Adaptive power balancing in LED lamps

Abstract

A lamp (406) comprising a light source (408) and a driver circuit for the light source; wherein the driver circuit comprises a power stage (412) for controlling a voltage supplied to the light source, an energy storage device (418) and a control means (416) configured to selectively deactivate the power stage; wherein power is supplied to the light source (408) by the energy storage device (418) when the power stage is deactivated; wherein the control means (416) is configured to deactivate the power stage (412) during the course of a selected period of a mains AC power cycle, wherein the selected period of the mains AC power cycle has a period during which the magnitude of the mains voltage has a maximum value; wherein the selected period of the mains AC power cycle is defined by a threshold such that the power stage is selectively deactivated when the magnitude of the mains voltage is equal to or exceeds the threshold; wherein the threshold is dynamically adjustable according to the operation of an electronic transformer (400) for use with the lamp in order to prevent the electronic transformer from resetting; such that when the electronic transformer (400) is reset, the threshold is lowered to lengthen the selected period, and when the electronic transformer (400) recovers, the threshold is raised to shorten the selected period.

Description

[0001] The present disclosure relates to adaptive power balancing in light-emitting diode (LED) lamps, and more particularly to a lamp, a lighting system, and a method for controlling power delivered to a light source by a driver circuit within a lamp. A "lamp" includes a light source that emits photons and may also be commonly referred to as a "luminaire." BACKGROUND

[0002] Low-voltage lighting systems are a popular alternative to incandescent bulbs that operate directly from mains voltage. Mains voltage is an alternating current of either approximately 110 V or approximately 220 V at a frequency of 50 Hz or 60 Hz, although these values ​​vary by country or region, ranging from 100-127 V to 220-240 V.

[0003] A low-voltage lighting system includes a lamp that requires an operating voltage lower than the mains voltage. A low-voltage lighting system is Fig. 1 and includes an electronic transformer 100 that converts an AC mains voltage 102 to a lower lamp input voltage 104 to power one or more low voltage lamps 106.

[0004] Fig. 2a shows how a mains voltage (V_MAINS) varies over time, and Fig. Figure 2b shows how a lamp input voltage (V_ET) provided by the transformer 100 varies over time.

[0005] Electronic transformers require a minimum output load to operate properly. If the load presented by the connected lamp(s) 106 drops below the threshold of the electronic transformer, the electronic transformer is reset, resulting in flickering of the emitted light. Fig. Figure 2c shows the operating threshold 200 of the electronic transformer and the operating load 202 of a lamp. The operating load 202 is inversely proportional to the AC mains input voltage waveform 204.

[0006] In this example, the operating load 202 is always higher than the transformer's operating threshold 200, so the transformer 100 is not reset. However, if a high-efficiency lamp is provided, the operating load 202 is much lower, significantly increasing the probability that the load will fall below the electronic transformer's threshold.

[0007] For example, the operating load 202 is typically higher than the transformer's operating threshold 200 when using a halogen lamp, but an equivalent light-emitting diode (LED) lamp has a higher probability of the load falling below the electronic transformer's threshold and is thus susceptible to flicker. An LED lamp is any type of lamp that uses an LED as its light source.

[0008] There is also a large variation in the output voltage and operating frequency of electronic transformers between different lighting systems. Furthermore, the threshold of the electronic transformer varies greatly from device to device. This reduces interoperability, as there is no guarantee that different types of transformers and lamps will work together correctly when combined.

[0009] CN 102723880 A describes an AC-DC circuit for controlling a light-emitting diode lamp.

[0010] US 2014 / 0028214 A1 describes a lighting system 500 including a control device 512 for providing compatibility between a low power lamp 542 and a dimmer 502. The control device 512 is connected to a boost converter stage 536 and a buck converter stage 538 (see Fig. 5).

[0011] US 2012 / 0169246 A1 describes a circuit figure 2 comprising a rectifier 22, a buffer 30 and a boost converter containing a switch 23 and a control device 24 for controlling the switch.

[0012] CN 103260318 A, also published as US 2014 / 0354166 A1, describes a dimmer circuit for light-emitting diodes, which includes a TRIAC 201, an electronic transformer 202, a rectifier bridge 203, a first power stage circuit 204 and a second power stage circuit 205 connected in series, and a first control circuit 206 and a second control circuit 207. SUMMARY

[0013] According to a first aspect of the disclosure, a lamp according to appended claim 1 is provided.

[0014] Optionally, the power stage comprises one or more power transistors, and selectively disabling the power stage comprises disabling both the ON and OFF cycles of the power transistors.

[0015] Optionally, the selected period of the grid AC power cycle excludes a period during which a phase switch is applied.

[0016] Optionally, the light source is an electroluminescent device.

[0017] Optionally, the light source is a light-emitting diode.

[0018] Optionally, the energy storage device has a capacitor.

[0019] Optionally, the capacitor is a storage capacitor that provides a voltage source for the power stage, and the lamp further comprises an output capacitor for providing energy to the light source.

[0020] According to a second aspect of the disclosure, a lighting system according to appended claim 8 is provided.

[0021] Optionally, the lighting system also has a phase switch dimmer.

[0022] Optionally, the dimmer is a trailing edge dimmer.

[0023] Optionally, the dimmer is a leading edge dimmer.

[0024] Optionally, the dimmer is a leading edge and trailing edge dimmer.

[0025] Optionally, the lighting system comprises means for monitoring and / or sensing a mains AC waveform.

[0026] Optionally, the means for monitoring and / or detecting the mains AC waveform comprises a peak detector.

[0027] Optionally, the lighting system comprises means for detecting one or more of: a presence of a dimmer; a type of dimmer; or a setting of a dimmer.

[0028] According to a third aspect of the disclosure, a method according to appended claim 16 is provided.

[0029] Optionally, the power stage comprises one or more power transistors, and selectively disabling the power stage comprises disabling both the ON and OFF cycles of the power transistors.

[0030] Optionally, the selected period of the grid AC power cycle excludes a period during which a phase switch is applied.

[0031] Optionally, the light source is an electroluminescent device.

[0032] Optionally, the light source is a light-emitting diode.

[0033] Optionally, the energy storage device has a capacitor.

[0034] Optionally, the capacitor is a storage capacitor that provides a voltage source for the power stage, and the lamp further comprises an output capacitor for supplying power to the light source.

[0035] According to a fourth aspect of the disclosure, a method according to appended claim 23 is provided.

[0036] Optionally, the lighting system also has a phase switch dimmer.

[0037] Optionally, the dimmer is a trailing edge dimmer.

[0038] Optionally, the dimmer is a leading edge dimmer.

[0039] Optionally, the dimmer is a leading edge and trailing edge dimmer.

[0040] Optionally, the method comprises monitoring and / or sensing a grid AC waveform.

[0041] Optionally, monitoring and / or capturing the grid AC waveform includes peak detection.

[0042] Optionally, the method comprises detecting one or more of: a presence of a dimmer; a type of dimmer; or a setting of a dimmer. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The disclosure is described below by way of example only with reference to the accompanying drawings in which: Fig. Figure 1 shows a low-voltage lighting system according to the prior art; Fig. 2 Aspects of the operation of the lighting system of Fig. 1 shows; Fig. Figure 3 shows the operation of a low-voltage lighting system in which undesirable flicker occurs due to the load of a lamp falling below the operating load of an electronic transformer; Fig. 4 shows a lighting system according to an embodiment of the disclosure, including a lamp and an electronic transformer; Fig. 5 Aspects of the operation of the lighting system of Fig. 4 shows; Fig. Shows 6 different thresholds of the electronic transformer; Fig. Figure 7 shows a prior art low voltage lighting system in which a dimmer switch is provided; Fig. 8 shows a lighting system according to another embodiment of the disclosure, comprising a lamp and an electronic transformer together with a dimmer switch and a dimmer control device; Fig. 9 Aspects of the operation of the lighting system of Fig. 8 shows; and Fig. 10 shows a lamp provided in accordance with embodiments of the disclosure. DETAILED DESCRIPTION

[0044] The use of high-efficiency lamps as replacements for incandescent and halogen lamps presents a challenge. LED lamps are discussed as an example.

[0045] LED lamps offer higher operating efficiency compared to incandescent lamps, including halogen lamps. LED lamps have a faster response time, and when the LED driver operates in continuous mode, the instantaneous power consumption closely follows the input voltage waveform. Thus, when using LED lamps in lighting systems, the load for the equivalent range of light intensity is significantly lower compared to incandescent lamps, including halogen lamps. This significantly increases the likelihood that the load will fall below the electronic threshold, generating unwanted flicker.

[0046] This problem is discussed with reference to Fig. 3 shown. Fig. Figure 3a shows how a mains AC voltage (V_MAINS) varies over time while Fig. 3b shows the operating threshold 300 of the electronic transformer and the operating load (I_LOAD) 302 of an LED lamp. The operating load 302 is inversely proportional to the AC mains input voltage waveform 304. During the course of a first period 306, the load is below the operating threshold of the transformer. When the load falls below the threshold of the electronic transformer, the electronic transformer turns off, eliminating the input power to the LED-based lamp and causing flicker. During the course of a second period 308, the load is above the operating threshold of the transformer, so the transformer operates normally.

[0047] The present invention provides a lighting system with an adaptive power balancing control such that a load current of an electronic transformer remains above its minimum operating threshold.

[0048] Fig. 4 shows a lighting system according to an embodiment of the disclosure. An electronic transformer 400 converts an AC mains voltage 402 to a lower lamp input voltage 404 for supplying power to a low-voltage lamp 406. It is also possible for the transformer 400 to supply power to multiple lamps 406. The low-voltage lamp includes a light source 408, which in this embodiment includes a light-emitting diode (LED). A plurality of LEDs may be provided, however, only one is shown for clarity. The lamp 406 also includes a rectifier 410 and a power stage 412. The power stage 412 includes circuitry that regulates the voltage supplied to the light source 408, thereby providing a stable voltage source (VDC_Boost). The power stage may include circuitry including a boost converter.The power stage 412 operates under the control of a switching device 414 and a power stage controller 416. The power stage controller 416 may be coupled to the output voltage of the electronic transformer 400. A peak detector 417 or equivalent may be provided (as part of the lamp, part of the transformer, or as another component) to determine the shape of the AC voltage. The switching device 414 may comprise one or more power transistors and is illustrated as a MOSFET, but may equally well be another type of transistor or equivalent switching element. The lamp 406 also includes an energy storage device 418 coupled between the rectifier 410 and the power stage 412.

[0049] The power stage control device 416 operates to selectively disable the ON and OFF cycles of the switching device 414 to ensure that the load current of the electronic transformer 400 remains above its operating threshold and thus the transformer 400 continues to operate normally.

[0050] This will be Fig. 5. As observed with other LED lamps, the load current waveform is inversely proportional to the AC mains input voltage waveform 504 when the LED lamp output power remains constant. Therefore, the probability that the lamp load current will fall below the electronic transformer's operating threshold 500 is greatest when the AC mains voltage (V_MAINS) is at its highest magnitude.

[0051] To reduce or eliminate this likelihood, the ON and OFF cycles are disabled during periods 506 while the magnitude of the AC line voltage is above a threshold V_MAX, thereby creating a no-load state of the electronic transformer 400. The LED lamp draws power from the energy storage device 418 during these periods 506 so that it can continue to maintain a constant light output. Current through the LED lamp can be regulated during these time periods. The energy storage device 418 may include a storage capacitor or equivalent that charges while the electronic transformer 400 provides an input voltage. The storage capacitor provides an unregulated voltage source for the power stage 412. Power for the light source 408 is provided by an output capacitor when the power stage 412 is not operating.Power stage components, such as a boost converter, can be coupled between the storage capacitor and the output capacitor.

[0052] During the course of the periods 508, when the magnitude of the AC mains voltage is below the threshold V_MAX, the control device activates the ON and OFF cycles of the switching device 414. In this range, the load current of the lamp exceeds the threshold 504 of the electronic transformer.

[0053] The value of the V_MAX threshold defines the duration of the periods 506 and 508 during which the ON and OFF cycles of the switching device 414 are deactivated and activated. The V_MAX threshold should be set relatively low (defining a relatively long period 506 during which the switching device 414 is deactivated) if the electronic threshold is relatively high; and conversely, it should be set relatively high (defining a relatively short period 506 during which the switching device 414 is deactivated) if the electronic threshold is relatively low. The value of the V_MAX threshold can be set by changing the operating parameters of the power stage control device 416.

[0054] By deactivating the switching device 414 at the optimal times, the present disclosure enables stable operation of the electronic transformer at all times.

[0055] As in Fig. As shown in Figure 6, the operating threshold varies from electronic transformer to electronic transformer. Therefore, existing LED lamps may function well with some electronic transformers, but are unstable or fail completely when used with other electronic transformers. However, the present disclosure allows for high operating load during periods when the ON and OFF cycles of power stage switching devices are enabled, enabling stable operation when used with all electronic transformers. The transformer load current 600 according to the disclosure is above various thresholds 602, 604, 606 of different electronic transformers.

[0056] In another aspect of the disclosure, the threshold periods during which the ON and OFF cycles of the switching device 414 are enabled / disabled can be adjusted. This can be achieved, for example, by adjusting the threshold V_MAX. This means that flickering can be avoided even when LED lamps have varying load current requirements and / or when electronic transformers have varying threshold levels. The threshold can also be dynamically adjusted according to the operation of the transformer 400. When the transformer is reset, the threshold can be lowered to skip a larger portion of each cycle; and similarly, when the transformer is restored, the threshold can be increased to skip a smaller portion of each cycle.

[0057] As mentioned above, Fig. 1 a generic low-voltage lighting system. The lamps are voltage-controlled devices, meaning that the light output varies with the RMS input voltage. Therefore, the light output can be controlled by including a triac-based dimmer switch in series with the electronic transformer. This is described in Fig. 7, in which a dimmer switch 700 together with the components of Fig. 1, which are provided with the same reference numerals.

[0058] Fig. Figure 8 shows a lighting system according to an embodiment of the disclosure, provided with a dimmer switch 700 and a dimmer control device 800 that controls the light output intensity of the LED device(s) by regulating the current through the LED device(s). The remaining components are the same as in Fig. 4 and are represented by the same reference numerals.

[0059] In addition to maintaining proper operation of the electronic transformer 400, the adaptive enabling and disabling of the ON and OFF cycles of the switching device 414 also ensures proper operation of the lighting system when the electronic transformer 400 is coupled to a phase switching dimmer switch 700, including leading edge dimmer switches and trailing edge dimmer switches.

[0060] The disclosure also provides for monitoring and sensing the low-frequency AC input waveform 504. This may include one or more of: detecting the presence of a dimmer switch 700, detecting the type of dimmer switch (e.g., leading edge or trailing edge), and detecting the setting of the dimmer (i.e., the portion of the AC waveform removed by the dimmer). This information may be acquired without the need to directly sense the input voltage to the lamp or, equivalently, the output of the electronic transformer. This information may be used to determine the optimal adaptive power balancing techniques to employ.

[0061] Fig. Figure 9 shows an AC input voltage coupled across a trailing-edge phase-switching dimmer switch. During the course of periods 908, switching device 414 is activated, while during the course of periods 906, switching device 414 is deactivated. Since most trailing-edge and / or leading-edge dimmer switches utilize a triac switching device, maintaining a load must be observed to ensure proper operation of the dimmer switch. Removing load current from the AC line near the zero crossing (0V) of the AC line waveform or near the phase-switching switching point causes the dimmer switch to reset, resulting in an interruption of the AC input voltage source. This causes improper operation of the lighting system, such as light flickering, or in some cases, a complete system failure.

[0062] The present disclosure can address this by using the sensed AC input voltage signal and ensuring that the ON and OFF cycles of the switching device 414 are not disabled during periods when the AC input voltage is near a zero crossing and near the edge of phase switching.

[0063] Technical protection bands can also be defined to ensure proper operation of the lighting system.

[0064] The present disclosure reduces flicker by detecting the operation of a lamp connected to an electronic transformer and adaptively controlling the lamp's driver circuit to prevent unexpected resetting of the electronic transformer, thereby eliminating operational flicker.

[0065] Furthermore, the adaptive control ensures maximum operating efficiency of the lighting system. It also ensures interoperability between different lamps and transformers.

[0066] The present disclosure has utility in a wide range of lighting systems. A typical lamp 106 is shown in Fig. 10. Here, a lamp housing 1000 contains a light source, which may include one or more LEDs. A base 1002 includes a driver circuit for the light source, and electrical connectors 1004 are provided. The electrical connectors can have various shapes.

[0067] An exemplary lighting system to which the disclosure may be applied is an MR16 lighting system, which typically provides a lamp operating voltage of 12 V at 50 kHz. The present disclosure allows LED lamps to be easily used in MR16 systems instead of halogen lamps without encountering flicker issues.

[0068] Various modifications and improvements may be made to the above without departing from the scope of the disclosure.

Claims

[1] A lamp (406) comprising a light source (408) and a driver circuit for the light source; wherein the driver circuit comprises a power stage (412) for regulating a voltage supplied to the light source, an energy storage device (418), and a control means (416) configured to selectively deactivate the power stage; wherein power is provided to the light source (408) by the energy storage device (418) when the power stage is deactivated; wherein the control means (416) is configured to deactivate the power stage (412) during the course of a selected period of a grid AC power cycle, the selected period of the grid AC power cycle comprising a period during which the magnitude of the grid voltage has a maximum value; wherein the selected period of the mains AC power cycle is defined by a threshold such that the power stage is selectively deactivated when the magnitude of the mains voltage is equal to or greater than the threshold; wherein the threshold is dynamically adjustable according to the operation of an electronic transformer (400) for use with the lamp to prevent resetting of the electronic transformer; such that when the electronic transformer (400) resets, the threshold is lowered to lengthen the selected period, and when the electronic transformer (400) recovers, the threshold is increased to shorten the selected period. [2] The lamp of claim 1, wherein the power stage (412) comprises one or more power transistors controlled with ON and OFF cycles, and selectively disabling the power stage comprises disabling both the ON and OFF cycles of the power transistors. [3] The lamp according to claim 1 or 2, wherein the selected period of the mains AC power cycle excludes a period during which a phase switch is applied. [4] The lamp according to any preceding claim, wherein the light source is an electroluminescent device. [5] The lamp according to claim 4, wherein the light source is a light emitting diode. [6] The lamp according to any preceding claim, wherein the energy storage device (418) comprises a capacitor. [7] The lamp of claim 6, wherein the capacitor (418) is a storage capacitor providing a voltage source for the power stage (412), and wherein the lamp further comprises an output capacitor for providing energy to the light source. [8] A lighting system comprising an electronic transformer (400) coupled to a lamp (406) according to any preceding claim, wherein the electronic transformer (400) is configured to convert a mains voltage into a lamp operating voltage for supply to the lamp. [9] The lighting system of claim 8, further comprising a phase switch dimmer (700). [10] The lighting system according to claim 9, wherein the dimmer is a trailing edge dimmer. [11] The lighting system of claim 9, wherein the dimmer is a leading edge dimmer. [12] The lighting system according to claim 9, wherein the dimmer is a leading edge and trailing edge dimmer. [13] The lighting system according to any one of claims 8 to 12, comprising means for monitoring and / or detecting a mains AC waveform. [14] The lighting system of claim 13, wherein the means for monitoring and / or detecting the mains AC waveform comprises a peak detector (417). [15] The lighting system of claim 9, comprising means for detecting one or more of: a presence of a dimmer; a type of dimmer; or a setting of a dimmer. [16] A method for controlling power supplied to a light source by a driver circuit in a lamp, comprising selectively disabling a power stage of the driver circuit and supplying power through an energy storage device when the power stage is disabled; wherein the power stage is deactivated during the course of a selected period of a mains AC power cycle, the selected period of the mains AC power cycle including a period during which the magnitude of the mains voltage is at a maximum value; and wherein the selected period of the mains AC power cycle is defined by a threshold such that the power stage is selectively deactivated when the magnitude of the mains voltage is equal to or greater than the threshold; wherein the threshold is dynamically adjusted according to operation of an electronic transformer for use with the lamp to prevent resetting of the electronic transformer; such that when the electronic transformer (400) is reset, the threshold is lowered to lengthen the selected period, and when the electronic transformer (400) recovers, the threshold is increased to shorten the selected period. [17] The method of claim 16, wherein the power stage comprises one or more power transistors controlled with ON and OFF cycles, and selectively disabling the power stage comprises disabling both the ON and OFF cycles of the power transistors. [18] The method of claim 16 or 17, wherein the selected period of the grid AC power cycle excludes a period during which a phase switch is applied. [19] The method according to any one of claims 16 to 18, wherein the light source is an electroluminescent device. [20] The method of claim 19, wherein the light source is a light emitting diode. [21] The method according to any one of claims 16 to 20, wherein the energy storage device comprises a capacitor. [22] The method of claim 21, wherein the capacitor is a storage capacitor providing a voltage source for the power stage, and the lamp further comprises an output capacitor for supplying power to the light source. [23] A method of controlling power supplied to a light source in a lighting system, the method comprising: - converting a mains voltage into a lamp operating voltage for supply to a lamp using an electronic transformer; - coupling the lamp operating voltage to a lamp; and - controlling power supplied by a driver circuit for the light source of the lamp according to the method of any one of claims 16 to 22. [24] The method of claim 23, wherein the lighting system further comprises a phase switch dimmer. [25] The method of claim 24, wherein the dimmer is a trailing edge dimmer. [26] The method of claim 24, wherein the dimmer is a leading edge dimmer. [27] The method of claim 24, wherein the dimmer is a leading edge and trailing edge dimmer. [28] The method according to any one of claims 23 to 27, comprising monitoring and / or detecting a grid AC waveform. [29] The method of claim 28, wherein monitoring and / or detecting the grid AC waveform comprises peak detection. [30] The method of any one of claims 23 to 29, comprising detecting one or more of: a presence of a dimmer; a type of dimmer; or a setting of a dimmer.

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