KR102543092B1 - Led drive circuit for parallel operation - Google Patents

Abstract

The present invention relates to an LED driving circuit for parallel operation capable of stably performing constant current control of a plurality of LED strings in an LED (Light Emitting Diode) lighting device. a constant current converter that receives the supply and outputs an output voltage (Vout+); a voltage compensation setting unit connected to an output terminal and a first terminal of the constant current converter to adjust an output voltage (Vout+) output from the constant current converter; a first LED string to which a second terminal of the voltage compensation setting unit and an anode are connected; a first current detector having a first end connected to a cathode of an LED provided at an end of the first LED string, detecting a first measurement current flowing at an end of the first LED string, and feeding back the first measurement current to the constant current converter; a first current limiting unit connected to an output terminal of the constant current converter and a first terminal, and connected in parallel with the voltage compensation setting unit to limit a second current value supplied to a second LED string; a second LED string connected in series with the second terminal (output terminal) of the first current limiting unit; The cathode and the first end of the LED provided at the end of the second LED string are connected, and the second end is connected to the contact point to which the first current detector and the first LED string are connected to receive the first measurement current. a second current detection unit having an output terminal connected to the first current limiting unit and feeding back a second measurement current flowing at an end of the second LED string to the first current limiting unit; and a first smoothing unit having a first end connected in parallel to a contact point to which the first current limiting unit and the second LED string are connected, and a second end connected to a ground power source to smooth an output of the first current limiting unit. includes

Description

LED drive circuit for parallel operation {LED DRIVE CIRCUIT FOR PARALLEL OPERATION}

The present invention relates to an LED driving circuit, and more particularly, to a plurality of LED strings that can stably perform constant current control of a plurality of LED strings in an LED (Light Emitting Diode) lighting device. It relates to an LED driving circuit for parallel operation.

Recently, LED lighting devices have been widely used to replace conventional light sources indoors and outdoors due to their miniaturization, long lifespan, and high efficiency compared to conventional light sources such as incandescent lamps and fluorescent lamps.

This LED lighting device is configured by connecting many LEDs in series and parallel. When the LEDs are connected in parallel, power consumption is not evenly distributed to all LEDs due to the driving voltage deviation of each LED, resulting in reduced efficiency and increased power consumption in a specific LED. This may cause failure or shorten life span.

1 is a view showing a device for emitting light of a plurality of LED groups (LS1, LS2, ..., LSN) controlled by a single converter 1 in the related art. As shown in FIG. 1, hundreds of LEDs are connected in series/parallel structure to form the LED array unit 2, and one sensing resistor (Rsence) 4 included in the control unit 3 constitutes the LED array unit ( The current of 2) is detected and feedback is given to the first block of the converter 1 to adjust the amount of power delivered to the second block.

However, this method causes a large difference in current flowing through each LED due to the deviation of the forward voltage (Vf) of each LED. there is a problem.

In addition, when LED groups are connected in parallel, power consumption is not evenly distributed to all LEDs due to forward voltage deviation of each LED, resulting in reduced efficiency and increased power consumption in a specific LED, which causes failure and shortened lifespan.

In order to solve this problem, according to Patent Document 1, a constant current circuit is used in each LED group to prevent the biasing of power consumption due to the deviation of the LED forward voltage (Vf), but this method has the highest current among LED groups connected in parallel. There is a problem in that the constant current control is performed based on the flowing LED group, so that the current of the same magnitude cannot flow through all the LEDs connected in series.

In addition, according to Patent Document 1, each LED group is equipped with a converter one by one to promote high reliability and high energy efficiency. Due to the increase in the number of circuit elements, the cost is high and the size is large, making it difficult to apply to LED lighting.

Republic of Korea Patent Registration No. 10-1916162, registration date 2018.11.01.

In order to solve the above problems, the present invention provides an LED driving circuit for parallel operation capable of performing constant current control so that the same current flows in each of a plurality of LED strings connected in parallel through a single converter. There is a purpose.

In addition, the present invention ensures that all LEDs are driven at rated current through a current limiting circuit, thereby preventing efficiency degradation, failure, and shortening of life due to forward voltage deviation of LEDs constituting each LED string when connected in parallel, and high reliability and high Another object is to provide an LED driving circuit for parallel operation that can promote light efficiency.

In order to achieve the above object, in the LED driving circuit for parallel operation according to an embodiment of the present invention, a constant current converter for receiving an AC power supply (Vcc) and outputting an output voltage (Vout+); a voltage compensation setting unit connected to an output terminal and a first terminal of the constant current converter to adjust an output voltage (Vout+) output from the constant current converter; a first LED string to which a second terminal of the voltage compensation setting unit and an anode are connected; a first current detector having a first end connected to a cathode of an LED provided at an end of the first LED string, detecting a first measurement current flowing at an end of the first LED string, and feeding back the first measurement current to the constant current converter; a first current limiting unit connected to an output terminal of the constant current converter and a first terminal, and connected in parallel with the voltage compensation setting unit to limit a second current value supplied to a second LED string; a second LED string connected in series with the second terminal (output terminal) of the first current limiting unit; The cathode and the first end of the LED provided at the end of the second LED string are connected, and the second end is connected to the contact point to which the first current detector and the first LED string are connected to receive the first measurement current. a second current detection unit having an output terminal connected to the first current limiting unit and feeding back a second measurement current flowing at an end of the second LED string to the first current limiting unit; and a first smoothing unit having a first end connected in parallel to a contact point to which the first current limiting unit and the second LED string are connected, and a second end connected to a ground power source to smooth an output of the first current limiting unit. The constant current converter further includes a constant current controller controlling an output voltage of the constant current converter according to a first measurement current fed back from the first current detector, wherein the first current limiter further includes a second measuring current fed back to the first current limiter. It is characterized in that current limiting is performed so that the second current value is equal to the first current value according to the current.

The constant current controller may include first and second voltage dividing resistors R1 and R2 configured to set the reference current value Iref; a resistor R3 having a first terminal connected to the first terminal of the first voltage dividing resistor R1 and a second terminal connected to an anode of an optocoupler; and an optocoupler having a cathode connected to an output terminal of the first current detection unit, wherein the first current detection unit has a first terminal connected to a cathode provided at an end of the first LED string, and a second a first sensing resistor (Rs1) having a terminal connected to the other output terminal of the constant current converter and measuring a first measurement current flowing at an end of the first LED string; and an inverting terminal (-) is connected to a contact point where the cathode of the first LED string and the first terminal of the sensing resistor Rs1 are connected, and a non-inverting terminal (+) is connected to the second terminal of the first voltage dividing resistor R1. The first measurement current flowing at the end of the first LED string measured through the sensing resistor Rs1 connected to the contact point to which the terminal and the first terminal of the second voltage dividing resistor R2 are connected and a preset reference current value (Iref It is characterized in that it is configured to include; a first comparator (OP-AMP1) for comparing ).

The first comparator has an output terminal connected to the cathode of the optocoupler, compares the first measurement current with a preset reference current value (Iref), and feeds back the outputted current to the constant current controller, and the constant current controller feeds back the feedback When the first measured current is greater than the predetermined reference current value (Iref), the optocoupler is conducted and controlled to lower the output voltage (Vout+) output from the constant current converter.

The voltage compensation setting unit is a resistor (R _Vout+ ) or a diode for adjusting the value of the output voltage (Vout+), and a first terminal of the resistor (R _Vout+ ) or diode is connected to an output terminal of the constant current converter, and a second terminal is connected to the output terminal of the constant current converter. Is characterized in that connected to the anode of the LED provided at the top of the first LED string.

The first current limiting unit has a first terminal connected to a contact connecting the output terminal of the constant current converter and a first terminal of the voltage compensation setting unit and a drain D of a field effect transistor, and a second terminal connected to a gate of the field effect transistor. a first current limiting resistor (R11) connected to the terminal; A second current limiting resistor having a first end connected to a junction where the second end of the first current limiting resistor R11 and the gate of the field effect transistor are connected, and having an output end of the second current limiting unit and a second end connected thereto ( R21); and a contact to which the first terminal of the first current limiting resistor R11 is connected to the drain, the first terminal of the first smoothing unit is connected to the source, and the first and second current limiting resistors R11 and R21 are connected. It is characterized in that it includes; a first field effect transistor (FET, Q1) to which a gate is connected.

The second current detector has a first end connected to the cathode of the LED provided at the end of the second LED string, and a second end connected to the other output end of the constant current converter, and flowing at the end of the second LED string. a second sensing resistor (Rs2) for measuring a second measurement current; And a second terminal and an output terminal of the first current limiting resistor (R21) are connected, and a non-inverting terminal (+) is connected to a contact point to which the cathode of the second LED string and the second sensing resistor (Rs2) are connected. and a second comparator (OP-AMP2) having an inverted terminal (-) connected to a contact point to which the cathode of the first LED string and the first terminal of the first sensing resistor (Rs1) are connected. A current that is output by comparing a second measurement current with the first measurement current is fed back to the first current limiting unit, and when the second measurement current fed back by the first current limiting unit is greater than the first measurement current, the first measurement current It is characterized in that the voltage applied to the gate of the first field effect transistor is adjusted so that the second current value supplied to the second LED string is controlled to perform current limiting with the first current value.

Each of the first and second LED strings has a plurality of light emitting diodes (LEDs) connected in series, and the first current limiting unit, the second LED string, the first smoothing unit, and the second current detecting unit It is connected as one unit, and the unit is characterized in that it is provided with a plurality and connected in parallel.

The constant current converter further includes a dimming voltage setting unit for adjusting the dimming of the LED string, and the constant current control unit has an input terminal and a first terminal connected to an AC power supply, and an anode and a second terminal of an optocoupler. A resistor (R3) to which the terminal is connected; and an optocoupler to which an output terminal of the first current detection unit and a cathode are connected, wherein the first current detection unit has a first terminal connected to a cathode provided at an end of the first LED string, and a second a first sensing resistor (Rs1) having a terminal connected to the other output terminal of the constant current converter and measuring a first measurement current flowing at an end of the first LED string; And an inverting terminal (-) is connected to the contact point to which the cathode of the first LED string and the first terminal of the sensing resistor (Rs1) are connected, and a non-inverting terminal (+) is connected to the output terminal of the dimming voltage setting unit to perform the sensing and a first comparator (OP-AMP1) that compares the first measurement current flowing at the end of the first LED string measured through the resistor (Rs1) and the output voltage of the dimming voltage setting unit. .

In addition, in the LED driving circuit for parallel operation according to another embodiment of the present invention, a constant voltage converter for receiving AC power and outputting DC power; n (n is a natural number equal to or greater than 2) current limiting units connected to the output terminal (Vout+) of the constant voltage converter and performing current limiting of the DC power supply; n smoothing units for smoothing outputs of each of the n current limiting units; n LED strings having an anode connected to a contact point where the current limiting unit and the smoothing unit are connected, and turned on by a voltage output from each of the n smoothing units; and connected to cathodes of LEDs provided at ends of each of the n LED strings, detecting an output voltage at an end of the LED string, and comparing the detected output voltage with a preset reference voltage (Vref) to limit the n currents. n current detectors that feed back to the negative; one current limiter, one smoother, one LED string, and one current detector are connected as one unit unit, and a plurality of the unit units are provided in parallel The constant voltage converter further includes first and second voltage dividing resistors R1 and R2 for setting a reference voltage Vref, and each of the n current limiting units is connected to an output terminal of a current detection unit connected as a unit. It is connected in series and limits the current output to the LED string according to the voltage fed back through the output terminal of the current detector.

Each of the n current limiting units includes first and second current limiting resistors R1n and R2n, a zener diode Dzn, and field effect transistors FET and Qn, and the first current limiting resistor R1n A first terminal is connected to the output terminal of the constant voltage converter, the cathode of the zener diode (Dzn) and the drain (D) of the field effect transistor (FET, Qn) to form a contact, and the anode of the zener diode (Dzn) And a gate and a second terminal of the field effect transistor (FET, Qn) are connected to form a contact, and the second current limiting resistor (R2n) is the second terminal of the first current limiting resistor (R1n), the zener. A first terminal is connected to a contact to which the anode of the diode (Dzn) and the gate of the field effect transistor (FET, Qn) are connected, and an output terminal of the current detector and a second terminal are connected to the current flowing to the zener diode (Dzn) , and the field effect transistor (FET, Qn) has a source connected in series to the anode of the upper LED of the LED string, and the first end of the smoothing part is connected to the contact point where the anode of the LED string and the source are connected , The first current limiting resistor (R1n), the zener diode (Dzn), and the field effect transistors (FET, Qn) are connected in parallel.

Each of the n smoothing units is connected between the output terminal of each of the n current limiting units and the ground, and is composed of a capacitor (C). characterized by output.

Each of the n current detectors includes a sensing resistor (Rsn) and a comparator (OP-AMP), and a first end of the sensing resistor (Rs) is connected to a cathode provided at an end of the LED string. The second terminal is connected to the other output terminal of the constant current converter and connected in series with the LED string, the voltage applied to the first terminal is measured and inputted to the non-inverting terminal (+) of the comparator, and the comparator (OP -AMP) has a non-inverting terminal (+) connected to a contact point where the cathode of the LED provided at the end of the LED string and the first end of the sensing resistor (Rs) are connected, and An inverting terminal (-) is connected to a contact to which the second stage and the first stage of the second voltage dividing resistor R2 are connected, and the voltage across the first stage measured through the sensing resistor Rsn and the preset reference voltage ( Vref) and outputting the comparison result to the second current limiting resistor R2n.

According to the present invention, by performing constant current control for a plurality of LED strings connected in parallel through a single converter, there is an effect that miniaturization and low-cost product manufacturing is possible.

In addition, according to the present invention, there is an effect capable of providing a constant current circuit type LED driving circuit with further improved efficiency by maintaining a constant current flowing through each LED string through a current limiting circuit.

In addition, according to the present invention, by allowing the same current to flow through each of a plurality of LED strings connected in parallel, all LEDs perform the same energy conversion operation, enabling high light efficiency and dispersing the stress of the LEDs to improve reliability, reduce failure, and extend life This is a possible effect.

1 is a circuit diagram showing an LED driving circuit according to the prior art.
2 is a circuit diagram schematically illustrating an LED driving circuit for parallel operation according to an embodiment of the present invention.
FIG. 3 is a circuit diagram showing a first embodiment of an LED driving circuit for parallel operation shown in FIG. 2 .
FIG. 4 is a circuit diagram showing a second embodiment of an LED driving circuit for parallel operation shown in FIG. 2 .
5 is a circuit diagram schematically showing an LED driving circuit for parallel operation according to another embodiment of the present invention.
FIG. 6 is a circuit diagram showing a first embodiment of an LED driving circuit for parallel operation shown in FIG. 5 .

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. At this time, the same components in each drawing are represented by the same reference numerals as possible. In addition, detailed descriptions of already known functions and/or configurations will be omitted. In the following description, parts necessary for understanding operations according to various embodiments will be mainly described, and descriptions of elements that may obscure the gist of the description will be omitted. In addition, some components in the drawings may be exaggerated, omitted, or schematically illustrated. The size of each component does not entirely reflect the actual size, and therefore, the contents described herein are not limited by the relative size or spacing of the components drawn in each drawing.

In describing the embodiments of the present invention, if it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of a user or operator. Therefore, the definition should be made based on the contents throughout this specification. Terms used in the detailed description are only for describing the embodiments of the present invention, and should not be limiting. Unless expressly used otherwise, singular forms of expression include plural forms. In this description, expressions such as "comprising" or "comprising" are intended to indicate any characteristic, number, step, operation, element, portion or combination thereof, one or more other than those described. It should not be construed to exclude the existence or possibility of any other feature, number, step, operation, element, part or combination thereof.

In addition, terms such as first and second may be used to describe various components, but the components are not limited by the terms, and the terms are used for the purpose of distinguishing one component from another. used only as

Hereinafter, an embodiment of the present invention will be described in more detail with reference to the accompanying drawings.

2 is a circuit diagram schematically showing an LED driving circuit for parallel operation according to an embodiment of the present invention.

As shown in FIG. 2, the LED driving circuit 100 for parallel operation according to an embodiment of the present invention includes a constant current converter 110, a voltage compensation setting unit 120, a first LED string LS1 to The Nth LED string 130, 131, 132, the first current detection unit to the Nth current detection unit 140, 141, 142, the first current limiting unit to the N−1th current limiting unit 150, 151, the first It includes smoothing units to N−1 th smoothing units 160 and 161 and a constant current control unit 170 . Here, N is set to a natural number of 2 or more, and through this, a circuit in which two or more LED strings are connected in parallel can be configured. And, the LED string means that a plurality of LEDs (LEDs, light emitting diodes) are connected in series to form one column.

First, the constant current converter 110 converts the supplied power (Vcc) into an output voltage (Vout+) required for driving the LED and outputs it. At this time, a rectifier circuit may be provided at the front end of the constant current converter 110 .

The constant current converter 110 includes a constant current controller 170 that controls the output voltage Vout+ output from the constant current converter 110 according to the current fed back through the first current detector 140 .

The constant current controller 170 includes first and second voltage dividing resistors R1 and R2 for setting the reference current Iref, an optocoupler 171 and a resistor R3.

The input terminal of the first current detector 140 is connected to the contact point to which the first and second voltage dividing resistors R1 and R2 are connected, and the first terminal of the first voltage dividing resistor R1 and the first terminal of the resistor R3 are connected. However, it forms a contact with the input terminal of the supply power (Vcc).

The second terminal of the resistor R3 is connected in series with the anode of the optocoupler 171 , and the cathode of the optocoupler 171 is connected to the output terminal of the first current detector 140 .

A circuit in which the voltage compensation setting unit 120, the first LED string LS1 130, and the first current detection unit 140 are connected in series is provided at the output terminal Vout+ of the constant current converter 110.

In this embodiment, the maximum current value flowing through the first LED string (LS1) 130 according to the values of the first and second voltage dividing resistors R1 and R2 of the constant current controller 170 in the constant current converter 110 is The constant current converter 110 performs a constant current operation according to the current determined and fed back from the first current detector 140 using the optocoupler 171 of the constant current controller 170 .

In addition, one current limiting unit, one smoothing unit, one LED string, and one current detection unit are connected to form one unit unit, and the input terminal of each current limiting unit of the plurality of unit units is a constant current converter 110 It is connected to the output terminal (Vout+) of and is connected in parallel.

At this time, the unit unit including the current limiting unit, the smoothing unit, the LED string, and the current detection unit is configured at the output terminal of the constant current converter 110 so that a current corresponding to the reference current Iref value flows in each of the second to N th LED strings. Except for the circuit consisting of the voltage compensation setting unit 120 for setting the value of the output voltage (Vout+), the first LED string 130 and the first current detection unit 140 (N-1) (N is 2 It consists of more than one natural number).

Specifically, the first terminal of the voltage compensation setting unit 120 is connected to the output terminal (Vout+) of the constant current converter 110, and the second terminal is the anode of the LED provided in the first LED string (LS1) 130 ( connected to the anode).

The voltage compensation setting unit 120 is an output output from the output terminal of the constant current converter 110 so that the current flowing through each of the plurality of (N) LED strings 130, 131, and 132 corresponds to the value of the reference current Iref. Set the voltage (Vout+) value.

For reference, since even LEDs manufactured on one wafer have different forward voltages (Vf), the Vf bins of the LEDs are set through a sorting process, and the LEDs are divided into groups. For example, the Vf distribution of LEDs coming out of one wafer appears as a normal distribution. If the reference voltage (Vref) is 2.8V, it comes out as 2.6V to 3V. It is sorted into ranks such as ~2.8V, 2.8V~2.9V, and 2.9V~3.0V. Therefore, when designing LED lighting, the range of forward voltage (Vf) values of the LED string can be calculated and configured according to the Vf bin of the LED to be used. Therefore, the total Vf of each of the plurality of LED strings connected in parallel is not completely equal and becomes larger or smaller.

In addition, in order for each circuit component to operate normally in the LED string where the sum of Vf of the LED string is the largest, it is more than (the sum of Vf of the corresponding LED string + the drop out voltage of the constant current controller + the drop out voltage of the current limiter) The output voltage (Vout+) must be the same or greater. For example, when the sum of Vf of the first LED string (reference string) is 100V at the reference current (Iref) and the sum of Vf of the other LED strings is 101V at the reference current (Iref), the constant current control unit and the current limiter fall ( drop out) Because the voltage is 1V short, the constant current control unit and the current limiting unit do not operate normally, so that the current of the corresponding LED string flows less than the reference current (Iref), and as a result, all the LED strings do not work equally.

Therefore, in the present invention, in consideration of this, the voltage compensation setting unit 120 is the LED corresponding to the case where the sum of the forward voltages (Vf) of each of the second to N th LED strings is greater than the sum of the forward voltages (Vf) of the first LED string. Voltage compensation is performed to increase the value of the output voltage (Vout+) output from the output terminal of the constant current converter 110 so that the current flowing in the string becomes the value of the reference current (Iref). Accordingly, the voltage compensation setting unit 120 may set the value of the output voltage Vout+ output from the output terminal of the constant current converter 110 .

For example, since the operation of the constant current control unit 170 is made so that the current flowing through each LED string flows to a predetermined value only when the drop out voltage at which the constant current control unit 170 operates is higher than the minimum operating voltage, the voltage compensation setting unit Step 120 adjusts the output voltage Vout+ of the constant current converter 110 so that a predetermined current flows through all the LED strings in consideration of the drop out voltage of the constant current controller 170 .

In other words, the forward voltage (Vf) of the first LED string, which is the standard for constant current driving, defines the largest value in which the sum of the forward voltages (Vf) of any LED string among the plurality of LED strings in the design is the largest. ) is small, the voltage compensation setting unit 120 is implemented to adjust the output voltage Vout+ of the constant current converter so that the current limiting unit of each LED string operates properly.

To this end, the voltage compensation setting unit 120 may be a resistor (R _Vout+ ) or a diode for adjusting the value of the output voltage (Vout+).

The N LED strings LS1, LS2, and LSN 130, 131, and 132 are connected in parallel, and each LED string has a circuit configuration in which a plurality of LEDs are connected in series.

The input end of the first current detector 140 is connected to the cathode of the LED provided at the end of the first LED string LS1 130, and the other input end is connected to the first and second voltage divider resistors R1 and R2 is connected to the connection contact of and the output terminal is connected to the cathode of the optocoupler.

The first current detector 140 measures the current flowing at the end of the first LED string LS1 (130) (hereinafter referred to as a first measurement current), and calculates the preset reference current value Iref and the first measurement current. It is used to control the switching of the optocoupler 171 of the constant current control unit 170.

Here, the first measurement current of the first LED string (LS1) 130 measured by the first current detector 140 is used to perform current limiting on the current flowing in the second to Nth LED strings. Current is applied to the detectors 141 and 142.

Through this configuration, the LED driving circuit 100 for parallel operation according to the present invention can perform a constant current operation so that the current flowing through all the LED strings is the same.

Each of the second to Nth current detectors 141 and 142 measures the value of the current flowing in the corresponding LED string (hereinafter, referred to as a measurement current), and measures the first LED string LS1 measured by the first current detector 140. ) Receives the first measurement current of 130, and outputs first to N-1th outputs to control the current flowing through each LED string using the first measurement current of the first LED string LS1 (130). It is transmitted to the current limiting units 150 and 151.

An output terminal of each of the first to N−1th current limiting units 150 and 151 is connected to the anode of each of the second to Nth LED strings 131 and 132, and a current detector connected to the cathode of the terminal LED of each LED string. A feedback signal is received from each to control the current flowing through the corresponding LED string, and accordingly, the current is limited so that the current flowing through the corresponding LED string is equal to the predetermined reference current value Iref.

In addition, in order to prevent flickering and floating according to ON-OFF of each of the first to N−1 th current limiting units 150 and 151, the output terminals of the first to N−1 th current limiting units 150 and 151 respectively It is configured to include smoothing units (C1, ..., CN-1) (160, 161).

The first to N-1th smoothing units (C1, ..., CN-1) (160, 161) are composed of smoothing capacitors (C), and the first terminal of each smoothing unit is the output terminal of the current limiting unit and the LED string. It is connected to the contact to which the anode is connected, and the second end is connected to the ground power supply.

Unlike conventional technologies that perform constant current driving by sensing the sum of currents flowing through all LED strings, the LED driving circuit according to an embodiment of the present invention uses a current value (first measurement current) flowing in the first LED string to obtain a constant current. The converter 310 performs constant current control.

That is, the LED driving circuit according to the present invention performs constant current control by performing current limiting so that the sensing resistor (RsN) connected to the end of the LED string does not exceed a certain current value using the current limiting circuit. Here, the constant current value is the first measurement current flowing through the first LED string, and current limiting is performed on the other LED strings using the first measurement current flowing through the first LED string, so that the current flowing through all the LED strings is first measured. Constant current control is performed to equal the current. As such, the constant current converter 110 performs control as if driving one series LED string load.

As such, the LED driving circuit for parallel operation according to an embodiment of the present invention operates as if the constant current converter controls one of the first LED strings, so that the second to Nth LED strings can be added or removed Plug & Play (Plug&Play) method.

That is, the constant current converter 110 according to the present invention can efficiently control only the necessary power even when an arbitrary LED string LSi (i is a natural number) is mounted or detached. For example, according to the conventional method, when four LED strings are connected in parallel and driven at 4A, an average current of 1A flows through one LED string. At this time, if one LED string is broken or detached due to poor contact, 4A still flows through the remaining three LED strings, so a current of 1.33A flows through each LED string, increasing the stress of the LED. failures easily occur.

However, in the LED driving circuit according to the present invention, the current limiting circuit is designed so that a current of 1A flows through one LED string, so that even when only two or three LED strings are mounted, the current of 1A is the same for each LED string. It can be electrically operated safely by controlling the flow.

FIG. 3 is a circuit diagram showing a first embodiment of an LED driving circuit for parallel operation shown in FIG. 2 . Here, the same reference numerals are used for components identical to those of the LED driving circuit of FIG. 2 , and overlapping descriptions of the same configurations will be omitted.

As shown in FIG. 3, the LED driving circuit 100 for parallel operation according to the first embodiment of the present invention includes a constant current converter 110, a voltage compensation setting unit 120, and a first to Nth LED string. LED string (130, 131, 132), the first current detection unit to the N-th current detection unit (140, 141, 142), the first current limiting unit to the N-1th current limiting unit (150, 151), the first smoothing unit to N-1th smoothing units 160 and 161 (where N is a natural number equal to or greater than 2).

The constant current converter 110 includes a constant current controller 170, and the constant current controller 170 includes first and second voltage divider resistors R1 and R2 for setting the reference current Iref, and an opto coupler. (171), and resistor R3.

A first terminal of the resistor R3 is connected to the input terminal of the supplied power supply Vcc, and a second terminal is connected to the anode of the optocoupler 171.

The cathode of the optocoupler 171 is connected to the output terminal of the first comparator (Op-amp1) of the first current detection unit 140, and the contact point to which the first and second voltage divider resistors R1 and R2 are connected is the first current detection unit. It is connected to the non-inverting terminal (+) of the first comparator (Op-amp1) of (140) and the reference current (Iref) measured at the first terminal of the second voltage dividing resistor (R2) is input.

A first terminal of the first voltage dividing resistor R1 is connected to the input terminal of the supplied power supply Vcc, and a second terminal of the second voltage dividing resistor R2 is connected to the ground power supply (ground).

The voltage compensation setting unit 120 is composed of a resistor (R _Vout+ ) or a diode for adjusting the value of the output voltage (Vout+), and the first terminal of the resistor (R _Vout+ ) or diode is the output terminal (Vout+) of the constant current converter 110. ) and the second end is connected to the anode of the LED provided at the top of the first LED string (LS1) 130, connected in series, and provided at the end of the first LED string (LS1) 130 The cathode is connected to the inverting terminal (-) of the first comparator (Op-amp1) of the first current detection unit (140).

For reference, in a conventional constant current converter, the output voltage (Vout+) of the output stage is made up of the sum of forward voltages (Vf) of each LED in the first LED string at a predetermined reference current value (Iref). The value of the forward voltage (Vf) of each LED at a specific current can be calculated from the graph of the characteristic curve of the LED. However, when the sum of Vf of the second LED string or the sum of Vf of the LED strings of subsequent stages is greater than the sum of Vf of the first LED string, the current flowing through the corresponding LED string is less than the reference current value Iref. Therefore, it is necessary to adjust the output voltage (Vout+) in order to have the same current flowing through the LEDs of all LED strings, strictly speaking, to have a constant current value within an allowable error range.

For this purpose, in the present invention, a circuit may be implemented to adjust the voltage of the voltage compensation setting unit 120 using a resistor (R _Vout+ ) or a diode.

The first current detector 140 includes a first comparator Op-amp1 and a first sensing resistor Rs1.

The inverting terminal (-) of the first comparator (Op-amp1) is connected to the cathode of the LED provided at the end of the first LED string (LS1) (130), and the non-inverting terminal (+) is connected to the first and second voltage dividing resistors (R1, R2) is connected to the connected contact, and the output terminal is connected to the cathode of the optocoupler 171 of the constant current controller 170.

As a result, the reference current (Iref) sensed from the first terminal of the second voltage dividing resistor (R2) is input through the non-inverting terminal (+) of the first comparator (Op-amp1), and the first LED string (LS1) (130) ), that is, the first measurement current measured from the first terminal of the first sensing resistor Rs1 is input through the inverting terminal (-).

The first comparator (Op-amp1) compares the reference current (Iref) and the first measurement current, transfers a feedback signal according to the comparison result to the optocoupler 171 of the constant current controller 170, and determines the reference current value (Iref) by reflecting and combining the feedback signal to the reference current (Iref), and the constant current controller 170 converts the input voltage (Vcc) to the required output voltage (Vout+) according to the determined reference current value (Iref) ) to control the output.

For example, the constant current control unit 170 controls the switching of the opto coupler 171 when the feedbacked first measurement current is greater than the reference current Iref, thereby increasing the output voltage Vout+ output to the first LED string. control to lower

The first terminal of the sensing resistor Rs1 is connected to the contact where the inverting terminal (-) of the first comparator Op-amp1 and the cathode of the first LED string LS1 are connected, and the second terminal is the constant current converter 110 It is connected to the other output terminal (Vout-) of or ground power.

This sensing resistor Rs1 is for measuring the terminal current of the first LED string LS1 130, and the current sensed at the first end of the sensing resistor Rs1 is passed through the first comparator Op-amp1. By feeding back to the constant current control unit 170, the output voltage (Vout+) of the constant current converter 110 is controlled, and through this, constant current control is possible so that the current flowing through the first LED string is constant.

The first current limiting unit 150 includes first and second current limiting resistors R11 and R21 and a transistor Q1.

A first terminal of the first current limiting resistor R11 is connected to the drain of the transistor Q1 and a second terminal is connected to the gate of the transistor Q1, respectively.

The first end of the second current limiting resistor R21 is connected to the contact point where the second end of the first current limiting resistor R11 and the gate of the transistor Q1 are connected, and the second end of the second current detection unit 141 2 It is connected to the output of the comparator (Op-amp2).

The source of the transistor Q1 is connected to the first terminal of the first smoothing unit 160 and is connected in parallel.

The first smoothing unit 160 is a capacitor C1, and the capacitor C1 smoothes the output voltage that has passed through the transistor Q1 into a DC voltage. A first terminal of the capacitor C1 is connected to the source terminal of the transistor Q1 and a second terminal is connected to the ground power supply. The first smoothing unit 160 is used to prevent flickering and floating due to ON-OFF of the transistor Q1 of the first current limiting unit 150 .

The second LED string (LS2) 131 is connected to a contact where the anode of the LED provided at the top is connected to the source terminal of the transistor Q1 and the first terminal of the capacitor C1 (160), and the LED provided at the end The cathode is connected to the non-inverting terminal (+) of the second comparator (Op-amp2) of the second current detection unit (141).

The second current detection unit 141 includes a second comparator (Op-amp2) and a second sensing resistor (Rs2) like the first current detection unit 140, but the output terminal of the second comparator (Op-amp2) is 1 It is connected to the second terminal of the resistor R21 of the current limiting unit 150 and the inverting terminal (-) of the second comparator (Op-amp2) is the LED provided at the end of the first LED string (LS1) (130). The cathode is connected to the contact point to which the first end of the first sensing resistor Rs1 is connected, and the non-inverting terminal (+) of the second comparator (Op-amp2) is provided at the end of the second LED string (LS2) (131) There is a difference in the configuration connected to the cathode.

The first comparator of the first current detection unit 140 and the second to Nth comparators of the second to Nth current detection units are input to input terminals in which the measured value (measured current) of the current flowing at the end of each LED string is opposite to each other do.

For example, the measurement current flowing at the end of the first LED string 130 is applied to the inverting terminal (-) of the first comparator Op-amp1 and to the end of the second to Nth LED strings 131 and 132. The measurement current is input to the non-inverting terminals (+) of the second to Nth comparators (Op-amp2 to Op-ampN), respectively, and the measurement current flowing at the end of the first LED string 130 is transferred to the second to Nth comparators. (Op-amp2 to Op-ampN) by inputting it to the inverted terminals (-), the first to N-1th current limiting units 150 and 151 have the same current value as the current flowing in the first LED string 130. It is possible to perform current limiting on the LED string.

And, in the present invention, the second to Nth comparators Op-amp2 to Op-ampN are the first measurement current flowing at the end of the first LED string and the second to Nth comparator flowing at the end of the second to Nth LED string. The N measured currents are compared, and if the second to Nth measured currents exceed the first measured current as a result of the comparison, the first to N−1th current limiting units 150 and 151 perform current limiting with the first measured current. It works.

As described above, according to the present invention, a technical feature is that constant current control is performed for other LED strings based on the first LED string.

In other words, the biggest technical feature of the present invention is that a reference current value for the first LED string is set, and constant current control for other LED strings is controlled through a current limiting circuit based on the reference current value.

Through this, since individual constant current control for each LED string is performed, an effect of stably operating the LED strings in parallel without affecting other LED strings occurs.

FIG. 4 is a circuit diagram showing a second embodiment of an LED driving circuit for parallel operation shown in FIG. 2 . Here, the same reference numerals are used for components identical to those of the LED driving circuits of FIGS. 2 and 3 , and overlapping descriptions of the same components will be omitted.

As shown in FIG. 4, the LED driving circuit 200 for parallel operation according to the second embodiment of the present invention includes a constant current converter 210, a voltage compensation setting unit 120, and a first LED string LS1 to the Nth LED string 130, 131, 132, the first current detection unit to the Nth current detection unit 140, 141, 142, the first current limiting unit to the N−1th current limiting unit 150, 151, the It includes 1 smoothing part to N-1th smoothing part 160, 161 (where N is a natural number of 2 or more).

The constant current converter 210 includes a constant current control unit 180 and a dimming voltage setting unit 190. The constant current controller 180 includes an opto coupler 181 and a resistor R3.

A first terminal of the resistor R3 is connected to the input terminal of the supplied power supply Vcc, and a second terminal is connected to the anode of the optocoupler 181.

The cathode of the optocoupler 181 is connected to the output terminal of the first comparator (Op-amp1) of the first current detection unit 240, and the output terminal of the dimming voltage setting unit 190 is connected to the first output terminal of the first current detection unit 240. It is connected to the non-inverting terminal (+) of the comparator (Op-amp1).

That is, the first comparator (Op-amp1) of the first current detection unit 240 outputs the output of the dimming voltage setting unit 190 and the measured current flowing to the end of the first LED string (LS1) 130 through an input terminal. When the input is received and compared, and the measured current flowing at the end of the first LED string (LS1) 130 exceeds the output voltage of the dimming voltage setting unit 190, the measurement flowing at the end of the first LED string (LS1) 130 The output voltage Vout+ is adjusted through the constant current controller 180 so that the current becomes the output voltage of the dimming voltage setting unit 190 . As a result, the current value flowing through the first LED string (LS1) 130 is set as a preset reference current value, and constant current control is performed.

As described above, according to the present invention, the output of the dimming voltage setting unit and the first measured current flowing through the first LED string are compared, and the current value for the first LED string is set as the reference current value through feedback based on the comparison result. At the same time, based on the current value flowing in the first LED string, current limiting is performed so that the same current constantly flows in the other LED strings, so that constant current control is possible, and through this, high frequency is not generated and uniform without flicker. There is an effect that dimming control is possible with one illuminance.

5 is a circuit diagram schematically showing an LED driving circuit for parallel operation according to another embodiment of the present invention. Here, the present invention performs constant current control using a constant voltage converter instead of a constant current converter compared to the invention shown in FIG. 2, and there is a difference in the driving method of the converter.

As shown in FIG. 5, the LED driving circuit 300 for parallel operation according to another embodiment of the present invention includes a constant voltage converter 310, first to nth current limiting units 320, 321, 322, It includes first to n-th smoothing units 350 , 351 , and 352 , first to n-th LED strings 330 , 331 , and 332 , and first to n-th current detection units 340 , 341 , and 342 . Here, n is a natural number of 2 or more, and thus has a circuit configuration in which two or more LED strings are connected in parallel.

Here, one current limiting unit, one smoothing unit, one LED string, and one current detection unit are connected to form one unit unit, and at this time, n (n is a natural number equal to or greater than 2) unit units are connected in parallel. .

Specifically, the constant voltage converter 310 converts the supplied input voltage (Vcc) into an output voltage (Vout+) required for driving the LED and outputs the first and second voltage dividing resistors (R1) for setting the reference voltage (Vref). , R2).

The first through n-th current limiting units 320, 321, and 322 are connected in parallel to the output terminal Vout+ of the constant voltage converter 310, respectively.

Each of the first to n-th current limiting units 320, 321, and 322 is connected to the output terminal Vout+ of the constant voltage converter 310, and the output voltage Vo output to each of the series-connected LED strings LS1, LS2, and LSn ) is a forward voltage (Vf) capable of driving all the LEDs constituting each LED string, and current limiting of the output voltage (Vout+) is performed.

For reference, since each LED has a different forward voltage (Vf) even if it is fabricated on one wafer, the deviation of the forward voltage (Vf) of these LEDs has a great effect on the reliability of the product. By setting Vf bin, the groups are divided and displayed. For example, in the case of domestic white LED products, they are usually classified and marked in 0.1V steps such as 2.7V ~ 2.8V, 2.8V ~ 2.9V, and 2.9V ~ 3.0V, and recently 0.05V such as 2.65V ~ 2.70V. There are also high-efficiency products marked up to . For example, the Vf distribution of LEDs coming out of one wafer appears as a normal distribution. If the reference voltage (Vref) is 2.8V, it comes out as 2.6V to 3V. It is sorted into ranks such as 2.8V, 2.8V~2.9V, 2.9V~3.0V, etc. Therefore, when designing the LED lighting, the range of the forward voltage (Vf) value of the LED string can be calculated by estimating the Vf bin of the LED to be used. Through this, the reference voltage (Vref) for current limiting can be set.

Each of the first to n-th smoothing units 350, 351, and 352 is connected to an output terminal of each of the first to n-th current limiting units 320, 321, and 322 to smooth the current-limited output voltage into a direct current voltage so that the output voltage ( Vo) is output to the first to n-th LED strings 330, 331, and 332, respectively.

Here, when the output voltage (Vo) is greater than the sum of the forward voltages (Vf) of all LEDs constituting each LED string, the LED driving circuit 300 is normally driven, so the first to nth current limiting units 320 and 321 , 322 adjusts the output voltage Vo so that the rated voltage is applied to each of the first to n-th LED strings 330, 331, and 332.

Each of the first to nth LED strings LS1 , LS2 , and LSn 330 , 331 , and 332 are connected in parallel to each other, and each LED string has a circuit configuration in which a plurality of LEDs are connected in series.

Each of the first to nth LED strings LS1, LS2, and LSn 330, 331, and 332 has one current limiting unit 320, 321, and 322 and one smoothing unit 350, 351, and 352 connected. The contact and the anode of the LED provided at the top are connected, and turned on by the output voltage Vo output from the connected smoothing units 350, 351, and 352.

Each of the first to n-th current detectors 340, 341, and 342 has a first input terminal connected to the cathode of the LED provided at the end of the series-connected LED string, and a second output terminal Vout- of the constant voltage converter 310. 2 The input terminal is connected, and the output terminal of the current detector is connected to the input terminal of the current limiting unit connected in series.

Each of the first to nth current detectors 340, 341, and 342 detects the output voltage at the end of the connected LED string, compares the detected output voltage with a preset reference voltage (Vref), and limits the current corresponding to the comparison result. give negative feedback

Accordingly, each of the current detection units 340, 341, and 342 feeds back the output voltage at the end of the LED string to the current limiting unit so that the current limiting unit can adjust the output voltage Vo output to the LED string.

As described above, the LED driving circuit for parallel operation according to the present invention uses a constant voltage converter to measure the voltage output to each LED string at the end of the corresponding LED string and the reference voltage (Vref) to perform current limiting By doing so, constant current control for a plurality of LED strings connected in parallel is possible.

FIG. 6 is a circuit diagram showing a first embodiment of an LED driving circuit for parallel operation shown in FIG. 5 . Here, the same reference numerals are used for components identical to those of the invention shown in FIG. 5, and descriptions of the same configurations will be omitted. In addition, since each unit unit has the same configuration including one current limiting unit, one smoothing unit, one LED string, and one current detection unit, only the operation of one unit unit will be described.

As shown in FIG. 6 , the first current limiting unit 320 includes first and second current limiting resistors R11 and R21, a zener diode Dz1 and field effect transistors FET and Q1.

The first current limiting resistor (R11) has a first terminal connected to the output terminal (Vout+) of the constant voltage converter 310, the cathode of the zener diode (Dz1) and the drain (D) of the field effect transistor (FET, Q1) to form a contact. and the second terminal is connected to the anode of the zener diode Dz1 and the gate of the field effect transistor (FET, Q1) to form a contact.

The first end of the second current limiting resistor R21 is connected to the contact point to which the second end of the first current limiting resistor R11, the anode of the zener diode Dz1, and the gate of the field effect transistor (FET, Q1) are connected. , the output terminal and the second terminal of the current detection unit 340 are connected in series to the zener diode Dz1, through which the current flowing to the zener diode Dz1 is limited.

The field effect transistor (FET, Q1) has a source connected in series to the anode of the upper LED of the LED string (LS1) 330, and a smoothing unit (C1) at the contact where the anode and the source of the LED string (LS1) 330 are connected. ) 350 is connected to the first end.

As such, the first current limiting resistor (R11), the zener diode (Dz1), and the field effect transistor (FET, Q1) are connected in parallel, and the first current limiting resistor (R11), the zener diode (Dz1), the field effect transistor (FET, A second current limiting resistor R21 is connected in series between the contact point Q1 connected in parallel and the first current detection unit 340 .

Also, the first current detector 340 includes one sensing resistor Rs1 and one comparator OP-AMP1.

The sensing resistor Rs1 has a first terminal connected to the cathode of the LED provided at the end of the first LED string LS1 330 and a second terminal connected to the other output terminal Vout- of the constant voltage converter 310 , The current flowing at the end of the first LED string LS1 330 is measured, and the output voltage at the end of the first LED string LS1 is detected using the measured current.

The comparator (OP-AMP1) has a non-inverting terminal (+) connected to the contact point where the terminal cathode of the first LED string (LS1) and the sensing resistor (Rs1) are connected, and the output voltage detected at the first terminal of the sensing resistor (Rs1) is input, the inverting terminal (-) is connected to the connection contact of the first and second voltage divider resistors (R1, R2) of the constant voltage converter 310 to receive the preset reference voltage (Vref), and the second current limiting resistor An output terminal is connected to the second terminal of R21 to feed back the voltage output according to the comparison result between the reference voltage Vref and the output voltage to the current limiting unit 320 .

Through this, the comparator (OP-AMP1) receives the output voltage detected through the first terminal of the sensing resistor (Rs1) through the non-inverting terminal (+) and the reference voltage (Vref) through the inverting terminal (-), The input output voltage is compared with the reference voltage (Vref), and the output according to the comparison result is fed back to the current limiting unit.

That is, the comparator (OP AMP1) applies the maximum output voltage (Vmax) to the second current limiting resistor (R21) when the output voltage detected at the end of the first LED string (LS1) exceeds the reference voltage (Vref) to generate a zener The current flowing through the diode Dz1 and the switching of the field effect transistor Q1 are controlled so that the terminal output voltage of the first LED string LS1 becomes the reference voltage Vref.

Accordingly, the current limiting unit 320 of the present invention performs current limiting by using the feedback voltage to set the voltage applied to the first LED string to the preset reference voltage Vref.

The operations of the first current limiting unit 320 and the first current detection unit 340 are performed identically for each unit composed of one current limiting unit, one smoothing unit, one LED string, and one current detection unit. do.

As a result, the LED driving circuit according to the present invention can perform a constant current operation so that the current flowing through all the LED strings is the same.

As such, in the embodiment of the present invention, unlike the conventional technology of performing constant current driving by sensing the sum of the currents flowing through all the LED strings, the current value (voltage value) flowing through one LED string is measured through the current detector, and the measured Constant current control may be performed such that the current flowing through all the LED strings is the same by performing current limiting on other LED strings using the current value (voltage value).

As the present invention has been described with reference to the drawings so far, the LED driving circuit according to the present invention uses a single converter to stably perform multiple of LED strings can be operated in parallel.

As described above, the embodiments according to the present invention have been reviewed, and the fact that the present invention can be embodied in other specific forms in addition to the above-described embodiments without departing from the spirit or scope is apparent to those skilled in the art. It is self-evident to Therefore, the embodiments described above are to be regarded as illustrative rather than restrictive, and thus the present invention is not limited to the above description, but may vary within the scope of the appended claims and their equivalents.

100. LED driving circuit 110. Constant current converter
120. Voltage compensation setting unit 130. First LED string
131. Second LED string 132. Nth LED string
140. First current detection unit 141. Second current detection unit
142. Nth current detection unit 150. First current limiting unit
151. N-1th current limiting unit 160. First smoothing unit
161. N-1th smoothing unit 170, 180. Constant current control unit
171, 181. Optocoupler 190. Dimming voltage setting unit

Claims (12)

delete delete delete delete delete delete delete delete In the LED driving circuit for parallel operation,
a constant voltage converter that receives AC power and outputs DC power;
n (n is a natural number equal to or greater than 2) current limiting units connected to the output terminal (Vout+) of the constant voltage converter and performing current limiting of the DC power supply;
n smoothing units for smoothing outputs of each of the n current limiting units;
n LED strings having an anode connected to a contact point where the current limiting unit and the smoothing unit are connected, and turned on by a voltage output from each of the n smoothing units; and
It is connected to the cathode of the LED provided at the end of each of the n LED strings, detects the output voltage of the end of the LED string, and compares the detected output voltage with a preset reference voltage (Vref) to the n current limiting units. Including; n current detectors for feedback;
One current limiting unit, one smoothing unit, one LED string, and one current detection unit are connected as one unit unit, and a plurality of the unit units are provided and connected in parallel;
The constant voltage converter further includes first and second voltage dividing resistors R1 and R2 for setting a reference voltage Vref,
Each of the n current limiting units is connected in series to the output terminal of the current detector connected as a unit, and limits the current output to the LED string according to the voltage fed back through the output terminal of the current detector Parallel operation, characterized in that LED driving circuit for 10. The method of claim 9, wherein each of the n current limiting units,
It includes first and second current limiting resistors (R1n, R2n), a zener diode (Dzn), and field effect transistors (FET, Qn),
The first current limiting resistor (R1n) is connected to the output terminal of the constant voltage converter, the cathode of the zener diode (Dzn) and the drain (D) of the field effect transistor (FET, Qn) and a first terminal to form a contact, , the anode of the zener diode (Dzn) and the gate and the second terminal of the field effect transistor (FET, Qn) are connected to form a contact,
The second current limiting resistor R2n is connected to the second end of the first current limiting resistor R1n, the anode of the zener diode Dzn, and the gate of the field effect transistors FET and Qn. A terminal is connected, and an output terminal of the current detection unit and a second terminal are connected to limit the current flowing to the zener diode (Dzn),
In the field effect transistor (FET, Qn), the source is connected in series to the anode of the upper LED of the LED string, and the first end of the smoothing part is connected to the contact point where the anode of the LED string and the source are connected,
The LED driving circuit for parallel operation, characterized in that the first current limiting resistor (R1n), the zener diode (Dzn), the field effect transistors (FET, Qn) are connected in parallel. According to claim 10,
Each of the n smoothing units is connected between the output terminal of each of the n current limiting units and the ground, and is composed of a capacitor (C). An LED driving circuit for parallel operation, characterized in that for outputting. According to claim 11,
Each of the n current detectors includes a sensing resistor (Rsn) and a comparator (OP-AMP),
The sensing resistor Rsn has a first terminal connected to a cathode provided at an end of the LED string and a second terminal connected to the other output terminal of the constant voltage converter to be connected in series with the LED string, Measure the voltage applied to the first terminal and input it to the non-inverting terminal (+) of the comparator,
The comparator (OP-AMP) has a non-inverting terminal (+) connected to a contact point where the cathode of the LED provided at the end of the LED string and the first terminal of the sensing resistor (Rsn) are connected, and the first voltage dividing resistor ( An inverting terminal (-) is connected to the contact point where the second terminal of R1) and the first terminal of the second voltage dividing resistor R2 are connected, and the voltage applied to the first terminal measured through the sensing resistor Rsn and the An LED driving circuit for parallel operation, characterized in that comparing the set reference voltage (Vref) and outputting the comparison result to the second current limiting resistor (R2n).

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