WO2013067704A1

WO2013067704A1 - Device for failure protection in lighting devices having light emitting diodes

Info

Publication number: WO2013067704A1
Application number: PCT/CN2011/082056
Authority: WO
Inventors: Gang Yao; Hongshan TAO
Original assignee: General Electric Company
Priority date: 2011-11-10
Filing date: 2011-11-10
Publication date: 2013-05-16
Also published as: CN104025712B; EP2777365A4; CN104025712A; CA2857527A1; EP2777365A1

Abstract

A lighting device comprises a light engine (102) with one or more LEDs (104), a drive circuit (108) coupled to the light engine (102) and energized the light engine (102) with a drive signal current, and a protection device (114) coupled to the drive circuit (108). The protection device (104) comprises a fault switch (234) having a position that maintains the drive signal current at or below a level that permits continued operation of the light engine (102) during a failure condition in the lighting device.

Description

DEVICE FOR FAILURE PROTECTION IN LIGHTING DEVICES HAVING

LIGHT EMITTING DIODES

BACKGROUND

Technical Field

[0001] The subject matter of the present disclosure relates to lighting devices and, more particularly, to failure protection (e.g., short circuit and component breakdown) for lighting devices with light emitting diodes (LEDs).

Description of Related Art

[0002] Light-emitting diodes (LEDs) are a popular light source. Examples of LEDs include an LED chip which emits light, a color conversion module including translucent sealing materials (e.g. epoxy resin and/or silicone resin), and a phosphor layer that covers the LED chip. The emergence of LEDs that emit white light make LEDs more widely available for use in commercial and residential lighting products. LEDs and the lighting devices in which they are found have advantages such as longer life, excellent responsiveness, and a compact configuration in comparison with incandescent lamps. Because LEDs are themselves a small and light-weight configuration, the formation of thin and three-dimensional lighting fixtures provides further advantages such as enhancing a degree of freedom in the design of lighting fixtures.

BRIEF DESCRIPTION OF THE INVENTION

[0003] The present disclosure describes embodiments of a protection device for use with lighting devices that include light-emitting diodes (LEDs). These protection devices activate in response to a variety of failure conditions including short circuit conditions and component breakdown conditions. Moreover, protection devices of the present disclosure meet industry requirements and standards, including, but not limited to: Underwriters Laboratories (UL) Class 2. [0004] Other features and advantages of the disclosure will become apparent by reference to the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Reference is now made briefly to the accompanying drawings, in which:

[0006] FIG. 1 depicts a block diagram of an exemplary lighting device that includes light-emitting diodes;

[0007] FIG. 2 depicts a schematic diagram of a topology for an exemplary protection device for use in the lighting device of FIG. 1;

[0008] FIG. 3 depicts a schematic diagram of a topology for an exemplary lighting device that includes the protection device of FIG. 2; and

[0009] FIG. 4 depicts a plot of voltage for various signals of a lighting device such as the lighting devices of FIGS. 1, 2, and 3.

[0010] Where applicable like reference characters designate identical or corresponding components and units throughout the several views, which are not to scale unless otherwise indicated.

DETAILED DESCRIPTION OF THE INVENTION

[0011] FIG. 1 illustrates a block diagram of an exemplary lighting device 100 with features that prevent damage during failure conditions that can include either or both of short circuit conditions and single component breakdown conditions. Such failure conditions cause rapid changes in current and/or voltage that can damage components in the lighting device 100. In many cases, industry standards (e.g., Underwriters Laboratories (UL) standards) define acceptable levels for such changes to protect against incidence of fire or other hazards. As discussed more below, embodiments of the lighting device 100 are configured to satisfy such industry standards and, in one embodiment, address both short circuit conditions and component breakdown conditions using a robust and cost-effective circuit design. [0012] In FIG. 1, the lighting device 100 includes a light engine 102 with one or more light-emitting diodes 104 as the primary light source. The light engine 102 couples with a drive device 106 that provides a drive signal to operate the LEDs 104. The drive device 106 has components such as an LED driving circuit 108 and a feedback circuit 110, both of which comprise various configurations of discrete electrical elements (e.g., resistors, capacitors, transistors, etc.). Failure conditions can occur when one or more of these elements fail or when a short-circuit occurs, e.g., at the light engine 102. These failure conditions often manifest themselves as changes to one or more operating conditions (e.g., current and/or voltage) of the lighting device 100 and, in particularly, to a rapid increase in drive signal current at the light engine 102.

[0013] To prevent failure and damage from the failure condition, a protection device 114 couples with the feedback circuit 110. The protection device 114 limits the drive signal current in response to the short circuit as well as in response to failure of one or more electrical elements. In one example, the protection device 114 maintains the drive signal current at or below a level that permits continued operation of the light-emitting diode during the failure. The protection device 114 includes a reference component 116, a comparator component 118 (e.g., an op-amp), and a switching component 120 (e.g., a field effect transistor (FET) or a metal oxide field effect transistor (MOSFET)). These components can comprise combinations of discrete electrical elements (e.g., resistors, capacitors, transistors, etc.), an example of which is shown by the topologies of FIGS. 2 and 3 below.

[0014] During operation of the lighting device 100, an external current input (e.g., an alternating current (AC) input) energizes the lighting device 100. The drive device 106 converts the AC input to the drive signal current, which causes the LEDs 104 to emit light. The feedback circuit 112 monitors the drive signal current and generates an input signal that the protection device 114 receives. Changes in the properties of the input signal determine whether the protection device 114 limits the drive signal current. In one example, the comparator component 118 compares the input signal to a reference signal from the reference component 116. The comparator 118 generates a switching signal that operates the switch component 120 between its open and closed positions. Deviation of the input signal from the reference signal causes the comparator 118 to change the switching signal, thereby causing the protection device 114 to limit the drive signal current.

[0015] In one example, the protection device 112 also includes a reset component 122, which couples with the switch component 120 to open and close the switch component 120 at periodic or pre-determined intervals. A timing circuit or other configuration of components measure the pre-determined interval. The timing circuit can activate concurrently with the protection device 112 in response to the failure condition. Expiration of the pre-determined interval opens the switch component 120 to remove the current limiting features of the protection device 114 from the drive device 106. The presence of the failure condition will cause the protection device 114 to re-engage until the end of the next pre-determined interval. On the other hand, if the failure condition is no longer present, then the protection device 114 remains disengaged and the lighting device 100 will continue to operate normally until the next failure occurs and the protection device 114 engages to limit the drive signal current.

[0016] FIGS. 2 and 3 depict topologies for an exemplary lighting device 200. The topologies show various components (e.g., resistors, capacitors, switches, diodes, etc.) that are useful for the present design. This disclosure does, however, contemplate other configurations of such components that would form topologies other than that shown the figures.

[0017] FIG. 2 focuses on the configuration of electrical elements for use in an exemplary protection device 214. In FIG. 2, the protection device 214 includes a reference component 216, a comparator component 218, a switching component 220, and a reset component 222. Moving from left to right in the diagram, the reference component 216 includes a voltage supply 224, a resistor 226, and a capacitor 228. These electrical elements generate a reference voltage Vr, which acts as a threshold to determine the operation of the protection device 200 as contemplated herein. The comparator component 218 includes an op-amp 230 having a first input that receives the reference voltage Vr. A second input of the op-amp 230 receives a feedback voltage Vb from the feedback circuit (not shown). The op-amp 230 also has an output that couples with the switch component 220 and the reset component 222. During operation, the op-amp 230 compares the reference voltage and the feedback voltage to deliver a switching signal from the output to the switch component 220 and the reset component 222.

[0018] In the example of FIG. 2, the switch component 220 includes a fault switch 234 that is responsive to the switching signal. The reset component 222 includes resistors (e.g., resistor 236 and resistor 238), a capacitor 240, a diode 242, and a reset switch 244. Both the fault switch 234 and the reset switch 244 can comprise a MOSFET and/or related switching element. In one embodiment, the switching signal changes the position of the fault switch 234 to lower the properties of an output signal that the protection device 214 provides to the drive circuit 206.

[0019] The topology of FIG. 3 shows details of an LED driving circuit 208 and a feedback circuit 210 found in the lighting device 200. The feedback circuit 210 includes an opto-coupler 246 and a voltage divider 248 comprising resistors (e.g., resistor 250, resistor 252, and resistor 254) and a capacitor 256. A regulator circuit 258 couples to the voltage divider 248 and to the protection device 214. The regulator circuit 258 provides the feedback voltage Vb. In one example, the regulator circuit 258 includes a resistor 260, a capacitor 262, and a regulator switch 264. The feedback circuit 210 also includes a Zener diode 266, a rectifier 268, and a transformer 272. The regulator circuit 258 provides a clamping voltage Va that controls operating frequency of a converter 276 (e.g., a half-bridge DC-DC converter) to get a drive voltage Vo that is appropriate for light-emitting diodes of the lighting device 200.

[0020] In one example, failure conditions in the lighting device 200 will cause the feedback voltage Vb to drop below the reference voltage Vr. This drop causes the switching voltage of the switching signal from the op-amp 230 to exceed the gate voltage of the fault switch 242. The fault switch 234 closes in response to the switching voltage. Closing the fault switch 234 drives the clamping voltage Va lower, which changes the operating frequency of the converter 276. In one example, the operating frequency increases and can reach about 300 kHz or more. At these operating frequencies, the drive signal voltage Vo and drive signal current are reduced to levels that maintain and protect the components of the lighting device 200 and that meet industry standards (e.g., UL standards).

[0021] FIG. 4 depicts plots of voltage for various components to help describe operation of the reset component 222. In FIG. 4, the plots show voltage for each of the clamping voltage Va, the switching voltage Vd, and a capacitor voltage Vc for the capacitor 228. Starting on the left side of the plots in FIG. 4, initiation of the fault condition causes the capacitor 228 to begin to charge, as evident by the increasing capacitor voltage Vc. When the capacitor 228 is fully charged, e.g., to the threshold or gate voltage of the reset switch 244, the reset switch 244 closes and the fault switch 242 opens, which causes the clamping voltage Va to increase. The feedback voltage Vb also increases because of Miller effect principles at the regulator switch 264. Artisans skilled in the electrical arts will recognize the Miller effect. When the feedback voltage Vb reaches the reference voltage Vr, the switching voltage Vd drops and the capacitor voltage Vc discharges through the output of the op-amp 230. When the Miller effect finishes, and if the fault condition is present, the feedback voltage Vb becomes low and the switching voltage Vd becomes high. In this configuration, the reset is complete and the reset component 222 begins another cycle.

[0022] As used herein, an element or function recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to "one embodiment" of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0023] This written description uses examples to disclose embodiments of the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

CLAIMS What is claimed is:

1. A lighting device, comprising: a light engine; a drive circuit coupled to the light engine, the drive circuit energizing the light engine with a drive signal current; and a protection device coupled to the drive circuit, the protection device comprising a fault switch having a position that maintains the drive signal current at or below a level that permits continued operation of the light engine during a failure condition in said lighting device.

2. The lighting device of claim 1, wherein the failure condition is a short circuit.

3. The lighting device of claim 1, wherein the failure condition occurs due to a single component breakdown.

4. The lighting device of claim 1, wherein the input signal current meets industry requirements set forth in Underwriters Laboratories class 2 specifications during the failure condition

5. The lighting device of claim 1, further comprising a reset component to actuate the fault switch at a pre-determined interval to cause the drive signal current to increase during the failure condition.

6. The lighting device of claim 5, wherein the reset component comprises a reset switch coupled to the fault switch, and wherein the drive signal current increases when the fault switch is open and the reset switch is closed.

7. The lighting device of claim 5, further comprising a capacitor that discharges to change the fault switch from closed to open.

8. The lighting device of claim 1, further comprising an opto-coupler coupled to the drive circuit, wherein actuation of the opto-coupler causes the fault switch to open.

9. The lighting device of claim 1, wherein the protection device comprises a comparator component coupled to the fault switch and a reference component that generates a reference voltage, and wherein the comparator component generates a switching signal with a switching voltage that closes the fault switch when voltage associated with the drive signal current falls below the reference voltage.

10. The lighting device of claim 1, wherein the fault switch comprises a metal oxide field effect transistor.

11. A protection device for a lighting device, said protection device comprising: a comparator with a first input, a second input, and an output; a fault switch coupled to the output; and a reset switch coupled to the fault switch, wherein the comparator generates a switching signal in response to a difference in voltage between the first input and the second input that actuates the fault switch and the reset switch to maintain a drive signal current at or below a level that permits continued operation of the lighting device during a failure condition.

12. The protection device of claim 11, wherein the comparator comprises an op-amp.

13. The protection device of claim 11, further comprising a reference component that provides a reference voltage to one of the first input and the second input, wherein the reference voltage provides a threshold that indicates a fault condition in the lighting device, and wherein the switching signal closes the fault switch in response to the fault condition.

14. The protection device of claim 11, further comprising a capacitor that discharges voltage to close the reset switch at a pre-determined interval.

15. The protection device of claim 11, wherein the fault switch and the reset switch comprise a metal oxide field effect transistor.

16. The protection device of claim 11, wherein the protection device is coupled to a power supply.

17. A drive circuit for a lighting device, said drive circuit comprising: a feedback circuit generating a feedback voltage in response to a drive voltage in the lighting device; and a protection device coupled to the feedback circuit to receive the feedback voltage, the protection device comprising a fault switch that opens in response to a decrease in the feedback voltage to maintain operation of the lighting device during a failure condition.

18. The drive circuit of claim 17, further comprising a converter coupled to the feedback circuit, wherein the protection device generates an output signal that increases the operating frequency of the converter.

19. The drive circuit of claim 18, wherein the converter comprises a half- bridge DC-DC converter.

20. The drive circuit of claim 17, wherein the protection device comprises a reset component that closes the fault switch at a pre-determined interval.