KR20150014592A - Multi channel light emitting diode driver - Google Patents

Abstract

The present invention relates to a multi-channel light emitting diode (LED) driver. The multi-channel LED driver for driving a multi-channel LED string including a first LED string and one or more second LED strings requiring power consumption lower than power consumption of the first LED string, includes: a constant voltage controller to generate a first output voltage for driving the multi-channel LED string and to generate a second output voltage when an input voltage is applied; a voltage divider to generate a reference voltage by dividing the second output voltage; and a switch connected to the second LED string in series, and to control a current flowing through the second LED string while being switched according to the reference voltage.

Description

[0001] MULTI CHANNEL LIGHT EMITTING DIODE DRIVER [0002]

The present invention relates to an LED driving circuit, and more particularly, to a multi-channel LED driving circuit for independently driving each of a plurality of LED strings having different driving characteristics.

When a driving circuit for a light emitting diode (LED) is designed, various types of driving circuits can be implemented according to the design purpose. In this case, since the LED driving circuit affects the efficiency and the lifetime of the LED depending on the application purpose, the driving characteristic of the LED, and the configuration of the LED array, in-depth study is needed.

In recent years, LED technology has been rapidly increasing in efficiency due to technological competition. As white LED has been developed, it is spreading to general lighting and high efficiency lighting market, and it is attracting attention as vehicle lighting.

On the other hand, since a liquid crystal display (hereinafter, LCD) can not emit light by itself, a backlight unit is coupled to the back of the LCD panel so that a screen displayed on the LCD can be seen. The design of the driving circuit for the backlight unit is relatively easy since the backlight unit generally employs an LED string and the voltages required to drive each of the plurality of LED strings are all the same.

On the other hand, in other fields including automotive lamps and the like, voltage and current required for driving may be different depending on the type of LED, and driving characteristics and driving conditions may vary depending on the number of the LEDs connected in series or parallel have.

Accordingly, it is difficult to design a driving circuit capable of independently controlling the driving characteristics of each of the multi-channel LED strings.

As a conventional technique for solving the above-mentioned problem, an LED driving circuit as shown in Fig. 1 is introduced.

Referring to FIG. 1, a conventional LED driving circuit includes a constant voltage control unit 100 for driving the LED string 120 for each LED string 120 independently, an LDO (Low Drop out regulator 110, and a switching unit 130 are connected.

The constant voltage controller 100 converts the input voltage VIN into a voltage suitable for driving the LED string 120 and outputs the converted voltage to the LDO 110. The LDO 110 receives a predetermined voltage, And serves to generate a voltage (V _REF ). Then, the switch 130 comprises an operational amplifier, includes a transistor (Q) and a sensing resistor (R _s), the operational amplifier is the voltage on the sense resistor across the inverting terminal (-) in the state applied to, LDO (110) the reference voltage (V _REF) generated by the generating an output voltage as applied to the non-inverting terminal (+) and the transistor (Q) is turned on as the output voltage to the gate terminal is applied (turn on) or off and adjusts the amount of current passing through the LED string 120 while being turned off.

However, in the LED driving circuit of the related art, since the LDO included in the constant voltage control unit is used only for supplying power to other control blocks in the constant voltage control unit, in order to drive the LED string, a separate LDO There was an uneconomical aspect to be installed.

In addition, when the number of channels of the LED string to be controlled increases, the number of the constant voltage control units and the number of LDOs as well as the number of transistors and operational amplifiers increases as well, which makes it difficult to miniaturize the LED driving circuit there was.

In addition, as the number and the number of devices to be mounted within a limited area increase, there is a problem that heat or electrical and physical interference between various devices occurs, thereby limiting the overall reliability of the LED driving circuit.

In the LED driving circuit of the related art, an additional constant voltage control unit and LDO are required as the number of LED strings increases, and there is a problem that power consumption for operating them increases and it is inefficient.

An object of the present invention to solve the above-mentioned problems is to provide a multi-channel LED driving circuit capable of driving a plurality of LED strings having different driving voltages or currents using a single constant voltage control unit.

In addition, the embodiments of the present invention are intended to minimize the heat and the electrical and physical interference between various devices by reducing the number and type of devices to be mounted within a limited area.

Embodiments of the present invention also seek to improve the overall reliability of an LED driving circuit by minimizing electric and physical interference between heat generation and various devices.

In addition, embodiments of the present invention eliminate the necessity of additionally installing the constant voltage control unit and the LDO as the number of LED strings increases, thereby reducing the power consumed by driving the LED.

According to an aspect of the present invention there is provided a multi-channel LED driver for driving a multi-channel LED string comprising a first LED string and at least one second LED string requiring power consumption less than the power consumption of the first LED string A constant voltage control unit for generating a first output voltage for driving the multi-channel LED string when an input voltage is applied and generating a second output voltage, a voltage divider for generating a reference voltage by distributing the second output voltage, And a switching unit connected in series to each of the second LED strings and adjusting a current flowing in the second LED string while switching according to the reference voltage applied from the voltage divider.

In addition, a plurality of the second LED strings may be connected in parallel, and a driving voltage of each of the second LED strings may be different from each other.

The input voltage may be 9V or more and 16V or less, but is not limited thereto.

The constant voltage control unit may further include an SMPS and an LDO that generate the first output voltage for driving the multi-channel LED string when the input voltage is applied, wherein the first output voltage generated by the SMPS is adjusted And a driver IC for controlling the current flowing through the first LED string and generating the second output voltage through the LDO.

In addition, the SMPS may be any one of a boost converter, a buck converter, and a SEPIC, but is not limited thereto.

The driver IC further includes a voltage divider including a high resistance and a low resistance and dividing the first output voltage according to a resistance ratio of the high resistance and the low resistance to generate a feedback voltage signal, The SMPS can be controlled.

In addition, the voltage divider may be provided in the same number as the number of the second LED strings, and each of the voltage dividers may generate a reference voltage corresponding to a predetermined current level for the second LED string.

The switching unit includes a transistor having a drain terminal connected in series with the second LED string, a sense resistor having one end connected in series to the source terminal of the transistor and the other end grounded, and an inverting input terminal connected to the source terminal of the transistor An operational amplifier connected in series, a non-inverting input terminal being supplied with the reference voltage, and an output terminal being connected to a gate terminal of the transistor.

The apparatus may further include an EMI filter disposed between the input voltage and the constant voltage control unit to remove noise or electromagnetic waves included in the input voltage.

In addition, the multi-channel LED string may be a vehicle lamp, but is not limited thereto.

According to embodiments of the present invention, it is possible to provide a multi-channel LED drive circuit capable of driving a plurality of LED strings using a single constant voltage control unit.

In addition, according to the embodiments of the present invention, it is possible to minimize heat and the electrical and physical interference between various components by reducing the number and types of parts to be mounted in a limited area.

In addition, according to the embodiments of the present invention, overall reliability of the LED driving circuit can be improved by minimizing heat generation and electrical and physical interference between various components.

In addition, according to the embodiments of the present invention, it is possible to eliminate the necessity of additionally installing the constant voltage control unit and the LDO as the number of channels of the LED strings increases, thereby reducing the power consumed by driving the LEDs .

1 is a block diagram briefly showing a configuration of a conventional LED driver.
2 is a block diagram briefly showing a configuration of a multi-channel LED driver according to an embodiment of the present invention.
3 is a circuit diagram showing an internal structure of a multi-channel LED driver according to an embodiment of the present invention.
4 is a circuit diagram showing an internal structure of a multi-channel LED driver according to another embodiment of the present invention.

The embodiments disclosed herein should not be construed or interpreted as limiting the scope of the present invention. It will be apparent to those of ordinary skill in the art that the description including the embodiments of the present specification has various applications. Accordingly, it is intended that the scope of the invention be limited not by the claims, but rather by the appended claims, rather than by the claims. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Channel LED driver 200 according to an embodiment of the present invention is a device for driving a first LED string 221 and one or more second LED strings 225 (i.e., a multi-channel LED string).

Here, the first LED string 221 refers to the LED string having the highest driving power consumption among the multi-channel LED strings 220, and the second LED string 225 refers to the first LED string Quot; means all of the LED strings except for the LED 221. Also, a plurality of the second LED strings 225 may be connected in parallel, and the driving voltage or current of each of the second LED strings 225 may be equal to or different from each other.

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

FIG. 2 is a block diagram briefly showing a configuration of a multi-channel LED driver 200 according to an embodiment of the present invention, and FIG. 3 is a circuit diagram illustrating an internal structure of a multi-channel LED driver 200 according to an embodiment of the present invention .

2 to 3, the multichannel LED driver 200 includes a constant voltage control unit 210, a voltage divider 230, and a switching unit 240. Referring to FIG.

The constant voltage control unit 210 may include an SMPS 211 and a driver IC 212. In this case, the driver IC 212 includes an LDO.

The SMPS 211 is an abbreviation of a switching mode power supply. When the input voltage V _IN is applied from a predetermined power source including a battery or the like, And serves to generate a first output voltage 214.

That is, the SMPS 211 converts the applied input voltage V _IN into a voltage suitable for driving the multi-channel LED string 220, that is, the first output voltage 214, anode. The multichannel LED string 220 blinks according to the current generated corresponding to the first output voltage 214 supplied from the SMPS 211. Meanwhile, the driving voltage of a typical LED is 2V to 3V, and the input voltage V _IN applied to the LED driver may be 9V or more and 16V or less, but the present invention is not limited thereto.

The SMPS 211 may be a Boost converter, a buck converter, a buck-boost converter, or a Single Ended Primary Inductance Converter (SEPIC).

The constant voltage control unit 210 may be set to generate the first output voltage 214 based on the driving voltage of the first LED string 221. [

For example, it can be assumed that a 4-channel LED string composed of a first LED string 221 and three second LED strings 225 is driven by receiving an input voltage V _IN of 12V.

If the driving voltage of the first LED string 221 is 16V and the driving voltages of the three second LED strings 225 are 12V, 8V and 4V, respectively, then the minimum voltage that can drive all four-channel LED strings is And the driving voltage of the first LED string 221 is 16V.

In this case, the constant voltage control unit 210 may step up the input voltage V _IN of 12V and generate the first output voltage 214 as 17V or the like according to a predetermined voltage level. The reason why the first output voltage 214 is set to be higher than the drive voltage of the first LED string 221 is that error and loss must be considered.

Voltage divider 230 includes a distribution resistor R _D , R _d . The second output voltage 215 generated by the LDO is distributed according to the resistance ratio of the distribution resistors R _D and R _d to generate a reference voltage.

The voltage dividers 230 are provided in the same number as the number of channels of the second LED string 225 and each of the voltage dividers 230 is connected to a reference voltage (V _REF ). When the SMPS and the driver IC are integrated, the voltage diverter 230 may have the same number as the number of channels of the multi-channel LED string.

As an example, FIG. 3 shows a voltage divider 230 when the second LED string 225 is n-channel.

3, the second output voltage 215 is divided according to the resistance ratio of the distribution resistors R _D1 and R _d1 and converted to a reference voltage V _REF1 for the first channel second LED string 225, _{Divided by} the resistance ratio of the distribution resistances R _Dn and R _dn and converted to the reference voltage V _REFn for the n-channel second LED string 225. Although only the first and n-channel second LED strings 225 are shown in FIG. 3, it should be understood that the second through (n-1) -th channel second LED strings 225 are included.

The driver IC 212 regulates the first output voltage 214 generated by the SMPS 211 and the current flowing through the first LED string 221. That is, the driver IC 212 applies a generally known modulation scheme such as PWM (Pulse Width Modulation) to turn on or off the switching elements (e.g., transistors) in the SMPS 211 the first output voltage 214 can be adjusted by controlling the turn-off of the first output voltage 214.

In addition, the driver IC 212 includes a low dropout regulator (LDO). The LDO is a low-dropout regulator that outputs a stable voltage with respect to input voltage (V _IN ) or load fluctuation. In an embodiment of the present invention, the LDO serves to generate a second output voltage 215 such that the voltage divider 230 can generate the reference voltage V _REF .

The switching unit 240 may include the same number of transistors as the number of channels of the second LED string 225, sense resistors R ₁ to R _n , and an operational amplifier 241.

Referring to FIG. 3, the switching unit 240 switches between the reference voltages V _REF1 to V _REFn to adjust the current flowing in the second LED string 225. Hereinafter, a specific configuration will be described.

The transistors Q ₁ to Q _n have a drain terminal connected in series with the cathode of the second LED string 225. Further, the transistor (Q ₁ ~ Q _n) is the 2-1 LED strings by being turned on (turn on) or off (turn off) depending on the voltage applied to the gate terminal (Gate) from the output terminal of the operational amplifier 241 (225) to the second-n LED string (225).

The sense resistors R _{1 to} R _n have one end connected in series to the source terminal of each of the transistors Q ₁ to Q _n and the other end grounded. The voltages applied across the sense resistors R ₁ to R _n are fed back to the inverting input terminal (-) of the operational amplifier 241.

The operational amplifier 241 has an inverting input terminal (-) connected in series to the source terminal of the transistors Q ₁ to Q _n , a non-inverting input terminal (+) receiving the reference voltage V _REF , And is connected to the gate terminal of the transistor. Here, the output terminal outputs the compensated voltage corresponding to the difference between the reference voltage applied to the non-inverting input terminal (+) and the voltage applied across the sense resistors (R ₁ to R _n ) Current control for the constant current.

Also, the multi-channel LED driver 200 according to an embodiment of the present invention may further include an EMI filter 250 (Electromagnetic Interference filter) and a voltage divider 260.

The EMI filter 250 is installed between the input voltage V _IN and the constant voltage control unit 210 and removes noise or electromagnetic waves included in the input voltage V _IN . Embodiments of the present invention are for driving a multichannel LED string 220 that includes a first LED string 221 and one or more second LED strings 225. In particular, as the number of channels increases, The stability of the input voltage V _IN is very important. That is, the EMI filter 250 stabilizes the input voltage V _IN and supplies the stabilized voltage to the constant voltage controller 210.

Also,

The voltage divider 260 includes a high resistance R _H and a low resistance R _L. That is, the voltage divider 260 generates the feedback voltage signal by dividing the first output voltage 214 according to the resistance ratio of the high resistance R _H and the low resistance R _L. This feedback voltage signal is sensed by the driver IC 212 and the driver IC 212 controls the turn on or turn off of the switching element (e.g., transistor) included in the SMPS 211 The first output voltage 214 can be adjusted.

For example, it can be assumed that the first output voltage 214 is set to 10V. In this case, if the feedback voltage signal generated by the voltage divider 260 is 7V, the driver IC 212 will cause the switching element included in the SMPS 211 to turn off until the feedback voltage signal reaches 10V Can be controlled. If the feedback voltage signal generated by the voltage divider 260 is 12V, the driver IC 212 controls the switching element included in the SMPS 211 to turn on until the feedback voltage signal reaches 10V can do.

4 is a circuit diagram showing an internal structure of a multi-channel LED driver according to another embodiment of the present invention.

4, a multi-channel LED driver 200 according to an exemplary embodiment of the present invention includes a constant voltage control unit 210, a voltage divider 230, and a switching unit 240. Referring to FIG.

In the constant voltage control unit 210, a driver IC integrated with the SMPS and the driver IC, that is, an LDO, may be included in the SMPS.

The SMPS 211 serves to generate a first output voltage 214 for driving the multi-channel LED string 220.

That is, the SMPS 211 converts the applied input voltage V _IN into a voltage suitable for driving the multi-channel LED string 220, that is, the first output voltage 214, anode. The multichannel LED string 220 blinks according to the current generated corresponding to the first output voltage 214 supplied from the SMPS 211.

Voltage divider 230 includes a distribution resistor R _D , R _d . The second output voltage 215 generated by the LDO is distributed according to the resistance ratio of the distribution resistors R _D and R _d to generate a reference voltage.

Also, the voltage divider 230 is provided with the same number of channels as the number of channels of the multi-channel LED string, and each voltage divider 230 generates a reference voltage V _REF corresponding to a predetermined current level for the multi-channel LED string As an example, FIG. 4 shows a voltage divider 230 when the multi-channel LED string is n-channel.

4, the second output voltage 215 is divided according to the resistance ratio of the distribution resistances R _D1 and R _d1 to be converted to a reference voltage V _REF1 for the first LED string 221, and the distribution resistor R _Dn and R _dn and converted to a reference voltage V _REFn for the second-n LED string 225. [ Although only the first LED string 221 and the second-n LED string 225 are shown in FIG. 4, it should be understood that the second through (n-1) th channel second LED strings 225 are included will be.

The switching unit 240 may include the same number of transistors as the number of channels of the multi-channel LED strings, the sense resistors R ₁ to R _n , and the operational amplifier 241.

Referring to FIG. 4, the switching unit 240 switches the reference voltages V _REF1 to V Channel LED string while switching according to the _REFn signal. The specific configuration will be described below.

The drain terminals of the transistors Q ₁ to Q _n are connected in series with the cathodes of the multi-channel LED strings. Further, the transistor (Q ₁ ~ Q _n) is the 1 LED strings (221 by being turned on (turn on) or off (turn off) according to the voltage applied from the output terminal to the gate terminal (Gate) of the operational amplifier 241 (I.e., n-channel) LED string that includes both the first LED string 225 and the second LED string 225.

The sense resistors R _{1 to} R _n have one end connected in series to the source terminal of each of the transistors Q ₁ to Q _n and the other end grounded. The voltages applied across the sense resistors R ₁ to R _n are fed back to the inverting input terminal (-) of the operational amplifier 241.

The operational amplifier 241 has an inverting input terminal (-) connected in series to the source terminal of the transistors Q ₁ to Q _n , a non-inverting input terminal (+) receiving the reference voltage V _REF , And is connected to the gate terminal of the transistor. Here, the output terminal outputs the compensated voltage corresponding to the difference between the reference voltage applied to the non-inverting input terminal (+) and the voltage applied across the sense resistors (R ₁ to R _n ) Control.

Meanwhile, in the multi-channel LED driver 200 according to another embodiment of the present invention, the multi-channel LED string 220 is preferably a vehicle lamp, but is not limited thereto.

The vehicle is equipped with various lamps using LEDs such as Rear Combination Lamp (RCL) and Daylight Running Lamp (DRL).

Even if only the rear combination lamp (RCL) is examined, various LED modules such as a break lamp and a back lamp are applied. Regarding the automobile safety standards, it is required that the break lamp should have a lightness of not less than 40 candelas and not more than 420 candelas, and a back lamp of not less than 2 candelas and not more than 25 candelas, Independent control of the voltage and current required by each string is essential.

Therefore, according to the embodiment of the present invention, the multichannel LED string 220 can be independently controlled, and is thus suitable for driving an LED module employed in a lamp for a vehicle.

The embodiments of the present invention described above are disclosed for the purpose of illustration, and the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention.

200: Multi-channel LED driver 210: Constant voltage control unit
211: SMPS 212: Driver IC
213: LDO 214: first output voltage
215: second output voltage 220: multi-channel LED string
221: first LED string 225: second LED string
230: voltage divider 240:
241: operational amplifier 250: EMI filter
260: voltage divider
V _REF1 to V _REFn : Reference voltage
Q ₁ to Q _n : transistors
R _D1 , R _Dn , R _d1 , R _dn : Distribution resistance
R ₁ to R _n : sense resistor
R _H : High resistance
R _L : Low resistance

Claims (10)

A multi-channel LED driver for driving a multi-channel LED string comprising a first LED string and at least one second LED string requiring power consumption less than the power consumption of the first LED string,
A constant voltage control unit generating a first output voltage for driving the multi-channel LED string when an input voltage is applied, and generating a second output voltage separately from the first output voltage;
A voltage divider for dividing the second output voltage to generate a reference voltage; And
A switching unit serially connected to each of the second LED strings and adjusting a current flowing to the second LED string while switching according to the reference voltage applied from the voltage divider;
A multi-channel LED driver The method according to claim 1,
Wherein a plurality of the second LED strings are connected in parallel and the driving voltages of the second LED strings are different from each other. The method according to claim 1,
Wherein the input voltage is greater than or equal to 9V and less than or equal to 16V. The method according to claim 1,
The constant-
An SMPS for generating the first output voltage for driving the multi-channel LED string when the input voltage is applied; And
A driver IC including a LDO to regulate the first output voltage generated by the SMPS, to control a current flowing in the first LED string, and to generate the second output voltage via the LDO;
A multi-channel LED driver 5. The method of claim 4,
In the SMPS,
A boost converter, a buck converter, or a SEPIC. 5. The method of claim 4,
A voltage divider including a high resistance and a low resistance and dividing the first output voltage according to a resistance ratio of the high resistance and the low resistance to generate a feedback voltage signal;
Further comprising:
And the driver IC controls the SMPS in accordance with the feedback voltage signal. 5. The method of claim 4,
Wherein the voltage divider comprises:
Channel LED driver, wherein the number of the second LED strings is equal to the number of the second LED strings, and each of the voltage dividers generates a reference voltage corresponding to a predetermined current level for the second LED string 5. The method of claim 4,
The switching unit includes:
A drain terminal coupled in series with the second LED string;
A sense resistor having one end connected in series to a source terminal of the transistor and the other end grounded; And
An operational amplifier having an inverting input terminal serially connected to the source terminal of the transistor, a non-inverting input terminal receiving the reference voltage, and an output terminal connected to the gate terminal of the transistor;
A multi-channel LED driver The method according to claim 1,
An EMI filter disposed between the input voltage and the constant voltage control unit for removing noise or electromagnetic waves included in the input voltage;
Channel LED driver < RTI ID = 0.0 > The method according to claim 1,
Channel LED string < RTI ID = 0.0 >

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