A lighting device that receives power from an external source

Abstract

The lighting device connects to an external power source and includes a light-emitting load and a secondary load. A temperature measurement is obtained relating to the temperature of the external power source. If the temperature measurement is below a threshold, the secondary load is enabled, thereby allowing the secondary load to be powered by the external power source. Thus, in cold conditions, an increased load is applied to the external power source to assist in starting up the external power source in cold conditions.

Description

[Technical Field]

[0001] The present invention relates to lighting devices, and in particular to lighting devices that receive power from an external power source. [Background technology]

[0002] The desire to reduce the power consumption of lighting devices has led to the development of many low-power lighting devices. Lighting devices, most commonly in the form of LED lamps, are becoming increasingly widely used. LED lamps offer many technical advantages, such as providing energy savings compared to traditional lighting technologies and therefore reducing environmental impact.

[0003] Low-voltage LED lamps such as MR11, Capsule G4, Capsule G8, Capsule G9, etc. are often used with electronic transformers. The circuit structures and parameters of mature electronic transformers on the market are mostly designed for incandescent lamps, halogen lamps, and other high-power, high-energy-consuming conventional lamps. The circuit structures, components, and parameters of electronic transformers require a high-power load so that the electronic transformer can operate normally.

[0004] When the ambient temperature is low, the performance of components in the electronic transformer decreases, and as a result, the electronic transformer requires a higher power load to operate normally at low ambient temperatures. Otherwise, the output voltage of the electronic transformer may be too low or unstable due to abnormal operation of the internal components and circuits of the electronic transformer. This problem is widespread. For example, both the electronic transformer and the lamp may be used in outdoor environments or cold indoor environments. Outdoor applications include, for example, outdoor corridors of some hotels on winter mornings or nights, or in cold regions. Cold indoor applications include, for example, fast food restaurants / drinks, store and hotel corridors, elevator waiting rooms, or living rooms on winter mornings or nights, or in cold regions. Summary of the Invention [Problem to be solved by the invention]

[0005] The luminous efficacy of LEDs is continually improving, and therefore the trend for LED lamps is to reduce power consumption. This can lead to compatibility issues between LED lamps and conventional electronic transformers, especially when the ambient temperature is low. For example, electronic transformers, especially when used with low-power LED lamps, can be difficult to start or tend to flicker when the ambient temperature is low. LED lamps themselves generally have specific requirements for their output lumens and input power, and these requirements may not be met.

[0006] There is a need to maintain compatibility of low power lighting devices with existing power supplies that are designed for, for example, higher power lighting solutions, especially at low temperatures where compatibility becomes a particular potential issue.

[0007] US20100264737A1 discloses a solution in which a battery for an LED load is used in a damped power supply cycle when the battery is cold. [Means for solving the problem]

[0008] Summary of the Invention

[0009] It is the concept of the present invention to provide temperature monitoring in a lighting device to indirectly monitor the temperature of an external power source, such as an electronic transformer. At low temperatures, a secondary load (in addition to the lighting load) is enabled to assist in the start-up (or indeed continuous operation) of the external power source.

[0010] The invention is defined by the claims.

[0011] According to an example according to an aspect of the present invention, an input adapted to connect to an external power source; a light-emitting load powered by the external power source; a secondary load powered by the external power source; a controller, receiving a temperature measurement relating to a temperature of the external power source; and a controller configured to enable the secondary load if the temperature measurement is below a threshold, thereby allowing the secondary load to be powered by the external power source.

[0012] If the measured temperature is low, the external power supply may require an increased load to operate properly, especially if the power supply is in the form of an electronic transformer. This increased load may be used, for example, during the start-up phase when the temperature is low. This helps the external power supply to start up and operate stably.

[0013] The measured temperature is related to the external power source. This means that the temperature rise of the external power source is captured by the measured temperature. The temperature sensor used for the temperature measurement does not need to be in direct thermal contact with the external power source. In fact, the temperature sensor is, for example, part of the lighting device. Before operation of the lighting device and the external power source, they are both considered to be at the same / similar ambient temperature. In most places, they are mounted in this way, for example, in the same room and above a false ceiling. During use, there is a positive correlation between the temperature of the external power source and the temperature of the lighting device, and both of their temperatures rise at the same, proportional, or correlated rate to the appropriate temperature of the external power source. Therefore, the temperature measurement is preferably an indirect measurement of the temperature of the external power source.

[0014] The secondary load is used to adjust the input power of the LED lamp (which forms the load of the external power supply) according to the operating state of the external power supply. This allows the external power supply to start and operate normally in a low-temperature environment, while the brightness of the lighting load can remain unchanged. The input power of the lighting load can meet specification requirements when the lighting load operates stably at an ambient temperature of, for example, 25 degrees Celsius or higher.

[0015] By disabling the secondary load when it is not needed, power is saved when the secondary load is not needed. The temperature of the external power source may increase in staged operation, or in other cases the ambient temperature may already be warm at start-up, in either case the secondary load may be able to be disabled. Thus, the secondary load need not cause a long-term increase in power consumption (and thus a decrease in efficiency) if the compatibility issue only occurs during start-up, but only during the cold start-up phase.

[0016] The threshold applied for temperature sensing corresponds to a temperature of the external power supply below which the external power supply will not operate normally for a load that only includes the light emitting load. If the temperature of the power supply is too low, the power supply may not start or operate properly when powering the light emitting load. The secondary load enables the power supply to operate correctly.

[0017] The controller may be adapted to disable the secondary load when the temperature measurement is above the threshold, thereby inhibiting the external power source from powering the secondary load, such that the secondary load is only for (temporarily) controlling the load seen by the power source.

[0018] The secondary load is non-light-emitting, for example a load resistor, which is a simple load that can be easily integrated into the circuit of the lighting device.

[0019] In the hysteresis / latch control method, the controller is adapted to continue disabling the secondary load after disabling it even if the temperature measurement value provided by the temperature sensor falls below the threshold again. This is based on the situation where the temperature measurement value provided by the temperature sensor in the lamp, i.e., the temperature of the lamp, falls again because the secondary load is disconnected and the heat generation of the lamp is reduced. However, since the electronic transformer has already warmed up, there is no need to re-enable the secondary load.

[0020] The secondary load is, for example, in series with the light-emitting load. An LED driver is placed between the electronic transformer and the light-emitting load, and the LED driver converts the output voltage of the electronic transformer into a drive current for the light-emitting load and the secondary load. Thus, the presence or absence of the secondary load in series does not change the light output, which is a function of current (assuming the drive voltage requirement is met). This is particularly simple and useful. Because the LED driver needs to power a larger load, the load seen by the electronic transformer is also larger, thereby allowing the electronic transformer to operate stably at low temperatures.

[0021] The lighting device may have a temperature sensor for supplying the temperature measurement to the controller, the temperature sensor being disposed within the lighting device and adapted to indirectly reflect the temperature of the external power source. Thus, the temperature sensor is within the lighting device, e.g., part of a lamp. This embodiment is also based on the fact that the temperature of the lamp is positively correlated with the temperature of the electronic transformer. The idea of ​​indirect monitoring means that monitoring is performed inside the lamp, not in the external power source. It does not require a temperature sensor in the external power source and notification to the lamp, and therefore requires no modification of the existing external power source at all, only modifications to the lamp circuit, thereby reducing costs for consumers. In another example, the controller could receive the temperature measurement from an external entity, such as a dedicated control signal from a dedicated temperature sensor mounted on or in the external power source, or a specific power waveform directly from the external power source indicating that the external power source has already warmed up.

[0022] The temperature sensor may, for example, comprise a negative temperature coefficient resistor, which is a simple and low-cost way to provide a temperature-dependent signal (e.g., the voltage across the resistor), which may, for example, be part of a resistor divider.

[0023] The controller may have a bypass switch in parallel with the secondary load to bypass the secondary load in response to the temperature measurement, so that the secondary load is either in-circuit or bypassed, providing a simple switch-controlled load change.

[0024] The controller may comprise a further switch controlled based on the temperature measurement, the switch state of the further switch determining the switch state of the bypass switch.

[0025] The lighting device may include an LED lamp, the load may include an LED device, and the lighting device may further include an LED driver circuit between the external power supply and the LED device. The driver circuit may, for example, provide a regulated current. The driver circuit may, for example, include a switch-mode power converter. The electronic transformer may, for example, provide a regulated high-frequency AC voltage, for example, 12 V rms, and the LED driver circuit may, for example, be a regulated current driver for providing the regulated current to the LED by rectifying and converting the AC voltage.

[0026] The LED driver may, for example, comprise a single-stage power converter. Since the external power supply already performs a PFC function, no PFC stage is required, and therefore a single-stage converter such as a buck converter, boost converter, or flyback converter may be used.

[0027] The external power source is preferably an electronic transformer.

[0028] The present invention provides a lighting device as defined above; and the electronic transformer adapted to power the lighting device.

[0029] The present invention provides a method for controlling a lighting device including a lighting load, comprising: obtaining a temperature measurement relating to a temperature at an external power supply; enabling a secondary load if the temperature measurement is below a threshold, thereby powering the lighting load and the secondary load using an external power source; and disabling the secondary load if the temperature measurement is greater than the threshold, thereby powering the lighting load but not the secondary load using the external power source.

[0030] The method may comprise using an electronic transformer external to the lighting device as the external power source, and obtaining the temperature measurement inside the lighting device, the temperature measurement indirectly reflecting the temperature of the electronic transformer.

[0031] These and other aspects of the invention will be elucidated and elucidated with reference to the following embodiments. [Brief explanation of the drawings]

[0032] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: [Figure 1] A typical low-power LED lighting device is shown. [Figure 2] 1 shows in schematic form a lighting device according to the invention; [Figure 3] 1 shows one possible embodiment of a lamp circuit. [Figure 4] Test results are presented showing the system input power at steady state for various ambient temperatures. [Figure 5] Further test results are shown, showing plots of sensed temperature versus ambient temperature. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be described with reference to the drawings.

[0034] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to indicate the same or similar parts.

[0035] The present invention provides a lighting device that connects to an external power source and includes a light-emitting load and a secondary load. A temperature measurement is obtained regarding the temperature of the external power source. If the temperature measurement is below a threshold, the secondary load is enabled, thereby allowing the external power source to power the secondary load. Thus, in cold conditions, an increased load is provided to the external power source to assist in start-up and stable operation of the external power source in cold conditions.

[0036] FIG. 1 shows a typical low-power LED lighting device, also referred to as an LED lamp 14. The lighting device connects to an external power source, in this example an electronic transformer 10, which receives, for example, an AC mains input 12. The electronic transformer 10 provides a reduced voltage (e.g., an AC 12V rms value) to the LED lamp 14. The LED lamp 14 includes an LED driver 16 and an LED device 18. The electronic transformer may provide an AC voltage, in which case the LED driver 16 provides AC / DC functionality to convert the AC voltage to the rated current of the LED device 18. The LED driver 16 may be a switched-mode power supply. The LED device 18 may be an array of LEDs, such as series, parallel, or hybrid series-parallel LEDs.

[0037] 2 shows in schematic form a lighting device according to the present invention. The LED driver 16 of the LED lamp 14 includes additional circuitry for switching the power of the load provided to the electronic transformer. A temperature detection circuit is used to determine the appropriate load, and a control circuit performs control of the power switching circuit. The additional circuitry addresses compatibility issues at low temperatures or with low-power LED lamps. The objective is to shift the input power of the LED lamp (as seen by the external power source) depending on the temperature of the external power source without affecting the output lumens of the LED lamp.

[0038] One possible embodiment of the lamp circuit is shown in Figure 3. However, there are many possible circuits that can shift the input power of an LED lamp in response to sensed temperature, and Figure 3 is only one example.

[0039] This circuit is based on the assumption that the temperature within the lamp 14 is correlated to the temperature of the electronic transformer 10. This assumption is reasonable because both the lamp 14 and the electronic transformer 10 are located in the same ambient environment and have similar power dissipation / efficiency for heating themselves. Therefore, the sensed temperature within the lamp is related to the temperature of the electronic transformer. For example, the initial temperature (e.g., ambient temperature) of both is the same at start-up, and the temperatures of both increase in a similar manner. Note that it is not necessary to have a hard thermal coupling between the electronic transformer and the LED lamp.

[0040] The circuit includes a detection circuit, a control circuit, and a power shifting circuit.

[0041] The detection circuit includes a negative temperature coefficient (NTC) resistor Rntc, which provides information about the temperature inside the lamp based on the temperature of the resistor Rntc of the LED lamp 14, and indirectly provides information about the temperature of the electronic transformer 10. Experiments can be performed to find an appropriate NTC coefficient such that the temperature caused by the notch closely reflects that the electronic transformer 10 has entered the appropriate temperature / operating state.

[0042] The circuit of the lamp 14 has an input 30 which is connected to the input of an LED driver unit 32 which is adapted to connect to the output Vout of an external power supply. This is, for example, a low voltage, e.g., a 12V AC or DC signal, generated by the electronic transformer 10. The LED driver 32 comprises, for example, a single-stage power converter. No PFC stage is required, so a single-stage converter such as a buck converter, boost converter, or flyback converter may also be used.

[0043] The LED device 18 forms a light-emitting load powered by an external power supply. However, there is also a secondary load 34 powered by the external power supply. The secondary load is in series with the LED device 18. Therefore, if a regulated current is supplied to the LED device and the secondary load, the secondary load 34 does not affect the light output (as long as the operating voltage is sufficient to drive the LED device). The secondary load is a non-light-emitting load, such as a resistor Rload.

[0044] The controller receives the temperature measurement as a voltage across resistor Rntc. The controller has a transistor circuit based on switches M1 and M2, shown as MOSFETs M1 and M2. The temperature measurement is related to the temperature of the external power source, i.e., the electronic transformer 10; that is, there is some correlation between the temperature at the electronic transformer and the temperature at the lamp, which is most noticeable when both are at ambient temperature and the rate of temperature rise is correlated. Power loss in the electronic transformer causes heat generation and therefore a temperature rise in the electronic transformer. Power loss in the LED driver 32 and heat generation in the LED 18 and resistor 34 cause a temperature rise in the LED lamp.

[0045] If the temperature measurement is below the threshold, the secondary load 34 may be enabled by the controller, thereby allowing the external power source to power the secondary load.

[0046] Resistor Rntc forms a voltage divider circuit together with a further resistor R1 (and level shifting Zener diode D1) and therefore a detection circuit which is used to control whether transistor M1 is on or off, and the state of transistor M1 is used to control whether transistor M2 is on or off.

[0047] Transistor M1 is powered via a level shifting Zener diode D2 and a supply resistor R2. When transistor M1 is turned off, transistor M2 is turned on by the same supply circuit D2, R2.

[0048] Capacitor C1 forms a filter circuit with resistor R2 that suppresses current spikes during power domain switching, as described further below.

[0049] At low temperatures, when the resistance of the NTC resistor Rntc is high, the voltage at Rntc is high, which turns on the transistor M1 and turns off the transistor M2, so the LED lamp operates in the high-power region. The LED device 18 and the secondary load 34 are in series and provide a large load to the LED driver 32, which then provides a large load to the external power supply. Therefore, when the transistor M2 is off, the output current flows through the LED device and the load resistor Rload, and there is additional power loss in Rload, so the LED lamp operates in the high-power region. However, the output lumens do not increase.

[0050] The resistance of the NTC resistor Rntc decreases as its temperature increases, and therefore the voltage at Rntc becomes lower. This turns off the transistor M1 at a certain point in time, and the transistor M2 turns on, and therefore the LED lamp operates in the low power region. The transistor M2 is used to bypass the secondary load 34. The output current flows through the LED device 18, and most of the current flows through the transistor M2, with very little flowing through the secondary load Rload. Therefore, there is almost no additional power loss in Rload, and the LED lamp operates in the low power region.

[0051] A temperature detection circuit can be placed in an LED lamp to indirectly derive information about the temperature / operating state of the electronic transformer. The operating environment temperature of the LED lamp and the operating environment temperature of the electronic transformer connected to the LED lamp are generally the same, especially at the moment of power-on. As mentioned above, these temperatures are positively correlated. Therefore, the temperature of the NTC resistor in the LED lamp is selected to have the same temperature rise characteristics as the temperatures of the main components / temperature rise components in the electronic transformer.

[0052] After the electronic transformer and the LED lamp start to operate, the temperatures of the main components in the electronic transformer also rise with time, and at a certain point in time, they reach a temperature at which they are in a stable operating state (note that this temperature may not be the final temperature of the electronic transformer for long-term operation), and the temperature of the NTC resistor in the LED lamp also rises with time, and at the above-mentioned certain point in time, reaches a trigger point. Therefore, until the electronic transformer and the LED lamp reach a stable state, there is a positive correlation between (i) the temperature of the NTC resistor in the LED lamp, (ii) the temperature of the main components in the electronic transformer, and (iii) the operating time of the electronic transformer since it is started.

[0053] When the ambient temperature is low and the power has just been turned on, the temperature of the NTC resistor is low, and the temperature of the main components in the electronic transformer is also low. When the ambient temperature is high (such as room temperature at 25 degrees Celsius) and the power has just been turned on, the temperature of the NTC resistor is high, and the temperature of the main components in the electronic transformer is also high.

[0054] After power-on, while the NTC resistor has not yet reached a stable temperature, the longer the operating time, the higher the temperature of the NTC resistor and the higher the temperature of the main components in the electronic transformer. Therefore, the temperature of the NTC resistor in the LED lamp not only reflects the information of the ambient temperature, but also indirectly reflects the information of the time the LED lamp has been operating. Therefore, it can be used to determine the operating state of the electronic transformer, and in particular, can be used as an indicator of whether the electronic transformer can start and operate normally under a light-weighted load such as an LED device only.

[0055] To illustrate how circuit parameters should be designed and selected for the above example circuit, specific design steps based on exemplary system requirements are provided below. This example uses only one possible set of parameters simply to illustrate the design process.

[0056] First, it needs to be started at a low ambient temperature. The LED lamp specifications, for example, require that the system input power of the combination of electronic transformer and LED lamp be within the range of 4.5W ±10% after the LED lamp reaches a steady state at a room temperature of 25 degrees Celsius. Therefore, taking into account the losses of the electronic transformer, in this example, the input power of the LED lamp cannot exceed 3.8W.

[0057] At low ambient temperatures, such as -10 degrees Celsius, when the electronic transformer is connected with a low-power LED lamp as the only load, the output voltage of the electronic transformer is only about 1.5V, much lower than the rated 12V output, causing the LED lamp to be very dim, low-power, and prone to flickering.

[0058] The heavier the load on the electronic transformer, the higher the chance that the electronic transformer will start and operate normally. Therefore, in such low ambient temperature situations, the LED lamp needs to operate in a high-power regime to start the electronic transformer. For example, the input power of the LED lamp needs to be increased from 3.8 W to 5.3 W so that the electronic transformer can still start normally at such low ambient temperatures and output a voltage close to the input voltage required by the LED lamp. This solves the problem of starting the electronic transformer and the LED lamp at low ambient temperatures.

[0059] The LED lamp then needs to operate with a stable input power at room temperature. When the electronic transformer and LED lamp are operated for a period of time (such as within 30 minutes) and can reach a normal temperature of 25 degrees Celsius, the electronic transformer will reach approximately its stable state. After that, the LED lamp needs to operate in a low power range, for example, presenting an input power of 3.8 W. In this way, the input power of the electronic transformer and LED lamp combination can meet the specification requirements.

[0060] Some considerations for parameter design and selection are now discussed.

[0061] When selecting the resistance of the secondary load Rload, please note that the output voltage of the LED driver circuit must not trigger the overvoltage protection (OVP) function when operating in the high power region. An example of a suitable value for Rload is 74Ω.

[0062] For an input current of about 130 mA, when the secondary load Rload is switched into the circuit, the output voltage of the LED driver circuit is increased by about 9.6 V (74×0.13), and the output power of the LED lamp is increased by about 1.25 W.

[0063] Thus, for various applications, the secondary load may have a resistance in the range of, for example, 50 ohms to 200 ohms.

[0064] When the LED lamp operates in the high power region, the input power of the LED lamp is 5.3 W and the output power is 4.45 W. When the LED lamp operates in the low power region, the input power of the LED lamp is 3.8 W and the output power is 3.2 W. When shifting from the high power state to the low power state, approximately 1.25 W of power dissipation associated with the secondary load Rload is saved. The short period of 1.25 W of power dissipation without light output until the electronic transformer reaches a steady state is a trade-off for the stable lighting output of the LED lamp.

[0065] The temperature at which the NTC resistor switches the circuit from a high-power state to a low-power state is also designed. During the design phase, the LED lamp is operated in a high-power state at a normal temperature of 25 degrees Celsius until a stable state is reached. The temperature of the NTC resistor is then checked, which may be, for example, about 95 degrees Celsius.

[0066] To ensure that the LED lamp can shift to a low power state at 25 degrees Celsius with some margin, the design may be such that when the ambient temperature is about 10 degrees Celsius, the LED lamp can shift from a high power state to a low power state just as it reaches steady state.

[0067] A test at an ambient temperature of 10 degrees Celsius, for example, will result in an NTC resistor temperature of about 80 degrees Celsius if the LED lamp is operating at high power for more than an hour, which means that the LED lamp has reached its steady state.

[0068] Therefore, the critical temperature of the NTC resistor when the LED lamp shifts from a high-power state to a low-power state can be set to 80 degrees Celsius in this example. This 80-degree temperature then serves as the threshold temperature of the external power supply, below which the external power supply will not operate normally for a load that only has a light-emitting load (i.e., 10 degrees Celsius). In other words, a stable temperature of 80 degrees corresponds to a power supply temperature of 10 degrees Celsius, and below 10 degrees Celsius there is a risk of the power supply malfunctioning.

[0069] The NTC resistor may have, for example, a resistance of 100 kΩ at room temperature of 25 degrees Celsius and a resistance of 11.75 kΩ at 80 degrees Celsius. Resistor R1 may then be selected to be 120 kΩ when operating at an ambient temperature of 10 degrees Celsius so that the LED lamp can shift from a high power state to a low power state just as it reaches its steady state, which may occur within 30 minutes after start-up.

[0070] Typically, an output capacitor (not shown but which may be present in the circuit of the present invention) with a large capacitance such as several hundred μF is used at the end of the LED driver circuit. When transistor M2 is suddenly switched on, this quickly discharges the capacitor from the LED device voltage plus Rload voltage to the LED device voltage alone.

[0071] This sudden voltage change causes a high output current spike, which can result in a spike in the LED lamp's light output and can damage the LED.

[0072] Resistor R2 and capacitor C1 are selected to form an RC filter circuit that can cause transistor M2 to turn on more slowly, thus discharging the LED driver output capacitor and slowing down the voltage drop, thus preventing current spikes from occurring through the LED device.

[0073] An example value for resistor R2 is 330 kΩ, and an example value for capacitor C1 is 2.2 μF. This gives an RC time constant of 0.726 ms. The power state shift takes approximately 1 second, with no visible light spike.

[0074] The Zener diodes Z1 and Z2 are selected to ensure the safe operation of the transistors M1 and M2. The output voltage of the LED driver circuit is, for example, 40V or less, which is guaranteed by the LED driver's overvoltage protection function. The maximum gate-source voltage of the transistors M1 and M2 is generally 20V, so the Zener diodes Z1 and Z2 can be 20V Zener diodes.

[0075] Transistors M1 and M2 must have a drain-source breakdown voltage greater than 40V.

[0076] The control circuit has a hysteresis function. After startup, if the temperature of the NTC resistor rises to 80°C, the system shifts to the low-power region, reducing the output voltage of the LED driver circuit by approximately 9.6V, which is the voltage across the secondary load Rload. The power shift reduces the voltage divider between Rntc and R1, resulting in a temperature hysteresis of approximately 41.5°C. As a result, the LED lamp returns to the high-power state only when the temperature of the NTC resistor drops to 80-41.5=38.5°C. In another example, if the lamp has already entered the low-power state, which means the electronic transformer has already warmed up, the lamp will no longer enter the high-power state during this power-on period. If the lamp is turned off and then turned on again, it will again measure and control the power.

[0077] Therefore, by using a regulated current driver, the supply voltage depends on the power state (which depends on the load present). Therefore, changing the driver output voltage with a change in load automatically introduces a hysteresis function into the operation of the circuit. The hysteresis function ensures a smooth shift of the LED lamp from a high power state to a low power state without oscillations between high and low power states.

[0078] The tested temperature difference of the NTC resistor between when the LED lamp is operating in a high-power state and when it is operating in a low-power state is approximately 25.8 degrees. Because the temperature hysteresis described above is much larger than the temperature difference, the LED lamp does not return to the high-power state after shifting to the low-power state. Therefore, the high-power state is only used for the initial startup of the circuit and does not contribute to long-term additional power consumption once the circuit is switched to the low-power state.

[0079] The operation of the circuit (in this particular example), based on the design of the circuit parameters described above, is such that when the system is powered on, it will operate in a high power state if the ambient temperature is above 10 degrees Celsius (and below a maximum level where the high power state is never required). After a period of time (e.g., less than 30 minutes), if the temperature of the NTC resistor reaches 80 degrees Celsius, the circuit will switch to and continue operating in a low power state.

[0080] If the ambient temperature is below 10 degrees Celsius, the system will operate in a high power state when powered on and may remain in that state (since it will not reach the threshold temperature of 80 degrees Celsius even in steady state).

[0081] To ensure proper functioning of the lamp with an external power supply, an additional power consumption of, for example, 1.25 W is permitted.

[0082] Figures 4 and 5 show the results of the test.

[0083] Figure 4 shows the steady-state system input power (y-axis, W) for various ambient temperatures (x-axis, degrees Celsius). The system input power is for the electronic transformer and LED lamp system.

[0084] It can be seen that for temperatures above 10 degrees Celsius, the steady state uses a low power state. For temperatures below 10 degrees Celsius, the steady state uses a high power state.

[0085] When measured at an ambient temperature of 25°C, after 5 minutes and 30 seconds of power-on, the temperature of the NTC resistor reaches 78°C, and the LED device shifts to a low-power state and operates stably. The input power of the LED lamp remains at 3.8W, and the input power to the electronic transformer remains at 4.45W, which meets the requirements.

[0086] When measured at a low ambient temperature of -10 degrees Celsius, the LED lamp can work normally when powered on and continues to work in a high power state where the input power of the LED lamp is 5.3 W. After 1 hour of stable operation, the NTC temperature reaches 61.5°C.

[0087] FIG. 5 shows a plot of the NTC temperature Tntc (y-axis, degrees Celsius) versus the ambient temperature Ta.

[0088] The low hysteresis threshold is due to the level shift in the voltage divider as explained above. The temperature of the NTC resistor as a function of ambient temperature is shown for low and high power states, and the steady state plot shows that below 10 degrees Celsius the low power state is used at steady state, while above 10 degrees Celsius the high power state is used at steady state.

[0089] The present invention is applicable to all low-voltage LED lamps that operate with electronic transformers, such as MR16, MR11, Capsule G4, Capsule G8, Capsule G9, etc. Most of these low-voltage LED lamps are used in warm indoor environments, but some of these low-voltage LED lamps are used in outdoor environments or cold indoor environments. Outdoor applications include, for example, winter mornings or nights, or outdoor corridors of some hotels in cold regions.

[0090] Cold indoor applications include, for example, food outlets, store and hotel corridors, elevator waiting rooms, or living rooms on winter mornings or evenings, or in cold climates.

[0091] Those skilled in the art can understand and effect variations to the disclosed embodiments in practicing the claimed invention, from a study of the drawings, the specification and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the singular does not exclude a plurality.

[0092] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0093] It should be noted that when the term "adapted to" is used in the claims or specification, the term "adapted to" is intended to be equivalent to the term "configured to."

[0094] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. an input adapted to connect to an external power source; a light emitting load powered by the external power source; a secondary load powered by the external power source; a controller, receiving a temperature measurement relating to a temperature of the external power source; a controller configured to enable the secondary load and allow the secondary load to be powered by the external power source when the temperature measurement is below a threshold; operating in a high power region by enabling the secondary load to present a relatively heavier load to the external power source when the temperature measurement is below a threshold; A lighting device adapted to operate in a low power region by disabling the secondary load so as to present a relatively less heavy load to the external power source when the temperature measurement is above the threshold.

2. the threshold corresponds to a predetermined temperature of the external power source below which the external power source will not operate normally with the lighting device with the secondary load disabled; 2. The lighting device of claim 1, wherein the output of the light-emitting load is the same in the high power region and the low power region.

3. 3. The lighting device of claim 2, wherein the input is adapted to connect to an electronic transformer as the external power source.

4. 3. A lighting device according to claim 1, wherein the controller is adapted to disable the secondary load when the temperature measurement value is higher than the threshold value, thereby prohibiting the external power source from supplying power to the secondary load, the secondary load being a non-light-emitting device.

5. 5. The lighting device of claim 4, wherein the secondary load is a load resistor.

6. 6. A lighting device according to any one of claims 1 to 5, wherein the secondary load is in series with the light-emitting load.

7. 7. A lighting device according to any one of claims 1 to 6, comprising a temperature sensor for supplying the temperature measurement to the controller, the temperature sensor being arranged within the lighting device and adapted to indirectly indicate the temperature of the external power source.

8. 8. The lighting device of claim 7, wherein the temperature sensor comprises a negative temperature coefficient resistor, and the controller is adapted to continue disabling the secondary load after an initial disabling even if the temperature measurement provided by the temperature sensor falls below the threshold again.

9. 9. A lighting device according to any preceding claim, wherein the controller comprises a bypass switch in parallel with the secondary load for bypassing the secondary load in response to the temperature measurement.

10. 10. A lighting device according to claim 9, wherein the controller comprises a further switch controlled based on the temperature measurements, the switch state of the further switch determining the switch state of the bypass switch.

11. 11. A lighting device according to any one of the preceding claims, comprising an LED lamp, the load comprising an LED device, the lighting device further comprising an LED driver circuit between the external power source and the LED device.

12. 12. The lighting device of claim 11, wherein the LED driver circuit comprises a single-stage power converter.

13. A lighting device according to claim 3, A lighting fixture comprising, as the external power source, the electronic transformer adapted to power the lighting device.

14. 1. A method for controlling a lighting device, comprising: obtaining a temperature measurement relating to the temperature of the external power supply; if the temperature measurement is below a threshold, allowing a lighting load and a secondary load to be powered by the external power source, and enabling the secondary load to present a relatively heavier load to the external power source; and if the temperature measurement is greater than the threshold, disabling the secondary load to allow the lighting load to be powered by the external power source and the secondary load not to be powered by the external power source, thereby presenting a relatively less heavy load to the external power source.

15. using an electronic transformer external to the lighting device as the external power source; and obtaining the temperature measurements internal to the lighting device, the temperature measurements indirectly indicative of a temperature of the electronic transformer; 15. The method of claim 14, wherein the output of the lighting load is the same both when the temperature measurement is below the threshold and when the temperature measurement is above the threshold.

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