KR20030030513A - Asynchronous driving circuit of back-light inverter for lcd panel - Google Patents

Abstract

PURPOSE: An asynchronous driving circuit of a backlight inverter for an LCD panel is provided to minimize the generation of switching noise during PWM switching. CONSTITUTION: In the asynchronous driving circuit, the first switching section(31,31a) switches an input voltage(Vin) according to a PWM driving signal. The first signal converting section(32,32a) converts a square wave signal passed through the first switching section(31,31a) into a sine wave signal. A trans and a driving section(33,33a) boost an output signal from the first signal converting section(32,32a) to supply it as a lamp driving signal. An LCD lamp(34,34a) is operated by the lamp driving signal. The second signal converting section(41,41a) converts the square wave signal from the first signal converting section(31) into a triangle wave. A feedback circuit section(42,42a) detects and feedbacks a voltage between both ends of the LCD lamp(34,34a). A comparator(45) compares the output of the feedback circuit section(42,42a) with that of the second signal converting section(41,41a). An output driving section(46) provides a PWM driving signal to the first switching section(31,31a) according to the output of the comparator(45).

Description

Asynchronous driving circuit of backlight inverter for LCD panel {ASYNCHRONOUS DRIVING CIRCUIT OF BACK-LIGHT INVERTER FOR LCD PANEL}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an asynchronous drive circuit of a backlight inverter for an LCD panel, and in particular, in a PWM dimming or a complex (analog and square dimming) method, two driving circuits for PWM operation are provided. Switching noise generated during PWM switching by mismatching switching during PWM operation by using a PWM shift oscillator without matching PWM switching operations in a lamp or more circuit. The present invention relates to an asynchronous driving circuit of a backlight inverter for an LCD panel capable of minimizing occurrence and securing performance and reliability.

In general, the driving circuit of the backlight inverter for the LCD panel adopts a circuit that matches the on / off operation during the PWM switching of the PWM operation section during the PWM dimming. In the LCD backlight inverter (Back_light Inverter) Dimming methods are known as Analog Dim (square wave input brightness adjustment), PWM Dim, Complex Dim (combination analog and square wave input) input brightness adjustment method.

1 is a driving circuit diagram of a conventional backlight inverter for an LCD panel, and FIG. 2 is a timing chart of main signals of FIG. 2.

1 and 2, a driving circuit of a backlight inverter for a conventional LCD panel includes first switching units 11 and 11a for switching an input voltage Vin according to a driving signal, and the first switching unit 11. And a first signal converter 12 and 12a for converting the square wave signal passing through 11a into a sine wave signal, and a transformer and driver for boosting the output signal of the first signal converter 12a as a ramp drive signal. (13, 13a), an LCD lamp (14) operated by the transformer and driver (13, 13a), a feedback circuit section (21) for detecting and feeding back a voltage between both ends of the LCD lamp (14), Generates a triangular wave (SS), and compares the voltage and the triangular wave (SS) by the brightness adjustment of the user to the PWM oscillator 22 for providing a pulse width modulation (PWM) signal, and the output signal of the PWM oscillator 22 A second switching unit 23 for switching between an output terminal of the feedback circuit unit 21 and a ground, and the feed Comparator 24 for comparing the output of the circuit unit 21 and the triangular wave (SS) converted the output signal of the first signal converter 12, and the first switching in accordance with the output of the comparator 24 The output unit 25 provides a PWM driving signal to the unit 11.

In such a conventional circuit, the triangular wave SS generated by the PWM oscillator 22 is output to each of the output drivers 25 and 25a of the transistors Q1 and Q2 included in the first switching units 11 and 11a. By switching Q1 and Q2) to the PWM operation, the on / off sections of waveforms c and d shown in FIG. 2 coincide, that is, the noise generated by the switching operation is synchronous. There is a problem in that the noise is further increased by the on / off switching operation to increase the noise component.

As described above, in the driving circuit of the conventional LCD panel backlight inverter, noise is generated, and such noise may cause shaking on the LCD screen or oscillation operation of the entire ground circuit, making the operation of the circuit unstable. Therefore, there is a problem of degrading the performance of the circuit.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and therefore, an object of the present invention is a square wave input brightness control or a complex method (analog and square wave methods), in which a driving circuit is two lamps during PWM operation. In order to minimize switching noise generated during PWM switching, the PWM shift oscillator can be used to mis-match the switching during PWM operation without matching the switching operation of the PWM. It is possible to provide an asynchronous drive circuit of a backlight inverter for LCD panels that can secure performance and reliability.

1 is a driving circuit diagram of a backlight inverter for a conventional LCD panel.

FIG. 2 is a timing chart of the main signal of FIG. 2.

3 is an asynchronous driving circuit diagram of a backlight inverter for an LCD panel according to the present invention.

4 is a detailed circuit diagram of the PWM shift oscillator 43 of FIG.

5 is a timing chart of the main signal of the present invention.

Explanation of symbols on the main parts of the drawings

31: first switching unit 32: first signal conversion unit

33: transformer and driver 34: LCD lamp

41: second signal conversion section 42: feedback circuit section

43: PWM shift oscillator 44: Second switching unit

45: comparison unit 46: output driver

411: reference voltage setting unit 412: control voltage setting unit

413: addition circuit portion 414: saw tooth wave generation portion

415: first comparator 416: second comparator

As a technical means for achieving the above object of the present invention, the circuit of the present invention converts the first switching unit for switching the input voltage according to the PWM drive signal, and the square wave signal passing through the first switching unit to a sine wave signal A first signal converting unit, a transformer and a driver for boosting an output signal of the first signal converting unit to provide a lamp driving signal, an LCD lamp operated by a lamp driving signal of the transformer and the driving unit, and the first signal A second signal conversion unit for converting the square wave signal of the conversion unit into a triangular wave (SS), a feedback circuit unit for detecting and feeding back a voltage between both ends of the LCD lamp, an output of the feedback circuit unit, and an output of the second signal conversion unit. And a comparator for comparing and an output driver for providing a PWM drive signal to the first switching part in accordance with the output of the comparator. In the asynchronous driving circuit of the backlight panel inverter for LCD panels each included for the LCD lamp, generating a triangular wave, comparing the first variable voltage by the user's brightness adjustment and the triangle wave, the first variable voltage by the user's brightness adjustment A PWM shift oscillator for comparing the second variable voltage and the triangular wave inversely proportional to and providing two first and second PWM signals which are incompatible according to the comparison result; And at least two second switching units for switching between the output terminal of the corresponding feedback circuit unit and the ground by each of the first and second PWM signals of the PWM oscillator.

Hereinafter, the asynchronous driving circuit of the backlight inverter for LCD panel according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is an asynchronous driving circuit diagram of an LCD panel backlight inverter according to the present invention. Referring to FIG. 3, an asynchronous driving circuit of the backlight panel inverter according to the present invention may switch an input voltage Vin according to a PWM driving signal. First switching units 31 and 31a, first signal converting units 32 and 32a for converting square wave signals passing through the first switching units 31 and 31a into sinusoidal signals, and first signal conversion. Transformers and drivers 33 and 33a for boosting the output signals of the units 32 and 32a and providing them as lamp drive signals, and LCD lamps 34 to be operated by the lamp drive signals of the transformers and drivers 33 and 33a. 34a, second signal converters 41 and 41a for converting the square wave signal of the first signal converter 31 into a triangular wave SS, and voltages between both ends of the LCD lamps 34 and 34a. Feedback circuits 42 and 42a for feeding back and outputting the outputs of the feedback circuits 42 and 42a and the second signal; Comparator 45, 45a for comparing the outputs of the affected parts 41, 41a, and an output for providing a PWM drive signal to the first switching units 31, 31a according to the output of the comparator 45, 45a. Drive parts 46 and 46a.

Although the present invention has shown a configuration for driving two LCD lamps as described above, such a configuration substantially consists of a plurality of configurations, the present invention shows a configuration for the two LCD lamps for the purpose of explanation and understanding. .

The present invention is applied to such a conventional circuit, the asynchronous driving circuit of the backlight inverter for LCD panel of the present invention generates a triangular wave (SS), the first variable voltage (Vo) and the triangular wave ( SS), and compares the second variable voltage (V2) and the triangle wave (SS) inversely proportional to the first variable voltage (Vo) by the user's brightness adjustment, and the two first non-synchronous according to each comparison result And an output terminal and a ground of the corresponding feedback circuit part by the PWM shift oscillator 43 for providing the second PWM signals PWM1 and PWMM2 and the first and second PWM signals PWM1 and PWMM2 of the PWM oscillator 43, respectively. At least two second switching sections 44.44a are provided for switching therebetween.

FIG. 4 is a detailed circuit diagram of the PWM shift oscillator 43 of FIG. 3. Referring to FIG. 4, the PWM shift oscillator 43 may include a reference voltage setting unit 411 for setting a reference voltage V1, and An adjustment voltage setting unit 412 for setting an adjustment voltage V2 which is variable according to screen brightness adjustment, a non-inverting (+) terminal connected to an output of the reference voltage setting unit 411, and the adjustment voltage setting unit An operational amplifier (op) including an inverting (-) terminal connected to the output of the (412) through the first resistor (Ra), and the inverting (-) terminal of the operational amplifier (op) and the output of the second An adder circuit portion 413 connected through a resistor Rb, a sawtooth wave generator 414 for generating a sawtooth wave SS of a preset frequency, and an inverted connection connected to the output of the adder circuit portion 413. Terminal), a first comparator 415 including a non-inverting (+) terminal connected to the output of the sawtooth wave generator 414, and a contact of the output of the regulating voltage setting unit 412. And a second comparator 416 including a non-inverting (+) terminal to which it belongs and an inverting (−) terminal connected to the output of the sawtooth wave generator 414.

The addition circuit unit 413 of the PWM shift oscillator 43 may set the resistance ratios of the first resistor Ra and the second resistor Rb differently according to the characteristics of the apparatus and system to which the PWM resistor oscillator 43 is applied. It is preferable to set 1: 1 to have two PWM signals in inverse relationship with each other.

The addition circuit unit 413 of the PWM shift oscillator 43 is configured such that the second variable voltage V2 decreases as the first variable voltage Vo increases, and the variable range of the second variable voltage V2 is reduced. Will be described to fall within the voltage range between the lowest voltage and the highest voltage of the sawtooth wave SS generated by the sawtooth wave generator 414 of the PWM shift oscillator 43.

FIG. 5 is a timing chart of the main signal of the present invention. Referring to FIG. 5, the waveform of FIG. 5 (a) is an output signal of the addition circuit section 413, that is, a signal waveform at the point “a”. The waveform of (b) is the signal waveform at the "b" point corresponding to the control voltage V2 (or the second variable voltage), and the waveform of FIG. 5 (c) is the first comparator 415 of the PWM shift oscillator 43. Signal waveform at the point "c" corresponding to the output voltage of (), and the waveform of FIG. 5 (d) is the signal waveform at the point "d" corresponding to the output voltage of the second comparator 416 of the PWM shift oscillator 43. 5 (e) is a signal waveform at the point “e” corresponding to the voltage input to the non-inverting (+) terminal of the comparison unit 45, and the waveform of FIG. 5 (f) is the comparison unit. The signal waveform at point "f" corresponding to the voltage input to the non-inverting (+) terminal of 45a is the signal waveform at point "g", and the waveform of FIG. Signal waveform to show.

Based on the accompanying drawings, the operation of the preferred embodiment of the present invention configured as described above will be described in detail below.

First, referring to FIG. 3, the asynchronous driving circuit of the LCD panel backlight inverter of the present invention will be briefly described. The first switching unit in which the input voltage Vin supplied from the power supply unit, which is not shown, switches according to a PWM driving signal The square wave signal is converted into a square wave signal by (31,31a), and the square wave signal is converted into a sine wave signal by the first signal converters 32 and 32a. Thereafter, the square wave signal is boosted by the transformer and the driving units 33 and 33a and then supplied to the LCD lamps 34 and 34a to drive signals to light up the LCD lamps 34 and 34a.

The second signal converters 41 and 41a convert the output signals of the first signal converters 31 and 31a into triangle waves SS, and the feedback circuits 42 and 42a convert the LCD lamps ( The voltage between both ends of the 34 and 34a is detected, and the comparing unit 45 and 45a compares the output of the feedback circuit unit 42 with the output of the second signal conversion unit 41, and then outputs the The driving units 46 and 46a provide driving signals to the first switching units 31 and 31a according to the outputs of the comparing units 45 and 45a, so that the first switching units 31 and 31a are connected to the driving signals. Accordingly, the square wave signal is output by performing the on / off operation. Since the configuration and operation are almost the same as the conventional configuration and operation, a detailed description thereof will be omitted.

Hereinafter, the operation of the present invention related to the configuration and operation of the drive circuit of the inverter described above will be described.

3 to 5, in the asynchronous driving circuit of the backlight inverter for LCD panel of the present invention, the PWM shift oscillator 43 shown in Figure 3 generates a triangular wave (SS), and the user's brightness adjustment 1 compares the variable voltage (Vo) and the triangular wave (SS), and compares the second variable voltage (V2) and the triangular wave (SS) in inverse proportion to the first variable voltage (Vo) by the user's brightness control, each comparison As a result, two first and second PWM signals PWM1 and PWM2 are asynchronous.

This will be described in more detail with reference to FIG. 4.

The reference voltage setting unit 411 of the PWM shift oscillator 43 provides a preset reference voltage V1, and adjusts an adjustment voltage V2 that is variable according to a user's screen brightness adjustment. And the addition circuit unit 413 connecting the inverting (-) terminal of the operational amplifier op and the output through the second resistor Rb is inputted through the non-inverting (+) terminal. The reference voltage V1 of the voltage setting unit 411 and the control voltage V2 of the control voltage setting unit 412 inputted through the inverting (-) terminal are added and output. The output voltage Vo, i.e., the voltage at the point "a", can be calculated as shown in Equation 1 below.

As shown in Equation 1, in the addition circuit unit 413 of the PWM shift oscillator 43, the resistance ratio of the first resistor Ra and the second resistor Rb for the purpose of explanation and understanding of the present invention. In the case of setting 1: 1 to be the second equation of the above equation.

As a simple example of the above Equation 1, when the reference voltage V1 is " 2V " and the control voltage is varied from " 1V " to " 3V ", the output voltage Vo of the addition circuit section 413 is described. ), That is, the voltage at the point "a" and the control voltage V2, that is, the voltage at the point "b", may be represented as shown in Table 1 below. Referring to Table 1 below, the PWM shift oscillator 43 In the addition circuit unit 413, it can be seen that as the first variable voltage Vo increases, the second variable voltage V2 decreases at a rate corresponding to the increase rate.

"a" point voltage (Vo) 3 V 2 V 1 V "b" point voltage (V2) 1 V 2 V 3 V

On the other hand, the sawtooth wave generator 414 generates a sawtooth wave SS of a predetermined frequency, which is related to the adjustable range of the second variable voltage (V2), which is shown in FIG. and (a) and (b) waveforms.

Subsequently, the first comparator 415 receives the output voltage Vo, a point voltage of the addition circuit unit 413 input through the inverting terminal and the sawtooth wave generator input through the non-inverting terminal. The sawtooth wave of 414 is compared and outputted. For example, when the voltage at the point “a” is lowered from a high voltage to a low voltage with reference to FIG. 5, as shown in FIG. As shown in Fig. 5 (c), the output voltage of the first comparator 415, that is, the voltage at the point “c”, becomes a first PWM signal having a variable width in which the pulse width gradually increases.

In addition, the second comparator 416 is the sawtooth wave generator 414 input through the control voltage V2 and the inverting (-) terminal of the control voltage setting unit 412 input through the non-inverting (+) terminal. Compared to the sawtooth wave of the output, for example, with reference to Figure 5, for example, as described above, when the voltage of the "a" point is lowered from a high voltage to a low voltage, the voltage of the "b" point is high at a low voltage Voltage, and in this case, as shown in Fig. 5 (b), the output voltage of the second comparator 416, that is, the voltage at the point “d” is shown in Fig. 5 (d). Similarly, the second PWM signal has a variable width in which the pulse width gradually increases.

At this time, it can be seen that the first PWM signal and the second PWM signal are asynchronous PWM signals whose pulses are not synchronized with each other. When the control voltage V2 is increased by the user's adjustment, the voltage at the point “b” increases. At this time, the pulse width of the second PWM signal is also increased. In addition, when the pulse width of the second PWM signal increases, the pulse width of the first PWM signal also increases, so that each of the first and second PWM signals depends on the brightness adjustment of the user, but the two PWM signals are asynchronous with each other. It will contain a pulse of.

Then, the second switching unit 44.44a switches between the output terminal of the corresponding feedback circuit unit and the ground by each of the first and second PWM signals PWM1.PWM2 of the PWM oscillator 43, in which case FIG. 5 As shown in (c) and (d), the first and second PWM signals PWM1.PWM2 allow each transistor of the second switching units 44 and 44a to perform asynchronous on / off operation. Accordingly, the voltage of each of the non-inverting terminals of the second switching units 44 and 44a is as shown in Figs. 5 (e) and (f). The voltage at point g of 3 is as shown in Fig. 5G, and it can be seen from the g signal that the noise is significantly reduced compared with the conventional one.

Like the noise generated by the contact when the mechanical switch is operated, the electronic switch generates fine noise during the switch operation. At this time, when the synchronous operation is performed, the generated noise is summed up to generate a large noise. It can cause adverse effects on the circuit and system, the present invention is to minimize such noise.

As described above, in the present invention, the PWM operation zones in the operation of Q1 and Q2 are divided into waveforms (e) and (f) by the signals of (a) and (b) generated by the PWM Shif OSC 10 during the PWM driving. As shown in (Fig. 2-2), the on / off operation is not matched to minimize the noise generated during PWM switching. Therefore, it is designed to minimize the PWM switching noise generated in the circuit for PWM driving, expect the effect of improving the screen noise (shaking, screen flow, etc.) on the LCD screen, and can further enhance the stabilization of the overall noise of the LCD module.

According to the present invention as described above, in the square wave input brightness control or the complex method (analog method and square wave method), the driving circuit during PWM operation does not match the switching operation of the PWM in two lamps or more circuits. In addition, by using the PWM shift oscillator to perform the mis-matching (switching) during the PWM operation, there is a special effect that can minimize the generation of switching noise generated during PWM switching.

In addition, another effect according to the present invention by using a PWM shift oscillator to attenuate the switching on and off of the PWM switching to improve the noise of the PWM switching during PWM dimming, to offset the switching noise, high-quality PWM Dimming inverter (Inverter) can be provided, and the product does not affect the noise of the LCD screen can be guaranteed the reliability.

The above description is only a description of specific embodiments of the present invention, and the present invention is not limited to these specific embodiments, and various changes and modifications of the configuration are possible from the above-described specific embodiments of the present invention. It will be apparent to those skilled in the art to which the present invention pertains.

Claims (9)

A first switching unit for switching the input voltage Vin according to the PWM driving signal, a first signal conversion unit for converting the square wave signal passing through the first switching unit into a sine wave signal, and an output signal of the first signal conversion unit A transformer and a driver for boosting and providing a ramp driving signal, an LCD lamp operated by a lamp driving signal of the transformer and the driver, and a second signal converter for converting a square wave signal of the first signal converter into a triangular wave (SS); And a feedback circuit unit for detecting and feeding back a voltage between both ends of the LCD lamp, a comparison unit comparing the output of the feedback circuit unit and the output of the second signal conversion unit, and the first switching unit according to the output of the comparison unit. Asynchronous drive of the backlight inverter for the LCD panel including an output driver for providing a PWM drive signal to the plurality of LCD lamps, respectively; In the circuit, The second variable voltage which generates the triangular wave SS, compares the first variable voltage Vo by the user's brightness control with the triangle wave SS, and is inversely proportional to the first variable voltage Vo by the user's brightness control. A PWM shift oscillator 43 for comparing V2 and the triangular wave SS and providing two first and second PWM signals PWM1 and PWM2 which are non-synchronous according to each comparison result; And And at least two second switching parts 44.44a for switching between the output terminal of the corresponding feedback circuit part and the ground by each of the first and second PWM signals PWM1.PWM2 of the PWM oscillator 43. Asynchronous drive circuit of backlight inverter for LCD panel. The method of claim 1, wherein the PWM shift oscillator 43 A reference voltage setting unit 411 for setting a reference voltage V1; An adjustment voltage setting unit 412 for setting an adjustment voltage V2 variable according to a user's screen brightness adjustment; And a non-inverting (+) terminal connected to the output of the reference voltage setting unit 411 and an inverting (-) terminal connected to the output of the control voltage setting unit 412 through a first resistor Ra. An addition circuit section 413 including an operational amplifier (op), and connecting an inverting (-) terminal of the operational amplifier (op) and an output through a second resistor (Rb); A sawtooth wave generator 414 for generating a sawtooth wave SS of a preset frequency; A first comparator (415) including an inverting (-) terminal connected to the output of the addition circuit unit 413 and a non-inverting (+) terminal connected to the output of the sawtooth wave generator 414; And a second comparator 416 including a non-inverting (+) terminal connected to the output of the regulated voltage setting unit 412 and an inverting (-) terminal connected to the output of the sawtooth wave generator 414. Asynchronous drive circuit of the backlight inverter for LCD panels. The control voltage setting unit 412 of the PWM shift oscillator 43 And a variable range of the second variable voltage (V2) is set to correspond to a voltage range of the sawtooth wave (SS) generated by the sawtooth wave generating unit (414). 3. The addition circuit portion 413 of the PWM shift oscillator portion 43 An asynchronous driving circuit of a backlight inverter for an LCD panel, characterized in that the resistance ratio of the first resistor Ra and the second resistor Rb is set to 1: 1. 5. The addition circuit portion 413 of the PWM shift oscillator portion 43 And a second variable voltage V2 decreases as the first variable voltage Vo increases. A first switching unit for switching the input voltage Vin according to the PWM driving signal, a first signal conversion unit for converting the square wave signal passing through the first switching unit into a sine wave signal, and an output signal of the first signal conversion unit A transformer and a driver for boosting and providing a ramp driving signal, an LCD lamp operated by a lamp driving signal of the transformer and the driver, and a second signal converter for converting a square wave signal of the first signal converter into a triangular wave (SS); And a feedback circuit unit for detecting and feeding back a voltage between both ends of the LCD lamp, a comparison unit comparing the output of the feedback circuit unit and the output of the second signal conversion unit, and the first switching unit according to the output of the comparison unit. Asynchronous drive of the backlight inverter for the LCD panel including an output driver for providing a PWM drive signal to the plurality of LCD lamps, respectively; In the furnace, A reference voltage setting unit 411 for setting a reference voltage V1; An adjustment voltage setting unit 412 for setting an adjustment voltage V2 variable according to a user's screen brightness adjustment; And a non-inverting (+) terminal connected to the output of the reference voltage setting unit 411 and an inverting (-) terminal connected to the output of the control voltage setting unit 412 through a first resistor Ra. An addition circuit section 413 including an operational amplifier (op), and connecting an inverting (-) terminal of the operational amplifier (op) and an output through a second resistor (Rb); A sawtooth wave generator 414 for generating a sawtooth wave SS of a preset frequency; A first comparator (415) including an inverting (-) terminal connected to the output of the addition circuit unit 413 and a non-inverting (+) terminal connected to the output of the sawtooth wave generator 414; A second comparator 416 including a non-inverting (+) terminal connected to the output of the regulating voltage setting unit 412 and an inverting (-) terminal connected to the output of the sawtooth wave generating unit 414; At least two second switching units 44.44 for switching between the output terminal of the corresponding feedback circuit unit and the ground by the first and second PWM signals PWM1.PWM2 of the first comparator 415 and the second comparator 416, respectively. A) asynchronous drive circuit of the backlight inverter for LCD panels characterized in that it comprises a). The method of claim 6, wherein the control voltage setting unit 412 of the PWM shift oscillator 43 And a variable range of the second variable voltage (V2) is set to correspond to a voltage range of the sawtooth wave (SS) generated by the sawtooth wave generating unit (414). The method of claim 6, wherein the addition circuit section 413 An asynchronous driving circuit of a backlight inverter for an LCD panel, characterized in that the resistance ratio of the first resistor Ra and the second resistor Rb is set to 1: 1. The method of claim 8, wherein the addition circuit unit 413 And a second variable voltage V2 decreases as the first variable voltage Vo increases.