LED lighting device and dimming control method therefor

An LED lighting device according to one embodiment of the present invention comprises: an LED array; a first control unit for controlling the dimming of the LED array; a second control unit for transmitting, to the first control unit, a dimming control signal for controlling the dimming of the LED array; and a transformer comprising a primary coil and a secondary coil spaced apart from each other, wherein the first control unit is connected to the primary coil, the second control unit is connected to the secondary coil, the primary coil and the secondary coil are insulated from each other, the transformer transmits a pulse signal that repeats on/off at predetermined intervals from the first control unit to the second control unit, and, when the pulse signal transmitted from the first control unit to the second control unit via the transformer becomes off, the dimming control signal is transmitted from the second control unit to the first control unit via the transformer and is used to control the dimming of the LED array.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a U.S. National Stage Application under 35 U.S.C. § 371 of PCT Application No. PCT/KR2018/007919, filed Jul. 12, 2018, which claims priority to Korean Patent Application No. 10-2017-0092798, filed Jul. 21, 2017, whose entire disclosures are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a light emitting diode (LED) lighting device, and more specifically, to a dimming control method of an LED lighting device.

BACKGROUND ART

A fluorescent lamp, an incandescent lamp, a light emitting diode (LED), and the like are used as indoor and outdoor lighting devices. Among the above, the lighting device using the LED has low power consumption and is semi-permanent in comparison with the fluorescent lamp.

FIG. 1is an example of a lighting system including an LED lighting device.

Referring toFIG. 1, an LED lighting device10receives power from a power source20and includes an LED array12and a dimming circuit14.

A plurality of LED lighting devices10can be controlled by one dimmer30.

In this case, when a failure occurs due to an overvoltage such as a short circuit or surge to one of the plurality of LED lighting devices10, the failure is spread to the dimmer30through DIM+ and DIM− wires. Accordingly, since the failure is spread to other LED lighting devices10which stably operate, secondary damage can occur.

Accordingly, there is an attempt to use a dimming circuit having an isolation structure. The dimming circuit having the isolation structure includes an isolation transformer which isolates a primary coil of an LED array and a secondary coil of a dimmer, and accordingly, the failure which occurs from the one LED lighting device may not be spread to other LED lighting devices.

Meanwhile, a dimming circuit having a general isolation structure uses a plurality of semiconductor elements, and thus has high circuit complexity, and it is difficult to accurately control dimming thereof. Further, since large inductance is demanded and thus the size of an isolation transformer increases, cost efficiency and space efficiency are low.

DISCLOSURE

Technical Problem

The present invention is directed to providing a light emitting diode (LED) lighting device including an isolation transformer, and a dimming control method thereof.

Technical Solution

One aspect of the present invention provides a light emitting diode (LED) lighting device including an LED array; a first control unit configured to control dimming of the LED array; a second control unit configured to transmit a dimming control signal, which controls the dimming of the LED array, to the first control unit; and a transformer including a primary coil and a secondary coil spaced apart from each other, wherein the first control unit is connected to the primary coil and the second control unit is connected to the secondary coil, the primary coil and the secondary coil are isolated from each other, the transformer transmits a pulse signal, which is repeatedly turned on and turned off at a predetermined interval, from the first control unit to the second control unit, the dimming control signal is transmitted from the second control unit to the first control unit through the transformer when the pulse signal transmitted from the first control unit to the second control unit through the transformer is turned off, and the first control unit rectifies the dimming control signal which is an alternating current signal transmitted from the second control unit to the first control unit through the transformer to a direct current signal and then controls the dimming of the LED array using a value in which an offset voltage is cancelled.

The first control unit may include a rectifier, which includes a diode configured to rectify the dimming control signal and a capacitor connected between the diode and a direct current power source, and an offset voltage cancellation part configured to cancel the offset voltage from a signal output from the rectifier, and the offset voltage may include a voltage value of the direct current power source.

The offset voltage cancellation part may cancel the offset voltage using voltage distribution.

The offset voltage cancellation part may include a plurality of resistors connected in series between the rectifier and the LED array, and a Zener diode or shunt regulator connected to one of the plurality of resistors in parallel.

The dimming control signal may be a signal in which a predetermined correction voltage is added to a voltage output from a dimmer.

The correction voltage may be generated by the plurality of resistors connected in series to the dimmer and the Zener diode or shunt regulator connected to the one of the plurality of resistors in parallel.

The offset voltage may further include the correction voltage.

Another aspect of the present invention provides a dimming control method of a light emitting diode (LED) lighting device including: generating a pulse signal, which is repeatedly turned on and turned off at a predetermined interval, in a first control unit including an LED array; transmitting the pulse signal generated in the first control unit to a second control unit including a dimmer through a transformer; transmitting, by the second control unit, a dimming control signal which controls the LED array to the first control unit through the transformer when the pulse signal of the first control unit transmitted through the transformer is turned off; rectifying, by the first control unit, the dimming control signal, which is an alternating current signal transmitted through the transformer, to a direct current signal; cancelling, by the first control unit, an offset voltage from the rectified signal; and controlling, by the first control unit, dimming of the LED array using a signal from which the offset voltage is cancelled.

A voltage of the signal from which the offset voltage is cancelled may be the same as a voltage output from the dimmer.

Advantageous Effects

According to an embodiment of the present invention, a simple structure can be realized, and a dimming circuit having high accuracy and isolation can be obtained using a small number of switching elements. Accordingly, dimming of a light emitting diode (LED) lighting device is easy and production costs of the LED lighting device can be reduced. Further, according to the embodiment of the present invention, since accuracy of dimming is not largely influenced by an inductance value of a transformer, the inductance value can be designed to be low, and a transformer having a small size can be used.

MODES OF THE INVENTION

Hereinafter, preferable embodiments of the present invention will be described in detail with reference to the accompanying drawings.

However, the technical spirit of the present invention is not limited to some embodiments which will be described and may be embodied in various forms, and one or more elements in the embodiments may be selectively combined and replaced to be used within the scope of the technical spirit of the present invention.

Further, terms used in the embodiments of the present invention (including technical and scientific terms), may be interpreted with meanings that are generally understood by those skilled in the art unless particularly defined and described, and terms which are generally used, such as terms defined in a dictionary, may be understood in consideration of their contextual meanings in the related art.

In addition, terms used in the description are provided not to limit the present invention but to describe the embodiments.

In the specification, the singular form may also include the plural form unless the context clearly indicates otherwise and may include one or more of all possible combinations of A, B, and C when disclosed as at least one (or one or more) of “A, B, and C”.

In addition, terms such as first, second, A, B, (a), (b), and the like may be used to describe elements of the embodiments of the present invention.

The terms are only provided to distinguish the elements from other elements, and the essence, sequence, order, or the like of the elements are not limited by the terms.

Further, when particular elements are disclosed as being “connected,” “coupled,” or “linked” to other elements, the elements may include not only a case of being directly connected, coupled, or linked to other elements but also a case of being connected, coupled, or linked to other elements by elements between the elements and other elements.

In addition, when one element is disclosed as being formed “on or under” another element, the term “on or under” includes both a case in which the two elements are in direct contact with each other and a case in which at least another element is disposed between the two elements (indirectly). Further, when the term “on or under” is expressed, a meaning of not only an upward direction but also a downward direction may be included with respect to one element.

FIG. 2illustrates a lighting system including a light emitting diode (LED) lighting device according to one embodiment of the present invention.

Referring toFIG. 2, an LED lighting device100receives power from a power source200and includes an LED array120and a dimming circuit140.

A plurality of LED lighting devices100may be controlled by one dimmer300.

In this case, the dimming circuit140is an isolation dimming circuit including a transformer which isolates a primary coil in the LED array120and a secondary coil in the dimmer300. Accordingly, even when a failure occurs due to an overvoltage such as a short circuit or surge to one of the plurality of LED lighting devices100, a problem that the failure is spread to the dimmer300or is spread to another LED lighting device10adjacent to the one LED lighting device may be prevented.

FIG. 3is a block diagram of the lighting system in the LED lighting device according to one embodiment of the present invention, andFIG. 4is a flow chart illustrating a dimming control method of the lighting system in the LED lighting device according to one embodiment of the present invention.

Referring toFIG. 3, the dimming circuit140includes a first control unit142, a second control unit144, and a transformer146.

The first control unit142is connected to the LED array120and controls dimming of the LED array120. The second control unit144is connected to the dimmer300and receives a dimming control signal for controlling the LED array120from the dimmer300and then transmits the dimming control signal to the first control unit142. Further, the transformer146includes a primary coil T1and a secondary coil T2spaced apart from each other, and the primary coil T1may be connected to the first control unit142and the secondary coil T2may be connected to the second control unit144. In addition, in the transformer146according to the embodiment of the present invention, the primary coil T1and the secondary coil T2may be isolated. Accordingly, in the specification, the transformer146may be used together with the isolation transformer146. Further, the transformer146may have a turn ratio of 1 to 1 between the primary coil T1and the secondary coil T2and operate in a flyback manner.

More specifically, referring toFIGS. 3 and 4, the first control unit142may include a pulse generator1422, a signal rectifier1424, and an offset voltage cancellation part1426, and the second control unit144may be used together with a signal processor.

The pulse generator1422of the first control unit142generates a pulse signal, which is repeatedly turned on and turned off at a predetermined interval (S400), and transmits the generated pulse signal to the second control unit144through the transformer146(S410). In this case, the pulse signal may be a pulse width modulation (PWM) signal and may be a signal having a predetermined duty ratio with respect to a voltage value of direct current power input to the first control unit142, for example, a duty ratio of 30%.

When the pulse signal transmitted from the first control unit142to the second control unit144through the transformer146is turned off, the second control unit144transmits the dimming control signal for controlling the LED array120to the first control unit142through the transformer146(S420). Here, the dimming control signal may have a value output from the dimmer300to control brightness of the LED array120and have a value set by a user or a value automatically set according to ambient light. For example, the dimming control signal may have a value of 0 to 10 V, or 1 to 10 V, and accordingly, the LED array120becomes brighter when the value increases, and the LED array120becomes darker when the value decreases. Alternatively, the dimming control signal may be a signal in which a predetermined correction voltage is added to the voltage output from the dimmer300. The predetermined correction voltage may be a value added so that the dimming control signal is processed to be readable in the first control unit142or so that the voltage output from the dimmer300maintains a stable value.

The dimming control signal transmitted from the second control unit144to the first control unit142through the transformer146may be an alternating current signal. Accordingly, the first control unit142rectifies the dimming control signal which is the alternating current signal to a direct current signal (S430). To this end, the signal rectifier1424may include a diode and a capacitor, and the dimming control signal transmitted from the second control unit144may be rectified to the direct current signal through the diode and then stored in the capacitor. In this case, one end of the capacitor may be connected to the direct current power source, and accordingly, a value output from the signal rectifier1424may be a value in which a voltage value of the direct current power is added to the dimming control signal transmitted from the second control unit144.

Further, the offset voltage cancellation part1426of the first control unit142cancels an offset voltage from a signal rectified by the signal rectifier1424of the first control unit142(S440) and then controls the dimming of the LED array120(S450). The offset voltage may refer to a value added to the voltage output from the dimmer300to control the dimming of the LED array120. For example, the offset voltage may include the voltage value of the direct current power added in the signal rectifier1424. Alternatively, the offset voltage may further include the correction voltage added to the voltage output from the dimmer300in the second control unit144. Accordingly, a voltage of the signal from which the offset voltage is cancelled may be the same as the voltage output from the dimmer300.

Although not shown, a main control unit (MCU) may be further disposed between the offset voltage cancellation part1426and the LED array120. When the offset voltage is cancelled, the dimming control signal may be converted to a value which is the same as a value of the voltage output from the dimmer300, that is, a value readable by the MCU.

Hereinafter, it will be described more specifically with reference to a circuit diagram.

FIG. 5illustrates a circuit diagram of a dimming circuit in the LED lighting device according to one embodiment of the present invention.

Referring toFIG. 5, the dimming circuit140includes the first control unit142, the second control unit144, and the transformer146.

The first control unit142is connected to the LED array120and controls the dimming of the LED array120. The second control unit144is connected to the dimmer300and receives the dimming control signal for controlling the LED array120from the dimmer300and then transmits the dimming control signal to the first control unit142. Here, it is shown and described that the first control unit142and the LED array120are separate configurations and the first control unit142is connected to the LED array120, but the present invention is not limited thereto. The first control unit142may be included in the LED array120or the LED array may be included in the first control unit142. As described above, it is shown and described that the second control unit144and the dimmer300are separate configurations and the second control unit144is connected to the dimmer300, but the present invention is not limited thereto. The second control unit144may be included in the dimmer300or the dimmer300may be included in the second control unit144. Further, the transformer146includes the primary coil T1connected to the first control unit142and the secondary coil T2connected to the second control unit144, and the primary coil T1and the secondary coil T2are isolated. Here, the transformer146may have a turn ratio of 1 to 1 between the primary coil T1and the secondary coil T2and operate in the flyback manner.

More specifically, the first control unit142may include the pulse generator1422, the signal rectifier1424, and the offset voltage cancellation part1426, and the second control unit144may be used together with the signal processor.

The pulse generator1422of the first control unit142generates a pulse signal which is repeatedly turned on and turned off at a predetermined interval. The pulse generator1422includes a transistor Q1, for example, a field effect transistor (FET), and the pulse signal may be applied to a gate electrode of the transistor Q1. Further, a drain electrode of the transistor Q1may be connected to the primary coil T1of the transformer146.

Accordingly, the pulse signal generated from the pulse generator1422is transmitted to the second control unit144through the transformer146. In this case, the pulse signal may have a predetermined duty ratio with respect to a Volts Direct Current (VDC) which is a voltage value of the direct current power input to the first control unit142. For example, when VDC is 12 V and the duty ratio is 30%, a pulse signal of which the duty ratio of 12 V is 30% is ordinarily applied to a P1 node of the second control unit144.

Meanwhile, when the dimmer300outputs a voltage value for controlling the dimming of the LED array120, the second control unit144, that is, a signal processor, receives the dimming control signal from the dimmer300through a DIM+ line and a DIM− line. Here, the dimming control signal has a value output from the dimmer300to control the brightness of the LED array120, and may have a value set by the user or a value automatically set according to the ambient light. For example, the dimming control signal may have a value of 0 to 10 V or 1 to 10 V, and accordingly, the LED array120becomes brighter when the value increases, and the LED array120becomes darker when the value decreases. In order to obtain a constant voltage, a Zener diode ZD1may be connected between the DIM+ line and the DIM− line

In this case, the second control unit144may add a predetermined correction voltage to the voltage output from the dimmer300. The predetermined correction voltage may be a value added so that the dimming control signal is processed to be readable in the first control unit142, or the voltage output from the dimmer300maintains a stable value. The correction voltage may be added by voltage distribution. To this end, the second control unit144may include two resistors R5and R6connected in series to the DIM−, a shunt regulator U2or Zener diode connected to the resistor R5in parallel, and a capacitor C4connected to the resistor R5in parallel. A level of the correction voltage may be controlled according to a resistance ratio between the two resistors R5and R6, and a stable value may be maintained according to the shunt regulator or Zener diode.

Although the pulse signal transmitted from the first control unit142is ordinarily applied to the P1 node, when the voltage value for controlling the dimming of the LED array120is output from the dimmer300, the dimming control signal is applied to the P1 node. Further, when the pulse signal transmitted from the first control unit142is turned off, the value applied to the P1 node is applied to the first control unit142through the transformer146using the flyback manner. Accordingly, the dimming control signal transmitted from the second control unit144may be reflected to a P3 node of the first control unit142.FIG. 6illustrates an example of dimming control information transmitted to the P3 node. InFIG. 6, an example in which the value of the voltage output from the dimmer300has a value of 1 V and a value of 10 V is described.

Further, the dimming control signal reflected to the P3 node is rectified by the signal rectifier1424of the first control unit142. To this end, the signal rectifier1424may include a diode D1and a capacitor C1. One end of the diode may be connected to the P3 node, and the other end may be connected to the P2 node. Further, one end of the capacitor C1may be connected to VDC which is the direct current power, and the other end of the capacitor C1may be connected to the P2 node. Accordingly, the dimming control signal which is an alternating current signal reflected to the P3 node is rectified to the direct current signal through the diode D1and then stored in the capacitor C1. Accordingly, a value in which the voltage value of the direct current power (VDC) is added to the dimming control signal reflected to the P3 node may be applied to the P2 node. To this end, the signal rectifier1424may include some components of a snubber circuit. The snubber circuit is a circuit which serves to cut spikes due to a cap component of the pulse signal and may be used to detect a level of the dimming control signal.

Further, the offset voltage cancellation part1426of the first control unit142cancels the offset voltage from a voltage applied to the P2 node and then controls the dimming of the LED array120. The offset voltage may be a value added to the value of the voltage output from the dimmer300. For example, the offset voltage may include the voltage value of the direct current power added in the signal rectifier1424. The offset voltage may further include a predetermined correction voltage added in the second control unit144.

The offset voltage cancellation part1426may cancel the offset voltage using the voltage distribution. To this end, the offset voltage cancellation part1426may include two resistors R1and R2which are connected in series, a shunt regulator U1, and a capacitor2, one end of the resistor R1may be connected to the P2 node, the other end of the resistor R1may be connected to the other resistor R2, and the capacitor2and the shunt regulator U1may be connected to the resistor R2in parallel. Accordingly, the offset voltage may be cancelled from the voltage applied to the P2 node, and a value actually output from the dimmer300may be applied for the dimming of the LED array120.

According to the embodiment of the present invention, since the dimming circuit includes the isolation transformer, although a failure occurs in one LED lighting device in the lighting system including the plurality of LED lighting devices, the failure may not be spread to other LED lighting device or the dimmer.

Further, according to the embodiment of the present invention, the pulse signal of the first control unit is transmitted to the second control unit, and the dimming control signal of the second control unit is transmitted to the first control unit in the flyback manner, and then a rectifying process and an offset voltage cancelling process are performed, and thus accurate dimming control may be performed using a simple circuit structure.

Although preferable embodiments of the present invention are described above, those skilled in the art may variously modify and change the present invention within the scope of the spirit and the area of the present invention disclosed in the claims which will be described later.