KR20120111628A - Led drive circuit - Google Patents

Abstract

PURPOSE: An LED driver circuit is provided to minimize power loss by only changing a voltage amount changed through an LED output current into power and compensating for the changed voltage amount. CONSTITUTION: An LED part(804) is applied with an operating voltage and runs an LED. A constant voltage part(802) provides a constant voltage to an LED part. A non-insulating voltage variation and compensation part(800) compensates for a voltage change amount in the constant voltage applied from the constant voltage part. The non-insulating voltage variation and compensation part comprises a first capacitor(Cb), a second capacitor(CF), a current sensor(806), and a current controller(808). The first capacitor accumulates the constant voltage applied from the constant voltage part. [Reference numerals] (808) Current controller

Description

LED drive circuit {LED DRIVE CIRCUIT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (LED) driving circuit, and in particular, to improve the efficiency of the LED driving circuit capable of controlling the constant current according to temperature change, the input voltage is used as the base voltage, and only the voltage variation through the LED output current is applied to the power. The present invention relates to an LED driving circuit capable of reducing power loss by converting and compensating and improving energy efficiency than an LED driving circuit using a conventional DC / DC converter.

In recent years, as the light emitting diode (LED) is spotlighted in the IT (information technology) and GT (green technology) industries, the global market is rapidly expanding. This is because LED is known as an eco-friendly material that saves energy and significantly reduces carbon emissions. In other words, current high-power LEDs are spotlighted as next-generation lighting devices because of their long life time, low maintenance cost, and high efficiency. Furthermore, they are eco-friendly materials because they do not emit pollutants or harmful gases and do not use mercury. It can be said.

The proliferation of the LED industry is most prominent in the lighting market, which is close to the general consumer. LEDs are expected to grow more than expected due to their low power consumption, long life, and small size compared to conventional light sources. In addition, the initial purchase cost, which was the biggest obstacle to the expansion of LED lighting, is expected to gradually replace incandescent lamps and halogen lamps as technology development gradually lowers.

In addition, the government has established a policy to replace incandescent lamps with LEDs in the EU and US. Australia and New Zealand have banned the use of less energy efficient incandescent lamps since 2010, and the United States and Canada have also banned the use of incandescent lamps above 100W since 2012 and 40W since 2014. Twenty-seven EU member states agreed to ban incandescent lamps by 2012, and Greenpeace, an international environmental protection organization, is planning to switch to energy-efficient lighting for India, where more than 98% of the 650 billion luminaires are incandescent lamps. I also recommended. Korea has been working on the 'LED Lighting 15/30 Project' to convert 30% of light sources into LEDs by 2015.

On the other hand, the illumination LED system (system) as described above is composed of a LED driving circuit composed of a power (power) and a drive (drive) to operate the light source and the LED light source using the LED.

1 and 2 illustrate a single-stage LED driving circuit and a two-stage LED driving circuit currently in use.

Conventional LED driving circuits generally use single-stage LED driving circuits and two-stage LED driving circuits as shown in FIGS. 1 and 2. In the case of a single-stage LED driving circuit, it has a simple circuit structure, which has the advantage of low cost. However, the dimming factor is not corrected and does not meet the IEC 61000-3-2 class C harmonic regulations required for luminaires above 25 [W]. On the other hand, two-stage LED driving circuits are more complicated than single-stage circuits, which increases the price, but satisfies all IEC 61000-3-2 class C harmonic regulations, insulation problems, and safety regulations. Currently, more than 25 W LED luminaires use two-stage LED drive circuits. However, the two-stage LED driving circuit is composed of two or more stages of power converters, which requires a high efficiency design of each stage of power converters compared to single stages.

Figure 3 shows the optical characteristic curve according to the power of the Cree XLamp Power LED currently on the market. 3A illustrates driving current characteristics according to forward voltage. As can be seen in FIG. 3A, the LED characteristics are the same as the diode characteristics, and at a voltage above the threshold voltage, the change width is smaller than that of the general diode, but the change width is increased rapidly. 3b shows a relative luminous flux curve according to the driving current. As can be seen in Figure 3b the luminous flux characteristic curve for the drive current is close to linear.

Due to such LED characteristics, DC power supplies for driving LEDs now prefer a constant current type method that controls current rather than the voltage controlled constant voltage method used in existing SMPS. 3C shows optical characteristics according to junction temperature. In the case of LED, the luminous flux drops inversely as the junction temperature increases.

가 될 경우 광속이 40%정도 떨어짐을 알 수 있다. 따라서 조명용 LED 시스템의 경우 광원에 온도 특성에 따른 직류전원 공급 장치의 출력 제어가 필요하다.Cree XLamp's junction temperature is 150

If it becomes, it can be seen that the luminous flux drops by 40%. Therefore, in the case of the lighting LED system, it is necessary to control the output of the DC power supply according to the temperature characteristics of the light source.

FIG. 4 is a view illustrating an LED driving circuit in which a series resistor is inserted in a parallel circuit in order to reduce a current deviation of a parallel circuit according to temperature in a conventional LED light source, and FIG. 5 is a graph showing voltage-current characteristics according to LED temperature. It is.

)는 아래의 [수학식 1]에서와 같이 정의된다.As shown in FIG. 4, in the conventional LED driving circuit, a series resistor 404 is inserted into an LED array 402 connected in parallel to a power supply unit 400 for supplying operating power, thereby reducing current variation according to temperature. The structure that makes it work is common. Where the rated current (

) Is defined as in Equation 1 below.

)은 아래의 [수학식 2]에서와 같다.At this time, the voltage variation to form the rated current according to the temperature change is determined by the LED characteristics.

) Is as shown in [Equation 2] below.

In addition, in the LED driving circuit, in order to reduce the current variation, the value of the series resistance must be increased, but there is a problem in that power loss increases.

)과 전류 안정화를 위한 전력손실(

)로 구별할 수 있으며, 각각 아래의 [수학식 3]과 [수학식 4]에서와 같이 계산될 수 있다. The above power loss is largely due to power loss for emitting light when power is supplied to the LED array 402.

) And power loss for current stabilization

), And can be calculated as shown in Equation 3 and Equation 4, respectively.

)과 전류 안정화를 위한 전력손실(

)을 이용하여 아래의 [수학식 5]에서와 같이 나타낼 수 있으며, 온도에 따라 LED 어레이에 전압 변동율이 있는 경우 LED 전압 변동에 따른 전류(I)는 아래의 [수학식 6]에서와 같이 나타낼 수 있다.At this time, the LED power utilization rate is the power loss for light emission (

) And power loss for current stabilization

) Can be expressed as in [Equation 5] below, and if there is a voltage change rate in the LED array according to temperature, the current (I) according to the LED voltage change is expressed as in [Equation 6] below. Can be.

FIG. 6 illustrates an LED driving circuit using a variable resistor to compensate for a voltage variation rate of an LED according to temperature.

Referring to FIG. 6, in order to form a constant current when the LED has a voltage change rate according to temperature, the series resistance value should be as shown in Equation 7 below.

At this time, the parallel circuit can form a constant current regardless of the temperature. To change the series resistance electronically, the equivalent resistance can be changed according to the switching function. Therefore, by using a DC / DC converter, the equivalent series resistance can be varied, and the resistance loss can be eliminated by returning the existing resistance loss to the power supply side.

However, the above-described conventional LED driving circuit has a problem that the power loss is increased because the entire power required for the LED lighting fixtures must be converted.

Therefore, in order to improve the efficiency of the LED driving circuit capable of controlling the constant current according to the temperature change, the present invention uses the input voltage as a base voltage, reduces power loss by compensating only the voltage variation through the LED output current, and reduces power loss. An object of the present invention is to provide an LED driving circuit which improves energy efficiency than an LED driving circuit using a / DC converter.

The present invention as described above is an LED driving circuit, the LED unit for receiving the operating power to drive the LED, the constant voltage unit for providing a constant voltage to the LED unit, the constant voltage applied from the constant voltage unit so that the current flowing from the LED unit is constant The non-isolated voltage fluctuation compensator compensates for the voltage fluctuation at.

The non-isolated voltage fluctuation compensator may include a first capacitor that accumulates a constant voltage applied from the constant voltage unit, a transformer that applies the constant voltage accumulated in the first capacitor to an operating power supply of the LED unit, and flows from the LED unit. A current sensor for detecting a current, a current controller for controlling an output voltage from the transformer so that a constant current flows into the LED unit according to the current value measured from the current sensor, and turned on or off by the current controller And a second capacitor connected between the transformer and the LED unit to control the operation of the second capacitor and storing the voltage variation for the constant current.

The transistor may be switched so that the constant voltage accumulated in the first capacitor is induced to the primary coil of the transformer during the turn-off.

The transistor may be switched so that the voltage stored in the primary coil of the transformer is applied to the secondary coil of the transformer when the transistor is turned on.

In addition, the transistor is characterized in that the gate is connected to the current controller, the drain is connected to one end of the primary coil of the transformer, the source is connected to the ground.

In addition, the LED unit is characterized in that a plurality of LED array is configured in parallel.

In addition, the LED array is characterized in that it comprises a plurality of LEDs connected in series.

In the present invention, in order to improve the efficiency of the LED driving circuit that can control the constant current according to the temperature change in the LED driving circuit, the input voltage is set as the base voltage, and power loss is reduced by compensating only the voltage change through the LED output current. In addition, it is possible to improve energy efficiency than LED driving circuit using existing DC / DC converter.

1 is a conventional single-stage LED driving circuit diagram,
2 is a conventional two-stage LED driving circuit diagram,
3a to 3c is a diagram illustrating an optical characteristic graph according to a power source of a conventional LED,
4 is a LED driving circuit diagram of a conventional series resistor inserted;
5 is a diagram illustrating a voltage current characteristic graph according to temperature in a conventional LED driving circuit;
6 is a LED driving circuit diagram using a conventional variable resistor,
7 is a conceptual diagram of a voltage variation compensation circuit according to an embodiment of the present invention;
8 is an LED driving circuit inserted with a non-isolated voltage compensation circuit according to an embodiment of the present invention,
9 is an exemplary view illustrating an LED light source for a street lamp to which an LED driving circuit is applied according to an embodiment of the present invention;
10 is a diagram illustrating an LED power system board according to an embodiment of the present invention;
11 is a view illustrating a chip voltage and a gate signal of an LED driving circuit according to an embodiment of the present invention;
12 is a view illustrating a reference voltage, a compensation voltage, and an output LED current of an LED driving circuit according to an embodiment of the present invention;
13 is a view illustrating a reference voltage, a compensation voltage, and an output LED current of an LED driving circuit according to an exemplary embodiment of the present invention;
14 is a view illustrating an input voltage, an input current, and an output LED current of an LED driving circuit according to an exemplary embodiment of the present invention.
15 is an exemplary view illustrating a startup characteristic at power-on of an LED driving circuit according to an embodiment of the present invention;
16 is an exemplary view illustrating a startup characteristic when the LED driving circuit is powered off according to an embodiment of the present invention;
17 is an exemplary comparison of efficiency of the LED driving circuit according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the present invention. In the following description of the present invention, if it is determined that a detailed description of a known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. The following terms are defined in consideration of the functions of the present invention, and may be changed according to the intentions or customs of the user, the operator, and the like. Therefore, the definition should be based on the contents throughout this specification.

7 illustrates a conceptual diagram of a conventional constant current controller and a voltage variation compensation circuit according to an embodiment of the present invention.

In order to flow constant current to LED regardless of temperature change in LED parallel circuit, the voltage between minimum voltage and maximum voltage should be varied and the range of variable voltage should be very small. The existing controller controls the constant current in the LED by varying the high voltage as shown in (a) of FIG. In this case, the width of the voltage to be converted is increased, thereby reducing the efficiency of the power converter.

On the other hand, the proposed circuit is composed of a constant voltage circuit of the minimum voltage of the LED as shown in (b) of FIG. It can be maximized.

8 illustrates an LED driving circuit according to an exemplary embodiment of the present invention, and implements a non-isolated voltage variation compensation circuit to compensate for a voltage variation rate according to temperature.

Hereinafter, with reference to Figure 8 will be described in detail the operation of each circuit component constituting the LED drive circuit of the present invention.

First, the constant voltage unit 802 supplies operating power to the LED unit 804. The LED unit 804 includes a plurality of LEDs connected in series to form an LED array, and the plurality of such LED arrays may be configured in parallel. The non-isolated voltage fluctuation compensator 800 refers to a non-isolated voltage fluctuation compensating circuit. The non-isolated voltage fluctuation compensator 800 refers to a constant voltage applied from the constant voltage part 802 such that a current flowing from the LED part 804 is constant, Compensating the voltage variation according to the constant current flows to the LED unit 804.

)와 제1 커패시터(capacitor)(

), 제2 커패시터(

), 트랜지스터(transistor)(

), 전류 센서(current sensor)(806), 전류 제어기(current contoller)(808)를 포함한다.The above non-isolated voltage fluctuation compensator 800 is a transformer (

) And the first capacitor (

), The second capacitor (

), Transistor (

), A current sensor 806, and a current controller 808.

)는 정전압부(802)로부터 인가되는 정전압을 축적한다. 변압기(

)는 제1 커패시터(

)에 축적된 정전압을 LED부(804)의 동작 전원으로 인가시킨다. 전류센서(806)는 LED부(804)로부터 흐르는 전류를 검출한다. 전류 제어기(current controller)(808)은 전류 센서(806)로부터 측정된 전류값에 따라 LED부(804)로 정전류가 흐르도록 변압기(

)로부터의 출력 전압을 제어한다. 트랜지스터(

)는 전류 제어기(808)에 의해 턴온(turn on) 또는 턴오프(turn off)되어 변압기(

)의 동작을 제어한다. 제2 커패시터(

)는 변압기(

)와 LED부(804) 사이에 연결되어 정전류를 위한 전압 변동분을 저장하고, LED부(804)의 동작 시 전압 변동분의 전압을 인가시킨다.First capacitor (

) Stores a constant voltage applied from the constant voltage unit 802. Transformers(

) Is the first capacitor (

) Is applied to the operating power supply of the LED unit 804. The current sensor 806 detects a current flowing from the LED unit 804. The current controller 808 is configured to generate a constant current to the LED unit 804 according to the current value measured from the current sensor 806.

Control the output voltage from transistor(

) Is turned on or off by the current controller 808 so that the transformer (

Control the operation of Second capacitor (

) Is a transformer (

) Is connected between the LED unit 804 and stores the voltage variation for the constant current, and applies the voltage of the voltage variation in the operation of the LED unit 804.

)는, 턴오프(turn off) 시 제1 커패시터(

)에 축적된 정전압이 변압기(

)의 1차 코일에 유도되도록 스위칭되며, 턴온(turn on) 시 변압기(

)의 1차 코일에 저장된 전압이 변압기(

)의 2차 코일로 인가되도록 스위칭된다.At this time, the transistor (

) Is the first capacitor at turn off

), The constant voltage accumulated in the

Is switched to be induced in the primary coil of) and, when turned on,

Voltage stored in the primary coil of the

Is switched to be applied to the secondary coil.

That is, the proposed non-isolated voltage fluctuation compensator 800 as shown in FIG. 8 shorts the ground part of the secondary circuit of the transformer with the primary input terminal in a circuit of a conventional flyback converter. Constant current control is performed by feeding back the output current of the LED unit 804 configured as an array. Subsequently, the input voltage from the constant voltage unit 802 is used as a base voltage, and only the voltage variation of the LED unit 804 according to the temperature change through the constant current control is added to the secondary winding of the transformer as an induced voltage for the voltage variation. Perform compensation Accordingly, the power conversion efficiency can be improved by controlling only the voltage variation in response to the temperature change in the LED unit 804.

As described above, in the present invention, in order to improve the efficiency of the LED driving circuit capable of controlling the constant current according to the temperature change in the LED driving circuit, the input voltage is set as the base voltage, and only the voltage variation through the LED output current is compensated for by power conversion. This reduces power loss and improves energy efficiency over LED drive circuits using conventional DC / DC converters.

Hereinafter, an experimental result of applying the LED driving circuit to which the non-isolated voltage compensation circuit described above is applied to the LED for street light will be described as an example.

Table 1 below shows the specifications of the LED light source for the street lamp applied to the experiment. For this experiment, Cree XLamp (1.3W) Power LED was used for the experiment and consisted of 98 in 7 series and 14 parallel.

Light source supply power 120 W Applicable LED Cree's XLamp LED rating 1.1 W (350 mA) LED series 7 Ea LED Parallel Circuit Count 14 parallel

FIG. 9 illustrates an LED light source for a street lamp to which an embodiment of the present invention is applied, and FIG. 10 illustrates a proposed LED power system for driving an LED light source for a street lamp.

Referring to FIG. 10, the LED power system is largely composed of an AC / DC converter and a proposed non-isolated voltage compensation circuit. AC / DC converter is composed of LLC topology DC / DC converter with excellent power conversion efficiency and boost type power factor control circuit to maintain unit power factor above 0.9. Table 2 below shows the specifications of the AC / DC converter.

Topology LLC resonant type Input specification 85? 264V Output specification 24 V, 5.2 A PF 0.94 (@ 220 VAC) efficiency 92% (@ 220 VAC)

The non-isolated voltage compensation circuit is constructed by shorting the primary input terminal and the secondary ground side based on a conventional flyback converter. The gate driver is configured to operate at 27kHz switching frequency using the UC3842 PWM chip, and the output current detector reduces the size of the detection resistor to minimize power loss.

FIG. 11 illustrates a non-isolated voltage compensation circuit control-chip voltage and a gate signal. Referring to FIG. 11, the capacitor capacity was calculated and applied so that the power supply voltage of the chip could be operated at 30 ms for rapid response of the circuit operation.

FIG. 12 shows the output LED current and its reference and compensation voltages and gate signals. As can be seen in Figure 12, after the initial power-up 400ms after the output reaches the steady state. In this case, it can be seen that the reference voltage represents 22V and the voltage compensation by the voltage variation rate is controlled at about 2 to 3V.

FIG. 13 illustrates waveforms of the waveform of FIG. 12 measured by magnifying a time domain. Referring to FIG. 13, it can be seen that as shown in the enlarged LED output current, there is no input power ripple in the 120 Hz band that affects the flicker operation of the light source, and only high frequency ripple in the 27 kHz band due to switching exists.

14 shows an input voltage, an input current, and an LED output current. As can be seen from the waveform shown in FIG. 14, the AC / DC converter has a unit power factor control and the power factor is maintained at 0.94 based on 220V.

FIG. 15 illustrates an input voltage, an input current, and an LED output current when the initial power is turned on, and FIG. 16 illustrates an input voltage, an input current, and an LED output current when the power is removed.

FIG. 17 illustrates the efficiency of the LED driving circuit using the conventional boost converter and the LED driving circuit using the proposed non-isolated voltage compensation circuit. In the case of the LED drive drive using the conventional boost converter, the entire input power is converted into power, whereas the proposed non-isolated voltage compensation circuit converts only about 10% of the total power. It can be seen that the 5% improvement can be improved.

As described above, in the case of the power converter for the constant current compensation according to the temperature change, the overall power of the LED power system is lowered when considering the efficiency of the input SMPS because the entire power is converted by using the constant current control using the boost converter. In order to solve the problem, the present invention proposed a new method for the constant current compensation according to the temperature change in the LED drive drive used to drive a large-capacity LED light source for a large number of parallel circuits.

That is, in the present invention, to improve the disadvantage of the two-stage LED power system, the LED drive drive for the constant current compensation according to the temperature change is configured as a circuit that can only convert the voltage change for the temperature change. At this time, the proposed non-isolated voltage variation compensation circuit can minimize the power conversion loss compared to the conventional boost method by compensating only the input voltage as a basic voltage and converting only the voltage variation through the LED output current. For the validity of the limited non-isolated voltage variation compensation circuit, we designed a 120W street light LED light source and a high efficiency LLC resonant AC / DC converter and experimented with the proposed compensation circuit. Also it can be seen that the voltage fluctuation rate can be compensated according to the temperature change. In addition, it can be seen that the overall efficiency is improved by 5% compared to the existing LED drive.

Meanwhile, in the above description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Accordingly, the scope of the invention should not be limited by the described embodiments but should be defined by the appended claims.

800: non-isolated voltage variation compensation unit 802: constant voltage unit
804: LED unit 806: current sensor
808: current controller

Claims (7)

LED unit for driving the LED by receiving the operating power,
A constant voltage unit providing a constant voltage to the LED unit;
A non-isolated voltage fluctuation compensator for compensating voltage fluctuations at a constant voltage applied from the constant voltage part such that the current flowing from the LED part is constant.
LED driving circuit comprising a.
The method of claim 1,
The non-isolated voltage fluctuation compensator,
A first capacitor for accumulating a constant voltage applied from the constant voltage unit;
A transformer for applying the constant voltage accumulated in the first capacitor to an operating power source of the LED unit;
A current sensor for detecting a current flowing from the LED unit;
A current controller for controlling the output voltage from the transformer such that a constant current flows to the LED unit according to the current value measured from the current sensor;
A transistor turned on or off by the current controller to control the operation of the transformer;
A second capacitor connected between the transformer and the LED unit to store a voltage variation for the constant current
LED driving circuit comprising a.
The method of claim 2,
The transistor,
And the constant voltage accumulated in the first capacitor is switched to be induced to the primary coil of the transformer during the turn-off.
The method of claim 2,
The transistor,
And the voltage stored in the primary coil of the transformer is switched to be applied to the secondary coil of the transformer during the turn-on.
The method of claim 2,
The transistor,
And a gate is connected to the current controller, a drain is connected to one end of the primary coil of the transformer, and a source is connected to ground.
The method of claim 1,
The LED unit,
LED driving circuit, characterized in that a plurality of LED array is configured in parallel.
The method according to claim 6,
The LED array,
LED driving circuit comprising a plurality of LEDs connected in series.

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