KR101048175B1 - LED driving circuit - Google Patents

Abstract

The present invention provides an LED driving circuit that can more effectively eliminate the characteristic difference for each string in a string having a plurality of LEDs. To this end, the present invention is a string comprising at least one LED element; And a feedback part for feeding back the current provided by the string to the string through an element having an inductance component.

LED, string, compensation voltage, MOS transistor.

Description

LED driving circuit {LED DRIVING CIRCUIT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (LED) driving circuit, and more particularly, to an LED driving circuit which can effectively adjust a voltage difference applied to each string.

Recently, a liquid crystal display (LCD) device widely used in computers, TVs, and the like is a device for forming a screen by light transmitted through liquid crystals arranged in a matrix form. That is, the LCD device displays a desired image by adjusting the amount of light transmitted through the liquid crystal by the video signal.

LCD devices require a light source that provides light to the liquid crystal, and the block with the light source is generally called a back light unit. Halogen Cathode Fluorescent tube lamps or Cold Cathode Fluorescent tube lamps are mainly used as light sources used in the backlight unit.

In recent years, technologies that use LED devices, which are environmentally friendly and consume less power than lamps used in conventional backlight units, have been developed as light sources for providing light to liquid crystals. LEDs have fast response times of several nanoseconds, making them effective for video signal streams. In addition, when the LED is used, color reproducibility is 100% or more, and luminance, color temperature, and the like can be arbitrarily changed by adjusting the amount of light of the red, green, and blue LEDs, compared to the case of using a conventional lamp. As such, LED has advantages that are suitable for light and small size reduction of LCD panel (Panel) has recently been widely applied as a light source for the backlight of the LCD panel.

When the LED is used as a light source of the LCD device, a plurality of LEDs are arranged at the rear of the LCD panel in a string. It is divided into direct type and edge type according to the position arranged at the back of the LCD panel. However, due to the difference in characteristics inevitably generated in the LED manufacturing process, there is a problem that the characteristics are different for each string consisting of a plurality of LEDs. This is a problem inevitably caused by an imbalance in the manufacturing process, and even if manufactured in the same process, the voltage applied to each string is different. Recently, to solve this problem, blocks that can be corrected for each string have been provided. However, there is a problem that the power consumption is increased due to the additional block provided.

The present invention provides an LED driving circuit that can more effectively eliminate the characteristic difference for each string in a string having a plurality of LEDs.

The present invention is a string comprising at least one LED element; And a feedback part for feeding back the current provided by the string to the string through an element having an inductance component.

In addition, the present invention provides a switch for selectively transferring the current provided by the feedback unit; And a current flow controller for controlling the switch by using current transmitted through the switch. A feedback unit comprising an inductor having the inductance component; And a diode connected in series with the inductor, wherein the string, the inductor, and the diode form a closed loop. The current flow controller may include a resistor including at least one resistor to transfer a current provided from the switch to a ground voltage supply terminal; And an operational amplifier for controlling the switch by comparing a signal applied to a common node of the switch and the resistor unit with a reference signal.

In addition, the present invention includes a first string and a second string each comprising at least one LED element; And a first feedback unit for feeding back a first current provided by the first string to the first string through a device having an inductance component. A second feedback unit for feeding back a second current provided by the second string to the second string through a device having an inductance component; A first current emitter for selectively emitting the first current; And a second current emitter for selectively emitting the second current.

In addition, in order to reduce the difference in the amount of current generated due to the voltage difference applied to each string by the characteristic difference between the first string and the second string, the first current emitter and the second current emitter may adjust the amount of current emitted. Optional control. The first feedback unit may include an inductor having the inductance component; And a diode connected in series with the inductor, wherein the string, the inductor, and the diode form a closed loop. The first current discharging unit may further include a switch for selectively transferring a current transmitted from the first feedback unit; And a current flow controller which controls the switch using the current transmitted through the switch. The current flow controller may further include a resistor including at least one resistor to transfer a current provided from the switch to a ground voltage supply terminal; And an operational amplifier for controlling the switch by comparing a signal applied to a common node of the switch and the resistor unit with a reference signal.

In addition, the present invention is a string comprising at least one LED element; An inductor connected to the string; A diode connected to the inductor, the diode forming a closed loop with the inductor; A switch connected to the inductor; A resistor unit for applying a sensing voltage corresponding to a current transmitted through the switch; And a controller controlling the switch by comparing the sensed voltage with a reference voltage.

According to the present invention, when there is a characteristic difference for each string having a plurality of LEDs, the characteristic difference can be effectively reduced without substantially increasing power consumption. The characteristic difference of each string is naturally occurring in the manufacturing process, and if it is to be reduced to the manufacturing process, expensive manufacturing equipment is required, which may cause a problem that the manufacturing cost increases significantly. Since the present invention can effectively reduce the characteristic difference for each string in circuit, the margin can be maintained in the manufacturing process. Therefore, in manufacturing a device having an LED string, it is possible to easily manufacture a device having an LED string that maintains a certain level of performance without significantly increasing the manufacturing cost.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, in order to facilitate a person skilled in the art to easily carry out the technical idea of the present invention. do.

1 is a circuit diagram showing an LED driving circuit.

Referring to FIG. 1, the LED driving circuit includes a first string driving circuit 10 and a second string driving circuit 20. The first string driving circuit 10 includes a first string 11 in which a plurality of LED elements are connected in series, and the second string driving circuit 20 includes a second string 21 in which a plurality of LED elements are connected in series. do. In addition, the first string driving circuit 10 includes a first current control unit 12 for discharging the current flowing out of the first string 11 and adjusting the amount of current discharged to the ground voltage supply terminal. The second string driving circuit 20 includes a second current controller 22 for discharging the current flowing from the second string 21 and adjusting the amount of current discharged to the ground voltage supply terminal.

The first string driving circuit 10 receives the output of the operational amplifier 12a and the operational amplifier 12a that receives the first reference voltage Vref1 as a positive input and receives the signal of the node A as a negative input. And a resistor (R1, R2) disposed between the bipolar transistor (T1) and the ground voltage supply terminal for inputting to the base terminal and transferring current provided from the first string (11). . The second string driver circuit 20 has a configuration substantially the same as that of the first string driver circuit 10. Here, although the first reference voltage Vref1 and the second reference voltage Vref1 are input to the first and second string driving circuits 10 and 20, the same voltage may be input.

As described above, the first current control unit 12 flows the current provided from the first string 11 to the ground voltage supply terminal, but a more important role occurs due to a difference in characteristics between neighboring strings. It is to reduce the difference in the amount of current. LED devices are manufactured by a semiconductor manufacturing process, and it is difficult for LED devices included in all strings to be manufactured with the same characteristics due to their manufacturing process characteristics. When the characteristics are different for each string, the amount of current flowing during operation also varies for each string, and thus, the voltage applied to each string is not constant and is different from each other. Even if a relatively large amount of current flows in one string due to the difference in voltage applied to each string, a difference in the amount of current flowing in each string may increase rapidly later. If the amount of current flowing in each string is different, the light from the backlight is uneven and different, which means that the image is not evenly displayed on the entire LCD screen.

The first current control unit 12 and the second current control unit 22 adjust the degree of turn-on of the bipolar transistors T1 and T2 provided in accordance with the amount of current provided from the strings, respectively. Adjust the amount of current provided by). For example, assuming that the first string voltage Vd1 across the first string 11 is lower than the second string voltage Vd2 across the second string 21, the first string voltage Vd1. As a result, the current flowing through the first string 11 is greater than the current flowing through the second string 21 by the second string voltage Vd2. Therefore, the voltage of node A becomes higher than the voltage of node B, and the voltage fed back to the operational amplifier 12a through the node A is relatively fed back to the operational amplifier 22a through the node B. Higher than the voltage being. Since the operational amplifiers 12a and 22a receive the voltages of the nodes A and B to the negative input terminal (-), respectively, the output voltage of the operational amplifier 12a becomes smaller than the output voltage of the operational amplifier 22a. . As a result, the degree to which the bipolar transistor T1 is turned on is smaller than that of the bipolar transistor T2, thereby reducing the amount of current flowing in the first string 11.

In conclusion, the voltage applied to the bipolar transistor T1 is higher than the voltage applied to the bipolar transistor T2, thereby controlling the amount of current in which a difference occurs due to the characteristics of each string. As shown in the equation shown at the bottom of FIG. 1, the voltage Vd1 + Vtr1 applied to the first string driver circuit 10 is equal to the voltage Vd2 + Vtr2 applied to the second string driver circuit 20. Even when a plurality of strings are arranged, the voltage level of all strings is adjusted by inducing only the voltage necessary for both ends of the bipolar transistor connected to the remaining strings based on the voltage applied to the highest string.

If the amount of current flowing through the first string and the second string in the same manner as described above is maintained, there is a problem that additional current consumption occurs. Since the difference according to the characteristics of each string is solved by adjusting the voltage difference applied to both ends of the bipolar transistor, the current amount is continuously consumed by the driving of the first current regulator 12 and the second current regulator 22. There is a problem. That is, the problem is that the power consumption continues to be generated by the first current control unit 12 and the second current control unit 22.

The present invention provides an LED driving circuit that reduces the voltage difference applied to each string and substantially eliminates the power consumption.

2 is a block diagram showing an LED driving circuit according to a preferred embodiment of the present invention.

Referring to FIG. 2, the LED driving circuit according to the present embodiment includes first and second strings 110 and 210 including at least one LED element, and an inductance component for the current provided from the first string 110. Feeding back the first feedback unit 120 for feeding back the first string 110 through the device having a second element and the current provided from the second string 210 to the second string 210 through the device having the inductance component. A second feedback unit 220, a switch SW1 for selectively transferring current provided by the first feedback unit 120, and an operational amplifier (described later) for controlling the switch SW1. A second having a first current emitting unit 130, a switch SW2 for selectively transferring current provided from the second feedback unit 220, and an operational amplifier (described later) for controlling the switch SW2. It includes a current discharge unit 230.

FIG. 3 is a circuit diagram of an embodiment of the LED driving circuit shown in FIG. 2.

Referring to FIG. 3, the LED driving circuit according to the present embodiment includes a first string driving circuit 100 and a second string driving circuit 200. The first string driving circuit 100 forms a closed loop with the first string 110 in which a plurality of LED elements are connected in series and the first string 110, and feeds back the current provided from the first string 110. And a first current emitter 130 for selectively discharging a current used when driving the first string 110 and the first feedback unit 120. The second string driver circuit 200 also includes a second string 210, a second feedback unit 220, and a second current discharge unit 230 in substantially the same configuration as the first string driver circuit 100. do. Here, the first reference voltage Va and the second reference voltage Vb are input to the first and second string driving circuits 100 and 200, respectively, but the same voltage may be input.

The first feedback unit 120 is connected to the inductor L1 connected to the first string 110 and the inductor L1 in series, and is connected to the inductor L1 and the first string 110 to be closed. A diode DF1 is formed in a loop. The first current emitter 130 corresponds to a switch MOS transistor M1 for selectively transferring the current provided by the first feedback unit 120, and a current transmitted through the switch MOS transistor M1. The resistor unit 133 for providing the sensing voltage Vr, and the operational amplifier 132 for controlling the MOS transistor M1 by comparing the sensing voltage Vr with the reference voltage Va. The resistor unit 133 includes a variable resistor Rd1 and a plurality of resistors R5 to R7 connected in parallel to the variable resistor Rd1. Here, the operational amplifier 132 and the resistor unit 133 check the amount of current provided through the switch MOS transistor M1 to control the flow of current by controlling the degree of turn-on / turn-off or turn-on of the MOS transistor. It acts as a current flow controller.

As described above, it is very difficult for the operation characteristics of each string 110 and 210 to be the same for the LED manufacturing process or for other reasons. Different operating characteristics of the strings 110 and 210 mean that the amount of current flowing through the strings is different in driving, and therefore, the voltages applied to the strings 110 and 210 are not the same.

For example, suppose that the voltage applied to the first string 110 is lower than the voltage of the second string 210 so that a relatively large amount of current flows. It is assumed that the MOS transistors M1 and M2 are turned off. In this case, the change amount of the current provided to the inductor L1 is larger than the change amount of the current provided to the inductor L2. Due to the closed loop formed by the diode DF1 and the inductor L1, the current applied to the inductor L1 is transferred to the first string 110 through the diode DF1. The amount of current fed back to the second string 210 by the inductor L2 and the diode DF2 is smaller than the amount of current fed back to the first string 110 by the diode DF1 and the inductor L1.

The MOS transistor M1 is turned on or off according to a result of the operational amplifier 132 comparing the sensing voltage Vr and the reference voltage Va generated by the resistor unit 133. When the sensing voltage Vr applied by the resistor unit 133 is high, the voltage of the signal output to the operational amplifier 132 is relatively low, and the MOS transistor 131 is turned off. When the sensing voltage Vr applied by the resistor unit 133 is low, the voltage of the signal output to the operational amplifier 132 is relatively high, and the MOS transistor 131 is turned on. High sensing voltage Vr applied to the resistor unit 133 means that a large amount of current is provided through the switching MOS transistor M1. This is a case where a relatively large amount of current flows due to a low voltage applied to the first string 110, which is sensed by the resistor unit 133 and the operational amplifier 132 so that the switch MOS transistor M1 is turned off. will be.

Therefore, by the above operation, as shown in the lower equation of FIG. 3, the sum of the voltage VL1 by the inductor L1 and the voltage Vd1 applied to the first string 110 is the voltage VL2 by the inductor L2. ) Is equal to the sum of the voltage Vd2 applied to the second string 210.

As described above, in the LED driving circuit according to the present embodiment, the inductors L1 and L2 do not flow the current output from the strings 110 and 210 to the ground voltage supply terminal as in the case of FIG. 1. ) And diodes DF1 and DF2. For this reason, the difference between the voltages applied to the strings 110 and 210 can be reduced. In this case, there is substantially no power consumption due to the characteristics of the inductor. By configuring the inductor as a string and a closed loop, the difference in the amount of current due to the characteristic difference of the strings 110 and 210 can be reduced, thereby effectively solving the problem due to the characteristic difference between the strings without increasing the power consumption.

In addition, the LED driving circuit according to the present embodiment is characterized by the characteristics of the first string 110 and the second string 210 by the current flow control operation of the first current emitter 130 and the second current emitter 230. The difference in the amount of current generated by the difference can be further reduced. In addition, the MOS transistors used to control the emission of the amount of current provided in the string have substantially no current flowing when turned off. Therefore, it is possible to effectively solve the problems caused by the difference in the characteristics of each string without using additional power consumption.

Although the present invention has been described in detail with reference to exemplary embodiments above, those skilled in the art to which the present invention pertains can make various modifications to the above-described embodiments without departing from the scope of the present invention. Will understand. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the scope of the appended claims, as well as the appended claims.

1 is a circuit diagram showing a general LED driving circuit.

2 is a block diagram showing an LED driving circuit according to a preferred embodiment of the present invention.

3 is a circuit diagram according to an embodiment of the LED driving circuit shown in FIG.

Explanation of symbols on the main parts of the drawings

100: first string drive circuit 200: second string drive circuit

110: first LED string 210: second LED string

120: first feedback circuit 220: second feedback circuit

130: first current emitter 230: second current emitter

Claims (15)

delete delete delete delete delete delete delete delete delete delete delete delete delete A string comprising at least one LED element; An inductor connected to the string; A diode connected to the inductor, the diode forming a closed loop with the inductor; A switch connected to the inductor; A resistor unit for applying a sensing voltage corresponding to a current transmitted through the switch; And Control unit for controlling the switch by comparing the detected voltage and the reference voltage LED driving circuit comprising a. The method of claim 14, The resistance unit LED driving circuit including a variable resistor and a plurality of resistors connected in parallel with the variable resistor.

Images