KR20110018250A - Light-emitting diode driving circuit having step-down converter capable of direct detection of output voltage/current - Google Patents

Abstract

PURPOSE: A step-down converter type light emitting diode driving circuit is provided to directly detect a voltage or current of an output terminal regardless of the on and off of a switching element at a high voltage. CONSTITUTION: A light emitting diode output terminal(200) includes a light emitting diode. A sensing element(160) outputs a voltage drop value. The voltage drop value is changed according to the amount of current flowing in the light emitting diode. A step driving controller receives driving power and compares the feedback signal of the sensing device with an internal reference voltage. A switching element(150) controls the amount of current supplied to a light emitting diode.

Description

LIGHT-EMITTING DIODE DRIVING CIRCUIT HAVING STEP-DOWN CONVERTER CAPABLE OF DIRECT DETECTION OF OUTPUT VOLTAGE / CURRENT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-emitting diode driving circuit of a step-down converter type having an output voltage lower than an input voltage. In particular, the circuit is configured to have the same operation voltage of the control / driver of the converter and the circuit for detecting the voltage / current of the output terminal. The present invention relates to a light-emitting diode driving circuit of a step-down converter type that makes it possible to directly use a voltage / current signal of an output stage detected in a circuit in a converter controller.

Conventional light emitting diodes have been mainly used for backlight functions of liquid crystal displays (LCDs) used in mobile phones, PDAs, and notebook computers. However, due to the development of light emitting diode manufacturing technology, the efficiency is increased and the luminance is greatly improved, and thus it is not only used as a light source of a large liquid crystal display such as a TV, but also widely applied to general lighting, security lamps, and street lamps. Due to the long lifespan, eco-friendliness, and continuous improvement of light efficiency of LEDs, the fluorescent lamps, which are currently used for lighting, are expected to be replaced substantially after 2012.

In general, a light emitting diode uses a constant current source driving method. When using a light emitting diode as a general lighting, it is required to convert AC 220V, which is a commercial power source, to AC-DC. However, when the simplest type of diode rectifier without a transformer is used, the DC voltage after AC-DC conversion is about 310V, which is very large to directly drive the light emitting diode. As a result, the first rectified voltage is lowered to a voltage suitable for driving the LED using a step-down DC-DC converter.

)에 흐르는 전류를 검출하기 위하여 스위칭 소자(

)의 소스(Source, Emitter)에 저항(

)을 사용하여 발광 다이오드(

)에 흐르는 전류(

)를 검출하고 있다. 하지만, 도 1과 같은 회로 구성은 발광 다이오드(

)에 흐르는 전류(

)를 스위칭 소자(

)가 턴온 되었을 때는 검출 저항(

)에 걸리는 전압을 통해 검출 할 수 있지만, 스위칭 소자(

)가 턴오프되면 발광 다이오드(

)에 흐르는 전류를 검출할 수 없다. 따라서, 스위칭 소자(

)가 턴온된 경우에만 전류를 검출하여 제어함으로서 출력 전류의 최대값만을 제어하게 된다. 이 경우, 발광 다이오드(

)에 흐르는 전류(

)의 평균치는 입력전압의 크기와 발광 다이오드(

)에 걸리는 전압의 크기에 따라 변동되어 실제 발광 다이오드(

)의 평균치 전류를 제어하지 못하는 문제점이 있다.A typical step-down DC-DC converter type light emitting diode current control circuit is shown in FIG. 1. In the prior art, a light emitting diode (

To detect the current flowing in the

Resistance of the source (Source, Emitter)

Using the light emitting diode (

Current in

) Is detected. However, the circuit configuration shown in FIG. 1 is a light emitting diode (

Current in

Switching element (

) Is turned on, the detection resistor (

Can be detected through the voltage across the

) Turns off, the light emitting diode (

Cannot detect the current flowing through Therefore, the switching element (

Only the maximum value of the output current is controlled by detecting and controlling the current only when) is turned on. In this case, the light emitting diode (

Current in

) Mean value of input voltage and light emitting diode (

Depending on the magnitude of the voltage across the

There is a problem that can not control the average current of the).

)에 흐르는 전류(

)를 검출하는 방법을 사용하고 있다. 하지만, 고전압 환경에서는 전류검출회 로의 고전압 절연 특성이 요구되어 간단한 형태의 전류센서를 사용할 수 없고 고전압 절연특성을 갖는 별도의 센서를 추가해야 하므로 전체 시스템의 크기가 증가하고 전체 시스템 가격이 상승하게 되는 문제점이 있다.In order to improve such a problem, as shown in FIG. 2, a light emitting diode using a separate current detection circuit including an isolated current sensor (

Current in

) Is used. However, in the high voltage environment, the high voltage insulation characteristics of the current detection circuit are required, so that a simple type of current sensor cannot be used, and a separate sensor having high voltage insulation characteristics must be added. There is a problem.

SUMMARY OF THE INVENTION An object of the present invention is to enable direct detection of voltage / current at an output stage capable of directly detecting a voltage or current at an output stage regardless of whether the input voltage is low voltage as well as in a high voltage environment. It is to provide a light emitting diode driving circuit of a step-down converter type.

In addition, an object of the present invention is to provide a light emitting diode driving circuit capable of precise control such as the average value control of the current / voltage flowing through the light emitting diode, the pulsation reduction of the output current / output voltage, etc. without a separate insulated current / voltage sensor.

In order to achieve the above object, the present invention is a light emitting diode driving circuit of a step-down converter method capable of directly detecting the voltage / current of the output terminal, as shown in Figure 4, the switching element, the emitter (source) of the switching element and A diode connected with a cathode, a step-down controller connected with a cathode of the diode, a sensing element connected at one end with the step-down controller, an inductor connected between the other end of the sensing element and an anode of the diode, A step-down converter comprising a filter capacitor connected in parallel to a sensing element and a light emitting diode, and a light emitting diode connected between the sensing element and the inductor, and feeding back the voltage of the sensing element to the step-down controller. Provided is a light emitting diode driving circuit.

), 제 1 센싱 저항(

)의 타단과 일단이 접속된 제 2 센싱 저항(

), 제 2 센싱 저항(

)의 타단과 상기 다이오드 아노드에 접속된 인덕터, 상기 다이오드의 캐소드와 인덕터 및 제 2 센싱 저항(

)에 접속된 커패시터, 상기 제 1 센싱 저항(

) 및 제 2 센싱 저항(

)과 접속된 피드백 전압을 상기 스텝다운 제어기에 피드백하여 출력전압(

)을 제어하는 것을 특징으로 하는 강압형 컨버터방식 발광 다이오드 구동 회로를 제공한다.In addition, as shown in FIG. 5, the present invention provides a switching element, a diode connected with an emitter (source) and a cathode of the switching element, a step-down controller connected with a cathode of the diode, and one step with the step-down controller. Connected first sensing resistor (

), The first sense resistor (

The second sensing resistor () having the other end connected to

), Second sensing resistor (

And an inductor connected to the other end of the diode anode, a cathode and an inductor of the diode, and a second sensing resistor

Is connected to the capacitor, the first sensing resistor (

) And the second sense resistor (

Feedback voltage connected to the feedback signal to the step-down controller to

It provides a step-down converter light emitting diode driving circuit characterized in that the control.

In addition, the present invention is a light-emitting diode driving circuit of the step-down converter method that can directly detect the voltage / current of the output terminal, the switching element, the diode connected to the emitter (source) and the cathode of the switching element as shown in FIG. And a transformer having a primary side connected to the step-down controller connected to the cathode of the diode, a sensing element connected to one end of the step-down controller, the other end of the sensing element, and an anode of the diode connected in series. And a light emitting diode connected to the secondary side of the transformer, and providing a step-down converter type light emitting diode driving circuit comprising feeding back a voltage of the sensing element to the step-down controller.

The step-down controller commonly used in the present invention includes a floating power supply connected to a cathode of the diode and one end of the sensing element and a low potential, and a difference between two values by comparing a reference voltage with a feedback voltage detected by the sensing element. And a controller for generating a duty corresponding to and controlling the feedback voltage to be equal to the reference voltage, and a gate driver for buffering the small signal duty signal generated by the controller and operating the switching element at a high frequency. The step-down controller can use a switching converter topology that includes any one of pulse width modulation control, pulse frequency modulation control, burst control, and hysteresis control.

As the switching element commonly used in the above, a gate driven power device including a metal oxide semiconductor field effect transistor, an insulated gate bipolar transistor, a junction transistor, and a junction field effect transistor can be used.

As a current / voltage sensing element commonly used above, a detection circuit may be used which uses a sensing ratio, a diode, a current source, and a size ratio of a transistor.

The present invention can provide a light emitting diode driving circuit of a step-down converter type that can directly detect and control the current flowing through the light emitting diode regardless of the on / off operation of the power switch in the control block at all times.

In addition, the present invention does not require the use of a separate sensing element in the constant current detection even in a high voltage environment, the LED converter circuit of the step-down converter type that can directly detect the voltage / current of the output stage that can reduce the size and number of devices Can be provided.

In addition, the present invention can provide a light emitting diode driving circuit of a step-down converter type that can directly detect and control the output voltage required for driving the LED regardless of the state of the switching element.

In addition, the present invention is a step-down converter method that can reduce the overall product size and the number of elements by omitting the additional high-insulation light-emitting diode current detection circuit or the voltage detection circuit required to drive the light emitting diode, especially when driving the LED in a high voltage environment. A light emitting diode driving circuit can be provided.

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

However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you. Like reference numerals in the drawings refer to like elements.

3 is an example of a LED driving circuit of a step-down converter type that can directly detect the output stage current according to the present invention. The step-down converter type LED driving circuit according to the present invention includes a floating power supply 120 and a control / driver 140 forming a step-down controller 100 and a driver of the control / driver 140. A switching element 150 connected to the switching element, a sensing element 160 connected in series with the switching element 150, a light emitting diode output terminal 200 connected in series with the sensing element 160, and a sensing resistor 160. do.

The floating power supply 120 is connected between the input power supply and the common terminal Vcom, and supplies a constant driving voltage to the control / driver 140 regardless of the variation of the common terminal. The control / driver 140 includes a first input terminal, a power supply terminal, a common connection terminal, and an output terminal, and generates an internal reference voltage Vref using a driving voltage supplied from the floating power supply 120. The voltage sensed by the sensing element 160 is applied to the first input terminal, the common connection terminal is connected to the common terminal, and the power supply terminal is connected to the + terminal of the applied power source Vs, so that the + of the applied power source Vs is applied. The internal reference voltage Vref generated internally is compared with the feedback voltage value input to the first input terminal by using the power supplied between the terminal and the floating power supply 120, and then a comparison signal is output to the output terminal.

The switching element 150 is connected to the output terminal of the control / driver 160 and the first electrode is on / off control, the second electrode is connected to the + terminal of the applied power supply (Vs), the third electrode is a common terminal Connected with. The sensing element 160 is connected in series or in parallel with the light emitting diode output terminal 200 (not shown in FIG. 3) and outputs a voltage value that is changed according to a change in a current value flowing through the light emitting diode or a voltage value applied to the light emitting diode. Feedback to the control / driver. The light emitting diode output terminal 200 is an output terminal including the light emitting diode, and may be configured in various forms as shown in the following drawings.

4 is a light emitting diode driving circuit of the step-down converter method capable of directly detecting the output stage current according to the present invention, FIG. 5 is a light emitting diode driving circuit of the step-down converter method capable of directly detecting the output stage voltage according to the present invention. FIG. 6 is a circuit diagram of a LED driving circuit of a step-down converter using a transformer capable of directly detecting current at an output stage according to the present invention.

)와, 스위칭 소자(

)와 직렬 접속된 센싱 저항(

)과, 센싱 소자(

)와 직렬 접속된 발광 다이오드(

)와, 발광 다이오드(

)와 직렬 접속된 인덕터(

)와, 센싱 저항(

) 및 발광 다이오드(

)와 병렬 접속된 필터 커패시터(

)와, 필터 커패시터(

) 및 인덕터(

)와 병렬 접속된 다이오드(

)를 포함한다.As shown in FIG. 4, the LED driving circuit of the step-down converter type capable of directly detecting the current at the output stage according to the present invention has a floating power supply 120 forming a step-down controller 100. And a switching element connected to the control / driver 140 and the driver of the control / driver 140.

) And the switching element (

Sensing resistor in series with

) And the sensing element (

LEDs in series with

) And a light emitting diode (

) In series with

) And sensing resistance (

) And light emitting diodes (

Filter capacitor in parallel with

) And filter capacitor (

) And inductor (

) And diode connected in parallel

).

)의 듀티를 제어하는 기능을 수행한다. 이러한 스텝다운 제어기(100)는 전술된 바와 같이 동작전원을 공급하는 플로팅 파워 서플라이(120)와, 기준 전압(

)과 출력 검출신호를 비교/제어하는 제어기 및 스위칭 소자(

)를 구동하는 게이트 구동회로를 구비한 제어/구동기(140)을 포함한다.Step-down controller (100) is a switching element (100) so that the voltage / current of the output stage is controlled at a constant value.

) To control the duty. The step-down controller 100 is a floating power supply 120 for supplying operating power as described above, and the reference voltage (

Controller and switching element for comparing and controlling the output detection signal with

Control / driver 140 having a gate driving circuit for driving < RTI ID = 0.0 >

)의 동작에 따라 기준전압 변동하게 된다. 대표적인 플로팅 파워 서플라이는 트랜스포머 방식, 전하 펌프(Charge Pump) 및 부트스트랩 방식이 있다. 본 발명에서는 모든 형태의 플로팅 파워서플라이가 사용가능하며 가장 간단한 형태인 부트스트랩 방식을 사용할 경우를 예시하였다. 스위칭 소 자(

)가 턴오프 되었을 경우에는 입력 전원(

)과 공통 전압(

)의 전압차를 이용하여 부트스트랩 커패시터(

)는 일정 전압(

)까지 충전을 하고 스위칭 소자(

)가 턴온 된 경우에는 부트스트랩 커패시터(

)가 전압을 유지하는 동작을 한다.Unlike the general power supply, the floating power supply 120 does not have a reference voltage but is grounded.

The reference voltage fluctuates according to the operation of. Representative floating power supplies include transformers, charge pumps and bootstraps. In the present invention, all types of floating power supplies can be used and the simplest form of bootstrap method is illustrated. Switching element (

Input power ()

) And common voltage (

Bootstrap capacitor (

) Is a constant voltage (

) Up to the switching element (

) Is turned on, the bootstrap capacitor (

) Maintains the voltage.

)에서 검출된 궤환 전압(

)을 기준 전압(

)과 비교하여 두 값의 차이에 해당하는 듀티를 발생시켜 궤환 전압(

)이 기준 전압(

)과 같도록 제어하는 기능을 한다. 즉, 기준 전압(

)과 본 발명에 따른 강압형 컨버터방식의 발광 다이오드 구동 회로 출력단에서 피드백된 발광 다이오드 전류(

)와 센싱 저항(

)에 대한 궤환 전압(

)을 인가 받아 비교함으로써 궤환 전압(

)이 기준 전압(

)보다 낮을 경우 스위칭 소자(

)를 턴온시키고 반대로 기준 전압(

)보다 높을 경우 스위칭 소자(

)를 턴오프시키는 동작에 의해서 인덕터(

)의 전류를 제어함으로서 발광 다이오드(

)에 흐르는 전류(

)를 입력제어 기준 전압이 기준 전압(

)에 수렴하도록 제어하게 된다. 제어기는 적분기를 사용하는 펄스 폭 변조(Pulse Width Modulation, PWM) 제어 혹은 펄스 주파수 변조(Pulse Frequency Modulation, PFM) 혹은 적분기 없이 비교 기능만을 가지는 히스테리시스(Hysteresis) 제어 등으로 구성할 수 있다. 즉, 일반적인 스위칭 모드 파워 서플라이(Switching Mode Power Supply, SMPS) 제어 기법을 그대로 적용할 수 있다.The controller has a sense resistor (

Feedback voltage detected at

) Is the reference voltage (

) To generate a duty corresponding to the difference between the two values.

) Is the reference voltage (

) To control the same as). That is, the reference voltage (

) And the LED current fed back from the output terminal of the LED driving circuit of the step-down converter type according to the present invention

) And sensing resistance (

Feedback voltage for

) By applying and comparing the feedback voltage (

) Is the reference voltage (

Lower than)

) And turn on the reference voltage (

Higher than)

) By turning off the

By controlling the current of the light emitting diode (

Current in

) Input control reference voltage is the reference voltage (

Control to converge). The controller can be composed of pulse width modulation (PWM) control using an integrator, pulse frequency modulation (PFM), or hysteresis control having only a comparison function without an integrator. That is, the general switching mode power supply (SMPS) control technique can be applied as it is.

)를 직접 구동하는 역할을 한다. 제어기에서 발생 된 소신호 듀티신호를 버퍼링하고 고전류 구동능력을 제공하여 고출력 스위칭 소자(

)를 높은 주파수에서 동작가능하게 한다.The driver is a switching element (

) To drive directly. By buffering small signal duty signals generated from the controller and providing high current driving capability,

Enable operation at high frequencies.

)의 전압은 다음의 수학식 1과 같이 나타낼 수 있다.Both ends of sensing resistance

) Can be expressed as Equation 1 below.

는 본 발명에 따른 강압형 컨버터방식의 발광 다이오드 구동 회로 출력단의 궤환 전압이며,

는 센싱 저항(

)의 저항값이고,

는 발광 다이오드(

)에 흐르는 전류값이다. 즉, 고정된 센싱 저항(

) 조건에서 제어기에 입력되는 궤환 전압(

)을 조절하여 발광 다이오드 전류(

)를 조절할 수 있다. here,

Is a feedback voltage of the output terminal of the LED driving circuit of the step-down converter type according to the present invention,

Is the sensing resistance (

Resistance of)

Is a light emitting diode (

Is the current value flowing through That is, a fixed sense resistor (

Feedback voltage input to the controller under

) To adjust the LED current (

) Can be adjusted.

)과 발광 다이오드(

)에 흐르는 전류(

)를 나타내는 궤환 전압(

)을 입력으로 인가받아 스위칭 소자(

)의 듀티를 조정하여 발광 다이오드(

)에 일정한 전류를 공급하는 기능을 한다.The light emitting diode driver, that is, the control / driver 140 composed of the above blocks has a reference voltage (

) And light emitting diodes

Current in

Feedback voltage ()

) Is applied as an input to the switching element (

) To adjust the duty of the light emitting diode (

) To supply a constant current.

)의 용량이 클 경우, 인덕터(

)에 흐르는 전류와 발광 다이오드(

)에 흐르는 전류(

)가 동일하지 않다. 인덕터(

)에 흐르는 전류는 큰 용량의 필터 커패시터(

)에 의해서 필터링되어 적분된 값의 전압으로 나타나므로, 필터 커패시터(

)에 저장되는 전압을 제어하여 발광 다이오드(

)에 흐르는 전류(

)를 제어할 수 있다. 또한, 센싱 저항(

)의 양단에 걸리는 전압은 항상 발광 다이오드(

)에 흐르는 전류(

)를 그대로 나타내므로 쉽게 발광 다이오드 전류(

)를 제어할 수 있다. 물론, 이에 따라, 기존의 스위칭 모드 파워 서플라이(Switching Mode Power Supply, SMPS) 제어방식인 펄스 폭 변조(Pulse Width Modulation, PWM), 펄스 주파수 변조(Pulse Frequency Modulation, PFM), 히스테리시스(Hysteresis) 제어 등의 제어 기법 역시 그대로 적용이 가능하다.Meanwhile, the filter capacitor shown in FIG. 4 of the present invention

), The inductor (

) And the light emitting diode (

Current in

) Is not the same. Inductor

Current through the

Filter capacitor ()

Control the voltage stored in the

Current in

) Can be controlled. In addition, sensing resistance (

Voltage across both sides of the

Current in

) As it is, so that the light emitting diode current (

) Can be controlled. Of course, according to this, pulse width modulation (PWM), pulse frequency modulation (PFM), hysteresis control, etc., which are conventional switching mode power supply (SMPS) control methods, are used. The control technique can also be applied as it is.

The capacitor Ch connected between the floating power supply 120 and the common terminal Vcom removes ripple supplied to the floating power supply 120 and the voltage of the common terminal is equal to the + terminal of the applied power. In addition, the driving voltage is maintained for a predetermined time, and the capacitor C _F connected to the light emitting diode (LED) is for removing ripple supplied to the light emitting diode (LED). In addition, the inductor L connected to the light emitting diode LED integrates the voltage value across the inductor which varies according to the on / off switching operation of the switching element sw to supply a constant current value to the light emitting diode LED. The diode is connected in parallel between the common terminal (Vcom) and the inductor (L) to provide a continuous supply of the inductor (L) accumulated current to the light emitting diode (LED) when the switching element (sw) off. Circuit element. Since the capacitor Ch, the capacitor C _F , and the inductor L are also shown in the conventional circuits shown in FIGS. 1 and 2, detailed descriptions thereof will be omitted.

)를 생략할 수도 있다. 이 경우, 인덕터(

)에 흐르는 전류값과 발광 다이오드(

)에 흐르는 전류값(

)이 동일하다. 발광 다이오드(

)에 흐르는 전류(

)의 최대값과 최소값을 설정하여 발광 다이오드(

)에 흐르는 전류(

)가 최대값에 도달할 경우에는 스위칭 소자(

)를 턴오프 시키고, 최소값보다 작은 경우에는 스위칭 소자(

)를 턴온 시키는 기존의 히스테리시스(Hysteresis) 제어기법을 적용할 수 있다. 물론, 필터 커패시터(

)의 용량이 작은 경우에도 이와 같은 제어 방법을 사용할 수 있다.Meanwhile, the filter capacitor shown in FIG. 4 of the present invention

) May be omitted. In this case, the inductor (

) And the light emitting diode (

Value of current flowing through

) Is the same. Light emitting diode

Current in

By setting the maximum and minimum values of the

Current in

) Reaches the maximum value, the switching element (

) And if it is smaller than the minimum value,

We can apply the existing hysteresis control method to turn on. Of course, filter capacitor (

This control method can be used even when the capacity of) is small.

)는 없는 경우에 쉽게 사용할 수 있는 히스테리시스(Hysteresis) 제어 기법을 적용할 수 있다. 도 7은 본 발명에 따른 출력단 전류의 직접적인 검출이 가능한 강압형 컨버터방식의 발광 다이오드 구동 회로에 히스테리시스 제어를 적용할 경우 인덕터의 전류 파형을 도시한 파형도이다. 최대 전류값(

)과 최소 전류값(

)내에서 동작하도록 제어함으로서 평균치의 제어가 가능하다. 이때, 인덕터(

)에 흐르는 전류는 발광 다이오드(

)에 흐르는 전류(

)와 동일하다.According to an embodiment of the present invention, a light emitting diode driving circuit having a step-down converter type capable of directly detecting a voltage / current of an output stage according to the present invention includes a filter capacitor (

) Can be applied to the hysteresis control technique that can be easily used when there is no. 7 is a waveform diagram illustrating a current waveform of an inductor when hysteresis control is applied to a light emitting diode driving circuit of a step-down converter type that can directly detect an output stage current according to the present invention. Current value (

) And the minimum current value (

By controlling to operate within), it is possible to control the average value. In this case, the inductor (

Current flowing through the

Current in

Same as).

)을 일정하게 유지하는 기능을 하며 이 전압을 기준으로 발광 다이오드(

)를 직접 구동하거나 정전류 구동단을 사용하여 다수의 발광 다이오드(

)를 구동할 수 있다. 이와 같은 정전압 제어의 경우 두 개의 센싱 저항(

,

)에 서 검출된 궤환 전압(

)을 기준 전압(

)과 비교하여 두 값의 차이에 해당하는 듀티를 발생시켜 궤환 전압(

)이 기준 전압(

)과 같도록 제어하는 같은 기능을 한다. 이 경우 출력전압(

)은 상기 설명한 펄스 폭 변조 제어 기법이 동일하게 적용되어 일정 전압으로 제어된다. 이때, 센싱 저항(

,

)에서 검출된 출력 전압은 다음의 수학식 2와 같이 나타낼 수 있다.The LED driving circuit of the step-down converter method capable of directly detecting the voltage of the output terminal according to the present invention is configured as shown in FIG. At this time, the controller

) To maintain a constant, and based on this voltage the light emitting diode (

) Directly or by using a constant current drive stage

) Can be driven. For this constant voltage control two sensing resistors (

,

Feedback voltage detected at

) Is the reference voltage (

) To generate a duty corresponding to the difference between the two values.

) Is the reference voltage (

It functions the same as controlling). In this case, the output voltage (

) Is controlled to a constant voltage by applying the same pulse width modulation control technique described above. At this time, the sensing resistance (

,

The output voltage detected at) can be expressed as Equation 2 below.

혹은

or

는 본 발명에 따른 강압형 컨버터방식의 발광 다이오드 구동 회로 출력단의 궤환 전압이며,

는 센싱 저항(

)의 저항값이고,

는 출력전압이고,

는 제어기의 기준 전압이다. here,

Is a feedback voltage of the output terminal of the LED driving circuit of the step-down converter type according to the present invention,

Is the sensing resistance (

Resistance of)

Is the output voltage,

Is the reference voltage of the controller.

,

)조건에서 제어기에 입력되는 궤환 전압(

)을 조절하여 제어될 일정 출력전압을 설정할 수 있다.That is, a fixed sense resistor (

,

Feedback voltage input to the controller

) Can be set to a certain output voltage to be controlled.

)와 인덕터(

)를 사용하지 않고 트랜스포머(

)를 사용할 수도 있으며, 이 경우, 다이오드(

)는 센싱 저항(

) 및 트랜스포머(

)의 1차과 병렬 접속된다. 물론, 발광 다이오드(

)는 트랜스포머(

)의 2차 측에 접속된다. 본 발명에 의한 LED 구동회로는 상기에 기술한 대로 출력전류의 직접적인 검출에 의한 트랜스포머의 1차측 출력전류 제어를 하게 되고 이때 2차 측의 전류는 LED에 흐르는 전류와 동일하다. 1 차측과 2차측의 전류비는 권선비에 의해서 정해지므로 1차측 출력전류의 직접적 검출과 제어에 의해서 2차측의 전류, 즉, LED 전류를 제어할 수 있다. 트랜스포머(

)를 적용한 구동회로의 경우 1차측과 절연된 LED 구동 특성을 얻을 수 있다.On the other hand, the present invention, as shown in Figure 6, the filter capacitor (

) And inductor (

Without the transformer

), In which case a diode (

) Is the sensing resistance (

) And transformers (

Is connected in parallel with the first order. Of course, light emitting diodes

) Is the transformer (

Is connected to the secondary side. The LED driving circuit according to the present invention controls the primary output current of the transformer by the direct detection of the output current as described above, where the secondary current is equal to the current flowing in the LED. Since the current ratio between the primary side and the secondary side is determined by the turns ratio, the secondary side current, that is, the LED current can be controlled by the direct detection and control of the primary side output current. Transformer(

In the case of the driving circuit with), LED driving characteristics isolated from the primary side can be obtained.

The step-down controller applied to FIGS. 5 and 6 has the same configuration as that applied to FIG. 4 and controls the output current in FIGS. 4 and 6 and the output voltage in FIG. 5.

)는 발광 다이오드(

)의 동작을 제어하기 위한 것으로서, 금속 산화막 반도체 전계효과 트랜지스터(metal-oxide-semiconductor field-effect transistor, MOSFET)와, 절연 게이트 양극성 트랜지스터(Insulated gate bipolar transistor, IGBT)와, 접합형 트랜지스터(Bipolar Junction Transistor, BJT), 접합형 전계효과 트랜지스터(Junction Field Effect Transistor, JFET) 등의 파워 스위치를 포함할 수 있다. 이러한 스위칭 소자(

)는 베이스(Gate)가 구동기에 접속되고, 콜렉트(Drain)는 입력 전원(

)과 접속되며, 에미터(소오스)는 센싱 저항(

)과 접속된다.In the LED driving circuit of the step-down converter method capable of directly detecting the voltage / current of the output terminal according to the present invention having the above-described structure (

) Is a light emitting diode (

), Metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), and bipolar junctions. Power switches, such as a Transistor (BJT), a Junction Field Effect Transistor (JFET), and the like. Such switching elements (

The base is connected to the driver, and the drain is the input power (

) And the emitter (source) is a sensing resistor (

) Is connected.

)은 발광 다이오드(

)에 인가되는 전류값(

)을 제어기에 피드백하기 위한 것으로서, 고정된 저항값을 갖는 센싱 저항(

) 대신에 다이오드 및 전류원, 트랜지스터의 크기비를 활용한 검출회로 등과 같은 센싱 소자, 즉, 전류 검출회로를 사용할 수 있다. 이때, 본 실시 예는 전류 검출 회로로 센싱 저 항(

)을 예시한다. 이러한 센싱 저항(

)은 발광 다이오드(

)에 인가되는 전류(

)를 제어에 필요한 궤환 전압(

)으로 변환한다.Sensing resistance (

) Is a light emitting diode (

Current value applied to

) Is fed back to the controller, where the sensing resistor (

Instead, a sensing element such as a diode, a current source, and a detection circuit utilizing the size ratio of the transistor may be used, that is, a current detection circuit. At this time, the present embodiment is a sensing resistor (

). These sensing resistors (

) Is a light emitting diode (

Current applied to

Feedback voltage required to control

To).

As described above, the present invention is provided with a sensing element connected in series with a light emitting diode, so that the step-down type capable of directly detecting voltage / current of an output stage capable of directly detecting and controlling a current flowing in the light emitting diode regardless of the state of the switching element. A converter-type LED driving circuit can be provided. In addition, the present invention can provide a step-down converter light emitting diode driving circuit that can directly detect the voltage / current of the output stage to reduce the product size and the number of elements by eliminating the additional sensing element even under high input voltage.

8, 9, 10, 11, and 12 are modifications of the LED driving circuit of the step-down converter type according to the embodiment of the present invention, wherein the voltage fed back to the control / drive unit is changed to + voltage. Yes. FIG. 8 illustrates a change of a common terminal, a control / driver 140, a sensing element 160, and a light emitting diode in order to supply a voltage fed back to the control / driver 140 as a + voltage as compared with the above-described embodiment of FIG. 4. The connection of the output terminal 200 is partially changed. Specifically, one end of which the voltage of the sensing element 160 is formed higher than the common terminal voltage is connected to the first input end of the control / driver, and the common terminal is changed to the other end of which the voltage of the sensing element 160 is formed low. It was. FIG. 9 illustrates an embodiment in which the positions of the light emitting diode and the inductor constituting the light emitting diode output terminal are changed in the embodiment of FIG. 8.

10, 11, and 12 illustrate an embodiment in which a coil is applied to the light emitting diode output terminal. The primary coil was connected to the sensing element 160, and the light emitting diode was connected to the secondary coil. Compared to the above-described embodiment of FIG. 4, the common terminal is changed, the control / driver 140, the sensing element 160, and the light emitting diode output terminal 200 are supplied to supply the voltage fed back to the control / driver 140 to + voltage. ), Some changes have been made. Specifically, one end of which the voltage of the sensing element 160 is formed to be high is connected to the first input terminal of the control / driver, and the common terminal is changed to the other end of which the voltage of the sensing element 160 is formed to be low. In FIG. 11, a rectifier is added to a secondary coil in the circuit of FIG. 10, and FIG. 12 is a configuration in which a simple rectifier circuit formed of a diode D1 and a capacitor Cf is shown.

Figure 13 is one embodiment according to the invention in which voltage is fed back to the control / driver. 13 is an example corresponding to FIG. 11. In comparison with FIG. 11, in order to supply a voltage fed back to the control / driver 140 with a negative voltage, a change of a common terminal, a connection between the control / driver 140, the sensing element 160, and the light emitting diode output terminal 200 are performed. Some changes were made. Specifically, a configuration in which one end of which the voltage of the sensing element 160 is formed to be high is formed as a common terminal, and the first input of the control / driver is connected to the other end of which the voltage of the sensing element 160 is formed to be low. .

Although described above with reference to the drawings and embodiments, those skilled in the art can be variously modified and changed within the scope of the invention without departing from the spirit of the invention described in the claims below You will understand.

1 and 2 is a light emitting diode driving circuit diagram of a step-down converter capable of detecting the voltage / current of the output stage according to the prior art.

3 is a light emitting diode driving circuit diagram of a step-down converter method capable of directly detecting output stage current according to the present invention.

Figure 4 is a light emitting diode driving circuit diagram of a step-down converter method that can directly detect the voltage / current of the output stage according to the present invention.

5 is a circuit diagram applied to a constant voltage driving circuit for controlling the output voltage by sensing the output voltage in the LED driving circuit of the step-down converter method capable of directly detecting the voltage / current of the output stage according to the present invention.

6 is a circuit diagram of a transformer applied to a light emitting diode driving circuit of a step-down converter type capable of directly detecting a voltage / current of an output terminal according to the present invention;

FIG. 7 is a waveform diagram illustrating current waveforms of an inductor when hysteresis control is applied to a step-down converter type LED driving circuit capable of directly detecting a voltage / current of an output terminal according to the present invention; FIG.

8 and 9 are diagrams illustrating an LED driving circuit of a step-down converter in which a constant voltage is fed back as an embodiment according to the present invention.

10, 11, and 12 are embodiments of the present invention, in which a constant voltage is fed back and a LED driving circuit diagram of a step-down converter method using a coil.

FIG. 13 is a circuit diagram of a LED driving circuit of a step-down converter method using a coil with voltage fed back as an embodiment according to the present invention.

<Description of the symbols for the main parts of the drawings>

10, 100: step-down controller 12: power supply

14, 140: control / driver 120: floating power supply

: 부트스트랩 커패시터

: 스위칭 소자

Bootstrap Capacitors

: Switching element

: 센싱 저항

: 발광 다이오드

Sensing resistance

LED

: 필터 커패시터

: 다이오드

Filter Capacitor

: Diode

: 인덕터

: 기준 전압

: Inductor

Reference voltage

: 궤환 전압

: 입력전압원

Feedback voltage

: Input voltage source

: 트랜스포머

: Transformer

Claims (22)

As a light-emitting diode driving circuit of step-down converter type that can directly detect the voltage / current of the output stage, Input power; A light emitting diode output stage including a light emitting diode; A sensing element having one end connected to a common terminal and the other end connected to one end of the light emitting diode output terminal and outputting a voltage drop value changed according to the amount of current flowing through the light emitting diode; Receiving a driving power connected to the + terminal of the input power and the common terminal, comparing a signal fed back from the other end of the sensing element with an internal reference voltage Vref generated therein, and outputting a comparison value; A drive controller; And A first electrode, a second electrode, and a third electrode, the first electrode is connected to the output terminal of the step driving controller, the second electrode is connected to the + terminal of the input power source, and the third electrode is the common terminal. And a switching element controlling the amount of current supplied to the light emitting diode by being turned on / off in accordance with the comparison value in connection with the voltage converter. The method of claim 1, wherein the step driving controller A floating power supply connected to the + terminal of the input power and the common terminal to receive power and to supply stable power; And And a first input terminal, a power supply terminal, a common connection terminal, and an output terminal, and connect the power supply terminal with the power supplied from the floating power supply, and connect the common connection terminal with the common terminal to supply an internal reference voltage (Vref). ), The one end of the sensing element is connected to the common connection terminal, and the other end of the sensing element is connected to the first input terminal to be applied to the internal reference voltage Vref and the first input terminal. And a control / driver for comparing the voltages and outputting the comparison value to the output terminal. The method of claim 1, And a diode connected in parallel between the one end of the sensing element and the other end of the light emitting diode output end. 3. The method of claim 2, Step-down converter light emitting diode driving circuit, characterized in that the + voltage is fed back between the first input terminal and the common terminal of the control / driver. 3. The method of claim 2, And a voltage is fed back between the first input terminal and the common terminal of the control / driver. The method of claim 1, The light emitting diode output terminal is a step-down converter light emitting diode driving circuit, characterized in that provided with at least one light emitting diode and an inductor (L) connected in series with the light emitting diode. The method of claim 6, And a capacitor C _F connected between the intermediate node to which the light emitting diode and the inductor are connected and the common terminal. The method of claim 6, Step-down converter light emitting diode driving circuit further comprises a capacitor (C _F ) connected in parallel to the light emitting diode. The method according to claim 1 or 2, The light emitting diode output terminal includes a transformer, and a step-down converter light emitting diode driving circuit, characterized in that the light emitting diode is connected to the secondary side of the transformer. The method according to claim 1 or 2, The LED output terminal includes a driving circuit including a DC / DC converter, a charge pump and a constant current source, and at least one light emitting diode or at least one light emitting diode array. The method according to any one of claims 1 to 8, The sensing element is a step-down converter light emitting diode driving circuit, characterized in that the resistance. The method according to any one of claims 1 to 8, And the step-down controller uses a switching converter topology including any one of pulse width modulation control, pulse frequency modulation control, burst control, and hysteresis control. The method according to any one of claims 1 to 8, The switching element is any one selected from a metal oxide semiconductor field effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), a junction transistor (BJT), and a junction field effect transistor (JFET), and the first electrode is a base electrode. Or a gate electrode, wherein the second electrode is a collect electrode or a drain electrode, and the third electrode is an emitter electrode or a source electrode. As a light-emitting diode driving circuit of step-down converter type that can directly detect the voltage / current of the output stage, Input power; A light emitting diode output terminal including a light emitting diode and having one end connected to a common terminal; A sensing element connected in parallel with the light emitting diode output terminal and outputting a voltage drop feedback value changed according to a voltage value applied to the light emitting diode; Step driving is connected to the + terminal of the input power and the common terminal to receive driving power, and compares the voltage drop feedback value output from the sensing element with a reference voltage Vref generated therein and outputs a comparison value. Controller; And A first electrode, a second electrode and a third electrode, the output terminal and the first electrode of the step driving controller is connected, the + terminal and the second electrode of the input power supply is connected, the common terminal and the third electrode And a switching element connected to the switch and controlling the voltage supplied to the light emitting diode by being turned on and off according to the comparison value. 15. The method of claim 14, wherein the step drive controller A floating power supply connected to the + terminal of the input power and the common terminal to receive power and to supply stable power; And And a first input terminal, a power supply terminal, a common connection terminal, and an output terminal, and connect the power supply terminal with the power supplied from the floating power supply, and connect the common connection terminal with the common terminal to supply an internal reference voltage (Vref). And a control / driver for connecting the first input terminal to the voltage drop feedback value to compare the internal reference voltage Vref with a voltage applied to the first input terminal and output a comparison value to the output terminal. A step-down converter light emitting diode drive circuit, characterized in that. The method of claim 15, And a diode connected in parallel between the common terminal and the other end of the light emitting diode output terminal. The method of claim 15, A step-down converter light emitting diode driving circuit further comprises an inductor between the other end of the light emitting diode output terminal and the − terminal of the input power source. The method of claim 15, A step-down converter type light emitting diode driving circuit further comprises a capacitor (C _F ) between the common terminal and the other end of the light emitting diode output terminal. The method of claim 15, The light emitting diode output terminal includes a driving circuit including a constant current source and at least one light emitting diode or at least one light emitting diode array. The method of claim 15, The sensing element includes two resistors connected in series, and a connection node between the two resistors is connected to the first input terminal of the control / driver. The method according to any one of claims 14 to 20, And the step-down controller uses a switching converter topology including any one of pulse width modulation control, pulse frequency modulation control, burst control, and hysteresis control. The method according to any one of claims 14 to 20, The switching element is any one selected from a metal oxide semiconductor field effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), a junction transistor (BJT), and a junction field effect transistor (JFET), and the first electrode is a base electrode. Or a gate electrode, wherein the second electrode is a collect electrode or a drain electrode, and the third electrode is an emitter electrode or a source electrode.

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