KR101977989B1 - Led driver apparatus - Google Patents

Abstract

An LED driving apparatus is disclosed. The LED driving apparatus includes a DC-DC converter for providing a driving voltage to the LED array, an input unit for receiving a dimming signal for driving the LED array, and a plurality of LED driving units for driving the LED array according to the dimming signal. Each of the drivers is connected in parallel with each other to provide a constant current to the LED array.

Description

LED DRIVER APPARATUS

The present invention relates to an LED driving apparatus, and more particularly, to an LED driving apparatus capable of providing a stable constant current to an LED array using a plurality of constant current sources.

Liquid crystal displays (LCDs) are widely used because they are thinner and lighter in weight than other display devices, have lower driving voltage and lower power consumption. However, since the liquid crystal display device is a non-light emitting device that can not emit light by itself, a separate backlight for supplying light to the liquid crystal display panel is required.

Cold cathode fluorescent lamps (CCFLs) and light emitting diodes (LEDs) are widely used as backlight sources for liquid crystal displays. Since cold cathode fluorescent lamps use mercury, they can cause environmental pollution, have a slow response time, have low color reproducibility, and are not suitable for light and short life of LCD panels.

On the other hand, the light emitting diode is environmentally friendly because it does not use environmentally harmful substances, and has an advantage that the impulse drive can be performed. In addition, it has excellent color reproducibility and is capable of arbitrarily changing the brightness and color temperature by adjusting the light quantity of red, green and blue light emitting diodes, and has merits suitable for thinning and shortening of LCD panel. And it is widely used as a backlight light source.

As described above, when a plurality of light emitting diodes are connected in series in an LCD backlight employing light emitting diodes (i.e., when an LED array is used), a DC-DC converter for adjusting the power supply to the light emitting diodes is required, A drive circuit (specifically, a constant current source) capable of providing a constant constant current is required.

Specifically, to maintain uniform brightness and color in the backlight, all LEDs must be driven with the same current, regardless of the voltage at each LED. In this regard, conventionally, one constant current source is provided at the lower end of the LED array so that the same constant current is provided to the LED array.

However, recently, in order to provide a high constant current as the LED current requirement increases, a transistor in a constant current source is largely realized. In a case where a transistor in a constant current source is largely implemented, a parasitic capacitance component inside the transistor also becomes large, Stability and settling time. Specifically, in order to compensate for the parasitic capacitance component inside the transistor (that is, for the stability of the system), a large capacitor is required. In this case, there is a problem that the settling time of the constant current source is slow.

Accordingly, an object of the present invention is to provide an LED driving apparatus capable of providing a stable constant current to an LED array using a plurality of constant current sources.

According to an aspect of the present invention, there is provided an LED driving apparatus including a DC-DC converter for providing a driving voltage to an LED array, an input for receiving a dimming signal for driving the LED array, And a plurality of LED driving units driving the LED array, wherein each of the LED driving units is connected in parallel to each other to provide a constant current to the LED array.

In this case, each of the LED drivers may provide a constant current of the same magnitude to the LED array.

In this case, each of the LED drivers may provide a constant current of different magnitude to the LED array.

Each of the LED driving units may include a resistor connected to one end of the LED array, a switching unit selectively connecting one end of the LED array and the other end of the resistor, And a comparator for comparing the reference voltage and controlling the switching unit.

In this case, the switching element may be a field effect transistor in which a drain is connected to one end of the LED array, a source is connected to the common node, and a gate is connected to the output terminal of the comparator.

In this case, the comparator may be an OP-AMP that receives the reference voltage as a positive terminal, receives the voltage of the common node as a negative terminal, and outputs the difference to the gate of the transistor.

Meanwhile, the comparator may be operated according to the input dimming signal.

The LED driving apparatus may further include a controller for controlling operation of each of the plurality of LED driving units according to a magnitude of a constant current required for the LED array.

Meanwhile, the LED array may be driven with a current ranging from 50 mA to 150 mA.

As described above, in the LED driving apparatus according to the present embodiment, since a plurality of LED driving units are used, stability can be ensured and a fast fixing time can be ensured.

1 is a block diagram of an LED driving apparatus according to an embodiment of the present invention;
2 is a circuit diagram of a plurality of LED driving units according to the present embodiment,
3 is a circuit diagram of a plurality of LED driving units according to another embodiment.

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

1 is a block diagram of an LED driving apparatus according to an embodiment of the present invention.

1, an LED driving apparatus 1000 includes an input unit 100, a PWM signal generating unit 200, a DC-DC converter 300, a plurality of LED driving units 400, and an LED array 500 .

The input unit 100 receives a dimming signal for driving the LED array 500. Specifically, a direct mode, a fixed phase mode, and a phase shift mode exist as a digital dimming method for an LED. In the direct mode, both the PWM frequency and the on duty are controlled from the outside (PAD). In the fixed phase mode and the phase shift mode, the PWM frequency is generated internally in the IC, . Here, the dimming signal is a signal for adjusting the brightness and color temperature of the LED or for temperature compensation. Although the direct mode method in which the dimming signal is inputted from the outside has been described in the present embodiment, the embodiment may be implemented in the same manner as the fixed phase mode and the phase shift mode.

The PWM signal generator 200 generates a PWM signal for adjusting the power of the LED array 500. Specifically, the PWM signal generator 200 generates a PWM signal for controlling the magnitude of the driving voltage of the DC-DC converter 300.

The DC-DC converter 300 includes a transistor for performing a switching operation, and provides a driving voltage to the LED array 500 by a switching operation of the transistor. Specifically, the DC-DC converter 300 converts the DC voltage based on the PWM signal generated by the PWM signal generator 200, and supplies the converted DC voltage (i.e., the driving voltage) to the LED array 500 do. At this time, the DC-DC converter 300 may provide the LED array 500 with a voltage corresponding to the forward bias voltage of the LED array 500 so that the LED array 500 operates in the saturation region.

The plurality of LED driving units 400 drives the LED array 500 according to a dimming signal. Specifically, the plurality of LED driving units 400 can adjust the driving current in the LED array 500 using the dimming signal input from the input unit 100. [ At this time, each of the plurality of LED driving units 400 may provide the same constant current to the LED array 500, and may provide different constant currents to the LED array 500. The specific configuration and operation of the plurality of LED driving units 400 will be described later with reference to Fig.

The controller 500 controls the operation of each of the plurality of LED drivers according to the magnitude of the constant current required for the LED array 500. Specifically, the controller 500 calculates the magnitude of the constant current necessary for the LED array 500 according to external control or internal calculation, and controls only the LED driver corresponding to the calculated constant current magnitude to operate.

For example, if each of the four LED drivers is capable of providing a constant current of up to 25 mA, and the maximum constant current required for the connected LED array 500 is 100 mA, the controller 500 controls all four LED drivers 400 Can be controlled to operate. If the maximum size of the constant current required for the connected LED array 500 is 50 mA, the controller 600 may operate only the two LED drivers 400.

As described above, the LED driving apparatus 1000 according to the present embodiment provides a constant current to the LED array 500 using a plurality of LED driving units, thereby ensuring stability and securing a fast fixing time.

2 is a circuit diagram of a plurality of LED driving units according to the present embodiment.

Referring to FIG. 2, each of the plurality of LED driving units 400-1, 400-2,... 400-N is connected in parallel to each other to provide a constant current to the LED array 500. FIG. At this time, the sizes of the constant currents provided to the LED array 500 by the plurality of LED driving units may be the same or different. Each of the plurality of LED driving units 400-1, 400-2, ... 400-N includes switching units 410-1, 410-2, ... 410-N, comparators 420-1, 420-2, -N and resistors 430-1, 430-2, ..., 430-N.

Each of the switching units 410-1, 410-2,... 410-N performs a switching operation in accordance with the output signals of the comparators 420-1, 420-2, ... 420-N. Specifically, the switching units 410-1, 410-2,... 410-N may be implemented as field effect transistors, and when implemented as field effect transistors, the drains are connected to one end of the array of LEDs 500 And each of the sources is connected to one end of the resistors 430-1, 430-2, ... 430-N and the gate is connected to the output terminal of each of the comparators 420-1, 420-2, ... 420-N.

Where each of the field effect transistors may have the same size and may have different sizes. Specifically, each of the field effect transistors may have the same allowable current and may have another allowable current.

Each of the comparators 420-1, 420-2, ... 420-N includes switching units 410-1, 410-2, ... 410-N and resistors 430-1, 430-2, ... 430- And controls the switching units 410-1, 410-2,... 410-N by comparing the voltage of the common node in common with the predetermined reference voltage V _REF . Specifically, the comparator 420 may be implemented as an OP-AMP. When implemented as an OP-AMP, a positive terminal is connected to a reference voltage, and a negative terminal is connected to the resistors 430-1, 430-2, ... 430-n and the switching units 410-1, 410-2,... 410-n are connected to a common node in common, and each output terminal is connected to the gate of the field effect transistor.

Each of the comparators 420-1, 420-2,... 420-N receives a dimming signal. More specifically, each of the comparators 420-1, 420-2, ..., 420-n receives a dimming signal as an enable signal so that a constant current is supplied to the LED array 500 when the dimming signal is on The switching units 410-1 and 410-2 are controlled such that the dimming signal is turned off and the supply of the constant current to the LED array 500 is interrupted, , ..., 410-n, respectively.

Each of the resistors 430-1, 430-2, ..., 430-n is connected to the switching units 410-1, 410-2, ... 410-n at one end and grounded at the other end. Here, the resistance values of the resistors 430-1, 430-2, ... 430-n may be the same or different. The respective LED drivers 400-1, 400-2, ..., and 400-n may provide constant currents of different magnitudes to the LED array 500 when the resistance values of the resistors are different.

With such a circuit configuration, the plurality of LED drivers 400 provide a constant current of I _LED size to the LED array. Where I _LED is the sum of the magnitudes of the constant currents of each LED driver 400, i _LED = I _L1 + I _L2 + ... + I _Ln . The constant current of each LED driver 400 has a VREF / R size, and I _LED = V _REF / R ₁ + V _REF / R ₂ + + V _REF / R _n .

On the other hand, when a constant current of 100 mA is required for the LED array 500, when one constant current source is used, the allowable current of one constant current source transistor should be 100 mA or more. Therefore, the parasitic capacitance of the transistor also increases.

However, in the case where a plurality of LED driving units are used, for example, when four LED driving units are used, a plurality of transistors having an allowable current of about 25 mA can be used to drive the LED array 500, Each parasitic capacitance is reduced. Accordingly, it is not necessary to increase the size of the compensation capacitor for reducing the parasitic capacitance, and thus it is possible to secure a fast fixing time.

In the description of FIG. 2, only the LED driver 400 is implemented as three or more LED drivers. However, the LED driver may be implemented using two LED drivers. In the description of FIG. 2, all of the plurality of LED drivers 400 provide a constant current to the LED array 500, but only a part of the plurality of LED drivers 400 may be driven. An embodiment of this will be described below with reference to Fig.

3 is a circuit diagram of a plurality of LED driving units according to the second embodiment.

Referring to FIG. 3, each of the plurality of LED driving units 400 is connected in parallel to each other. The switching units 410-1 and 410-2, the comparators 420-1 and 420-2, and the resistors 430-1 and 430-2 -2).

Each of the switching units 410-1 and 410-2 performs a switching operation in accordance with the output signals of the comparators 420-1 and 420-2. Specifically, the switching units 410-1 and 410-2 may be implemented as a field effect transistor. When implemented as a field-effect transistor, the drain is connected to one end of the LED array 500, 430-1 and 430-2, and the gates thereof are connected to the output terminals of the comparators 420-1 and 420-2, respectively. Where each of the field effect transistors may have the same size and may have different sizes.

Each of the comparators 420-1 and 420-2 includes a comparator 420-1 and a comparator 420-2 that compares the voltage of the common node common to the switching units 410-1 and 410-2 and the resistors 430-1 and 430-2 and the predetermined reference voltage V _REF , And controls the switching units 410-1 and 410-2. Specifically, the comparator 420 may be implemented as an OP-AMP. When implemented as an OP-AMP, a positive terminal is connected to a reference voltage, and a negative terminal is connected to the resistors 430-1 and 430-2 And the switching units 410-1 and 410-2 are commonly connected to a common node, and each output terminal is connected to the gate of the field effect transistor.

Each of the comparators 420-1 and 420-2 receives a control signal. More specifically, each of the comparators 420-1 and 420-2 controls the switching units 410-1 and 410-2 so that a constant current is supplied to the LED array 500 when the control signal of the controller 600 is received. And controls the switching units 410-1 and 410-2 so that the supply of the constant current to the LED array 500 is interrupted when the control signal is turned off.

Each of the resistors 430-1 and 430-2 is connected to the switching units 410-1 and 410-2 at one end and grounded at the other end. Here, the resistance values of the resistors 430-1 and 430-2 may be the same and may be different. When the resistance values of the resistors are different from each other, each of the LED drivers 400-1 and 400-2 may provide a constant current of different magnitude to the LED array 500. [

The controller 600 controls the operation of each of the plurality of LED drivers 400-1 and 400-2 according to the magnitude of the constant current required for the LED array 500. [ Specifically, the controller 600 calculates the magnitude of the constant current necessary for the LED array 500 according to external control or internal calculation, and controls the LED driver to operate only the LED driver corresponding to the calculated constant current. For example, if each of the two LED drivers is capable of providing a constant current of up to 25 mA, and the maximum constant current required for the connected LED array 500 is 50 mA, the controller 600 controls both of the two LED drivers 400 Can be controlled to operate. If the maximum size of the constant current required for the connected LED array 500 is 25 mA, the controller 600 can control the operation of only one LED driver 400-1.

The controller 600 receives the dimming signal, generates a control signal corresponding to the dimming signal, and provides the control signal to each of the comparators 420-1 and 420-2. In the present embodiment, the control unit 600 receives the input dimming signal and provides the corresponding control signals to the comparators 420-1 and 420-2, respectively. However, The dimming signal and the control signal may be input to the AND logic circuit and the output thereof may be provided as an enable signal of the comparator.

1 to 3, only a constant current is provided to only one LED array. However, in an implementation, the LED driving device uses a plurality of LED drivers for each of the plurality of LED arrays, Or may be realized by providing a plurality of constant currents to each of them.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.

1000: LED driving device 100: input part
200: PWM signal generator 300: DC-DC converter
400: LED driver 500: LED array
600:

Claims (9)

In the LED driving device,
A DC-DC converter for providing a driving voltage to the LED array;
An input unit for receiving a dimming signal for driving the LED array;
A plurality of LED drivers driving the LED array according to the dimming signal;
And a controller for controlling at least one LED driver selected among the plurality of LED drivers according to the dimming signal and an enable signal generated based on the control signal according to a magnitude of a constant current required for the LED array,
Each of the LED drivers includes:
A resistor whose one end is grounded;
A switching unit selectively connecting one end of the LED array and the other end of the resistor; And
And a comparator for comparing the voltage of the common node, which is common to the switching unit and the resistor, with a predetermined reference voltage to control the switching unit,
Wherein each of the LED driving units is connected in parallel to provide a constant current to the LED array according to two or more same or different resistance values,
The control unit
And an AND logic circuit receiving the dimming signal and the control signal and outputting the enable signal. The method according to claim 1,
Each of the LED drivers includes:
And provides a constant current of the same magnitude to the LED array. The method according to claim 1,
Each of the LED drivers includes:
And provides the LED array with constant currents of different sizes. delete The method according to claim 1,
Wherein the switching unit is a field effect transistor in which a drain is connected to one end of the LED array, a source is connected to the common node, and a gate is connected to an output terminal of the comparator. 6. The method of claim 5,
The comparator comprising:
And an OP-AMP which receives the reference voltage as a positive terminal, receives the voltage of the common node as a negative terminal, and outputs the difference to the gate of the transistor. The method according to claim 1,
The comparator comprising:
Wherein the LED driving device is operated according to the input dimming signal. The method according to claim 1,
And a controller for controlling the operation of each of the plurality of LED drivers according to a magnitude of a constant current required for the LED array. The method according to claim 1,
The LED array includes:
And is driven with a current of 50mA to 150mA.

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