or voltage to at least one additional corresponding one of the lighting devices, and wherein the second controlling alternatively directs energy from the magnetic storage element to supply the first output current or voltage, the second output current or voltage, and the at least one additional current or voltage during the alternating flyback intervals.

24. The method of claim 19, wherein the two or more lighting devices are two or more light-emitting diode circuits each having one or more light-emitting diodes connected in series, and wherein the first and second providing provide the first output current or voltage and the second output current or voltage to corresponding ones of the light-emitting diode circuits.

25. The method of claim 24, wherein the corresponding total forward bias voltages of the two or more light-emitting diode circuits have different values, and wherein the second controlling comprises controlling a switching device coupling the first lighting device to the second lighting device, wherein the secondary winding of the transformer is statically coupled to the first lighting device, wherein the first lighting device has a higher total forward bias voltage value than a lower total forward bias voltage value of the second lighting device, whereby when the switching device is disabled the first output current is conducted through the first lighting device, but when the switching device is enabled, the second output current is conducted through the second lighting device.

26. The method of claim 25, wherein the magnetic storage element is a transformer having a primary winding and a secondary winding, wherein the first controlling controls charging of the primary winding of the transformer to different volt-second product values during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby the first output current differs from the second output current, and wherein the method further comprises:

sensing differing reflected voltages across the primary winding of the transformer during the alternating flyback intervals; and

determining whether the alternating flyback intervals are following the correct corresponding charging intervals, and changing the order of the charging intervals according to a result of the determining.

27. The method of claim 24, wherein the magnetic storage element is a transformer having a primary winding and a secondary winding, wherein the corresponding total forward bias voltages of the two or more light-emitting diode circuits have different values, wherein the first lighting element has a higher total forward bias voltage value than a lower total forward bias voltage value of the second lighting element, wherein the first controlling controls the first switching circuit to charge the primary winding of the transformer to different volt-second product values during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby the first output current differs from the second output current, and wherein the method further comprises:

sensing differing reflected voltages across the primary winding of the transformer during the alternating flyback intervals; and

determining whether the alternating flyback intervals are following the correct corresponding charging intervals, and changing the order of the charging intervals according to a result of the determining.

28. The method of claim 24, wherein the magnetic storage element is a transformer having a primary winding and a secondary winding, wherein the corresponding total forward bias voltages of the two or more light-emitting diode circuits have different values, wherein the first lighting element has a higher total forward bias voltage value than a lower total forward bias voltage value of the second lighting element, wherein the first controlling controls the first switching circuit to charge the primary winding of the transformer to different volt-second product values during alternating ones of the charging intervals corresponding to the alternating flyback intervals, whereby the first output current differs from the second output current, and wherein the method further comprises:

detecting differing durations of the alternating flyback intervals; and

determining whether the alternating flyback intervals are following the correct corresponding charging intervals, and changing the order of the charging intervals according to a result of the determining.