CN201017135Y

CN201017135Y - Liquid crystal display LCD backlight inverter

Info

Publication number: CN201017135Y
Application number: CNU2007201190988U
Authority: CN
Inventors: 陈光明; 李锦乐; 何北凯
Original assignee: Shenzhen TCL New Technology Co Ltd
Current assignee: Shenzhen TCL New Technology Co Ltd
Priority date: 2007-03-22
Filing date: 2007-03-22
Publication date: 2008-02-06
Anticipated expiration: 2017-03-22

Abstract

The utility model provides a LCD backlighting inverter comprising a pulse width modulating wave PWM control unit and a full-bridge driving unit which are connected; the output end of the full-bridge driving unit is connected with a full-bridge power switch circuit consisting of four N-channel MOS pipes; the output end of the full-bridge power switch circuit is connected with a plurality of transformers connected in parallel on the primary side and the secondary sides of the transformers are connected with cold cathode ray tubes CCFL one to one.

Description

A kind of liquid crystal display LCD back light inverter

Technical field

The utility model belongs to the LCD technical field, relates in particular to the LCD backlight technology.

Background technology

At present, because CCFL (Cold Cathode Fluorescent Lamp, cold cathode ray tube) technology is through for many years exploitation, technical matters comparative maturity, reliability height, stable performance.So be to adopt CCFL that light source is provided the back lighting of large LCD panel (as the LCD TV).

See also Fig. 1 to Fig. 4, traditional back light inverter power switch adopt more Royer (self-oscillation, self-oscillating), half-bridge, recommend, the mode of full-bridge circuit.Wherein, the Royer circuit such as can't accurately control at electric current or frequency, and giant-screen LCD screen is backlight without this kind topological structure, only adopts in product small part below 20 cun; Half-bridge circuit needs the P channel MOS tube, and it is big that required MOS bears electric current, requires the transformer (cost is higher) of the higher turn ratio, in the also seldom employing of back light inverter of low suppling voltage; The withstand voltage height of the required metal-oxide-semiconductor of push-pull circuit occupies certain application percentage; The power supply scope of application of full-bridge circuit is wide, and it is low that required metal-oxide-semiconductor is withstand voltage, and full-bridge circuit is a back light inverter main flow topological structure at present.

The switching tube that common full-bridge circuit is gone up (containing the transposition full-bridge) bridge circuit mostly is the P channel MOS tube, and the price of equal specification is more than the height of N raceway groove.Owing to the difficult problem of semiconductor technology, the N-channel MOS pipe conducting resistance of full-bridge circuit is bigger simultaneously, and heating is the difficult problem that must face.Many CCFL fluorescent tube LCD display back light inverter of existing 26 cun and above size, the multi-channel parallels that adopt more, the mode of difference driving transformer, disperse power, adopt 4 to 8 road power circuits to promote a plurality of transformers, for arrange plate convenient, reduce to disturb, improve heat-sinking capability, adopt two-sided pcb board material (some adopts a plurality of switching tubes mode directly in parallel especially) more.

The utility model content

The purpose of this utility model is to provide a kind of LCD back light inverter, is intended to solve the too high problem of back light inverter cost that exists in the prior art.

The utility model is achieved in that a kind of LCD back light inverter, and described inverter comprises:

Pulse width modulated wave PWM control module links to each other with the full-bridge driver element, described full-bridge driver element output terminal is connected with the full bridge power on-off circuit of being made up of 4 N-channel MOS pipes, described full bridge power on-off circuit output terminal connects the transformer of a plurality of primary side parallel connections, and described transformer secondary links to each other with cold cathode ray tube CCFL one to one.

The primary side leakage inductance of described transformer, transformer secondary distributed capacitance and primary side external capacitor constitute resonant circuit.

Described transformer high-voltage output is anti-phase in twos.

Each CCFL links to each other the other end ground connection of described transformer secondary output coil with two secondary coils of described transformer.

Described back light inverter also comprises current detecting unit, and described current detecting unit one end connects the output terminal of described CCFL, and an end connects described PWM control module.

Described back light inverter also comprises voltage detection unit, and described voltage detection unit is taken a sample and is input to described PWM control module behind two secondary coil output voltages of described transformer.

Described metal-oxide-semiconductor and transformer are distributed in the same one side of printing board PCB.

The utility model adopt four N-channel MOS pipes constitute single group full-bridge circuits promote 12 only reach above (1 push away 2 transformers then quantity reduce by half) transformer of elementary parallel connection, light more than 12 or 12 and step-up side CCFL fluorescent tube one to one; Adopt the single face pcb board, circuit is succinct, has improved reliability, has reduced cost; In addition, the stable working frequency of 40KHz to 70KHz can be set, the single fluorescent tube of drive waveform near sine of transformer output makes the fluorescent tube maximizing efficiency, and brightness uniformity is better; Regulate brightness and can adopt PWM (pulse width modulated wave) control mode of setting single fixed frequency (120Hz to 300Hz), avoided the sweep signal of drive plate of PWM modulation signal and LCD approaching, cause the phenomenon of interference easily; Adopt the anti-phase in twos technology of transformer output high pressure phase place, further eliminated horizontal moire disturbance.

Description of drawings

Fig. 1 is the circuit diagram of existing Royer driver.

Fig. 2 is the circuit diagram of existing half-bridge driver.

Fig. 3 is the circuit diagram of existing push-pull driver.

Fig. 4 is the circuit diagram of existing full bridge driver.

The circuit diagram of Fig. 5 the utility model full bridge driver.

Embodiment

The technical scheme that the utility model provides is: drive 4 full-bridge circuits that the N-channel MOS pipe is formed by the full-bridge drive IC, full-bridge circuit drives the transformer of a plurality of elementary parallel connections, CCFL fluorescent tube of each transformer secondary output side joint produces sinusoidal wave high pressure and lights the CCFL fluorescent tube by transformer secondary output leakage inductance, transformer secondary output end distributed capacitance and primary side external capacitor (the secondary external capacitor C of Fig. 5 mesohigh) resonance.

In order to make the purpose of this utility model, technical scheme and advantage clearer,, the utility model is further elaborated below in conjunction with drawings and Examples.Should be appreciated that specific embodiment described herein only in order to explanation the utility model, and be not used in qualification the utility model.

Along with development of semiconductor, big conducting electric current, low on-resistance, the cost of the N-channel MOS pipe of low switch loss reduces rapidly, see also Fig. 5, the described back light inverter of the utility model embodiment adopts special-purpose full-bridge drive IC, full-bridge circuit adopts 4 N channel high power metal-oxide-semiconductors, constitute single group full-bridge circuit, drive a plurality of transformers (12 only reach above quantity) of elementary parallel connection, by the transformer secondary output leakage inductance, transformer secondary output end distributed capacitance and secondary external capacitor resonance produce sinusoidal wave high pressure, make the CCFL lamp tube starting that links to each other with each step-up side respectively.Simultaneously,, can adopt the single face pcb board, utilize its surperficial Copper Foil to dispel the heat for metal-oxide-semiconductor owing to the conducting of N-channel MOS pipe, switching loss have bigger reduction than the P channel MOS tube of equal specification pairing.

The CCFL fluorescent tube backlight of giant-screen LCD display adopts a termination high pressure, during the multitube parallel mode of another termination current detecting (low level), many CCFL lamps are by work in unity frequency and unified PWM dim signal control, when the refresh rate multiple of PWM light modulating frequency and liquid crystal display self is identical or close, easily generation level is disturbed line; When the point modulation frequency of INVERTER (inverter) was close with the horizontal refreshing frequency of screen, also easily generation level was disturbed; Also adopt in the present embodiment transformer output high pressure in twos inverse technique solve this problem, as shown in Figure 5, with the 1st, the 2 two adjacent fluorescent tube with same around to transformer connect, with the 3rd, the 4 two adjacent fluorescent tube with same around to transformer connect, with the 5th, the 6th adjacent two fluorescent tubes with same around to the transformer connection Wherein the high pressure output phase of the the the 1st, the 2nd and the 5th, the 6th transformer is identical, 1st, the high pressure output phase of the the 2nd and the 3rd, the 4th transformer is opposite, this kind connected mode, the horizontal interference signals of large screen display is cancelled out each other, weakened, thoroughly eliminated the horizontal interference phenomenon that may occur in the light modulation process.

The PWM control module can be supported intermittently dimming mode of simulation, the PWM of inside/outside portion, adopts inner PWM dimming mode in the present embodiment, and modulating frequency is made as about 190Hz.After the ENA terminal of PWM CONTROLLER (width modulation wave controller) obtains the control signal of high level, the IC internal oscillator (start frequency, frequency of operation can be respectively by external resistance, hold components set) begin the work of higher startup frequency, the soft-start circuit action, drive signal output, in the time of setting of lighting a lamp (being generally) more than or equal to 1.5 seconds, (for example: 0.7V) reach certain value when detecting current feedback signal, think and light a lamp successfully that oscillator reduces frequency and changes normal working frequency over to.Under the selected light-modulating mode, import suitable control signal,, regulate suitable dutycycle, keep the brightness of lamp by detecting current detecting pin voltage.

In the process of lighting a lamp, when detected high pressure feedback voltage reaches 3V, PWM CONTROLLER begins to suppress the increase of dutycycle, high pressure output with this control transformer, make it can not continue to raise, guaranteed the security of elements such as transformer, electric capacity, finish the start-up time that this function can be maintained to light a lamp success or setting.If a certain lamp open circuit; in the process of lighting a lamp; the high pressure of this street lamp pipe is far above the voltage of other fluorescent tubes; pass through feedback network; make VSEN reach upper voltage limit 3V, the increase of restriction point modulating signal dutycycle can not be lighted other fluorescent tubes fully; finally make current detecting pin voltage (voltage that ISEN produces on RSEN among Fig. 5) be lower than threshold value (0.7V), above entering guard mode after the time of setting of lighting a lamp.

If a certain lamp short circuit, in the process of lighting a lamp, this road high pressure is lower, and VCS is lower than datum, and overvoltage protection deboost (OVP) is reduced to 0V, enters guard mode;

In course of normal operation; if a certain lamp open circuit; the high pressure on this road may rise to and be higher than default deboost; cause its feedback voltage (VSEN) that obtains by feedback network to be higher than overvoltage protection deboost (OVP) value of setting; turn-off output drive signal, enter the locking guard mode.

In course of normal operation, if a certain lamp short circuit, the feedback voltage V SEN that obtains by feedback network will reduce, and be lower than the high precision datum, and voltage detecting pin voltage VSENS reduces to 0V, keep the time delay of setting after, enter guard mode;

Work as load short circuits, the PWM modulation signal dutycycle that makes PWM CONTROLLER entered guard mode greater than 45% o'clock; When power switch metal-oxide-semiconductor short circuit damage, fuse can fuse immediately.

Above-mentioned defencive function can be avoided the overvoltage infringement by the protection transformer when startup or fluorescent tube open circuit.

When cold light lamp cools off (in one period that does not have to turn round), the voltage that activates cold light lamp is 2 times of general normal working voltage.The about 50KHz of switching frequency during the back light inverter operate as normal in the present embodiment, the about 62KHz of some modulation frequency is higher than frequency of operation, is convenient to by transformer secondary output and institute's high-voltage capacitance that connects and distributed capacitance resonant, and generation is higher than the some modulating voltage of normal working voltage twice.

The utility model back light inverter comprise be used for driving 12 and more than a plurality of transformers of corresponding one by one CCFL lamp.The primary coil of each transformer is parallel with one another, and each fluorescent tube one end links to each other with the secondary coil of corresponding transformer, the other end (perhaps by the current sampling networking) is connected to ground, the equivalent resistance of each fluorescent tube and transformer secondary output leakage inductance, distributed capacitance, transformer secondary output shunt capacitance are formed independently resonant network, thereby overcome the irregular problem of each road CCFL tube circuit.

The utility model adopts unique full-bridge driver element circuit, adopts 4 N-channel MOS pipes, has improved whole efficiency, has reduced the usage quantity of power MOS pipe; Use the single face pcb board, optimize wiring and eliminate when disturbing, just utilize the monolayer surface Copper Foil to finish the purpose of switching power tube heat radiation.Simplify circuit, improved reliability, reduced the cost of complete machine.

The above only is preferred embodiment of the present utility model; not in order to restriction the utility model; all any modifications of within spirit of the present utility model and principle, being done, be equal to and replace and improvement etc., all should be included within the protection domain of the present utility model.

Claims

1. a LCD back light inverter is characterized in that, described inverter comprises:

2. back light inverter according to claim 1 is characterized in that, the primary side leakage inductance of described transformer, transformer secondary distributed capacitance and primary side external capacitor constitute resonant circuit.

3. back light inverter according to claim 1 is characterized in that, described transformer high-voltage output is anti-phase in twos.

4. back light inverter according to claim 1 is characterized in that, each CCFL links to each other the other end ground connection of described transformer secondary output coil with two secondary coils of described transformer.

5. back light inverter according to claim 1 is characterized in that described back light inverter also comprises current detecting unit, and described current detecting unit one end connects the output terminal of described CCFL, and an end connects described PWM control module.

6. back light inverter according to claim 1 is characterized in that described back light inverter also comprises voltage detection unit, and described voltage detection unit is taken a sample and is input to described PWM control module behind two secondary coil output voltages of described transformer.

7. back light inverter according to claim 1 is characterized in that, described metal-oxide-semiconductor and transformer are distributed in the same one side of printing board PCB.