DRIVER CIRCUIT FOR AT LEAST ONE LOAD AND METHOD OF OPERATING THE SAME

• US 20150028769A1
• Filed: 02/08/2013
• Published: 01/29/2015
• Est. Priority Date: 02/10/2012
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Lai, Bing
• Granted Patent: US 9,282,605 B2
• Time in Patent Office: Days
• US Class Current: 315/294
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 45/50 responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
• CPC Class Codes: H05B 45/59 for reducing or suppressing flicker or glow effects
• CPC Class Codes: H05B 47/24 Circuit arrangements for protecting against overvoltage

Abstract

A driver circuit (1) for operating at least one load, such as a LED unit (7) is provided, comprising an input (2) for receiving an input voltage (V IN) from a power supply (6), an output (3) for providing an output voltage (V OUT) to said load and a switching converter (4) with at least a storage inductor (11) connected with a switching device (13), said switching converter (4) being disposed to generate an average output current by sequential switching operation of said switching device (13) between at least a charging mode and a discharging mode. Furthermore, a switching controller (5) is connected with said switching device (13) to control the switching operation of said switching device (13) and comprises a feedback inductor (24), inductively coupled to said storage inductor (11) to provide a feedback voltage, corresponding to the variation of an inductor current (I S) through said storage inductor (11) and a voltage compensation circuit (25), connected with said feedback inductor (24) to determine at least one compensation signal from said feedback voltage, said compensation signal corresponding to said input voltage (V IN) or said output voltage (V OUT). To provide a cost-efficient and versatile driver circuit (1), the switching controller (5) is configured to at least control said switching device (13) between said discharging and said charging mode in dependence on said inductor current (I s) and to control a duty cycle of the switching operation in dependence on said at least one compensation signal, so that in case of a variation of said input (V IN) or output voltage (V OUT), said average output current, provided to the load, is maintained substantially constant.

Claims

1. Driver circuit for operating at least one load, such as a LED unit, the driver circuit comprising

an input for receiving an input voltage from a power supply,

an output for providing an output voltage to said load,

a switching converter with at least a storage inductor connected with a switching device, said switching converter being disposed to generate an average output current by sequential switching operation of said switching device between at least a charging mode and a discharging mode and

a switching controller, connected with said switching device to control the switching operation of said switching device, comprising at least

a feedback inductor, inductively coupled to said storage inductor to provide a feedback voltage, corresponding to the variation of an inductor current (IS) through said storage inductor and

a voltage compensation circuit, connected with said feedback inductor to determine at least one compensation signal from said feedback voltage, said compensation signal corresponding to said input voltage or said output voltage, wherein

said switching controller being configured to at least control said switching device between said discharging and said charging mode in dependence on said inductor current (Is) and to control a duty cycle of the switching operation in dependence on said at least one compensation signal, so that in case of a variation of said input or output voltage, said average output current, provided to the load, is maintained substantially constant.

2. Driver circuit according to claim 1, wherein said voltage compensation circuit is configured to determine a first and a second compensation signal from said feedback voltage, said first compensation signal corresponding to said input voltage and said second compensation signal corresponding to said output voltage and where said switching controller being configured to control said duty cycle in dependence of said first and said second compensation signal.

3. Driver circuit according to claim 2, wherein said voltage compensation circuit is configured to determine said first compensation signal from said feedback voltage during said charging mode.

4. Driver circuit according to claim 2, wherein said voltage compensation circuit is configured to determine said second compensation signal from said feedback voltage during said discharging mode.

5. Driver circuit according to claim 1, wherein said switching controller further comprises a first threshold circuit, connected with said feedback inductor, said first threshold circuit being configured to set said switching device from said discharging mode to said charging mode when said feedback voltage corresponds to a predefined minimum current threshold.

6. Driver circuit according to claim 5, wherein said switching controller further comprises a second threshold circuit, said second threshold circuit being configured to set the switching device to the discharging mode when a current control signal, corresponding to said inductor current (Is), corresponds to a maximum current threshold.

7. Driver circuit according to claim 6, wherein said second threshold circuit being connected to said voltage compensation circuit to control the duty cycle of said switching operation by varying said current control signal and/or said maximum current threshold in dependence on said first and/or second compensation signal.

8. Driver circuit according to claim 7, wherein said second threshold circuit being configured to bias said maximum current threshold in dependence of said second compensation signal.

9. Driver circuit according to claim 8, wherein said second threshold circuit being configured to bias said current control signal in dependence of said first compensation signal.

10. Driver circuit according to claim 9, wherein said current control signal is determined by a current sensor, connected in series with said storage inductor.

11. Driver circuit according to claim 10, wherein said switching controller further comprises an open-circuit detector, said open-circuit detector being configured to compare said second compensation signal with a predefined safety voltage threshold, so that said duty cycle of the switching operation is substantially decreased in case said output voltage exceeds the predefined safety voltage level.

12. Driver circuit according to claim 11, wherein the open-circuit detector is configured to substantially decrease said duty cycle by reducing said maximum current threshold in case the output voltage exceeds said predefined safety voltage threshold.

13. Driver circuit according to claim 12, wherein said switching converter is a tapped switching converter.

14. LED light source comprising at least a driver circuit according to claim 11 and at least one LED unit, connected to the output of said driver circuit.

15. Method of operating a load, such as a LED unit, with a driver circuit, comprising

receiving an input voltage from a power supply,

providing an output voltage to said load,

connecting a switching converter comprising at least a storage inductor with a switching device,

generating, by the switching converter, an average output current by sequential switching operation between at least a charging mode and a discharging mode,

inductively coupling a feedback inductor to said storage inductor to provide a feedback voltage, corresponding to the variation of an inductor current (Is) through said storage inductor and

connecting a voltage compensation circuit with said feedback inductor to determine at least one compensation signal from said feedback voltage, said compensation signal corresponds to said input voltage or said output voltage,

operating said switching device between said discharging and said charging mode in dependence of said inductor current (Is) and

controlling a duty cycle of said switching operation in dependence of said at least one compensation signal, so that in case of a variation in said input 44 or output voltage, said average output current, provided to the load, is maintained substantially constant.