LED lighting system and control method

Abstract

A system for creating an LED lighting system for efficient dimming, and the system includes a voltage source, an electronic switch controlled by a pulse width modulation (PWM) drive signal, and a series connected LED lighting module. The LED includes an LED set and a constant current drive circuit to drive a constant current through the LED set. The voltage source and a bypass branch in parallel with the electronic switch are adapted such that when the electronic switch is off, the power delivered to the constant current drive circuit is sufficient to maintain operation of the constant current drive circuit, ensuring the ability for deep dimming.

Description

Technical Field

[0001] This invention relates to the field of lighting systems, and more specifically, to the field of LED lighting systems. It particularly relates to, but is not limited to, LED lighting systems, including dimming functions based on interruptions in the current supply to the lighting load. Background Technology

[0002] There are many different driving schemes used for LED-driven luminaires. For example, complex circuits such as high-frequency switching-mode power converter circuits are used in power supply lighting systems; they can achieve high power factors and low total harmonic distortion, but they are costly solutions. Lower-cost circuits, for example, use linear drivers. The most basic driving circuit can simply supply DC voltage to the LED through a so-called ballast resistor, which acts as a current limiter.

[0003] A sophisticated driver would include dimming functionality, for example, with a dimming input that provides control over the settings of the switch-mode power converter. To implement dimming in a simpler circuit, the current supply to the LED arrangement can be interrupted, for example, using a series switch controlled by a pulse-width modulation (PWM) signal. The duty cycle of the PWM signal then determines the light output.

[0004] To ensure optimal LED performance, it is driven by the manufacturer-specified current to achieve the desired light output at the most efficient operating point. This can be achieved most simply by connecting the LED to the voltage source described above, connected in series with a resistor. This is a low-cost solution and is typically used for low- and medium-power LEDs. Therefore, the current through the LED is determined by (V... VS -V LED ) / R is determined, where V VS It is the voltage provided by the voltage source, V LED R is the forward voltage of the LED, and R is the resistance of the series resistor. However, this resistor causes losses, thus reducing the efficiency of the lighting system.

[0005] To improve this efficiency, the voltage drop across the resistor must be kept as low as possible. One way to do this is to use multiple LEDs connected in series. Maintaining the same light output from multiple LEDs requires less drive current compared to a single LED, which in turn reduces resistive losses. However, this also means that if the forward voltage of the LED differs from the expected value (e.g., due to manufacturing errors or tolerances), the brightness will vary significantly. To eliminate this fluctuation problem, V... VS and V LED There needs to be a significant difference between them, but this will lead to a lot of losses.

[0006] A constant current circuit that regulates current via an LED can improve efficiency and avoid the need for a current-limiting resistor, but at the cost of a slightly more complex circuit, thus increasing system cost.

[0007] One problem with using constant current circuits is that they tend to have an associated start-up time before they can supply a constant current. This means that for the standard PWM dimming schemes described above, which typically operate in the range of 1 kHz or higher, there is a lower limit to the duty cycle, and therefore a lower limit for the LED lighting system to be dimmed.

[0008] There is still a need for a driver architecture that can achieve low-cost dimming based on interruptions to the current supply to the LED arrangement, while still allowing for a wide range of dimming levels. Summary of the Invention

[0009] This invention is defined by the claims.

[0010] According to an example of one aspect of the present invention, an LED lighting system is provided, comprising:

[0011] Voltage source;

[0012] An electronic switch connected in series with a voltage source, the electronic switch being controlled by a pulse width modulation (PWM) drive signal;

[0013] Bypass branch connected in parallel with electronic switch; and

[0014] An LED lighting module connected in series with a voltage source and an electronic switch, the LED lighting module includes:

[0015] Constant current drive circuit; and

[0016] LED group

[0017] The constant current drive circuit is suitable for driving a constant current through the LED group, and

[0018] The bypass branch and / or voltage source are adapted such that when the electronic switch is turned off, the power delivered to the constant current drive circuit is sufficient to maintain the operation of the constant current drive circuit.

[0019] This LED lighting system enables dimming of individual LEDs or groups of LEDs. A PWM signal with a duty cycle selected for the desired dimming level is applied to an electronic switch. When the switch is open, the LEDs turn off. A bypass branch is connected in parallel with the switch. This parallel combination of the switch and bypass branch is connected in series with a voltage source and the LED lighting module. The LED lighting module consists of an LED group and a constant current drive circuit. The constant current drive circuit ensures a constant current through the LED group, which ensures the correct light output specified by the LED group's manufacturer. This contrasts with a more basic system using a series static resistor, which results in lower efficiency and less consistent light output characteristics. Furthermore, several LED lighting modules can be connected together in parallel.

[0020] The bypass branch enables the constant current drive circuit to remain powered when the LED is off. For example, the delivered power is used as a supply voltage sufficient to maintain the operation of the drive circuit.

[0021] When using certain constant current drive circuits, there is a turn-on delay of several microseconds. PWM-controlled LED systems typically operate at PWM frequencies greater than 1kHz, so the delay becomes significant, especially for low duty cycles of the PWM signal. For example, using a 4kHz PWM signal, a 1% dimming level would produce a 2.5μs pulse, which is comparable to the turn-on delay. Therefore, the lowest possible dimming level is limited.

[0022] Furthermore, when the constant current drive circuit is turned on, a large turn-on current may occur, which may require additional delay to ensure that this current is controlled, potentially resulting in an additional delay of a few microseconds. These delays push up the minimum possible dimming level. This problem is eliminated by adding a bypass branch, which allows the constant current drive circuit to continue being powered even when the switch is off.

[0023] For example, bypass branches and / or voltage sources are adapted so that when the electronic switch is off, the voltage across each LED in the LED group remains below its respective threshold voltage. Due to the addition of bypass branches, the LEDs can also still emit light at a very low but still visible level. This is particularly problematic when several LED modules are connected in parallel, as a higher current is required to keep all the constant current drive circuitry energized, resulting in a higher current flowing through the LED group. By keeping the voltage across the LEDs below their threshold voltages, no current flows through the LEDs. Therefore, when the electronic switch is off, the constant current drive circuitry remains on, but the LEDs are off.

[0024] For example, an LED group consists of one or more LEDs connected in series. This means that the overall threshold voltage of the LED group can be selected so that the threshold voltage is not reached when the electronic switch is off. Each additional LED placed in series increases the threshold voltage. The desired lighting level can also be selected based on the number of LEDs in the group.

[0025] For example, a bypass branch includes a resistor. The resistor reduces the voltage across the LED group to prevent any current from flowing through the LED group when the electronic switch is off, but allows a sufficiently high voltage to ensure the operation of the constant current drive circuit.

[0026] For example, the bypass branch includes a Zener diode. The Zener diode provides a predetermined voltage drop, thus reducing the voltage across the LED group to prevent any current from flowing through the LED group when the electronic switch is off, but allowing a sufficiently high voltage to ensure the operation of the constant current drive circuit.

[0027] For example, a bypass branch includes a resistor and a Zener diode in series. If either the Zener diode or the resistor cannot provide a voltage low enough to turn off the LED and a voltage high enough to operate a constant current drive circuit, a resistor in series with the Zener diode can be used.

[0028] For example, a constant current drive circuit is a buck converter. Buck converters can be used to maintain a constant current across an LED array in a known manner through high-speed switching. This provides a highly electricalally efficient design, but with relatively high circuit costs.

[0029] A constant current drive circuit can be replaced by a linear constant current converter. A linear constant current converter maintains a constant current across the LED array by operating the drive transistor within its linear range. This is more efficient than a simple resistor circuit and has a lower system cost than using a buck controller.

[0030] For example, an electronic switch is a transistor.

[0031] The system may also include multiple LED lighting modules, each comprising a corresponding constant current drive circuit and a corresponding LED group. Each LED lighting module is in a corresponding parallel branch, wherein a bypass branch is adapted so that when the electronic switch is off, the voltage across each constant current drive circuit remains sufficient to operate the constant current drive circuit. Therefore, the lighting system can have multiple LED branches.

[0032] According to an example of an aspect of the present invention, a method for controlling an LED lighting system is provided, comprising:

[0033] PWM control is used to control the electronic switch, thereby achieving dimming, in which the electronic switch is connected in series with the voltage source and the LED lighting module;

[0034] When the electronic switch is closed, a voltage source powers the constant current drive circuit of the LED module, thereby driving a constant current through the LED group of the LED lighting module; and

[0035] When the electronic switch is off, a voltage source delivers power to the constant current drive circuit through a bypass branch connected in parallel with the electronic switch, wherein the delivered power is sufficient to maintain the operation of the constant current drive circuit.

[0036] In one example, when the electronic switch is off, the voltage of each LED across the LED group remains below the corresponding threshold voltage.

[0037] Bypass branches may include, for example, resistors, Zener diodes, or resistors and Zener diodes in series.

[0038] Powering a constant current drive circuit includes, for example, operating a buck converter or a linear constant current converter.

[0039] In one example, when the electronic switch is closed, the method includes powering a constant current drive circuit for a plurality of LED lighting modules, each LED lighting module including a corresponding constant current drive circuit and a corresponding LED group, each LED lighting module in a corresponding parallel branch, wherein when the electronic switch is open, the voltage across each constant current drive circuit is still sufficient to operate the constant current drive circuit.

[0040] These and other aspects of the invention will be apparent from the embodiments described below and will be illustrated therewith. Attached Figure Description

[0041] To better understand the invention and to more clearly illustrate how to implement it, reference is now made to the accompanying drawings by way of example only, wherein:

[0042] Figure 1A This illustrates a basic LED lighting system with LEDs, a voltage source, and a resistor connected in series.

[0043] Figure 1B This illustrates a basic LED lighting system with LED groups and resistors connected in series.

[0044] Figure 2A An LED lighting system is shown, featuring a step-down controller that provides a constant current through the LED array;

[0045] Figure 2B The diagram illustrates an LED lighting system with a linear constant current converter that provides a constant current through the LED array.

[0046] Figure 3 Show Figure 2BThe LED lighting system features a PWM-driven electronic switch connected in series with a voltage source and an LED lighting module for dimming.

[0047] Figure 4A Show Figure 3 The LED lighting system has a first bypass branch, including a resistor, connected in parallel with the electronic circuitry;

[0048] Figure 4B Show Figure 3 The LED lighting system has a second bypass branch, including a Zener diode, connected in parallel with the electronic circuitry;

[0049] Figure 4C Show Figure 3 The LED lighting system has a first bypass branch connected in parallel with the electronic circuitry, comprising a resistor and a Zener diode connected in series; and

[0050] Figure 5 An LED dimming lighting system is shown, which has multiple LED lighting modules connected in parallel. Detailed Implementation

[0051] The invention will be described with reference to the accompanying drawings.

[0052] It should be understood that the detailed descriptions and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are for illustrative purposes 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 be better understood through the following description, the appended claims, and the accompanying drawings. It should be understood that these drawings are schematic only and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to indicate the same or similar parts.

[0053] This invention provides an LED lighting system comprising a voltage source, an electronic switch controlled by a pulse-width modulation (PWM) drive signal, and an LED lighting module, all connected in series. The LED lighting module includes an LED array and a constant current drive circuit adapted to drive a constant current through the LED array. Furthermore, the LED lighting system includes a bypass branch connected in parallel with the electronic switch. This bypass branch and / or voltage source is adapted such that when the electronic switch is open, the power delivered to the constant current drive circuit is sufficient to maintain the operation of the constant current drive circuit.

[0054] Figure 1A and 1B Examples of LED lighting circuits 100 and 101 are shown. Figure 1A The circuit includes a voltage source 110, a resistor 120, and an LED 130 connected in series. Figure 1B Show Figure 1AThe LED lighting circuit 100 has an LED group 131 instead of a single LED 130. The LED group 131 includes a plurality of LEDs 132 connected in series.

[0055] The current level required for the brightness output of an LED is specified by the manufacturer, but it must also be limited to avoid damaging the LED. In both examples, this drive current is provided by connecting a voltage source and a resistor in series.

[0056] The driving current through the LED is determined by: (Vvs - VLED) / R, where VVS is the voltage supplied by the voltage source, and V LED R is the forward voltage of the LED and the resistance of the series resistor. The voltage drop across the LED, i.e., the forward voltage, is relatively constant within the driving current range.

[0057] Therefore, the resistor value can be determined using the forward voltage and drive current specified by the LED manufacturer, as well as the voltage source. However, this resistor introduces losses, thus reducing system efficiency.

[0058] For example, if Figure 1A LED 130 has a forward voltage of 3V at 200mA, and voltage source 110 supplies 10V, so resistor 120 will need to be a 35Ω resistor to supply 200mA. This will result in a resistor loss of 1.4W.

[0059] if Figure 1B LED group 131 includes 3 LEDs and... Figure 1A Using the same voltage source 110 as in the example above, to achieve the same brightness, a current of 66.6mA and a forward voltage of 9V are required through LED group 131. In this case, the value of resistor 121 will need to be 15Ω. This results in a resistor loss of 0.066W, which is more than... Figure 1A The example resistor has approximately 21 times lower losses.

[0060] The increased efficiency is due to a lower voltage drop across the resistor. Unfortunately, the forward voltage of an LED is a production factor, meaning that this value can vary by several percentage points.

[0061] If in Figure 1A In the example, if the LED forward voltage is 10% higher due to tolerance, the required forward voltage for LED 130 will be 3.3V. For a 35Ω resistor, this means the current through LED 130 is reduced by 5% to 191mA, resulting in a 5% decrease in light output.

[0062] exist Figure 1BIn the given example, if the LED forward voltage is 10% higher due to tolerance, the required forward voltage for LED group 131 will be 9.9V. For a resistor value of 15Ω, this means that the current through LED group 131 is reduced by 90% to 6.66mA, resulting in a 90% reduction in light output.

[0063] In summary, a lower voltage drop across resistor 120 results in lower resistor losses and improved efficiency of the lighting system. However, this makes the system's light output more susceptible to variations in the forward voltage of LED group 131. This is because the headroom between the voltage supplied by voltage source 110 and the forward voltage of LED group 131 is small, meaning that small changes in the forward voltage lead to large changes in the drive current.

[0064] Figure 2A An example of an LED lighting circuit 200 is shown, including a voltage source 210 and an LED lighting module 220. The LED lighting module 220 includes a constant current drive circuit 240 and an LED group 230. The constant current drive circuit 240 is adapted to control the current through the LED group 230.

[0065] The constant current drive circuit 240 is a current-drop controller circuit. It is operated by power supply rails including the supply voltage VCC and the ground voltage GND. These power supply rails are derived from the output of voltage source 210. For example, the constant current drive circuit has a minimum supply voltage (relative to ground) for circuit holding operation.

[0066] A constant current through the LED group 230 is achieved in a known manner with high switching speed by a buck controller. The current is sensed by a current-sensing resistor 270. The current-sensing buck controller 240, in response to the monitored current through the sensing resistor 270, controls the series-connected main converter switch 260. Capacitor C1 and inductor L1 form the oscillation circuit of the buck converter, and diode D1 is the freewheeling diode of the buck converter. This provides an efficient design and consistent light output from the LED group 230. However, this solution requires the use of inductors and a high-speed buck controller, increasing system cost.

[0067] Figure 2B An alternative example of an LED lighting circuit 201 is shown, which also includes a voltage source 210 and an LED lighting module 221. The LED lighting module 221 includes a constant current drive circuit 241 and an LED group 230. The constant current drive circuit 241 in this example is a linear constant current converter.

[0068] The constant current converter includes a main transistor 261 (T1) operating within its linear range. A current-sensing resistor 270 again senses the current flowing through the LED group 230. The resulting voltage is compared at comparator U1 with a reference voltage represented by voltage source 251. The comparator output determines the conduction state of transistor T2, thereby determining its output impedance. Transistor T2 and resistor R1 form a divider such that the voltage at the connection between transistor T2 and resistor R1 varies according to the current flowing through the LED group. This, in turn, controls the base voltage of the main transistor T1. In this way, a feedback path is formed to regulate the conduction state of T1 to maintain the desired current set by reference 251. If the current decreases, T2 is driven to a lower impedance state, thus increasing the voltage at the base of T1 to provide current regulation (in this case, an increase).

[0069] The constant current drive circuit 241 is operated by power supply rails including the supply voltage VCC and the ground voltage GND. These power supply rails are derived from the output of voltage source 210. The constant current drive circuit can be an integrated circuit (with peripheral circuit components), and the integrated circuit also has a minimum supply voltage (relative to ground) for circuit holding operation.

[0070] This provides an efficient design and consistent light output from the LED group 230. The linear constant current converter has a lower system cost than a buck controller and is a simpler design.

[0071] exist Figure 2A and 2B In, with Figure 1A and 1B Unlike the lighting circuit shown, the current through LED group 230 will remain constant, even if there is a difference between the actual forward voltage of the LED group and the expected value supplied by the manufacturer.

[0072] Figure 3 An example of an LED lighting circuit 201 is shown, which includes a pulse-width modulation (PWM) controlled electronic switch 350 connected in series with a voltage source 210 and an LED lighting module 320, and is applied to... Figure 2B Circuit design.

[0073] For example, electronic switch 350 may be, for example, a transistor or another switch known to those skilled in the art, which can be turned on and off by electronic signals.

[0074] A PWM-controlled electronic switch 350 enables dimming of the light output from the LED group 230. This is achieved by repeatedly and periodically opening and closing the electronic switch 350, connecting and disconnecting the voltage source 210 from the LED lighting module 221. By decreasing the duty cycle, the average light output from the LED group 230 decreases, an effect perceived by the human eye as dimming. By increasing the duty cycle, the average light output from the LED group 230 increases to its maximum level, with the LED group 230 continuously on. Accordingly, the duty cycle can be selected for the desired dimming level.

[0075] This dimming method becomes problematic if the constant current drive circuit is a current-to-down converter, a linear constant current converter, or any other constant current system that requires a start-up time. Figure 3 In the case of the linear constant current converter 241 shown, the startup time, or the time required for the electronic device to begin operation, is typically a few microseconds. During this startup time, a large turn-on current could damage the LED group 230, so additional measures are taken to limit the current, thereby introducing additional delay.

[0076] PWM-controlled LED systems typically operate at PWM control frequencies above 1 kHz. Therefore, the cycle is less than 1 ms. Given a PWM control frequency of 1 kHz, at 0.1% dimming, the LED lighting module 230 is connected for only 1 microsecond during the on / off cycle. Due to the high on-state current during electronic device startup, the connection of the constant current drive circuit may have to be delayed. If the delay time is only 2 microseconds, the minimum dimming level of the LED lighting system will be at least 0.2%. If the PWM control frequency increases to 5 kHz, this minimum dimming level increases to 1%. Therefore, there is a lower limit to the dimming level when a startup time exists.

[0077] Therefore, to overcome the minimum dimming level of the gauge, startup time needs to be avoided. To achieve this, the present invention is based on an implementation that continuously supplies power to the constant current drive circuit. However, this is not easily achieved in a system with a series interrupt switch 350 (i.e., a single-wire system), because the switch 350 will interrupt power from the LED lighting module and thus from the constant current drive circuit.

[0078] Figure 4A , 4B And 4C illustrates the present invention and is based on the Figure 3 An example of an LED lighting system with modified circuitry.

[0079] Figure 4A The lighting system 400 is shown, including an electronic switch 350 driven by a PWM signal, a voltage source 210, and an LED lighting module 221 connected in series as described above.

[0080] The LED lighting system 400 also includes a bypass branch 460 connected in parallel with the electronic switch 350.

[0081] In the first example, bypass branch 460 includes resistor 461.

[0082] The addition of resistor 461 in parallel with electronic switch 350 provides a path for current to flow when electronic switch 350 is open. This allows the power supply to linear constant current converter 241 to be maintained, particularly VCC supplying power to comparator U1 and other circuit components. Therefore, linear constant current converter 241 will be able to operate continuously even when electronic switch 350 is open. This means that there is no lower limit to the dimming level, as there is no need to start linear constant current converter 241.

[0083] By ensuring that the voltage drop across resistor 461 results in a voltage across the LED group below the combined threshold voltage of the LEDs, LED group 230 will preferably be turned off. However, the voltage supply VCC to the linear constant current converter 241 is maintained above its minimum operating voltage (as described above), enabling the linear constant current converter to operate. Therefore, there is a voltage range between the minimum operating voltage of the constant current drive circuit and the forward voltage of the LED group, within which the LED group can be turned off while the constant current drive circuit remains active by delivering the drive voltage.

[0084] The minimum supply voltage VCC is, for example, 2.5V, therefore the operating voltage of the LED string must be higher than this value. The resistor value should allow the linear constant current converter to operate with the lowest possible current flowing through the LEDs.

[0085] During this period, transistor T2 will be driven to turn off (or to the lowest conduction state corresponding to the lowest output voltage from comparator U1) because no current flows through the current sensing resistor 270. This causes the base voltage of T1 to rise. Therefore, when switch 350 is open and the circuit is bypassed when the LED is off, the current in the sensing resistor is zero, and thus the current-controlled transistor T1 will be maximally de-energized.

[0086] When switch 350 is closed, transistor T1 will conduct current again, and this current will be regulated by the constant current drive circuit.

[0087] Therefore, even with a very low duty cycle, the circuit is ready to deliver current to the LED array; the circuit is energized and the transistors are in the appropriate conduction state to deliver current immediately when the forward voltage of the LED array is reached.

[0088] The circuit has a response time to restore the current transistor to the correct value, which depends on the sensing resistor, and there is a risk of "flash" current. This problem depends on both time and the speed of the circuit's control loop. Any such flash should not be visible, and more importantly, the LED must be able to handle any current spikes that may occur without damage.

[0089] The gain of transistor T1 can be limited so that the maximum current does not become too high.

[0090] Figure 4B A second example of a lighting system 401 is shown, in which, apart from the bypass branch, the branch is connected to... Figure 4A Similarly, in this example, the bypass branch includes a Zener diode 462. This provides a step voltage drop (independent of current). The Zener diode 462 also provides a path through which current can flow when the electronic switch 350 is open. The Zener diode 462 is adapted such that it reduces the voltage across the LED group 230 to a voltage lower than the forward voltage of the LED group 230, preventing current from flowing through the LED group 230 and thus preventing it from emitting light.

[0091] As described above, the voltage supplied to the linear constant current converter 241 is kept above its minimum operating voltage, enabling the linear constant current converter to operate.

[0092] Figure 4C A third example of lighting system 402 is shown, in addition to the bypass branch, which is connected to... Figure 4A Similarly, the bypass branch includes a Zener diode 462 and a resistor 464 connected in series. When the switch is open, the resistor 464 can additionally prevent unwanted high current from flowing through the LED lighting module 221.

[0093] exist Figures 4A to 4C The number of LEDs connected in series in LED group 230 can be selected to achieve the required overall forward voltage for LED group 230. The forward voltage of LED group will be the sum of the forward voltages of all LEDs in LED group. This allows the minimum operating voltage of the constant current drive circuit to be set at an appropriate level below the combined threshold voltage of the LEDs.

[0094] Figure 5 An example of an LED lighting system 500 is shown, which includes a PWM-controlled electronic switch 550, a voltage source 510, and LED lighting modules 520 connected in series. A bypass branch 560 is present in parallel with the PWM-controlled electronic switch 550. Multiple optional LED lighting modules 521 are also present in parallel with each other.

[0095] Multiple LED lighting modules 520, 521 allow multiple LED groups to be added to an LED lighting system, with multiple threshold voltages and drive current options. A bypass branch 560 is correspondingly adapted to the multiple LED lighting modules to ensure that the voltage across the multiple constant current drive circuits remains sufficiently high for continuous operation when the electronic switch 550 is open. The bypass branch 560 is also adapted to ensure that the voltage between the multiple LED groups 530 remains below the forward voltage of the LED groups 530, thereby preventing illumination when the electronic switch 550 is open.

[0096] The present invention has been described with reference to a linear constant current driver. This provides a low-cost solution. However, the same approach can also be applied to buck converters. Any other constant current converter can be used. Essentially, the current driver is a current source circuit, and any suitable current source circuit can be used.

[0097] For example, the present invention is applicable to LED systems (such as LED strings) driven by DC voltage. For example, DC voltage can be obtained through power supply rectification.

[0098] For example, the system operates at voltages ranging from 2V to 50V. The maximum voltage depends on the IC process, and may range from 18V to 50V. For instance, the IC's operating range could be 2.5V to 18V.

[0099] Those skilled in the art, through studying the accompanying drawings, this disclosure, and the appended claims, can understand and implement modifications to the disclosed embodiments. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plural.

[0100] The mere fact that certain measures are described in mutually distinct dependent claims does not indicate that a combination of these measures cannot be used advantageously.

[0101] If the term “suitable” is used in the claims or specification, it should be noted that the term “suitable” is intended to be equivalent to the term “configured as”.

[0102] Any reference marks in the claims should not be construed as limiting the scope.

Claims

1. An LED lighting system, comprising: Voltage source (210); The electronic switch (350) connected in series with the voltage source is controlled by a pulse width modulation (PWM) drive signal; A bypass branch (460) connected in parallel with the electronic switch (350); as well as An LED lighting module (221) connected in series with the voltage source and the electronic switch (350), the LED lighting module (221) comprising: A constant current drive circuit (241) is adapted to receive power via a power supply (VCC) having a loop (GND) coupled to the voltage source (210) via the electronic switch (350) and / or the bypass branch (460); as well as LED group (230) includes multiple LEDs (132) connected in series. The constant current drive circuit (241) is adapted to drive a constant current through the LED group, and The bypass branch (460) is adapted such that when the electronic switch (350) is open, the power delivered to the constant current drive circuit (241) via the power supply (VCC) is sufficient to maintain power supply to the constant current drive circuit (241). The bypass branch (460) is adapted such that the voltage drop across the bypass branch (460) causes the voltage across the LED group (230) to be lower than the combined threshold voltage of the LEDs (132).

2. The LED lighting system according to claim 1, wherein the bypass branch includes a resistor (461), and the circuit (GND) is coupled between the electronic switch (350) and the LED lighting module (221).

3. The LED lighting system according to any one of claims 1 to 2, wherein the bypass branch comprises a Zener diode (462).

4. The LED lighting system according to any one of claims 1 to 2, wherein the bypass branch comprises a resistor (464) and a Zener diode (462) connected in series.

5. The LED lighting system according to any one of claims 1 to 2, wherein the constant current drive circuit is a buck converter.

6. The LED lighting system according to any one of claims 1 to 2, wherein the constant current drive circuit is a linear constant current converter.

7. The LED lighting system according to any one of claims 1 to 2, wherein the electronic switch (350) is a transistor.

8. The LED lighting system according to any one of claims 1 to 2, comprising a plurality of LED lighting modules (520, 521), each LED lighting module comprising a corresponding constant current drive circuit and a corresponding LED group, each LED lighting module in a corresponding parallel branch, wherein the bypass branch is adapted such that when the electronic switch is off, the voltage across each constant current drive circuit remains sufficient to operate the constant current drive circuit.

9. A method for controlling an LED lighting system, comprising: PWM control is used to control the electronic switch (350) to achieve dimming, wherein the electronic switch is connected in series with the voltage source (210) and the LED lighting module (221); When the electronic switch is closed, the voltage source is used to power the constant current drive circuit (241) of the LED lighting module (221), thereby driving a constant current through the LED group (230), which includes a plurality of LEDs (132) connected in series in the LED lighting module. as well as When the electronic switch is off, the voltage source delivers power to the constant current drive circuit through a bypass branch (460) connected in parallel with the electronic switch, wherein the delivered power is sufficient to power the constant current drive circuit, wherein the bypass branch (460) is adapted such that the voltage drop across the bypass branch (460) causes the voltage across the LED group (230) to be lower than the combined threshold voltage of the LEDs (132).

10. The method of claim 9, wherein the bypass branch comprises a resistor (461), a Zener diode (462), or a series resistor (464) and a Zener diode (462).

11. The method according to any one of claims 9 to 10, wherein powering the constant current drive circuit comprises operating a buck converter or a linear constant current converter.

12. The method according to any one of claims 9 to 10, further comprising, when the electronic switch is closed, supplying power to constant current drive circuits of a plurality of LED lighting modules, each LED lighting module including a corresponding constant current drive circuit and a corresponding LED group, each LED lighting module being in a corresponding parallel branch, wherein when the electronic switch is open, the voltage across each constant current drive circuit remains sufficient to operate the constant current drive circuit.

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