CN1667458B

CN1667458B - Liquid crystal display system with lamp feedback

Info

Publication number: CN1667458B
Application number: CN 200510008141
Authority: CN
Inventors: 林永霖; 柳达
Original assignee: O2 Tech International Ltd
Current assignee: O2 Tech. International Ltd.
Priority date: 2004-02-11
Filing date: 2005-02-08
Publication date: 2012-09-26
Anticipated expiration: 2025-02-08
Also published as: TWI270839B; TW200537407A; CN1667458A

Abstract

A liquid crystal display system and CCFL power converter circuit is provided using a high-efficiency zero-voltage-switching technique that eliminates switching losses associated with the power MOSFETs. An optimal sweeping-frequency technique is used in the CCFL ignition by accounting for the parasitic capacitance in the resonant tank circuit. Additionally, the circuit is self-learning and is adapted to determine the optimum operating frequency for the circuit with a given load. An over-voltage protection circuit can also be provided to ensure that the circuit components are protected in the case of open-lamp condition.

Description

Liquid crystal display system with lamp feedback

Technical field

The present invention about direct current to exchanging power converter circuit.More particularly, the invention provides a kind of efficient controller circuitry, this controller circuitry uses the zero voltage switching technology to be adjusted to the power of load.The present invention generally is applied to drive the circuit of one or more cold-cathode fluorescence lamps (CCFL), and still, those skilled in the art can learn that the present invention can be applied to the load of the efficient and accurate power control of any needs.

Background technology

Fig. 1 has described a traditional C CFL power-supply system 10.This system comprises a power supply 12, one CCFL driving circuit 16, one controllers, 14, one feedback control loops 18 and the one or more CCFL that are associated with LCD plate 20 substantially.Power supply 12 provides a DC voltage to circuit 16, and is controlled by controller 14 through transistor Q3.Circuit 16 is self-resonance circuit, is known as Roy's circuit (Royer circuit).In essence, circuit 16 be a self-oscillation direct current to a-c transducer, its resonance frequency determines by L1 and C1, N1 to N4 specifies the number of turn of Transformer Winding and winding.At work, alternately conducting and switch in the input voltage on winding N1 and the N2 respectively of transistor Q1 and Q2.If the Q1 conducting, then input voltage is added on the winding N1.Voltage with relative polarity will be placed on another winding.The base stage that the induced voltage of N4 makes Q2 is for just, and Q1 is by the small voltage drop conducting between the collector and emitter.The induced voltage of N4 also makes Q2 remain on cut-off state.The Q1 conducting is till the magnetic flux in the TX1 magnetic core reaches capacity.

When saturated, the voltage of the collector of Q1 rises rapidly (to the numerical value by base circuit determined), and the induced voltage in the transformer descends rapidly.Q1 far is pulled away from state of saturation and V _CERise, cause that the voltage on the N1 further descends.Loss in the base drive causes Q1 to end, like this and magnetic flux in the iron core is descended slightly and in N4, produce an electric current and make the Q2 conducting.The induced voltage of N4 makes Q1 remain on the saturation conduction state, and is saturated in inverse direction until iron core, and a similar inverse process generation, switches circulation to accomplish.

Although anti-phase appliance circuit 16 is made up of quite few element, the non-linear complicated interaction of transistor and transformer is depended in its suitable work.In addition, the variation of C1, Q1 and Q2 (typically being 35% tolerance) does not allow circuit 16 to be applicable to the parallel pressure change apparatus, because any duplicating of circuit 16 all can produce extra undesirable frequency of operation, this frequency of operation maybe be at some harmonic wave place resonance.When being applied to the CCFL load, this circuit produces " flapping " effect of significantly not expecting in CCFL.Even tolerance almost meets, but because circuit 16 is operated in the self-resonance pattern, " flapping " effect can not be removed, because duplicating of any this circuit will have himself distinctive frequency of operation.

In United States Patent (USP) the 5th, 430,641; 5,619,402; 5,615,093; Can find some other drive system in 5,818, No. 172.These reference papers all have poor efficiency, two-stage power conversion, and frequency conversion operation, and/or the shortcoming of correlativity is arranged with load.In addition, when load comprises CCFL and assembly, can introduce stray capacitance, thereby influence the impedance of CCFL itself.In order to design the circuit of a suitable job effectively, this circuit design must be considered the spurious impedance that is used to drive the CCFL load.This type of effort is not only consuming time, expensive, and when handling different loads, also is difficult to produce the converter design an of the best.Therefore, need overcome these shortcomings and a circuit solution is provided, this circuit have reliably the lighting a lamp of high-level efficiency, CCFL, with the characteristics of the power transfer of irrelevant power adjustments of load and single-frequency.

Summary of the invention

The invention provides a liquid crystal display systems, this system comprises: a LCD panel; One be used for throwing light on said LCD panel cold-cathode fluorescence lamp; One is coupled to the secondary transformer winding of cold-cathode fluorescence lamp, and this winding provides electric current to cold-cathode fluorescence lamp; One is coupled to the primary transformers winding of secondary transformer winding, and this winding provides magnetic flux for the secondary transformer winding; One is coupled to the switch of primary transformers winding, and this switch allows electric current primary transformers winding of flowing through; One is coupled to the feedback control loop circuit of cold-cathode fluorescence lamp; This circuit receives an expression and provides to the feedback signal of the power of cold-cathode fluorescence lamp; And and if only if said feedback signal during greater than predetermined threshold value control be sent to the power of cold-cathode fluorescence lamp; When said feedback signal is not higher than a predetermined threshold, the minimum power that said feedback control loop is scheduled to said cold-cathode fluorescence lamp maintenance one.

In an alternate embodiments, liquid crystal display systems comprises: a LCD panel; One be used for throwing light on LCD panel cold-cathode fluorescence lamp; One is coupled to the secondary transformer winding of cold-cathode fluorescence lamp, and this winding provides electric current to cold-cathode fluorescence lamp; One is coupled to the primary transformers winding of secondary transformer winding, and this winding provides magnetic flux for the secondary transformer winding; One is coupled to the switch of primary transformers winding, and this switch allows electric current primary transformers winding of flowing through; One is coupled to the feedback control loop circuit of cold-cathode fluorescence lamp, and this circuit receives a feedback signal from cold-cathode fluorescence lamp, when said feedback signal is expressed as open-circuit condition, makes said cold-cathode fluorescence lamp keep a predetermined minimum power.

The present invention also provides the method for controlling the power that offers cold-cathode fluorescence lamp in the liquid crystal display systems, and this method comprises step: provide a pulse signal to the guiding path of transistor as the primary transformers winding; Generation one comes from the feedback signal of the cold-cathode fluorescence lamp that is coupled to the secondary transformer winding, and this signal indication is at the residing electricity condition of cold-cathode fluorescence lamp; Reception is from the feedback signal of cold-cathode fluorescence lamp; When feedback signal that and if only if representes that cold-cathode fluorescence lamp is lit a lamp, regulate the power that offers said cold-cathode fluorescence lamp; With represent when said feedback signal not have when normally lighting a lamp, make said cold-cathode fluorescence lamp keep the power of a predetermined minimum amount.

Those skilled in the art will know, though following embodiment will explain as a reference with preferred embodiment and method of application, and do not mean that the present invention is limited to these preferred embodiments and method of application.More exactly, the present invention has scope more widely, and the claim scope of only being enclosed limits and illustrates.

Other characteristics of the present invention and advantage will be illustrated in following embodiment, and with reference to accompanying drawing, wherein same section is described with identical numbering.

Description of drawings

Shown in Figure 1 is traditional AC/DC converter circuit;

Shown in Figure 2 is a preferred embodiment of AC/DC converter circuit of the present invention;

Fig. 2 a-2f is depicted as the typical sequential chart of Fig. 2 circuit;

Shown in Figure 3 is another preferred embodiment of AC/DC converter circuit of the present invention;

Fig. 3 a-3f is depicted as the typical sequential chart of Fig. 3 circuit;

Fig. 4 a-4f is depicted as the analogous diagram of Fig. 2 and circuit shown in Figure 3;

Shown in Figure 5 is an embodiment of liquid crystal display systems of the present invention;

Shown in Figure 6 is an embodiment of liquid crystal display systems of the present invention;

Shown in Figure 7 is an embodiment of liquid crystal display systems of the present invention;

Shown in Figure 8 is an embodiment of the display illumination system of liquid crystal display systems of the present invention; With

Shown in Figure 9 is waveform among the embodiment of liquid crystal display systems of the present invention;

Embodiment

Though do not hope to be limited by instance, following detailed description will be carried out as the load of circuit of the present invention with reference to the display screen with CCFL.Yet significantly, the present invention is not limited to only drive one or more CCFL, and the present invention more should be interpreted as a power converter circuit and a method that is independent of the certain loads that application-specific is arranged widely.

Generally speaking, the present invention provides and uses feedback signal and pulse signal, the ON time of two pairs of switches of adjustment, and then control is sent to power in the circuit of load.When the conducting controllably of pair of switches quilt, make that its ON time is overlapping, power will be along by this defined guiding path of switch being sent to load through a transformer.Likewise, when another to switch by conducting controllably, make when its ON time is overlapping that power is transported to load to the defined guiding path of switch through transformer along this another.Therefore, through overlapping between actuating switch and CS selectively, the present invention can accurately control be sent to one give fixed load power.In addition, the present invention comprises excess current and excess voltage protection, and this circuit is ended the power to load under the situation of short circuit or open circuit.And controllable switch topological structure described herein makes that circuit can be irrelevant down with load, and uses one to work down with the irrelevant one working frequency of the resonance effect of transformer configuration.These characteristics will be in following discussion, with reference to accompanying drawing.

Circuit diagram shown in Figure 2 shows the preferred embodiment of phase shift of the present invention, full-bridge, zero voltage switching power converter.In fact, circuit shown in Figure 2 comprises: a power supply 12; A plurality of switches 80, definition alternate conduction path, right with the switch of diagonal line arrangement; Drive the driving circuit 50 of each switch; One produces the frescan 22 of square-wave pulse to driving circuit 50; An one transformer TX1 (a primary side and the defined relevant resonance groove of a C1 circuit by TX1 arranged) and a load.Advantageously, the present invention also comprises an overlapping feedback control loop 40, and each splits at least one pair of the ON time in the Central Shanxi Plain control of this loop, allows may command power to be sent to load thus.

Power supply 12 is applied to this system.Originally, produce a biasing/reference signal 30 from this power supply and be used for control circuit (at control loop 40).Best, frescan 22 generations one dutycycle is 50% pulse signal, begin with a upper frequency, and with a set rate and the downward frequency sweep of predetermined process (i.e. the square-wave signal of a variable pulse width).Frescan 22 is preferably a programmable frequency generator known in the art.(from frescan 22) pulse signal 90 is transferred into B_ driving circuit (B_Drive) (its driving switch _ B, the i.e. grid of CS _ B), and is transferred into A_ driving circuit (A_Drive), and this circuit produces a complementary pulse signal 92 and a ramp signal 26.This complementation pulse signal 92 differs greatly with pulse signal 90 and is about 180 degree, and ramp signal 26 approximately differs 90 degree with pulse signal, and this will be like the following stated.Ramp signal 26 is preferably a serrated signal, and is as shown in the figure.Ramp signal 26 will be compared with the output signal 24 (being called CMP here) of error amplifier 32 through comparer 28, produce signal 94 thus.The output signal 94 of comparer 28 is similarly one, and to be transferred into C_ driving circuit (C_Drive) dutycycle be 50% the pulse conducting with trigger switch _ C (Switch_C), and this signal is again between determine switch B and the switch C and the lap between switch A and the switch D subsequently.Its complementary signal (differ and be about 180 degree) is applied to switch _ D through D_ driving circuit (D_Drive).Those skilled in the art can know that driving circuit _ A is coupled respectively to the control line (for example grid) of switch _ A and switch _ D to the circuit of driving circuit _ D, as said, allows the conducting controllably of each switch.Accomplishing lamp current through the lap between adjustment switch B, C and A, the D regulates.In other words, be that switch has determined the quantity of power handled in the converter to the lap under the conducting state.Therefore, switch B and switch C and switch A and switch D are referred to herein as overlapping switch.

Though do not hope to be limited to by the example among this embodiment, the B driving circuit is preferably by totem-pote circuit, common Low ESR operation amplifier circuit, or emitter follower circuit constitutes.The D_ driving circuit has similar structure.Because A_ driving circuit and C_ driving circuit are not direct ground connection (promptly floating), so these driving circuits preferably are made up of boot-strap circuit (boot_strap circuit) or other high side (high_side) driving circuits known in the art.In addition, as stated, A_ driving circuit and C_ driving circuit comprise a phase inverter, the signal (being phase place) that this phase inverter is used for reversing respectively and comes from B_ driving circuit and D_ driving circuit.

Reach efficient operation through a zero voltage switching technology.(switch _ A is to switch _ D) 80 conductings after its intrinsic diode (D1 to D4) conducting for four MOSFET; This provide one in transformer/capacitor (TX1/C1) configuration the current flow path of energy; Guarantee thus that when these switch conductions the voltage above them is zero.Because this controllable operation, handoff loss is minimized and has kept high-level efficiency.

The preferable blocked operation of overlapping switch 80 is with reference to the sequential chart among the figure 2a to 2f.Switch _ C breaks off (Fig. 2 f) in a certain period of switch B and C conducting simultaneously.After switch _ C breaks off; Electric current in the groove (with reference to figure 2) flows through the diode D4 (Fig. 2 e) among switch _ D, primary side, C1 and the switch _ B of transformer at present; Make the voltage and current resonance in capacitor C 1 and the transformer thus, the result (Fig. 2 f) of energy delivery during as switch B and switch C conducting.Notice that this situation must occur, because will violate Faraday's law in the sudden change of transformer primary side current direction.Therefore, the electric current D4 that must flow through when switch _ C breaks off.During the D4 conducting, just closed conducting of switch _ D.Likewise, switch _ B breaks off that (Fig. 2 a), electric current is sent to the diode D1 (Fig. 2 e) that is associated with switch _ A before switch _ A closure.Likewise, switch _ D is disconnected (Fig. 2 d), and electric current is from switch _ A, through C1, transformer primary side and diode D3 now.Switch _ C is closed (Fig. 2 e) after the D3 conducting.It is closed that switch _ B breaks off the back at switch _ A, and this allows diode D2 before switch _ B closure, at first to be switched on.Attention is the energy that the overlapping decision of the closure time of the switch B, C and the A that are the diagonal angle, D is delivered to transformer, shown in Fig. 2 f.

In this embodiment, Fig. 2 b shows and only when switch _ A is closed, just produces ramp signal 26.Therefore, the driving circuit _ A that produces ramp signal 26 preferably comprises a constant current generator circuit (not shown), this circuit comprise one the appropriate time constant arranged electric capacity, be used for producing ramp signal.For this purpose, utilize a reference current (not shown) to realize the electric capacity charging, and this capacity earth (through a for example transistor switch), discharge rate exceeds charge rate like this, produces a saw-tooth ramp signal 26 thus.Certainly, as stated, this can realize through integrated pulse signal 90, therefore, can use an integrator circuit (for example, operational amplifier and electric capacity) to form ramp signal 26.

In the process of lighting a lamp, (promptly between switch A, D and B, C) produces a predetermined minimum overlay between two switches that are the diagonal angle.This produces one by the least energy that inputs to the groove circuit that comprises C1, transformer, C2, C3 and CCFL load.Notice that load can be ohmic and/or capacitive.Driving frequency starts from a predetermined upper frequency, and up to its convergence groove circuit with by the resonance frequency of the equivalent electrical circuit that Circuit Fault on Secondary Transformer reflected, lot of energy is transferred into the load that is connected with CCFL.Because its high-impedance behavior before lighting a lamp, CCFL receives and comes from the high-tension influence that offers the primary side energy.This voltage is enough to make CCFL to light a lamp.The CCFL impedance drops to its operate as normal value (for example 100K ohm is to 130K ohm), and the energy that work offers primary side based on minimum overlay no longer is enough to keep the steady operation of CCFL.It is overlapping to be used for increasing this that the output of error amplifier 26 begins its adjustment function.The size that is error amplifier 26 outputs has determined overlapping amount.For example:

Feedback control loop 40 with reference to figure 2b, 2c and Fig. 2 is important to note that, when comparer 28 judged that ramp signal 26 (being produced by driving circuit _ A) equates with the value of signal CMP24 (being produced by error amplifier 32), switch _ C was closed.Shown in the point of crossing among Fig. 2 b 36.In order to prevent short circuit, switch A, B and C, D definitely can not be closed simultaneously.Through the size of control CMP, regulate the energy that is delivered to transformer the overlapping time between switch A, D and B, the C.In order to adjust the energy (with regulating the energy that is delivered to the CCFL load thus) that is delivered to transformer, through the output CMP24 of departure amplifier, switch C and D are relevant to switch A and B does time shift.Can know if move to right through the size that increases CMP by sequential chart, will realize increase overlapping between switch A and D, B and the C so, thereby the energy that is delivered to transformer is increased from the output entering switch C of comparer 28 and the driving pulse of D.In fact, this is corresponding to higher lamp current work (higher-lamp current operation).On the contrary, the driving pulse of switch C and D move to left (reduce CMP signal) energy of transmission will be reduced.

For this purpose, error amplifier 32 compares a feedback signal FB and a reference voltage REF.FB measures through detecting the current value of resistance R s, and its expression is through the total current of load 20.REF is the signal of an expression desired load situation, for example the expectation electric current through load.In operate as normal, REF=FB.Yet, if load condition is by intentionally compensation, for example by one be connected in the LCD flat panel display dimmer switch compensation, the value of REF can correspondingly increase/reduce.This fiducial value correspondingly produces CMP.The value of CMP has reflected load condition and/or a bias voltage intentionally, and is realized by the difference between REF and the FB (being REG-FB).

In order to protect load and circuit (for example not to be in open-circuit condition at load end; Open circuit CCFL state under the operate as normal); The FB signal is preferably compared in current sense comparator 42 with a reference value (not shown and different with above-mentioned REF signal), and its output is described below and defines the state of switch 38.This reference value can be programmable, and/or is that the user is definable, and the minimum that preferably reflects system and allowed or maximum current (for example, can specifiedly be used for individual elements, especially for CCFL load).If the value of feedback FB signal and reference signal is (operate as normal) in allowed limits, then current sense comparator is output as 1 (or high).This allows the CMP switch 38 of flowing through, and circuit is like this works saidly, with delivering power to load.Yet if the value of FB signal and reference signal (open circuit or short-circuit condition) outside preset range, current sense comparator is output as 0 (or low), forbids that the CMP signal flow is through switch 38.(certainly, inverse process can realize that wherein switch triggers under 0 state).Allow electric current through stream Rs up to the current sense comparator indication, just minimum voltage Vmin is provided and is sent to comparer 28 by switch 38 (not shown).Correspondingly, switch 38 comprises and is used for when the detection electric current is 0, suitably selecting programmable voltage Vmin.Refer again to Fig. 2 b, the effect of this work is that the CMP D. C. value is reduced to specified or minimum value (being CM=Vmin), and transformer TX1 just high-voltage state can not occur like this.Therefore, point of crossing 36 is moved to left, and has reduced the lap between the complementary switch (closed at point of crossing 36 switches _ C) thus.Likewise, when detected value was 0 (or preset value of other expression open-circuit conditions), current sense comparator 42 was connected to frequency generator 22, to close generator 22.CMP is fed back to holding circuit 62.If CCFL is removed (open-circuit condition) at work, this is to turn off frescan 22.

For holding circuit is not in overvoltage condition, present embodiment preferably comprises holding circuit 60, and its work will provide (to the description of the overcurrent protection through current sense comparator 42 as stated) as follows.Circuit 60 comprises a protection comparer 62, and it is compared with one signal CMP by the voltage signal 66 of load 20 derivation.Preferably voltage signal is derived by dividing potential drop capacitor C 2 as shown in Figure 2 and C3 (parallelly connected with load 20).Under open-circuit condition (open-lamp condition), frescan continues frequency sweep, reaches a threshold value up to OVP signal 66.OVP signal 66 is taken from the dividing potential drop capacitor C 2 and the C3 of output, to detect the voltage of transformer TX1 output.In order to simplify analysis, these electric capacity are also represented the total capacitance of equivalent load capacitance.Threshold value is a reference value, and the voltage that circuit is designed to make Circuit Fault on Secondary Transformer is greater than smallest point modulating voltage (for example by the needed voltage of LCD display), and less than the rated voltage of transformer.When OVP exceeded threshold value, frescan stopped frequency sweep.Simultaneously, current detecting 42 detects less than signal on detection resistance R s.Therefore, in the signal sets at switch block 38 output 24 places in minimum value, overlapping between switch A and D, B and the C be minimum so.Best, in case when OVP exceeded threshold value, timer 64 was started working, start timing (time-out) sequence regularly thus.The cycle of this TG time series is preferably designed according to load request (the for example CCFL of LCD display), but also can be set at some programmable value.In case timing time finishes, driving pulse is invalid, and the trouble free service output of converter circuit is provided thus.That is, circuit 60 provides a sufficient voltage so that this lamp is lit a lamp, if this lamp is not connected to converter, then after the certain hour section, is closed, and therefore can avoid the high voltage in the mistake of output place.Must be arranged, because the non-process of lighting a lamp is similar to open-circuit condition such time period.

Fig. 3 and 3a-3f have described another preferred embodiment of AC/DC circuit of the present invention.In this embodiment, circuit is worked with the mode that is similar to Fig. 2 and 2a-2f and is provided, however present embodiment also comprised one be used for controlling frescan 22 phase-locked loop circuit (PLL) 70 and be used for regularly importing the flip-flop circuit 72 of the signal of C_ driving circuit.Be appreciated that if make the driving pulse of switch C and D move to right 50% through sequential chart, just can realize increase overlapping between switch A and D, B and the C, thereby increase the energy that is delivered to transformer through the size that increases CMP.In fact, this is corresponding to higher lamp current work (possibly need the manual increase through aforesaid REF voltage).On the contrary, move to left (through reducing the CMP signal) of the driving pulse of switch C and D reduced the energy that is transferred.Phase-locked loop circuit 70 keeps the phase relation between feedback current (through Rs) and the cell current (through TX1/C1) under operate as normal, as shown in Figure 3.PLL circuit 70 preferably comprises from groove circuit (C1 and TX1 primary side) input signal, signal 98 and Rs (above-mentioned FB signal).In case CCFL is lit a lamp and detect the electric current among the CCFL through Rs, just activates the PLL70 circuit, phase place between this circuit locking lamp current and a resonant slots (C1 and the transformer primary side) electric current.That is, PLL is because of any parasitic frequency of regulating frescan 22 of changing that resembles temperature action, mechanical arrangements, and said mechanical arrangements is like the distance between the metal chassis of the converter that influences capacitance and inductance value and the wiring between the LCD plate, lamp and LCD plate.This system preferably keeps phase differential 180 degree between the electric current (load current) of the resonant slots circuit and the Rs that flows through.Therefore, no matter the frequency of operation of certain loads state and/or resonant slots circuit, this system can find a best operating point.

The operation class of Fig. 3 feedback loop is similar to above explanation to Fig. 2.Yet shown in Fig. 3 b, this embodiment carries out timing through the enabling signal of 72 pairs of C_ driving circuit outputs of trigger.For example, in operate as normal, the output of error amplifier 32 will be fed back through CS piece 38 (as stated), and the result is a signal 24.Obtain the certain lap between switch A and D, B and the C through comparer 28 and trigger 72, this trigger 72 driving switch C and D (the D driving circuit produces the complementary signal of C_ driving circuit).This is that CCFL (display board) load provides steady operation.Consider and when operate as normal, remove CCFL (display board), CMP increases to the boundary value (rail ofoutput) of error amplifier output, and trigger protection circuit immediately.This function is under an embargo when lighting a lamp.

Briefly with reference to figure 3a-3f, in this embodiment, through C_ driving circuit and D_ driving circuit alternately trigger switch C and D as the working result of trigger circuit 72.Like Fig. 3 b, trigger is every at a distance from once triggering, thus initialization C_ driving circuit (and, correspondingly initialization D_ driving circuit).Timing then as above-mentioned with reference to figure 2a-2f, is worked in an identical manner in addition.

Refer now to Fig. 4 a-4f, analogous diagram 2 or 3 output current.For example, Fig. 4 a is presented at 21V when input, and when frescan during near 75.7KHz (0.5us is overlapping), output reaches 1.67KVp-p.If CCFL needs 3300Vp-p to light a lamp, then this undertension is to light a lamp to CCFL.When frequency was reduced to like 68KHz, minimum overlay produced about 3.9KVp-p in output place, and this is enough to the CCFL that lights a lamp.Shown in Fig. 4 b.In this frequency, the overlapping 1.5u s that increases to makes the about 1.9KVp-p of output be used for moving the lamp impedance of 130K ohm.This illustrates in Fig. 4 c.Like another instance, Fig. 4 d shows the work when input voltage is 7V.When 71.4KHz, before lamp is lit a lamp, be output as 750Vp-p.When frequency reduced, output voltage increased till lamp is lit a lamp.When Fig. 4 e illustrated 68.5KHz, output reached 3500Vp-p.The adjusting of CCFL electric current is through regulating overlapping the completion, and supports the impedance of 130K ohm in the back that lights a lamp.The voltage of CCFL is 1.9KVp-p for the 660Vrms lamp.This is also shown in Fig. 4 f.Though not shown, the circuit simulation of Fig. 3 carries out in a similar fashion.

The difference (that is, adding trigger and PLL among Fig. 3) that it should be noted first and second embodiment will can not have influence on the overall operation parameter that in Fig. 4 a-4f, proposes.Yet it is the imperfect impedance of considering in circuit that decision adds PLL, and can be used as the replacement circuit of the circuit shown in Fig. 2 and add.Simultaneously, add trigger and allowed to remove above-mentioned constant-current circuit.

Therefore, the AC/DC converter circuit of an efficient adaptive is provided clearly, it satisfies the target in this proposition.For those skilled in the art, clearly, can carry out some modifications.For example, use the effect of MOSFET as switch, those skilled in the art can know that entire circuit can use the BJT transistor, or the transistorized combination of any kind, comprise MOSFET and BJT makes up though the present invention has described.Other modifications also are possible.For example related with driving circuit _ B and driving circuit _ D driving circuit can be formed by collecting a level circuit altogether, because therefore the transistor ground connection that is associated floating state can not occur.PLL circuit described here is preferably the known common PLL circuit 70 of this specialty, through suitably revising in order to receiving inputted signal and generation control signal, as stated.Pulse generator 22 is preferably a pulse-width modulation circuit (PWM) or frequency range modulation circuit (FWM), and the both knows for this specialty.Likewise, holding circuit 62 is made up of known circuit with timer and suitably revises, with the said work of carrying out like this.

Fig. 5 has described an embodiment of liquid crystal display systems of the present invention.Liquid crystal display systems 500 comprises thin film transistor 501.Thin film transistor 501 is coupled to column drive circuit 502.Column drive circuit 502 is controlled at the row on the thin film transistor 501.Thin film transistor 501 also is coupled to horizontal drive circuit 503.Horizontal drive circuit 503 is controlled at the row on the thin film transistor 501.Column drive circuit 502 is coupled to time schedule controller 504 with horizontal drive circuit 503.The sequential of time schedule controller 504 control column drive circuits 502 and horizontal drive circuit 503.Time schedule controller 504 is coupled to video signal preprocessor 505.Video signal preprocessor 505 is handled vision signal.In another embodiment, video signal preprocessor 505 can be certain mark apparatus.

Thin film transistor 501 is by display illumination system 599 illuminations.Display illumination system 599 comprises cold-cathode fluorescence lamp 562.Cold-cathode fluorescence lamp 562 is coupled to secondary transformer winding 560.Secondary transformer winding 560 provides electric current for cold-cathode fluorescence lamp 562.Secondary transformer winding 560 is coupled to primary transformers winding 518.Primary transformers winding 518 provides magnetic flux for secondary transformer winding 560.Primary transformers winding 518 is coupled to switch 532.Switch 532 allows the electric currents primary transformers winding 518 of flowing through.Primary transformers winding 518 also is coupled to switch 512.Switch 512 allows electric current through primary transformers winding 518.Switch 532 is coupled to controller 550 with switch 512.Controller 550 provides pulse signal, is used for switching between CS 532 and the switch 512.It should be noted that any controller described here all can be used as controller 550.It should be noted that all alternative display illumination system 599 of any display illumination system described here equally.

Fig. 6 has described another embodiment of liquid crystal display systems of the present invention.Liquid crystal display systems 600 comprises thin film transistor 601.Thin film transistor 601 is coupled to column drive circuit 602.Column drive circuit 602 is controlled at the row on the thin film transistor 601.Thin film transistor 601 also is coupled to horizontal drive circuit 603.Horizontal drive circuit 603 is controlled at the row on the thin film transistor 601.Column drive circuit 602 is coupled to time schedule controller 604 with horizontal drive circuit 603.The sequential of time schedule controller 604 control column drive circuits 602 and horizontal drive circuit 603.Time schedule controller 604 is coupled to video signal preprocessor 605.Video signal preprocessor 605 is handled vision signal.Video signal preprocessor 605 is coupled to video demodulator 606.Video demodulator 606 demodulated video signals.Video demodulator 606 is coupled to tuner 607.Tuner 607 provides vision signal for video demodulator 606.Tuner 607 is adjusted to a CF to liquid crystal display systems 600.Video demodulator 606 also is coupled to microcontroller 608.Tuner 607 also is coupled to audio demodulator 611.The sound signal that audio demodulator 611 demodulation come self-tuner 607.Audio demodulator 611 also is coupled to audio signal processor 610.The sound signal that audio signal processor 610 is handled from audio demodulator 611.Audio signal processor 610 is coupled to note amplifier 609.The sound signal that note amplifier 609 amplifies from audio signal processor 610.

Thin film transistor 601 is by display illumination system 699 illuminations.Display illumination system 699 comprises cold-cathode fluorescence lamp 662.Cold-cathode fluorescence lamp 662 is coupled to secondary transformer winding 660.Secondary transformer winding 660 provides electric current for cold-cathode fluorescence lamp 662.Secondary transformer winding 660 is coupled to primary transformers winding 618.Primary transformers winding 618 provides magnetic flux for secondary transformer winding 660.Primary transformers winding 618 is coupled to switch 632.Switch 632 allows the electric currents primary transformers winding 618 of flowing through.Primary transformers winding 618 also is coupled to switch 612.Switch 612 allows electric current through primary transformers winding 618.Switch 632 is coupled to controller 650 with switch 612.Controller 650 provides pulse signal, is used for switching between CS 632 and the switch 612.It should be noted that any controller described here can be used as controller 650.It should be noted that equally any display illumination system described here can substitute display illumination system 699.

Fig. 7 has described another embodiment of liquid crystal display systems of the present invention.Liquid crystal display systems 700 comprises EGA 790.Liquid crystal display systems 700 also can comprise the parts above-mentioned and liquid crystal display systems 500 shown in Fig. 5, or the parts of the liquid crystal display systems 600 that shows among above-mentioned and Fig. 6.EGA 790 is coupled to a video signal preprocessor, and this video signal preprocessor 505 can be the video signal preprocessor 505 shown in above-mentioned and Fig. 5, or above-mentioned and the video signal preprocessor 605 shown in Fig. 6.

EGA 790 is coupled to chipset core logic 791.Chipset core logic 791 is transmitted in the data between the coupled device.Chipset core logic 791 also is coupled to microprocessor 792.Microprocessor 792 deal with data comprise video data.Chipset core logic 791 also is coupled to reservoir 793.Reservoir 793 random access memorys, and the short-term storage of data is provided.Chipset core logic 791 also is coupled to hard disk drive 794.Hard disk drive 794 provides the longer-term storage of data.Chipset core logic 791 also is coupled to CD drive 795.CD drive 795 is from CD-ROM or DVD-ROM retrieve data.

With reference to figure 8, an embodiment of switching mode CCFL feed circuit 100 of the present invention has been described.The present invention is a switched-mode power supply, and (CCFL) provides energy for cold-cathode fluorescence lamp.This power supply is a direct current (DC) low voltage transition one interchange (AC) high voltage, and offers CCFL.

The switched-mode power supply circuit comprises one first switch, and this switch contains source electrode, drain and gate.The drain electrode of first switch is connected to the elementary winding of step-up transformer.The number of turn of the secondary winding of this step-up transformer is 20 times of elementary umber of turn at least, is preferably 50 to 150 times.The source electrode of first switch is connected to a power supply.

Second switch also contains source electrode, drain and gate.The drain electrode of second switch is connected to the drain electrode of first switch and an end of primary winding simultaneously.The source electrode of second switch is connected to the ground connection reference of a power supply.Elementary winding contains one second end, and this second end is connected to the mid point of one or two capacitive dividers.Like this, these two switch series connection, input voltages of equal independent power source approx.Link to each other with both ends of power after these two capacitances in series.

One control circuit transmits and controls signal to first and second switches, is alternately closed switch with 180 degree phase shifts.When first switch closure, an electric current is with an elementary winding with reference to positive flow warp first switch and transformer.When second switch was closed, this electric current was with the elementary winding of reverse direction flow through transformer, and the second switch of flowing through.

Transformer is driven from both direction, so magnetic flux unshakable in one's determination is swept two quadrants employing in the B-H loop relevant with transformer.So just reduce the size of transformer core, thereby saved the cost of transformer.

Two electric capacity have been formed a capacitive divider, are connected to an end of primary winding.When each switch closure, two electric capacity the flowed through current charges or the discharge of primary winding.When first switch closure, be second electric capacity charging when electric current is first capacitor discharge, and in the disconnection of first switch, when being connected the body diode conducting of second switch, this electric current is reset.When second switch is closed, the current reversal of the primary of flowing through winding.Along with this direction of current flow, first electric capacity is recharged, and second electric capacity is discharged.After second switch was disconnected, electric current was able to recover via the body diode of first switch.If switch is closed when their body diode conducting, switch is closed when no-voltage basically so.It is minimum that this zero voltage switching technology drops to the handoff loss of switch.Therefore, the efficient of power converter is improved.

Feed circuit 100 comprise a controller 150; One first switch, 112, one second switches 132 and a transformer 120; And to be connected to that power supply 274 is used for be that a load (for example the CCFL162 in the flat-panel monitor, this flat-panel monitor can be a LCD) provides power.

First switch 112 can be N-channel mos FET (MOSFET) grid-control switch, and comprises a drain electrode 114, and this drain electrode is connected to an end of the elementary winding 118 of step-up transformer 120.Second end 125 of elementary winding 118 is connected on the node of first electric capacity 124 and second electric capacity 126.The source electrode 128 of first switch 112 is connected to the ground connection reference of power supply 274.Second switch 132 can be P-passage MOSFET grid-control switch.The drain electrode of P-channel switch 132 also is connected to the drain electrode 114 of switch 112.Switch 112 all comprises

intrinsic diode

134 and 136 respectively with switch 132.The grid 138 of

switch

132 and 112 grid 152 are connected to the output terminal of controller 150.

The secondary winding 160 of step-up transformer 120 is connected to CCFL162.Compare with the nonlinear magnetism conductance of the saturable core of transformer adopting in the prior art Roy circuit, can form the magnetic core that linear magnetic permeability is arranged in the step-up transformer 120, this magnetic core is unsaturation when feed circuit 100 work.The turn ratio of step-up transformer 120 was at least 20: 1, and usually in 50: 1 to 150: 1 scope.

The secondary winding 160 of step-up transformer 120 and two electric capacity, 163,164 parallel connections of connecting.Electric capacity 163,164 constitutes a voltage divider, is used for detecting the voltage of the secondary winding 160 of step-up transformer 120, and the square wave of elementary winding 118 is transformed to the near sinusoidal ripple offers CCFL load 162.Under operate as normal, detect voltage 186 and often reset by switch 170, this switch is by the Current Control of the CCFL162 that flows through.The function of switch 170 will detail below.

Controller 150 can be a PDM keyer, and it provides the grid 152 of first grid drive signal 152 to switch 112, and the grid 138 of second grid drive signal 138 a to switch 132 is provided.Except providing the drive signal for switch 112,132, controller 150 also provides other functions, and for example two are used for the CCFL distinct frequency with operate as normal of lighting a lamp.The identification circuit 250 of turning on light in controller 150 is used to judge whether CCFL162 is lighted, and judges that which is exported in two frequencies.When CCFL162 lit a lamp, the signal 252 of turning on light was not set up (de-asserted), and represented that CCFL162 is not lighted, and showed on its circuit it is open circuit.Based on signal 252, oscillator 254 places obtain a first frequency.Detect after lighting a lamp one flow through CCFL162 electric current.Therefore, signal 252 is set up (asserted), represents CCFL to be lit a lamp.Obtain a second frequency in oscillator 254 outputs place.It should be noted that the signal 252 of turning on light also determines the output 256 of low frequency width modulation (PWM) circuit 258.In the process of lighting a lamp, signal 256 not interfere provides the waveform to CCFL162, to obtain a level and smooth some modulating voltage.In other words, before signal 252 was set up, signal 256 can not influence output control logic 286.

Controller 150 also comprises lamp current and voltage detecting and control function.Lamp current is detected through resistance 182.Detected value 184 is compared with benchmark 212 through a comparer (the for example error amplifier 230 of

CS

112 and 132 closure times).Modulating voltage is detected through capacitive divider 163 and 164.Detected value 186 is compared with benchmark 214 through a comparer 232.The startup of the output 234 decision digital dock timers 236 of comparer 232.After clock timer 236 starts (for example one to two second) after a while, still be not set up if export 234, the output signal 238 of clock timer 236 is set up holding circuit 240, with the work of shutdown switch 112 and 132.This period is to be used for for CCFL162 one light a lamp the time (for example one to two second) being provided.Oscillator 254 is for the work of feed circuit 100 provides two frequencies, and a upper frequency is used to light a lamp, and a lower frequency is used for operate as normal.Upper frequency can exceed 20% to 30% than lower frequency.Lower frequency can be the 68KHz shown in Fig. 4 b, or the 65.8KHz shown in Fig. 4 e, or is lower than arbitrary frequency values of these two frequencies.

Low frequency pulse-width modulation circuit 258 is in order to produce signal 256, and adjustment is sent to the energy of lamp, thereby realizes brilliance control.The frequency of signal 256 is preferably in 150Hz to the 400Hz scope.The identification circuit 250 of turning on light receives lamp current detection signal 184, and its output signal 252 is provided for discerning the existence of CCFL load 162 or the completion of lighting a lamp.Holding circuit 240 receives the signal 252 that expression CCFL162 exist, the signal 238 when being illustrated in CCFL162 and detecting the TG of signal 260 that electric current exists and expression open-circuit condition.Therefore, when open circuit, excess current, overvoltage condition appear in lamp 162, or take place when under-voltage in voltage input 130, the output signal 262 of holding circuit 240 is set up, with the work of

shutdown switch

112 and 132.

Controller 150 comprise one be connected to circuit ground (circuit ground) ground pin 272 and be connected to the voltage input pin 130 of a direct current voltage source.In controller 150, voltage input pin 130 is connected to one benchmark/biasing circuit 210, and this circuit produces different reference voltage 212,214 etc., supplies internal use.Voltage input pin 130 also is connected to a undervoltage lockout circuit (under-voltage lock-out circuit) 220 and output driving circuit 222.When providing when the voltage of voltage input pin 130 surpasses a threshold value, the output signal 224 of circuit 220 is started working other part of controller 150.On the other hand, if the voltage at voltage input pin 130 places is during less than threshold value, signal 224 is with the work of stop control 150 other parts.

In CCFL when work,, function that function and open circuit are turned down in the brightness of CCFL comes down to complementation.Advantageously, two

signals

168 and 186 can be multiplexing, receives signal 168 and 186 at a pin two 84 places of controller 150.This operation has reduced the cost of controller 150.

The clock pin two 76 of controller 150 is connected to oscillator 254, and this oscillator is connected to circuit ground through an electric capacity 278, or is connected to voltage input pin 130 through a resistance 280, so that a clock signal (being preferably a ramp signal) to be provided at 276 places.

Advantageously, in the present invention, feed circuit 100 utilize with controller 150 minimum linking numbers has realized maximum functions, drives the CCFL load.The work of this power supply is described below.

VIN puts on feed circuit 100 with direct current (DC) voltage.In case the input of the voltage at 130 places surpasses the threshold value that undervoltage lockout circuit 220 sets, controller 150 is started working.Benchmark/I-biasing circuit 210 is that other circuit in the controller 150 produces reference voltage.

Because CCFL162 is not lit a lamp, and not from the current feedback signal 184 of CCFL load 162, oscillator 254 produces a upper frequency pulse signal.Driving circuit 222 output one pulse width modulated drive signal 152 and 138 are given switch 112 and 132 respectively.Electric capacity 216 is by charging gradually, and voltage 260 is along with the time increases gradually like this.Because the voltage at 260 places is along with the time increases gradually, so the pulsewidth of drive signal 138 and 152 increases gradually.Therefore, be sent to the also increase gradually of power of step-up transformer 120 and load 162.Electric capacity 124 and 126 design make the voltage through each electric capacity be about the half the of input voltage.In first semiperiod, switch 132 closures, an electric current is from power supply, flow to elementary winding 118 through switch 132.This electric current flows into electric capacity 126 then, and comprises magnetization current and reflected load current (reflected load circuit).When electric capacity 126 chargings, electric capacity 124 discharges.When switch 132 broke off, the electric current of elementary winding 118 continued to flow with same direction.Diode 134 makes this electric current continue equidirectional circulation.After switch 132 closures through about 180 the degree differ after, switch 112 closures.Power supply makes electric current flow to elementary winding 118 through electric capacity 124, flow to reference circuit ground 272 along opposite direction through switch 112.This electric current (comprising magnetization current and reflected load current) can be along reversed flow.Meanwhile, when electric capacity 126 discharges, electric capacity 124 chargings.When switch 112 disconnections, diode 136 supports the continuation of electric current in elementary winding 118 to flow.After switch 112 closures through about 180 the degree differ after, switch 132 closures.Switch continues periodically to work.Therefore, the voltage of elementary winding 118 is essentially a square wave.

Fig. 9 has described the waveform at different port place.Fig. 9 (a) shows the drive waveforms at 152 places.Fig. 9 (b) shows 138 place's corresponding driving waveforms.The switch closure of noting switch 112 and 132 differs 180 degree during the time.Certainly, switch 132 can be used the N lane device instead.In the case, the logic of drive signal 138 is reversed, in order to expression ON/OFF (ON/OFF) drive signal.Fig. 9 (c) shows the waveform at 125 places.Be superimposed upon ripplet on the DC voltage (input voltage VIN half the) and represent the charging and the discharge of electric capacity 126.The voltage that input voltage VIN deducts 125 places obtains a similar waveform, and this waveform is represented the voltage of electric capacity 124, and this voltage also has the ripplet that is superimposed upon on 1/2nd input voltages.Fig. 9 (d) illustrates the voltage at 114 places, and Fig. 9 (f) shows the electric current of the elementary winding 118 of flowing through.Notice that when switch was closed at the t1 place, the voltage at 114 places was near VIN.The electric current of elementary winding 118 is with a benchmark forward flow, so that electric capacity 126 chargings make electric capacity 124 discharges simultaneously.Therefore, the voltage at electric capacity 126 places increases (positive slope).At time t2 place, switch 132 breaks off.The electric current at elementary winding 118 places continues to flow with same direction, and is the trend that reduces.Diode 134 makes this electric current continue circulation, is decreased to zero up to electric current during at t3.In the period of t2 to t3, the voltage at 114 places approaches zero obviously.Because electric current flows with same direction, the voltage at electric capacity 126 places still increases.Moment behind t3, because the reverse mmf of elementary winding 118, a little electric current is with reversed flow, diode 136 conductings, and 114 voltage equals the forward pressure drop that VIN adds diode 136.At time t4, switch 112 closures.Voltage 114 drops to and approaches zero, and the electric current of elementary winding 118 is with reverse increase.When electric capacity 124 is recharged, electric capacity 126 discharges.Therefore, the voltage of electric capacity 126 reduces (negative slope).Switch 112 breaks off when time t5, diode 136 conductings, and electric current continues to flow.When the electric current of elementary winding 118 reaches zero, diode 136 stop conductings.Meanwhile, little electric current is with the benchmark forward flow.In other words, because diode 134 conductings, so the voltage at 114 places approaches zero.Working condition continues, and until beginning in time t7 following one-period, and switch 132 is closed once more.Step-up transformer 120 is driven from both direction, has utilized magnetic flux to sweep so substantially, to provide power to the CCFL load.Step-up transformer 120, output capacitance 163,164 constitutes a groove circuit with all with the relevant stray reactance element of transformer 120 secondary side circuit.This groove circuit is selected the relevant higher harmonics element of square wave that occurs with elementary winding 118 places, and produces a waveform shaping, near sinusoidal at the CCFL162 place.Shown in Fig. 9 (e).Notice that based on the parasitic elements and the load 162 of secondary winding 160, waveform 172 possibly have different phase shifts with regard to the waveform shown in Fig. 9 (a)-9 (d) and Fig. 9 (f).The voltage at 172 places is by electric capacity 163 and 164 dividing potential drops.Therefore, electric capacity 163 and 164 has two kinds of purposes.A purpose is to be used for voltage detecting 186, and another purpose is the shaping that is used for ripple.

When the CCFL162 conducting, the electric current through CCFL162 is detected by resistance 182.Detected signal 184 is transferred into a current amplifier 230, and this amplifier is exported 260 places at it and linked to each other with building-out capacitor 216.A signal 260 and a signal from oscillator 254 compare, and produce an output, and this output is sent to steering logic 286, with the closure time of determine switch 112 and 132.A kind of method that one adjusting is sent to the power of load is with a command signal 168 input 284 to controller 150 to be provided.The signal at 284 places is converted into a low frequency pulse signal through low frequency pulse-width modulation circuit 258; Be sent to output control logic 286; Use the

output

138 and 152 of low frequency pulse signal modulation drive circuit 222 thus, thereby control the energy that is sent to CCFL162 effectively.

During lighting a lamp, CCFL162 is connected to feed circuit 100 as the infinitely-great element of an impedance.Equally, during this period, CCFL162 requires a predetermined forward voltage usually.The feed circuit 100 that comprise electric capacity 163 and 164 detect the voltage of CCFL162.Thus, this predetermined forward voltage is definite by in proportion at signal 186 places, and is sent to the input 284 of controller 150, is used for voltage-regulation.The identification circuit 250 of turning on light produces a signal 252, and this signal indication CCFL162 does not open.Signal 234 is set up, and starts digital dock timing circuit 236.Equally, signal 252 order oscillators 254 produce the upper frequency that a suitable CCFL162 lights a lamp.During this period, the voltage at CCFL162 place is adjusted to predetermined value.In about one or two second after signal 234 is set up, digital dock timer 236 produces a signal 238.If CCFL162 lights a lamp before being set up at signal 238, as above a paragraph is said works on for CCFL162 so.If CCFL162 is not lit a lamp (damage, do not connect or connect loosening), signalization 238 starts holding circuit 240.The output of holding circuit 240 produces a signal 262, is used for stopping the work of driving circuit 222, so switch 112 and 132 is disconnected.Because CCFL162 is not lit a lamp, do not have power to be sent to CCFL162 during this period, so power control instruction signal 168 natures are inoperative to the work of power supply.In other words, when feed circuit 100 are realized the CCFL162 lighting function, stop brilliance control to the power that is adjusted to CCFL162.Equally, in operate as normal, switch 170 reset voltage detection signals 186 are not so this signal influences the brilliance control of CCFL.Therefore, the multiplex technique function has reduced the quantity of pin, like this, has saved the cost of controller 150 and power circuit.

Oscillator 254 is connected to reference circuit ground through electric capacity 278; Or be connected to input voltage through resistance 280; And produce pulse signal when pierce circuit 254 when electric capacity 278 is connected to circuit ground, pierce circuit 254 generation electric current to electric capacity 278, also absorption comes the electric current of self-capacitance 278.When pierce circuit 254 when resistance 280 is connected to input voltage, pierce circuit 254 absorbs the electric current from voltage input and resistance 280.Absorb and to make to distinguish with the characteristic that produces (sink-and-source) electric current or only absorb (sink-only) electric current and regulate the different control models that are sent to CCFL162 power.For linear model, in order to distinguish low frequency PWM mode as discussed previously, power control instruction signal 168 orders are also regulated the power that is sent to CCFL162, make the transmission of this power need not pass through low frequency pulse-width modulation circuit 258.When pierce circuit 254 is connected to voltage when input through resistance 280, signal 168 284 is flowed through low frequency pulse-width modulation circuit 258 with generation/rewriting one reference signal 212 then, is sent to amplifier 230.The size of command signal 168 thereby direct Control current feedback signal 184 is regulated the electric current through CCFL162.Under this mode of operation, the signal cut low frequency pulse-width modulation circuit 258 at 282 places, and allow signal 284 directly to pass through.Therefore, resistance 280 or electric capacity 278 are connected to pierce circuit 254 not only produce pulse signal, also determined the control model (or under linear mode control, or under the low frequency PWM mode) of CCFL load 162 power adjustments.Such design has reduced controller 150 number of employed element on every side, has but improved deviser's dirigibility greatly.

As stated; Corresponding to first switch 112 of feed circuit 100 of the present invention and second switch 132 by 150 controls of controller; And be alternately closed; Therefore electric current is alternately with first direction and the second direction CCFL162 that flows through, and feed circuit 100 convert direct supply into AC power, for CCFL162 provides power.

Therefore, those skilled in the art will be found various modification of the present invention and/or alternate application after reading above-mentioned disclosure, and these modifications and/or alternate application do not break away from the spirit and scope of the present invention situation.So equivalent structures is intended to explain and comprises all modification or alternate application in spirit and scope of the invention.

Other circuit and all such modifications that those skilled in the art will be found are subject in the spirit and scope of the present invention, and are only limited additional claim.

Claims

1. liquid crystal display systems comprises:

One LCD panel;

The cold-cathode fluorescence lamp of the said LCD panel of one illumination;

A level Transformer Winding, said secondary transformer winding coupled to said cold-cathode fluorescence lamp is for said cold-cathode fluorescence lamp provides electric current;

One primary transformers winding, said primary transformers winding coupled to said secondary transformer winding is for said secondary transformer winding provides magnetic flux;

First switch, said first switch is coupled to said primary transformers winding, allows the electric current said primary transformers winding of flowing through;

One second switch, said second switch are coupled to said primary transformers winding, allow electric current with reverse direction flow through said primary transformers winding;

One the 3rd switch, said the 3rd switch are coupled to said primary transformers winding and said first switch, when having an overlap condition between said the 3rd switch and said first switch, for said primary transformers winding provides electric current;

One is coupled to the feedback control loop of said cold-cathode fluorescence lamp; Said feedback control loop receives the feedback signal that an expression is sent to the power of said cold-cathode fluorescence lamp; When said feedback signal that and if only if was higher than a predetermined threshold, control offered the power of said cold-cathode fluorescence lamp

Wherein when said feedback signal was not higher than a predetermined threshold, said feedback control loop passed through to keep the minimum overlay between said the 3rd switch and said first switch, the minimum power that said cold-cathode fluorescence lamp maintenance one is scheduled to.

2. liquid crystal display systems according to claim 1 also comprises:

One input voltage source, said input voltage source are coupled to said first switch, for said first switch provides electric current.

3. liquid crystal display systems according to claim 2, wherein said input voltage source are a power supply.

4. liquid crystal display systems according to claim 2 also comprises:

One is coupled to said primary transformers winding and earthy first electric capacity; With

One is coupled to second electric capacity of said primary transformers winding and said input voltage source.

5. liquid crystal display systems according to claim 1 also comprises:

One voltage-level detector, said voltage-level detector is coupled to said cold-cathode fluorescence lamp, to detect the voltage of said cold-cathode fluorescence lamp.

6. liquid crystal display systems according to claim 5 also comprises:

One voltage protection circuit, said voltage protection circuit is coupled to said voltage-level detector, when the said voltage of said cold-cathode fluorescence lamp surpasses a predetermined threshold, to reduce to be sent to the power of said cold-cathode fluorescence lamp.

7. liquid crystal display systems according to claim 6 also comprises:

One timer, said timer is coupled to said voltage protection circuit, to produce a timing timing period.

8. a liquid crystal display systems comprises:

One LCD panel;

The cold-cathode fluorescence lamp of the said LCD panel of one illumination;

One is coupled to the feedback control loop of said cold-cathode fluorescence lamp; Said feedback control loop receives a feedback signal from said cold-cathode fluorescence lamp; When said feedback signal is represented an open-circuit condition; Said feedback control loop makes said cold-cathode fluorescence lamp keep a predetermined minimum power through keeping the minimum overlay between said the 3rd switch and said first switch.

9. liquid crystal display systems according to claim 8, wherein said feedback signal is represented the voltage of said cold-cathode fluorescence lamp, and when said voltage surpasses a predetermined threshold, representes said open-circuit condition.

10. liquid crystal display systems according to claim 8, wherein said feedback signal is represented the voltage of said cold-cathode fluorescence lamp, and when said voltage reaches a scheduled time slot above a predetermined threshold, representes said open-circuit condition.

11. liquid crystal display systems according to claim 8 also comprises:

One is coupled to second electric capacity of said primary transformers winding and voltage input.

12. liquid crystal display systems according to claim 8 also comprises:

One is coupled to said first switch, and the input voltage source of electric current is provided for said first switch.

13. liquid crystal display systems according to claim 12, wherein said input voltage source are a power supply.

14. liquid crystal display systems according to claim 8, wherein said feedback signal are represented the electric current of said cold-cathode fluorescence lamp of flowing through, and when said electric current is lower than a predetermined threshold, represent said open-circuit condition.

15. in a liquid crystal display systems, control the method that is sent to a cold-cathode fluorescence lamp power, comprise step for one kind:

Provide first pulse signal to the first transistor, as first guiding path of a primary transformers winding;

Provide one second pulse signal to a transistor seconds, as one second guiding path of said primary transformers winding;

Provide one the 3rd pulse signal to one the 3rd transistor, as said first guiding path of said primary transformers winding;

Produce a feedback signal from a cold-cathode fluorescence lamp, said feedback signal is represented the electricity condition at said cold-cathode tube fluorescent light place, and said cold-cathode fluorescence lamp is coupled to the level Transformer Winding one time;

Acceptance is from the said feedback signal of said cold-cathode fluorescence lamp;

When said feedback signal that and if only if representes that said cold-cathode fluorescence lamp is lit a lamp, regulate the power that is sent to said cold-cathode fluorescence lamp;

When said feedback signal representes that nothing is normally lit a lamp, keep the minimum overlay between said the first transistor and said the 3rd transistor, make said cold-cathode fluorescence lamp keep the power of a predetermined minimum amount.

16. method according to claim 15, wherein said feedback signal is represented the voltage of said cold-cathode fluorescence lamp, and when said voltage is lower than a predetermined threshold, representes that said cold-cathode fluorescence lamp lights a lamp.

The electric current of said cold-cathode fluorescence lamp 17. method according to claim 15, wherein said feedback signal are represented to flow through, and when said electric current surpasses a predetermined threshold representes that said cold-cathode fluorescence lamp lights a lamp.

18. method according to claim 15 also comprises step:

Represent not have when said feedback signal and normally light a lamp when reaching a schedule time, cut off the power that is sent to said cold-cathode fluorescence lamp.