CN102117599A - Backlight driving circuit suitable for liquid crystal display panel - Google Patents

Abstract

The invention is a backlight driving circuit suitable for liquid crystal display panel, which is suitable for liquid crystal display panel to drive multiple strings of light emitting diodes, and at least comprises: a self-excited oscillation circuit receiving the DC voltage to generate an oscillation voltage according to the DC voltage; the transformer comprises a first primary winding and a first secondary winding, the first primary winding is connected with the self-excited oscillation circuit, and the first primary winding receives the oscillation voltage so that the first secondary winding induces to generate an alternating current output voltage; a rectifying circuit connected to the first secondary winding of the transformer and rectifying the ac output voltage into a dc driving voltage; and the filter circuit is connected with the rectifying circuit and the plurality of strings of light emitting diodes and used for filtering the direct current driving voltage so as to drive the plurality of strings of light emitting diodes to operate by the filtered direct current driving voltage. The invention adopts a self-excited driving mode without additionally adding a driving chip, has the advantage of low cost and can solve the problem of overlarge volume of the backlight module.

Description

Backlight driving circuit for liquid crystal display panel

technical field

The invention relates to a backlight driving circuit, in particular to a backlight driving circuit suitable for a liquid crystal display panel.

Background technique

In recent years, with the gradual popularization of LCD TVs, more and more different forms of backlights have been developed one after another. Among them, with the development of light-emitting diodes (LEDs), LEDs have replaced cold cathode lamps (CCFLs) as backlights for LCD TVs. , the advantages of using LED as a backlight include that the volume and power consumption of LED are smaller than that of CCFL, it can achieve thinner product design, and the color saturation is better, as well as the trend of mercury-free environmental protection.

At present, the LED panel in the LCD TV is composed of multiple groups of LED strings, and each LED string is composed of multiple LEDs. The driving method of each LED string uses a driver chip to control the switching element of a voltage conversion circuit to conduct and cut-off, and convert the input voltage to the driving voltage required by the LED string to drive the LED string. However, as the size of the LCD TV continues to increase, the LED strings included in the LED panel also need to be added. In order to maintain For the same brightness, the number of light-emitting diodes in each LED string must be increased correspondingly, so the number of driver chips must also be increased. It is known that using a driver chip to drive the operation of the LED string will make the backlight module of the LCD TV too large. Using a large number of driver chips will also increase the cost of the circuit and fail to meet market competition.

Therefore, how to develop a backlight driving circuit suitable for liquid crystal display panels that can improve the above-mentioned defects of the known technology is an urgent problem to be solved at present.

Contents of the invention

The main purpose of the present invention is to provide a backlight drive circuit suitable for liquid crystal display panels, to solve the problem of using a drive chip to drive the operation of LED light strings, in addition to making the backlight module of the LCD TV too large, and using a large number of drivers. The chip will also increase the cost of the circuit and cannot meet the shortcomings of market competition.

In order to achieve the above purpose, a broad implementation of the present invention is to provide a backlight drive circuit, which is suitable for liquid crystal display panels to drive multiple strings of light-emitting diodes, at least including: a self-excited oscillator circuit, receiving a DC voltage , to generate an oscillating voltage according to the DC voltage; the transformer includes a first primary winding and a first secondary winding, the first primary winding is connected to a self-excited oscillating circuit, and the first primary winding receives the oscillating voltage to induce the first secondary winding Generate an AC output voltage; a rectifier circuit, connected to the first secondary winding of the transformer, and rectify the AC output voltage into a DC drive voltage; and a filter circuit, connected to the rectifier circuit and multiple strings of light-emitting diodes, which filter the DC drive voltage , so that the filtered DC driving voltage drives multiple strings of light-emitting diodes to operate.

In order to achieve the above purpose, the present invention further provides a backlight drive circuit, which is suitable for liquid crystal display panels to drive multiple strings of light-emitting diodes, at least including: a voltage adjustment circuit, which receives an input voltage and adjusts the input voltage to a DC voltage; The excited oscillating circuit is connected with the voltage adjustment circuit, receives the DC voltage, and generates an oscillating voltage according to the DC voltage; the transformer includes the first primary winding and the first secondary winding, and the first primary winding is connected with the self-excited oscillating circuit. A primary winding receives an oscillating voltage to induce the first secondary winding to generate an AC output voltage; a rectifier circuit is connected to the first secondary winding of the transformer and rectifies the AC output voltage into a DC drive voltage; and a filter circuit is connected to the rectifier The circuit and multiple strings of light-emitting diodes filter the DC drive voltage so that the filtered DC drive voltage drives the light-emitting diode elements to operate.

The backlight drive circuit suitable for liquid crystal display panels of the present invention generates an oscillating voltage on the primary side of the transformer through a self-excited oscillating circuit, so that the first secondary winding of the transformer induces an AC output voltage, and the output voltage is generated through a rectifier circuit and a filter circuit. After rectification and filtering, the multiple strings of light-emitting diodes can be driven to run. The self-excited driving method of the present invention does not need to add additional driving chips, which has the advantage of low cost, and can solve the problem that the known use of driving chips will cause the backlight module to be too bulky. Big question. In addition, the present invention can control the conduction phase of the direct current voltage through the voltage adjustment circuit and the dimming signal, so as to control the oscillation time of the oscillation voltage in each half-wave cycle, and further control the luminance of multiple strings of LEDs.

Description of drawings

FIG. 1 is a schematic block diagram of the hardware structure of a backlight driving circuit suitable for a liquid crystal display panel according to a first preferred embodiment of the present invention.

FIG. 2 : It is a schematic block diagram of the hardware structure of the backlight driving circuit suitable for the liquid crystal display panel according to the second preferred embodiment of the present invention.

FIG. 3 : It is a schematic diagram of the internal circuit structure of the voltage adjustment circuit shown in FIG. 2 of the present invention.

FIG. 4 : It is a schematic diagram of the voltage and signal waveform time series in FIG. 2 and FIG. 3 .

The reference numerals in the above-mentioned accompanying drawings are explained as follows:

Backlight drive circuit: 1, 3 Voltage adjustment circuit: 10

Rectifier circuit: 101, 13 Silicon controlled rectifier: 102

Drive circuit: 103 Self-excited oscillation circuit: 11

Transformer: 12 Primary side: 121

Secondary side: 122 Central tap: 123

The first rectifying element: 131 The second rectifying element: 132

Filter circuit: 14 The first filter element: 141

The second filter element: 142 Current sharing circuit: 15

Multiple strings of LEDs: 2 First string of LEDs: 21

The first string of LEDs: 22 Time: t1

Capacitance: C _a , C _r , C _b Resistance: R ₁ , R ₂

First switching element: Q ₁ Second switching element: Q ₂

First primary winding: N _p1 Second primary winding: N _p2

Auxiliary winding: Na The first secondary winding: Ns

Common contact: COM1, COM2 Input voltage: V _in

Oscillation voltage: V _{k AC} output voltage: V _AC

Dimming signal: V _D DC voltage: V _DC

Detailed ways

Some typical embodiments embodying the features and advantages of the present invention will be described in detail in the description in the following paragraphs. It should be understood that the present invention is capable of various changes in different ways without departing from the scope of the present invention, and that the description and drawings therein are illustrative in nature rather than limiting the present invention.

Please refer to FIG. 1 , which is a block diagram of a hardware structure of a backlight driving circuit suitable for a liquid crystal display panel according to a first preferred embodiment of the present invention. As shown in Figure 1, the backlight drive circuit 1 of this embodiment can be applied to a liquid crystal display panel to drive multiple strings of light-emitting diodes 2, wherein the backlight drive circuit 1 at least includes a self-excited oscillator circuit 11, a transformer 12, and a rectifier circuit 13. The filter circuit 14 and the current equalizing circuit 15. The self-excited oscillating circuit 11 can be but not a Royer converter (Royer converter), mainly receiving a DC voltage V _DC , and according to the DC voltage V _DC in the primary circuit of the transformer 12 Side 121 generates an oscillating voltage V _k .

Please refer to FIG. 1 again, the self-excited oscillating circuit 11 of the present invention includes an inductor L _r , a capacitor C _a , a capacitor C _r , a resistor R ₁ , a resistor R ₂ , a first switching element Q ₁ and a second switching element Q ₂ , Wherein, the inductance L _r , the capacitor C _r and the equivalent inductance of the transformer 12 will produce a resonance effect to generate the oscillating voltage V _k on the primary side 121 of the transformer 12. The first switching element Q ₁ and the second switching element Q ₂ can be They are respectively an NPN bipolar junction transistor, but not limited thereto.

The transformer 12 includes a primary side 121, a secondary side 122, and an auxiliary winding _Na . The primary side 121 has a first primary winding _Np1 , a second primary winding _Np2 , and a center tap 123, and the center tap 123 is arranged on the first primary winding. Between _Np1 and the second primary winding _Np2 and connected to the inductor _Lr , one end of the first primary winding _Np1 is connected to the capacitor _Cr and the first switching element _Q1 , the other end is connected to the central tap 123, and the second One end of the primary winding N _p2 is connected to the capacitor C _r and the second switching element Q ₂ , and the other end is connected to the central tap 123 . As for, the secondary side 122 of the transformer 12 has a first secondary winding N _s , one end of which is connected to the common node COM2. One end of the auxiliary winding _Na is connected to the resistor _R1 and the first switching element _Q1 , and the other end is connected to the resistor _R2 and the second switching element _Q2 .

The first switching element _Q1 and the second switching element _Q2 can be respectively an NPN bipolar junction transistor, but not limited thereto, wherein the collector (C) of the first switching element _Q1 and the capacitor _Cr and the second A primary winding _Np1 is connected, the base (B) is connected with the auxiliary winding Na and the resistor _R1 , and the emitter (E) is connected with _the common point COM1. As for the collector of the second switching element _Q2 , the capacitor _Cr and the first The two primary windings _Np2 are connected, the base is connected with the auxiliary winding Na and _the resistor _R2 , and the emitter is connected with the common point COM1.

The auxiliary winding N _a induces a control voltage according to the voltage change of the primary side 121 of the transformer 12, so as to control the interleaved operation between the first switching element _Q1 and the second switching element _Q2 , so that the oscillating voltage V _k is respectively interleaved and transmitted to the first primary winding N _p1 and the second primary winding N _p1 of the transformer 12 , and then the first secondary winding N _s of the secondary side 122 of the transformer 12 is induced to generate an AC output voltage V _AC . Wherein when the control voltage is at a high voltage level, the first switching element _Q1 will be turned on and the second switching element _Q2 will be turned off, so that the oscillating voltage V _k is transmitted to the first primary winding N _p1 of the transformer 12, otherwise, when the control voltage When the voltage level is low, the first switching element Q ₁ is turned off and the second switching element Q ₂ is turned on, so that the oscillating voltage V _k is transmitted to the second primary winding N _p2 of the transformer 12 .

Please refer to Fig. 1 again, the rectifying circuit 13 of the present invention rectifies the AC output voltage V _AC produced by the first secondary winding N _s of the transformer 12 into a DC driving voltage, and includes a first rectifying element 131 and a second rectifying element 132, wherein the first rectifying element 131 and the second rectifying element 132 can be but not limited to a diode. The filter circuit 14 includes a first filter element 141 and a second filter element 142, which mainly filters the DC drive voltage, so that the filtered DC drive voltage drives the corresponding multiple strings of light-emitting diodes 2 to operate, wherein the first filter element 141 And the second filter element 142 can be but not limited to be a capacitor. The first rectifying element 131 is connected with the first secondary winding N _s of the transformer 12 , the first string of LEDs 21 of the multiple strings of LEDs 2 and the first filter element 141 , and the second rectifying element 132 is connected with the first secondary winding N s of the transformer 12 The primary winding N _s , the second string 22 of the multiple strings of LEDs 2 and the second filtering element 142 are connected.

The connection mode of the first rectifying element 131 and the second rectifying element 132 is opposite, the connection mode of the first string of light emitting diodes 21 and the second string of light emitting diodes 22 is opposite, the first rectifying element 131 is in the same phase as the first string of light emitting diodes 21, and the second string of light emitting diodes 21 is in the same phase. The rectifying element 132 is in phase with the second string of LEDs 22, so that the positive voltage of the AC output voltage V _AC is transmitted to the first string of LEDs 21 through the first rectifying element 131, while the negative voltage of the AC output voltage V _AC is rectified by the second string. The components 132 are transmitted to the second string of LEDs 22 so that the first string of LEDs 21 and the second string of LEDs 22 operate alternately.

In addition, a current equalizing circuit 15 is provided between the first secondary winding N _s of the transformer 12 of the present invention and the rectifying circuit 13, which can be but not limited to a capacitor C _b , mainly to maintain the current flowing through the rectifying circuit 13 stable, so as to balance the current flowing through the first string of LEDs 141 and the second string of LEDs 142 .

Please refer to FIG. 2 , which is a block diagram of a hardware structure of a backlight driving circuit suitable for a liquid crystal display panel according to a second preferred embodiment of the present invention. As shown in FIG. 2 , the backlight drive circuit 2 of this embodiment includes a self-excited oscillator circuit 11, a transformer 12, a rectifier circuit 13, a filter circuit 14 and a current equalizing circuit 15, and a voltage adjustment circuit 10, wherein, The circuit structures and connection methods of the self-excited oscillation circuit 11 , the transformer 12 , the rectification circuit 13 , the filter circuit 14 , and the current equalization circuit 15 are the same as those of the first preferred embodiment, and will not be repeated here.

The voltage adjustment circuit 10 controls the voltage or conduction phase of the direct current voltage V _DC according to a dimming signal (Dimming signal) V _D sent by the system circuit board. The voltage adjustment circuit 10 receives an input voltage V _in and a dimming signal. signal V _D , so as to adjust the input voltage V _in to a DC voltage V _DC according to the control of the dimming signal V _D .

In some embodiments, when the input voltage _Vin is a DC voltage, the voltage regulation circuit 10 can be a step-down DC-DC converter, such as a Bulk Converter.

Please refer to FIG. 3 and FIG. 4, wherein FIG. 3 is a schematic diagram of the internal circuit structure of the voltage adjustment circuit shown in FIG. 2 of the present invention, and FIG. 4 is a schematic diagram of the voltage and signal waveform timing diagrams in FIG. The voltage adjustment circuit 10 of this embodiment may include a rectifier circuit 101, a silicon controlled rectifier 102, and a drive circuit 103. The silicon controlled rectifier (SCR) 102 is arranged between the rectifier circuit 101 and the drive circuit 103. When the input voltage _Vin is an AC voltage , the rectifier circuit 101 needs to be converted into a transitional DC voltage first, and the drive circuit 103 receives the dimming signal V _D , and triggers the conduction of the silicon-controlled rectifier 102 mainly according to the control of the dimming signal V _D to control the transmission to the self-excited The conduction phase of the DC voltage V _DC of the oscillating circuit 11 is used to control the oscillating time of the oscillating voltage V _k in each half-wave cycle.

In some embodiments, the silicon controlled rectifier 102 can be replaced by a silicon controlled rectifier.

Please refer to FIG. 4. For example, when the dimming signal V _D is at a high voltage level, such as 6V, the silicon controlled rectifier 102 will output a DC voltage with a low conduction phase, such as 30 degrees. V _DC , on the contrary, when at time t1, the dimming signal V _D is at a low voltage level, for example: 1V, the silicon controlled rectifier 102 will have a high conduction phase, for example: 120 degrees, and output a DC with a smaller conduction phase The voltage V _DC is controlled by the dimming signal V _D to control the conduction phase of the DC voltage V _DC , so that the oscillation time of the oscillation voltage V _k in each half-wave cycle can be controlled, so that the output of the multiple strings of light-emitting diodes 12 in the DC voltage V _DC When the conduction phase is larger, the luminous brightness is higher. On the contrary, when the output conduction phase of the direct voltage V _DC is smaller, the output luminance of the multiple strings of LEDs 12 is weaker.

To sum up, the backlight drive circuit suitable for liquid crystal display panels of the present invention generates an oscillating voltage on the primary side of the transformer through a self-excited oscillating circuit, so that the first secondary winding of the transformer induces an AC output voltage, which is rectified After rectifying and filtering the electric circuit and filter circuit, the multiple strings of light-emitting diodes can be driven to run. The self-excited driving mode of the present invention does not need to add additional driving chips, has the advantage of low cost, and can solve the problem of using the known driving chips. Problems that make the backlight module too bulky. In addition, the present invention can control the conduction phase of the DC voltage through the voltage adjustment circuit and the dimming signal to control the oscillation time of the oscillation voltage in each half-wave cycle, thereby controlling the luminance of multiple strings of LEDs.

The present invention can be modified in various ways by those skilled in the art without departing from the scope of protection as claimed in the appended claims.

Claims (14)

1. backlight drive circuit, it is applicable to a display panels, to drive many string light emitting diodes, comprises at least:

One auto-excitation type oscillating circuit receives a direct current voltage, to produce an oscillating voltage according to this DC voltage;

One transformer comprises the one first elementary winding and first secondary winding, and this first elementary winding is connected with this self-excited oscillation circuit, and this first elementary winding receives this oscillating voltage so that this first secondary winding induction produces an ac output voltage;

One rectification circuit is connected with this first secondary winding of this transformer, and is a direct current driving voltage with this ac output voltage rectification; And

One filtering circuit is connected in this rectification circuit and described many string light emitting diodes, and it carries out filtering to this driving DC voltage, so that filtered this driving DC voltage drives the operation of described many string light emitting diodes.

2. backlight drive circuit as claimed in claim 1, wherein this transformer also has one second an elementary winding and a center tap, and this center tap is arranged between this first elementary winding and this second elementary winding.

3. backlight drive circuit as claimed in claim 2, wherein this auto-excitation type oscillating circuit also comprises an inductance and an electric capacity, this inductance is connected with this center tap, and receive this DC voltage, the two ends of this electric capacity are connected with this first elementary winding and this second elementary winding respectively, the equivalent inductance of this inductance, this electric capacity and this transformer can produce resonance effect, produces this oscillating voltage with the primary side in this transformer.

4. backlight drive circuit as claimed in claim 3, wherein this transformer has an auxiliary winding, and its change in voltage according to the primary side of this transformer is responded to generation one control voltage.

5. backlight drive circuit as claimed in claim 4, wherein this auto-excitation type oscillating circuit also comprises one first on-off element and a second switch element, this first on-off element was connected with assisting an end, this electric capacity and this first elementary winding of winding, this second switch element was connected with assisting the other end, this electric capacity and this second elementary winding of winding, this first on-off element and this second switch element are subjected to the driving of this control voltage and interleaved operation, make this first secondary winding induction produce this ac output voltage.

6. backlight drive circuit as claimed in claim 1, wherein this rectification circuit comprises one first rectifier cell and one second rectifier cell, be connected with this first secondary winding of this transformer respectively, this first rectifier cell is connected with the first string light emitting diode of described many string light emitting diodes, and this second rectifier cell is connected with one second string light emitting diode of described many string light emitting diodes.

7. backlight drive circuit as claimed in claim 6, wherein the connected mode of this first rectifier cell and this second rectifier cell is opposite, make the positive voltage of this ac output voltage be sent to this first string light emitting diode, and the negative voltage of this ac output voltage is sent to this second string light emitting diode via this second rectifier cell via this first rectifier cell.

8. backlight drive circuit as claimed in claim 7, wherein this first string light emitting diode is opposite with the connected mode of this second string light emitting diode.

9. backlight drive circuit as claimed in claim 6, wherein this filtering circuit comprises one first filter element and one second filter element, this first filter element is connected with this first rectifier cell and this first string light emitting diode, and this second filter element is connected with this second rectifier cell and this second string light emitting diode.

10. backlight drive circuit as claimed in claim 1, wherein this backlight drive circuit also comprises a flow equalizing circuit, it is connected with this first secondary winding and this rectification circuit of this transformer, it is stable that the electric current of this rectification circuit of flowing through is kept, with the electric current of this equiulbrium flow through described many string light emitting diodes.

11. backlight drive circuit as claimed in claim 1, wherein this backlight drive circuit also comprises a voltage-regulating circuit, it is connected with this auto-excitation type oscillating circuit, and receives an input voltage, with the control according to a dim signal this input voltage is adjusted into this DC voltage.

12. backlight drive circuit as claimed in claim 1, wherein this voltage-regulating circuit comprises a thyristor.

13. backlight drive circuit as claimed in claim 1, wherein this voltage-regulating circuit comprises a silicon controlled rectifier.

14. a backlight drive circuit, it is applicable to a display panels, to drive many string light emitting diodes, comprises at least:

One voltage-regulating circuit receives an input voltage, this input voltage is adjusted into a direct current voltage;

One auto-excitation type oscillating circuit is connected with this voltage-regulating circuit, receives this DC voltage, to produce an oscillating voltage according to this DC voltage;

One transformer comprises the one first elementary winding and first secondary winding, and this first elementary winding is connected with this self-excited oscillation circuit, and this first elementary winding receives this oscillating voltage so that this first secondary winding induction produces an ac output voltage;

One rectification circuit is connected with this first secondary winding of this transformer, and is a direct current driving voltage with this ac output voltage rectification; And

One filtering circuit is connected in this rectification circuit and described many string light emitting diodes, and it carries out filtering to this driving DC voltage, so that filtered this driving DC voltage drives this light-emitting diode operation.

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