System with LED driver and LED load

Abstract

The invention relates to a system comprising a LED driver and a LED load, comprising: output terminals for supplying the LED load; DC voltage output terminals for supplying a DC voltage preferably to supply a logic unit e.g. microcontroller or sensor; a DC voltage generation circuit connected to the DC voltage output terminals.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the technical field of lighting technology, and particularly to a system comprising the LED driver and a LED load.BACKGROUND OF THE INVENTION

[0002] Many circuits or system arrangements are known where a LED driver is connected with a luminaire which has a microcontroller (arranged within the housing of the luminaires, but external to the LED driver). However, a problem of such luminaires is that the microcontroller in the luminaire needs a separate low voltage DC power supply. Such an additional power supply may be provided by the driver. However, this requires a more complex driver design which increases the costs of the driver. Therefore, a majority of less expensive drivers do not have such additional power supply capabilities.

[0003] Thus, it is an objective to provide an improved system with LED driver and LED load with low (compared to mains voltage) DC voltage supply implemented outside the LED driver.SUMMARY OF THE INVENTION

[0004] The object of the present invention is achieved by the solution provided in the enclosed independent claim 1. Particularly, the invention is defined by a system according to claim 1.

[0005] Advantageous implementations of the present invention are further defined in the dependent claims.

[0006] Document US 2014 / 361623 A1 describes an auxiliary power supply to provide auxiliary power to a current source that drives an LED string. The current source provides a current through the LED string, which in turn may be selectively fed to the auxiliary power supply to provide auxiliary power back to the current source or to provide auxiliary power to other circuitry.

[0007] Document US 2018 / 213620 A1 describes a direct AC driving circuit and a luminaire for driving at least one LED. The driving circuit comprises means configured to provide a low supply voltage which is also derived from the rectified AC mains voltage.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention will be explained in the followings together with the figures. Fig. 1shows a luminaire comprising a LED driver according to the invention; Fig. 2shows a DC voltage generation circuit according to an example not part of the subject-matter of the claims; and Fig. 3shows a DC voltage generation circuit according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Aspects of the present invention are described herein in the context of a LED driver.

[0010] Fig. 1 shows a luminaire 1 comprising a system comprising a LED driver 3 and a LED load 40 according to the invention.

[0011] The LED driver 3 comprises output terminals 41a, 41b for supplying the LED load 40.

[0012] In addition thereto, the luminaire 1 comprises DC voltage output terminals 5, 6 for supplying a DC voltage to supply a logic unit 50, e.g. microcontroller or a sensor etc., and a DC voltage generation circuit 44 connected to the DC voltage output terminals 5, 6.

[0013] The DC voltage generation circuit 44 is arranged in parallel to the output terminals for supplying the LED load 41a, 41b and comprises at least one Zener diode 44A (see also Fig. 2 and 3).

[0014] Besides the LED driver 3, the luminaire 1 can comprise within its housing the logic unit 50 (e.g. microcontroller or sensor) external to the LED driver 3, and supplied off the DC voltage output terminals 5,6 of the DC voltage generation circuit 44. Furthermore, the luminaire 1 can comprise the LED load 40 supplied off the output terminals 41a, 41b. Thus, the luminaire 1 can be a LED luminaire, i.e., a luminaire with a light source comprising one or more LEDs or OLEDs.

[0015] The LED load 40 can comprise at least two LED strings in parallel 42, 43, each string 42, 43 comprising more than one LED connected in series, and a switch 45A for selectively activating one of said LED strings 42, 43, wherein the switch 45A is controlled by said logic unit 50.

[0016] Moreover, the switch 45A can have a third state in which none of the LED strings 42, 43 is activated, but the DC voltage generation circuit still being active, i.e. supplying its associated DC voltage output terminals with electrical power.

[0017] Moreover, the switch 45A can be configured to select, in dependence of one or more first pulse-width-modulation PWM control signals 46A one of the plurality of LED strings 42, 43 for feeding by the LED driver 3. The duty cycle of the PWM signal from the microcontroller thus sets the duty cycle of the respective LED string (one being selected by the switch during the on phase of the PWM signal, and the other one during the OFF phase). If the LED strings produce different spectra thus as e.g. white with different color temperatures, the duty cycle of the PWM cycle is used to "dim" the color or color temperature of the combined light output of both LED strings.

[0018] The one or more first PWM control signals 46A may be provided by a control unit such as the logic unit 50. A 16-bit resolution of the one or more first PWM control signals 46A may attain an accuracy sufficient for state-of-art color consistency.

[0019] In other words, the first switch 45A is configured to toggle between the two branches of the first LED string 42 and the second LED string 43. As such, a PWM duty cycle of the first PWM control signal 46A determines a ratio of cool white and warm white illumination by the plurality of LED lighting means 42, 43.

[0020] Each of the two branches has one PWM pulse per switching period T = 1 / f. Conclusively, the switching frequency f is the same for all branches, and the PWM duty cycles of the branches add up to 1.

[0021] In connection with the single first switch 45A, a single-channel constant current (CC) LED driver 3 may suffice to drive the LED strings 42, 43 of the LED load 40, which may in turn reduce a form factor and a cost with respect to a two-channel LED driver.

[0022] In addition, the LED driver 3 may have a feed / output current tolerance beyond ±5%, and up to ±10%, which may facilitate further cost savings and miniaturization.

[0023] In accordance with FIG. 1, the LED driver 3 can be configured to feed the LED load 40 off a mains grid 2.

[0024] In particular, the LED driver 3 may be configured to feed a constant current (CC).

[0025] Furthermore, the LED strings 42, 43 can have different color temperatures.

[0026] In particular, the LED strings 42, 43 may comprise a first LED string 42 having a color temperature greater than or equal to 5.000 K ("cool white") and a second LED string 43 having a color temperature greater than or equal to 2.700 K and less than or equal to 3.000 K ("warm white").

[0027] In the implementation of FIG. 1, the DC voltage generation circuit 44 may comprise a Zener diode 44A connected in parallel to the LED stings 42, 43 (see also Fig. 2 and Fig. 3).

[0028] A Zener diode is a special type of diode designed to allow a reversed current to flow when the diode is reverse-biased beyond a certain voltage, known as the Zener voltage, and to allow the reverse current to keep the voltage drop across the Zener diode close to the Zener voltage across a wide range of reverse currents.

[0029] The Zener diode 44A acts as a shunt regulator by maintaining a nearly constant voltage across itself when the reverse current through it is sufficient to take it into the Zener breakdown region. A choice of the Zener voltage is higher than the forward bias voltage of any of the LED strings 42, 43. As a result, the current path of the Zener diode is activated only if the LED strings 42, 43 are turned off.

[0030] In particular, the logic unit 50 within the luminaire 1 can be provided with electrical power by an internal power supply such as the DC voltage generation circuit 44 established within the luminaire 1 and the required electrical characteristics can be generated from an input intended to supply electrical energy to the LED strings 42, 43.

[0031] At least two distinct LED strings 42, 43 are provided in the luminaire 1 and the logic unit 50 is configured to switch between the different LED strings 42, 43.

[0032] Fig. 2 shows a DC voltage generation circuit 44 according to an an example not part of the subject-matter of the claims.

[0033] In the example shown in Fig. 2, the DC voltage generation circuit 44 comprises a capacitor 201 in parallel to the at least one Zenner diode 44A.

[0034] Fig. 3 shows a DC voltage generation circuit 44 according to the invention.

[0035] In the example shown in Fig. 3, the DC voltage generation circuit 44 comprises at least two Zener diodes 44A, 44B connected in series with same polarity, and one of the DC voltage output terminals 5 is connected to a midpoint between two Zener diodes 44A, 44B.

[0036] The DC voltage supplied at the DC voltage output terminals 5,6 can be a DC voltage tapped off across one of the Zener diodes 44A, 44B.

[0037] In fact, through the bumper 44A, 44B, electrical energy can be supplied from the LED connection terminals of the luminaire 1. The bumper unit 44A can comprise a series connection of a diode 200 and two Zener diodes 44A. From the connection point between the two Zener diodes 44A, the power supply for the logic unit 50 (e.g. 5 V for a microcontroller) can be extracted and, in order to ensure that the logic unit 50 is continuously provided with electrical energy, the capacitor 201 can also be provided in parallel connection to the two consecutive Zener diodes 44A, 44B.

[0038] The capacitor 201 is charged only during operation of the bumper.

[0039] However, the logic unit 50 is continuously provided with electrical energy. In order to ensure that no consequences result from a breakdown of the power supply, the logic unit 50 may have a so-called Brown-out-Detector (BOD) monitoring the input electrical power. As soon as a power failure (voltage drop) on the input side of the logic unit 50 is detected, the logic unit 50 can be kept in a reset state in order to avoid any undefined output.

[0040] In addition to the capacitor 201, which shall ensure a stable power supply of the logic unit 50, it may be advantageous to regularly, or on demand, power up the driver while no LED load 40 is connected to ensure an auxiliary power supply to be continuous. For such an arrangement, the switch 45A may allow a third position disconnecting both of the LED strings 42, 43. This is particularly useful in cases where the auxiliary power supply shall also power other auxiliary devices including sensor devices.

Examples

Embodiment Construction

[0009]Aspects of the present invention are described herein in the context of a LED driver.

[0010]Fig. 1 shows a luminaire 1 comprising a system comprising a LED driver 3 and a LED load 40 according to the invention.

[0011]The LED driver 3 comprises output terminals 41a, 41b for supplying the LED load 40.

[0012]In addition thereto, the luminaire 1 comprises DC voltage output terminals 5, 6 for supplying a DC voltage to supply a logic unit 50, e.g. microcontroller or a sensor etc., and a DC voltage generation circuit 44 connected to the DC voltage output terminals 5, 6.

[0013]The DC voltage generation circuit 44 is arranged in parallel to the output terminals for supplying the LED load 41a, 41b and comprises at least one Zener diode 44A (see also Fig. 2 and 3).

[0014]Besides the LED driver 3, the luminaire 1 can comprise within its housing the logic unit 50 (e.g. microcontroller or sensor) external to the LED driver 3, and supplied off the DC voltage output terminals 5,6 of the DC voltage...

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the technical field of lighting technology, and particularly to a system comprising the LED driver and a LED load.BACKGROUND OF THE INVENTION

[0002] Many circuits or system arrangements are known where a LED driver is connected with a luminaire which has a microcontroller (arranged within the housing of the luminaires, but external to the LED driver). However, a problem of such luminaires is that the microcontroller in the luminaire needs a separate low voltage DC power supply. Such an additional power supply may be provided by the driver. However, this requires a more complex driver design which increases the costs of the driver. Therefore, a majority of less expensive drivers do not have such additional power supply capabilities.

[0003] Thus, it is an objective to provide an improved system with LED driver and LED load with low (compared to mains voltage) DC voltage supply implemented outside the LED driver.SUMMARY OF THE INVENTION

[0004] The object of the present invention is achieved by the solution provided in the enclosed independent claim 1. Particularly, the invention is defined by a system according to claim 1.

[0005] Advantageous implementations of the present invention are further defined in the dependent claims.

[0006] Document US 2014 / 361623 A1 describes an auxiliary power supply to provide auxiliary power to a current source that drives an LED string. The current source provides a current through the LED string, which in turn may be selectively fed to the auxiliary power supply to provide auxiliary power back to the current source or to provide auxiliary power to other circuitry.

[0007] Document US 2018 / 213620 A1 describes a direct AC driving circuit and a luminaire for driving at least one LED. The driving circuit comprises means configured to provide a low supply voltage which is also derived from the rectified AC mains voltage.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention will be explained in the followings together with the figures. Fig. 1shows a luminaire comprising a LED driver according to the invention; Fig. 2shows a DC voltage generation circuit according to an example not part of the subject-matter of the claims; and Fig. 3shows a DC voltage generation circuit according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Aspects of the present invention are described herein in the context of a LED driver.

[0010] Fig. 1 shows a luminaire 1 comprising a system comprising a LED driver 3 and a LED load 40 according to the invention.

[0011] The LED driver 3 comprises output terminals 41a, 41b for supplying the LED load 40.

[0012] In addition thereto, the luminaire 1 comprises DC voltage output terminals 5, 6 for supplying a DC voltage to supply a logic unit 50, e.g. microcontroller or a sensor etc., and a DC voltage generation circuit 44 connected to the DC voltage output terminals 5, 6.

[0013] The DC voltage generation circuit 44 is arranged in parallel to the output terminals for supplying the LED load 41a, 41b and comprises at least one Zener diode 44A (see also Fig. 2 and 3).

[0014] Besides the LED driver 3, the luminaire 1 can comprise within its housing the logic unit 50 (e.g. microcontroller or sensor) external to the LED driver 3, and supplied off the DC voltage output terminals 5,6 of the DC voltage generation circuit 44. Furthermore, the luminaire 1 can comprise the LED load 40 supplied off the output terminals 41a, 41b. Thus, the luminaire 1 can be a LED luminaire, i.e., a luminaire with a light source comprising one or more LEDs or OLEDs.

[0015] The LED load 40 can comprise at least two LED strings in parallel 42, 43, each string 42, 43 comprising more than one LED connected in series, and a switch 45A for selectively activating one of said LED strings 42, 43, wherein the switch 45A is controlled by said logic unit 50.

[0016] Moreover, the switch 45A can have a third state in which none of the LED strings 42, 43 is activated, but the DC voltage generation circuit still being active, i.e. supplying its associated DC voltage output terminals with electrical power.

[0017] Moreover, the switch 45A can be configured to select, in dependence of one or more first pulse-width-modulation PWM control signals 46A one of the plurality of LED strings 42, 43 for feeding by the LED driver 3. The duty cycle of the PWM signal from the microcontroller thus sets the duty cycle of the respective LED string (one being selected by the switch during the on phase of the PWM signal, and the other one during the OFF phase). If the LED strings produce different spectra thus as e.g. white with different color temperatures, the duty cycle of the PWM cycle is used to "dim" the color or color temperature of the combined light output of both LED strings.

[0018] The one or more first PWM control signals 46A may be provided by a control unit such as the logic unit 50. A 16-bit resolution of the one or more first PWM control signals 46A may attain an accuracy sufficient for state-of-art color consistency.

[0019] In other words, the first switch 45A is configured to toggle between the two branches of the first LED string 42 and the second LED string 43. As such, a PWM duty cycle of the first PWM control signal 46A determines a ratio of cool white and warm white illumination by the plurality of LED lighting means 42, 43.

[0020] Each of the two branches has one PWM pulse per switching period T = 1 / f. Conclusively, the switching frequency f is the same for all branches, and the PWM duty cycles of the branches add up to 1.

[0021] In connection with the single first switch 45A, a single-channel constant current (CC) LED driver 3 may suffice to drive the LED strings 42, 43 of the LED load 40, which may in turn reduce a form factor and a cost with respect to a two-channel LED driver.

[0022] In addition, the LED driver 3 may have a feed / output current tolerance beyond ±5%, and up to ±10%, which may facilitate further cost savings and miniaturization.

[0023] In accordance with FIG. 1, the LED driver 3 can be configured to feed the LED load 40 off a mains grid 2.

[0024] In particular, the LED driver 3 may be configured to feed a constant current (CC).

[0025] Furthermore, the LED strings 42, 43 can have different color temperatures.

[0026] In particular, the LED strings 42, 43 may comprise a first LED string 42 having a color temperature greater than or equal to 5.000 K ("cool white") and a second LED string 43 having a color temperature greater than or equal to 2.700 K and less than or equal to 3.000 K ("warm white").

[0027] In the implementation of FIG. 1, the DC voltage generation circuit 44 may comprise a Zener diode 44A connected in parallel to the LED stings 42, 43 (see also Fig. 2 and Fig. 3).

[0028] A Zener diode is a special type of diode designed to allow a reversed current to flow when the diode is reverse-biased beyond a certain voltage, known as the Zener voltage, and to allow the reverse current to keep the voltage drop across the Zener diode close to the Zener voltage across a wide range of reverse currents.

[0029] The Zener diode 44A acts as a shunt regulator by maintaining a nearly constant voltage across itself when the reverse current through it is sufficient to take it into the Zener breakdown region. A choice of the Zener voltage is higher than the forward bias voltage of any of the LED strings 42, 43. As a result, the current path of the Zener diode is activated only if the LED strings 42, 43 are turned off.

[0030] In particular, the logic unit 50 within the luminaire 1 can be provided with electrical power by an internal power supply such as the DC voltage generation circuit 44 established within the luminaire 1 and the required electrical characteristics can be generated from an input intended to supply electrical energy to the LED strings 42, 43.

[0031] At least two distinct LED strings 42, 43 are provided in the luminaire 1 and the logic unit 50 is configured to switch between the different LED strings 42, 43.

[0032] Fig. 2 shows a DC voltage generation circuit 44 according to an an example not part of the subject-matter of the claims.

[0033] In the example shown in Fig. 2, the DC voltage generation circuit 44 comprises a capacitor 201 in parallel to the at least one Zenner diode 44A.

[0034] Fig. 3 shows a DC voltage generation circuit 44 according to the invention.

[0035] In the example shown in Fig. 3, the DC voltage generation circuit 44 comprises at least two Zener diodes 44A, 44B connected in series with same polarity, and one of the DC voltage output terminals 5 is connected to a midpoint between two Zener diodes 44A, 44B.

[0036] The DC voltage supplied at the DC voltage output terminals 5,6 can be a DC voltage tapped off across one of the Zener diodes 44A, 44B.

[0037] In fact, through the bumper 44A, 44B, electrical energy can be supplied from the LED connection terminals of the luminaire 1. The bumper unit 44A can comprise a series connection of a diode 200 and two Zener diodes 44A. From the connection point between the two Zener diodes 44A, the power supply for the logic unit 50 (e.g. 5 V for a microcontroller) can be extracted and, in order to ensure that the logic unit 50 is continuously provided with electrical energy, the capacitor 201 can also be provided in parallel connection to the two consecutive Zener diodes 44A, 44B.

[0038] The capacitor 201 is charged only during operation of the bumper.

[0039] However, the logic unit 50 is continuously provided with electrical energy. In order to ensure that no consequences result from a breakdown of the power supply, the logic unit 50 may have a so-called Brown-out-Detector (BOD) monitoring the input electrical power. As soon as a power failure (voltage drop) on the input side of the logic unit 50 is detected, the logic unit 50 can be kept in a reset state in order to avoid any undefined output.

[0040] In addition to the capacitor 201, which shall ensure a stable power supply of the logic unit 50, it may be advantageous to regularly, or on demand, power up the driver while no LED load 40 is connected to ensure an auxiliary power supply to be continuous. For such an arrangement, the switch 45A may allow a third position disconnecting both of the LED strings 42, 43. This is particularly useful in cases where the auxiliary power supply shall also power other auxiliary devices including sensor devices.

Examples

Embodiment Construction

[0009]Aspects of the present invention are described herein in the context of a LED driver.

[0010]Fig. 1 shows a luminaire 1 comprising a system comprising a LED driver 3 and a LED load 40 according to the invention.

[0011]The LED driver 3 comprises output terminals 41a, 41b for supplying the LED load 40.

[0012]In addition thereto, the luminaire 1 comprises DC voltage output terminals 5, 6 for supplying a DC voltage to supply a logic unit 50, e.g. microcontroller or a sensor etc., and a DC voltage generation circuit 44 connected to the DC voltage output terminals 5, 6.

[0013]The DC voltage generation circuit 44 is arranged in parallel to the output terminals for supplying the LED load 41a, 41b and comprises at least one Zener diode 44A (see also Fig. 2 and 3).

[0014]Besides the LED driver 3, the luminaire 1 can comprise within its housing the logic unit 50 (e.g. microcontroller or sensor) external to the LED driver 3, and supplied off the DC voltage output terminals 5,6 of the DC voltage...

Claims

1. A system comprising: - a logic unit (50), - a LED load (40), - a LED driver (3) comprising output terminals (41a, 41b) for supplying the LED load (40); and - a DC voltage generation circuit (44) external to the LED driver (3), supplied by the LED driver (3) and comprising: - DC voltage output terminals (5,6) for supplying a DC voltage to supply the logic unit (50), wherein the logic unit (5) is a microcontroller or sensor; wherein the system is characterized in that the DC voltage generation circuit (44) is configured to further comprise: - two Zener diodes (44A, 44B) connected in series with same polarity, and one of the DC voltage output terminals (5) is connected to a midpoint between the two Zener diodes (44A, 44B) , wherein the DC voltage supplied at the DC voltage output terminals (5,6) is tapped off across one of the Zener diodes (44A, 44B).

2. The system of claim 1, wherein the DC voltage generation circuit (44) comprises a capacitor (201) in parallel to the two Zener diodes (44A, 44B).

3. A luminaire (1), comprising a system according to claim 1.

4. The luminaire (1) of claim 3, comprising, as LED load (40), at least two LED strings in parallel (42, 43), each LED string of the at least two LED strings (42, 43) comprising more than one LED connected in series, and a switch (45A) for selectively activating one of said at least two LED strings (42, 43), wherein the switch (45A) is controlled by the logic unit , wherein the logic unit is external to the LED driver (3).

5. The luminaire (1) of claim 4, wherein the switch (45A) has a third state in which none of the LED strings (42, 43) is activated.

Images