KR100691188B1 - LED array driving device - Google Patents

Abstract

The present invention relates to a LED array driving apparatus capable of PWM dimming control according to an external control signal while driving a constant current of the LED, the configuration is a predetermined driving power supply through a switching transistor for switching the input power (Vin) on / off A driving circuit unit for applying a to the LED array; A comparison unit which receives a voltage corresponding to the driving current applied from the driving circuit unit to the LED array and compares the reference voltage to obtain a deviation thereof; A PWM IC for generating a switching pulse whose on / off duty ratio is adjusted according to a deviation value output from the comparing unit so that the driving circuit unit is driven with a constant current, and applying the same to a switching transistor of the driving circuit unit to perform constant current control; PWM IC controller which receives the PWM dimming control signal from the outside and transfers the output voltage of the comparator to the PWM IC according to the PWM dimming control signal, or transmits 0V instead of the output voltage of the comparator to the PWM IC to perform dimming control. Characterized in that it comprises a.

LED, constant current, PWM, dimming, color coordinates, luminance

Description

LED array driving apparatus

1 is a circuit diagram showing a conventional LED array driving apparatus.

2 is a block diagram showing a detailed configuration of a PWM IC used in a conventional LED array driving apparatus.

3 is a circuit diagram showing an LED array driving apparatus according to the present invention.

4 (a) and 4 (b) are graphs showing simulation results of the LED driving apparatus according to the present invention.

Explanation of symbols on the main parts of the drawings

31: driving circuit part

32: PWM IC

33: comparator

34: PWM IC control

The present invention relates to an apparatus for driving an LED used as a back light source of an LCD panel, and more particularly, to provide an LED array driving apparatus that enables PWM dimming control for adjusting luminance and color coordinates while driving a constant current of an LED array. It is.

Backlight is a device that illuminates a display panel. In the past, a CCFL (Cold Cathode Fluorescent Lamp) was used as a light source.However, the CCFL may cause environmental hazards due to the use of mercury. In recent years, LED (Light Emitting Diode) devices have been in the spotlight as a light source because they have various problems such as 15ms slow, 75% lower color reproducibility than NTSC, and generate a predetermined white light.

Compared with CCFL, LED is eco-friendly, response speed is several nanoseconds, high speed response is possible, impulsive driving is possible, color reproducibility is over 100%, and the amount of red, blue, and green LEDs is adjusted. Therefore, there are various advantages in that the brightness and color temperature of the backlight can be arbitrarily adjusted.

The driving device for lighting the LED may be implemented in a buck, boost, or buck-boost type, and the LED array is a series of LED devices connected in series. Because there is a forward voltage deviation per connected LED, the LED drive must be driven with a constant current.

Figure 1 shows the LED array driving circuit of the conventional step-down type.

Referring to FIG. 1, a conventional LED array driving apparatus includes a switching element 11 that is provided in series on a power line to which an input power Vin is applied, and switches on / off of the switching element 11. A pin diode D10 and an inductor L10 configured to apply an output voltage to the LED array 10, and a PWM IC to turn on / off the switching element 11 by applying a PWM switching pulse to the switching element 11; (12) is made.

As shown in FIG. 2, the PWM IC 12 compares a reference voltage and a feedback voltage to obtain an deviation thereof, and compares an output signal and a sensing voltage of the error amplifier 123 with a comparator ( 126, an oscillator 127 for generating a reference clock, logic circuits 128, 129, 131 for logically combining the comparison signal, the reference clock, and the like to determine an on / off interval of the pulse, and the logic circuits 128, 129, 131 And a transistor (Q1, Q2) for outputting a predetermined high level voltage (5V) in the on-period and the low level (0V) in the off-period while operating in accordance with the output signal of the 121a, the FB terminal 121b to which the feedback signal fed back from the LED array is input, the CS terminal 121c to receive the sensing voltage, and the RT / CT terminal 121d to which the reference frequency signal is applied, are connected to ground. GND terminal 121e and the switching pulse An input / output terminal including an OUT terminal 121f to be output, a VDD terminal 121g to which a power supply voltage is output, and a VREF terminal 121h to which a reference voltage is applied are provided.

The driving device further includes a sensing resistor Rs for detecting a driving current applied to the LED array 10, and the PWM IC 12 receives the sensing voltage Vs of the sensing resistor Rs from a sensing voltage input terminal ( CS), the width of the switching pulse applied to the switching element 11 is adjusted by comparing the sensing voltage with the reference voltage. By the above, the drive current applied to the LED array 10 is kept constant and constant current control is performed.

The LED array driving apparatus may vary the driving current by adjusting the sensing voltage by implementing the sensing resistor Rs as a variable resistor, but in general, the sensing resistor Rs has a wattage due to a high driving current. ) Because resistance must be used, it is not easy to change, and when using multiple LED driving devices in LED backlight unit, LED driving current deviation occurs due to resistance variation between LED driving devices. Adversely affects control and uniformity.

In addition, the conventional driving circuit cannot take advantage of the LED that can change the brightness and color temperature, and can not satisfy the various brightness and color temperature of the user.

SUMMARY OF THE INVENTION The present invention has been proposed to solve the conventional problems, and an object thereof is to provide a LED array driving apparatus capable of adjusting the luminance and color coordinates by performing PWM dimming control according to an external control signal while driving an LED with a constant current. will be.

As a configuration means for realizing the above object, the LED array driving apparatus according to the present invention, the driving circuit unit for applying a predetermined driving power to the LED array through a switching transistor for switching the input power (Vin) on / off; A comparison unit which receives a voltage corresponding to the driving current applied from the driving circuit unit to the LED array and compares the reference voltage to obtain a deviation thereof; A PWM IC for generating a switching pulse whose on / off duty ratio is adjusted according to a deviation value output from the comparing unit so that the driving circuit unit is driven with a constant current, and applying the same to a switching transistor of the driving circuit unit to perform constant current control; PWM IC controller which receives the PWM dimming control signal from the outside and transfers the output voltage of the comparator to the PWM IC according to the PWM dimming control signal, or transmits 0V instead of the output voltage of the comparator to the PWM IC to perform dimming control. Characterized in that it comprises a.

Hereinafter, an LED array driving apparatus according to the present invention will be described with reference to the accompanying drawings.

3 is a block diagram showing an LED array driving apparatus according to the present invention.

Referring to FIG. 3, the LED array driving apparatus according to the present invention includes a driving transistor 31 that provides driving power to the LED array 30 including a switching transistor Q30 that switches input power Vin on / off. And a PWM IC 32 for outputting a switching pulse of the switching transistor Q30 of the driving circuit part 31 whose on / off duty ratio is adjusted according to the voltage input to the Comp terminal, and the LED in the driving circuit part 31. Comparing unit 33 to compare the voltage applied to the array 30 and the reference voltage and output the deviation to the Comp terminal of the PWM IC 32, and receives the PWM dimming control signal (Vp) from the outside, off And a PWM IC controller 34 which applies 0V to the Comp terminal of the PWM IC 32 so that the switching pulse of the PWM IC 32 becomes 0V when requested.

In the above description, the driving circuit unit 31 may include an inductor L30 connected to an input power source Vin, a switching transistor Q30 connected to the inductor L30, and between the switching transistor Q30 and ground. The sensing resistor Rs provided, the pin diode D30 provided between the inductor L30 and the LED power output terminal Vled connected to the LED array 30, and the cathode and ground of the pin diode D30. It includes a capacitor (C30) provided between.

In the driving circuit unit 31, the input power Vin having a constant amplitude is transformed into a square wave pulse by the on / off switching operation of the switching transistor Q30, which is connected to the pin diode D30 and the capacitor C30. Is applied to the LED array 30. In this case, by adjusting the on / off duty ratio of the switching transistor Q30, the driving current applied to the LED array 30 may be adjusted.

The PWM IC 32 is a constant current mode PWM control circuit. As shown in FIG. 2, the COMP terminal 121a receiving a comparison result and the FB terminal 121b receiving a feedback signal fed back from the LED array. And the CS terminal 121c receiving the sensing voltage, the RT / CT terminal 121d to which the reference frequency signal is applied, the GND terminal 121e connected to the ground, and the OUT terminal 121f to which the switching pulse is output. A VDD terminal 121g for outputting a power supply voltage, a VREF terminal 121h for outputting a reference voltage, a buffer 122 for buffering an output voltage of the VREF 121h, and an output signal of the buffer 122 And an error amplifier 123 for comparing the voltage input to the FB terminal 121b and outputting the deviation, and outputting the output voltages of the error amplifier 123 to the plurality of pin diodes 124, resistors R and Zener. A comparator 126 which is received through the diode 125 and compared with the voltage input to the CS terminal 121c, and the RT / CT The oscillator 127 for generating a reference clock of a predetermined frequency according to the signal input to the terminal 121d and the output signal of the comparator 126 are applied to the set terminal with the output signal of the oscillator 127 being reset. SR flip-flop 128 in operation, a timer 129 for maintaining the output signal of the oscillator 127 for a predetermined time, an output signal of the oscillator 127, an output signal of the timer 129, and the SR flip The OR gate 131 logically sums the output signal of the flop 128 and the ON / OFF operation according to the output signal of the OR gate 131 to output the high level signal 5V or the low level 0V signal to the OUT terminal 121f. Transistors Q1 and Q2 are applied. In addition, reference numerals 130, 132, and 133, which are not described in FIG. 2, are related to the reference voltage VREF, and are not directly related to the PWM dimming operation related to the present invention.

In the present invention, in the PWM IC 32 having the above-described configuration, the Comp terminal 121a is connected to the output of the comparator 33 through the PWM IC control unit 34, and the FB terminal 121b and the GND terminal. The 121e is connected to the ground, the CS terminal 121c is connected to the sensing resistor Rs of the driving circuit unit 31 to receive the sensing voltage Vs, and the OUT terminal 121f is the driving circuit unit 31. Is connected to the gate of the switching transistor Q30, and the power supply V _DD is connected to the VDD terminal 121g. In other words, the LED array driving apparatus of the present invention does not use the FB terminal 121b of the PWM IC 32 described above, but generates a switching pulse using the Comp terminal 121a. There is a big difference.

The comparison unit 33 compares the sensing voltage detected by the sensing resistor Rs of the driving circuit unit 31 with the reference voltage Vref and outputs a voltage corresponding to the deviation. In this case, the reference voltage Vref ) May use the voltage output from the VREF terminal 121h of the PWM IC 32 or may be provided externally.

The PWM IC controller 34 controls the voltage applied to the Comp terminal 121a of the PWM IC 32 according to the PWM dimming control signal Vp applied from the outside, and is connected to the PWM dimming control signal Vp. Connected to the resistor R31, the base is connected to the resistor R31, the emitter is grounded, and the collector is connected to the output of the comparator 33, the NPN transistor Tr1, and the base of the NPN transistor Tr1; A resistor R32 connecting the emitter, a resistor R33 connecting the collector of the NPN transistor Tr1 and the Comp terminal 121a of the PWM IC 32, and a base of the NPN transistor Tr1. The PNP transistor Tr2 is connected to the collector and the emitter is connected to the Comp terminal 121a of the PWM IC 32 and the collector is grounded.

Next, the operation of the LED array driving apparatus shown in FIG. 3 will be described.

The LED array driving apparatus of the present invention described above can control the on / off duty ratio during PWM dimming control from the outside, and corresponds to the on / off ratio of the externally applied PWM dimming control signal Vp. Outputs a switching pulse of a pulse width corresponding to the deviation value of the comparison section 33 to the OUT terminal 121f of the PWM IC 32, or outputs OV regardless of the deviation value of the comparison section 33, The driving current applied to the LED array 30 is adjusted.

In addition, the externally applied PWM dimming control signal Vp has a pulse signal type in which a high level (for example, 5V) and a low level (for example, 0V) are repeated. The operation is divided into a case where the PWM dimming control signal is high level and low level.

First, in the high level section of the externally applied PWM dimming control signal, the base voltage of the NPN transistor Tr1 is turned on and becomes on, thereby maintaining the base potential of the PNP transistor Tr2 at almost OV. Regardless of the output voltage of the comparator 33, the PNP transistor Tr2 is turned on to connect the Comp terminal 121a of the PWM IC 32 to ground.

At this time, the input voltage of the Comp terminal 121a of the PWM IC 32 is input to the comparator 126. Since the input voltage of the Comp terminal 121a is OV in the high level period of the PWM dimming control signal, the comparator In the comparison circuit consisting of the oscillator 127, the SR flip-flop 128, and the or gate 131, the on-period of the switching pulse becomes 0, and OV is output to the OUT terminal 121f.

Since the output voltage of the OUT terminal 121f is applied to the switching transistor Q30, the switching transistor Q30 to which the voltage of OV is applied is turned off.

Accordingly, the output voltage of the PWM IC 32 is maintained at 0 V and the switching transistor Q30 is maintained in the OFF state during the high level period in the PWM dimming control signal Vp.

On the contrary, in the low level section of the externally applied PWM dimming control signal, the base voltage of the NPN transistor Tr1 becomes almost OV, and becomes lower than the threshold voltage, thereby turning off. Therefore, the output voltage of the comparator 33 is applied to the base of the PNP transistor Tr2. Therefore, when the output voltage of the comparator 33 falls below a threshold voltage (for example, 0.7 V), the PNP transistor Tr2 is turned on to turn the Comp terminal 121a of the PWM IC 32 to ground. When the PNP transistor Tr2 is turned off when the voltage of the PNP transistor Tr2 is higher than that of the PWM IC 32, the PNP transistor Tr2 is turned off. It is applied to the Comp terminal 121a.

In this case, the output voltage of the comparator 33 is a deviation between the sensing voltage corresponding to the driving current applied to the LED array 30 and the reference voltage Vref, and is an error amplifier of the PWM IC 32. Corresponds to the deviation value output from 123. As described above, the deviation voltage output from the comparator 33 and input to the Comp terminal 121a is controlled by the comparator 126, the SR flip-flop 128, and the or gate 131. Compared with the sensing voltage of 121c and the output signal of the oscillator 127, in the period corresponding to the frequency of the oscillator 127, the on and off period of the switching pulse corresponding to the deviation is determined, the transistor Q1 By operation Q2), the VDD voltage is output in the set on-region and 0 V is output in the off-region.

That is, during the low level period of the externally applied PWM dimming control signal, the PWM IC 32 operates normally to control the switching of the switching transistor Q30 so that the LED array 30 drives a constant current.

Therefore, by adjusting the ratio between the high level section and the low level section of the PWM dimming control signal, luminance and color coordinate control are possible while driving the LED array 30 with a constant current. In addition, by setting a target luminance or color coordinate, and adjusting the ratio between the high level section and the low level section of the PWM dimming control signal according to the color coordinate or luminance deviation of the actual LED array detected using the sensor, the LED backlight unit It is possible to control to exhibit uniform luminance and color coordinate characteristics in the entire area.

4 (a) and 4 (b) are graphs showing simulation results of the LED array driving apparatus according to the present invention.

4A illustrates a driving current If and driving voltage of the LED array 30 after setting the ratio of the low level section of the PWM dimming control signal to 51.2% in the LED array driving apparatus according to the present invention. (Vf) is measured. At this time, the frequency of the PWM dimming control signal is set to 20 kHz, and the PWM dimming control signal becomes a high level for 24.4 Hz. At this time, the driving current If and the driving voltage Vf applied to the LED array 30 are turned off for 48.8% and turned on for the remaining 51.2%, and a driving power of a predetermined level is applied.

4B shows the case where the on-duty ratio of the PWM dimming control is 73.8%. In the LED array driving apparatus according to the present invention, when the PWM frequency is 20 kHz, the PWM dimming control signal is at a high level for 13.1 kHz. The low level is applied for the rest of the time. At this time, the driving current If and the driving voltage Vf of the LED array 30 operated by the LED array driving apparatus according to the present invention are turned off for 26, 2%, as shown in FIG. It can be seen that it is applied for the remaining 73.8%.

As described above, by changing the PWM dimming control signal applied from the outside, it is possible to adjust the on / off ratio of the drive current of the LED array 30, thereby adjusting the average value of the LED drive current, The amount of light can be adjusted, and as a result, the luminance and color coordinates can be changed.

As described above, the LED array driving apparatus according to the present invention can enable the control of the luminance and color coordinates by PWM dimming while driving the LED array constant current, and further simplify the PWM dimming circuit for luminance and color coordinate control. There is an excellent effect that can be implemented.

Claims (4)

A driving circuit unit for applying a predetermined driving power to the LED array through a switching transistor for switching the input power Vin on / off; A comparison unit which receives a voltage corresponding to the driving current applied from the driving circuit unit to the LED array and compares the reference voltage to obtain a deviation thereof; A PWM IC for generating a switching pulse whose on / off duty ratio is adjusted according to a deviation value output from the comparing unit so that the driving circuit unit is driven with a constant current, and applying the same to a switching transistor of the driving circuit unit to perform constant current control; PWM IC controller which receives the PWM dimming control signal from the outside and transfers the output voltage of the comparator to the PWM IC according to the PWM dimming control signal, or transmits 0V instead of the output voltage of the comparator to the PWM IC to perform dimming control. Including; The driving circuit unit An inductor L30 connected to an input power Vin terminal to which a predetermined level of DC power is applied; A switching transistor Q30 connected to the inductor L30; A sensing resistor Rs provided between the switching transistor Q30 and ground; A pin diode D30 provided between the inductor L30 and the LED power output terminal Vled connected to the LED array 30; It includes a capacitor (C30) provided between the cathode of the pin diode (D30) and the ground, The PWM IC COMP terminal 121a for receiving a comparison result, FB terminal 121b to which a signal corresponding to the LED driving current fed back from the driving circuit unit is input, CS terminal 121c for receiving the sensing voltage; An RT / CT terminal 121d to which a reference frequency signal is applied; OUT terminal 121f to which a switching pulse is output, A buffer 122 for buffering a reference voltage, An error amplifier 123 for comparing the output signal of the buffer 122 with the voltage input to the FB terminal 121b and outputting a deviation thereof; A comparator 126 that receives the output voltage of the error amplifier 123 through a plurality of pin diodes 124, resistors R and zener diodes 125, and compares the voltage with the voltage input to the CS terminal 121c; , An oscillator 127 for generating a reference clock of a predetermined frequency in accordance with the signal input to the RT / CT terminal 121d; SR flip-flop 128 which operates by receiving the output signal of the comparator 126 to the reset stage and the output signal of the oscillator 127 to the set stage, A timer 129 which maintains an output signal of the oscillator 127 for a predetermined time; An OR gate 131 for ORing the output signal of the oscillator 127, the output signal of the timer 129, and the output signal of the SR flip-flop 128; Transistors Q1 and Q2 which are turned on / off according to the output signal of the or gate 131 to apply a high level signal 5V or a low level 0V signal to the OUT terminal 121f; The output terminal of the comparator is applied to the Comp terminal (121a), and the FB terminal (121b) is grounded LED drive device characterized in that the ground. delete delete The method of claim 1, wherein the PWM IC control unit NPN transistor Tr1 to which the PWM dimming control signal Vp is applied to the base and the emitter is grounded through the resistor R31, A resistor R32 connecting the base and the emitter of the NPN transistor Tr1; A resistor R33 connecting the output of the comparator and the Comp terminal 121a of the PWM IC 32; The base is simultaneously connected to the collector of the NPN transistor Tr1 and the output of the comparator, the emitter is connected to the Comp terminal 121a of the PWM IC 32 and the collector comprises a PNP transistor Tr2 which is grounded. LED array drive device.

Images