Background technology
(cold cathode fluorescent lamp is CCFL) traditionally as LCD (liquid crystal display, LCD) light source backlight for cathode fluorescent tube.Because use mercury gas, cathode fluorescent tube may cause environmental pollution.Similarly.Cathode fluorescent tube has low reaction speed and low color rendition degree (color reproducibility), and is not enough to reduce the weight and the size of panel of LCD.Moreover, require to start and the operating voltage height, the light source of adding LCD backlight is a power consumption the best part in the system, so under the harsh day by day situation of Power Limitation, (Light Emitting Diode LED) replaces cathode fluorescent tube by light emitting diode gradually at present.
Compared to cathode fluorescent tube, light emitting diode is environmental protection (environment-friendly) and can be counting nanosecond (nano second) rapid reaction, thereby more efficient at video signal flow.In addition, light emitting diode can be by pulsed drive, with 100% or more multiple existing color, and changes lightness and colour temperature (color temperature) arbitrarily by the light quantity of adjusting ruddiness, green glow, blue light-emitting diode.Light emitting diode also has the advantage that causes than light weight and less panel of LCD.Therefore, light emitting diode is by the backlight of active adoption as panel of LCD.
Light emitting diode is the device by current drives, and its brightness and forward current are proportionate relationship.There are two kinds of methods can control forward current.
First method is to adopt light emitting diode V-I curve, and voltage source of general using and a dead resistance device determine to produce the required voltage that light emitting diode is provided of expection forward current.But this method has some shortcomings, and for example: any variation of light emitting diode forward voltage all can cause the variation of led current.
Suppose that fixed voltage is that 3.6V, electric current are 20mA, when voltage became 4.0V, the specific pressure that temperature or manufacturing variation can cause became, and 30% variation significantly may appear in electric current so.So when bigger changes appears in forward voltage, can cause bigger forward current to change, in addition, pressure drop and power consumption also all can be wasted power and reduction light emitting diode serviceable life.
Second method is to utilize fixed current to come the driven for emitting lights diode.Fixed current can be eliminated forward voltage and change the electric current variation that is caused, and therefore, can produce fixing light-emitting diode luminance.Utilize fixed current only need adjust voltage, and need not adjust the output voltage of power supply by current sensing resistor.Supply voltage and current sense resistor value have determined led current, when driving a plurality of light emitting diode, only need series connection just can reach fixed current in each light emitting diode.
In addition, many LCD backlights are used all needs to regulate brightness.Can adopt two kinds of dimming modes in this part, be exactly simulation or pulse-length modulation (Pulse Width Modulation, method PWM).Adopt the simulation light modulation,, on light emitting diode, increase by 50% electric current, so just can improve 50% brightness just as what everybody was familiar with.But this method is imperfect, and that can occur the led color skew exactly, and needs to adopt analog control signal, and therefore, this pattern in general utilization rate is not high.
Pulse-length modulation is at present more common, and for being applied in the brightness adjustment approach of light emitting diode the best.The use of pulse-length modulation is popularized along with the increase of digital control logic circuit.Pulse-length modulation provides simple method, can allow the digital control logic circuit set up the function that is equivalent to simulate.
Please refer to shown in Figure 1ly, it is ball bearing made using and corresponding pulse width modulated waveform by pulse-length modulation control light-emitting diode luminance.When the switch conduction (on) of circuit, the waveform of pulse-length modulation is the position of on, and when the switch of circuit cut out (off), the waveform of pulse-length modulation then was the position of off.
If shorten the time span that switch is positioned at " conducting " position, light emitting diode will deepening.In the example of Fig. 1, the light emitting diode of being showed has time of 50% to open, and other 50% time closes.Utilize repeated signal controlling light emitting diode to be cut into several sections, utilize the single cycle, within one-period, finish, to " conducting ", return " closing " by " closing " because of the cycle.Signal can be made further characteristic description in the basis signal cycle, that is the time length of " conducting " is divided by resulting ratio of cycle.The long signal cycle can make light emitting diode brighten, and the short signal cycle then can make the light emitting diode deepening.
And the key of utilizing pulse-length modulation to regulate brightness is, can't see the pulse phenomenon of pulse-length modulation for the eyes of guaranteeing the user, and generally speaking, the frequency of pulse width modulating signal must be higher than 100Hz.
As mentioned above, many open source literatures have proposed the brightness with the light emitting diode in the pwm pulses technology control backlight module, improve backlight efficiency whereby, and keep the homogeneity of backlight illumination.More can reduce the backlight module temperature in addition and reduce energy loss, shown in U.S. Pat 20070091057 and the patent EP of European Union 1780701.
In addition, Chinese patent CN 11013559 discloses a kind of light-emitting diode luminance control circuit, its principal character is regulated and control the light emitting diode of at least one pair of backlight module separately by pulse-length modulation, and can not influence the brightness of all the other light emitting diodes when regulation and control.
Yet, regulating brightness by pulse-length modulation then needs pulse-length modulation driving circuit (PWMIC) to drive, when light emitting diode quantity is got over for a long time, the quantity of pulse-length modulation driving circuit also increases thereupon, thereby the raising manufacturing cost, and make LED backlight driving design more become complicated.
Embodiment
The light emitting diode matrix that the present invention is a kind of LCD in this direction of inquiring into.In order to understand the present invention up hill and dale, detailed step and composition thereof will be proposed in following description.Apparently, execution of the present invention is not defined in the specific details that the technician was familiar with of the light emitting diode matrix of LCD.On the other hand, well-known composition or step are not described in the details, with the restriction of avoiding causing the present invention unnecessary.The preferred embodiments of the present invention can be described in detail as follows, yet except these were described in detail, the present invention can also be implemented among other the embodiment widely, and scope of the present invention do not limited, and it is as the criterion with appended claim.
Based on allowing LCD (liquid crystal display, LCD) can maintain under the prerequisite of basic brightness and carry out even light modulation, the present invention proposes a kind of light emitting diode of LCD 100, and (LightEmitting Diode, LED) array is shown in figure 2A.Above-mentioned light emitting diode matrix comprises one or more by pulse-length modulation (Pulse Width Modulation, PWM) first light emitting diode 142 of signal controlling is decided second light emitting diode 152 of electric current power supply with one or more by direct current, wherein at least one first light emitting diode 142 constitutes a light-adjusting module 140, and at least one second light emitting diode 152 constitutes a permanent optical module 150.
In order to make LCD can adjust brightness equably, above-mentioned light-adjusting module 140 can be staggered with permanent optical module 150, as Fig. 2 A, Fig. 2 B and Fig. 2 C.Fig. 2 A shows that a plurality of light-adjusting modules 140 and a plurality of permanent optical modules 150 are spaced 140 configurations of wherein per two light-adjusting modules, one permanent optical module 150 in laterally and vertically being all.
Fig. 2 B shows a plurality of light-adjusting modules 140 and a plurality of permanent optical modules 150 also for laterally arranging with longitudinal separation, and also promptly on horizontal direction, the configuration mode of light-adjusting module 140 and permanent optical module 150 is all shown in Fig. 2 A.Yet on the longitudinal direction in Fig. 2 B, light-adjusting module 140 is big than the lateral separation distance with the spacing distance of permanent optical module 150.In a preferred embodiment of the present invention, light-adjusting module 140 is the twice of lateral separation distance with the spacing distance of permanent optical module 150.
Fig. 2 C shows that a plurality of light-adjusting modules 140 and a plurality of permanent optical modules 150 are oblique being spaced, also promptly on oblique direction, and 140 configurations of per two light-adjusting modules, one permanent optical module 150.Moreover according to different light modulation purposes, the present invention more can comprise the staggered light emitting diode matrix of other types, not with the above-mentioned limit that is illustrated as.Yet the mistake that the present invention proposes row array can be simplified the design that LED backlight drives, and can reduce the drive IC cost.
Above-mentioned light emitting diode matrix also comprises one or more pulse-length modulation driving circuits (PWM IC) 160, wherein each pulse-length modulation driving circuit 160 output pulse width modulation signal is to together or together above (channel) light modulation district 120, and each light modulation district, road 120 comprises the light-adjusting module 140 of one or more series connection.When in the light-adjusting module 140 with string certain led failure being arranged, design of the present invention can be with local bright band obfuscation.
Each light-adjusting module 140 and permanent optical module 150 except can be shown in Fig. 2 A comprise respectively one first light emitting diode 142 and one second light emitting diode 152, each light-adjusting module 140 more can comprise first light emitting diode 142 of a plurality of series connection.Each permanent optical module 150 is as the same, more can comprise second light emitting diode 152 of a plurality of series connection.In another preferred embodiment of the present invention, above-mentioned light-adjusting module 140 can comprise two first light emitting diodes 142, and permanent optical module 150 comprises two second light emitting diodes 152, shown in Fig. 2 C.
With reference to shown in Figure 3, the present invention also proposes a kind of LED drive system 110 of LCD 100, and it comprises multiple tracks (channel) light modulation district 120, multiple tracks Heng Guang district 130, a plurality of pulse-length modulation driving circuit 160 and certain current and power supply device 170.
Each light modulation district, road 120 comprises the light-adjusting module 140 of a plurality of series connection, and each light-adjusting module 140 comprises at least one first light emitting diode 142, wherein each pulse-length modulation driving circuit 160 output pulse width modulation signal is to the multiple tracks light modulation district 120 of part, to adjust the brightness of first light emitting diode 142.
Each Heng Guang district, road 130 comprises the permanent optical module 150 of a plurality of series connection, and each permanent optical module 150 comprises at least one second light emitting diode 152, wherein decide the stable electric current of current and power supply device 170 outputs to a plurality of Heng Guang district 130, so that the brightness constancy of second light emitting diode 152.Moreover above-mentioned a plurality of light-adjusting modules 140 can be staggered to adapt to different light modulation purposes with a plurality of permanent optical modules 150.
As above-mentioned,, then need driving circuit to provide light emitting diode fixing electric current if in liquid crystal display backlight module, use a plurality of light emitting diodes of series connection.More in detail, when the user adjusts brightness and look school temperature or compensation temperature, then need to be used to adjust the light adjusting circuit of brightness.And dc power converter utilizes pulse-length modulation mechanism to control breakover element usually, this technology can change the duty cycle, the ratio of transistor turns time and shut-in time just, the electric power storage capacity that cooperates inductance again allows output voltage be maintained fixed in limited input voltage and load current range.Shown in Fig. 4 A and Fig. 4 B, it shows known LED driving circuit.
At first, Fig. 4 A is the sample circuit diagram of the LED driving circuit of known step-down dc-dc converter (buck DC-DC converter).Shown in Fig. 4 A, in LED driving circuit, use traditional decompression DC to direct current transducer, inductor L and LED serial are connected on the anodal terminal of DC current source Vin, and diode D is in parallel with inductor L and LED serial 11.In addition, switch 13 is connected on LED serial 11 and the connected node of diode D and the negative pole end of DC current source Vin with voltage detecting resistance R s.The magnitude of voltage that voltage detecting resistor R s is detected inputs to pulse width modulation drivers 12, according to the magnitude of voltage that detects, adjusts the conducting of switch 13/close dutycycle (duty ratio).Shown in Fig. 4 A, switch 13 can adopt mos field effect transistor (Metal Oxide Semiconductor Field-Effect Transistor, be called for short MOSFET), when applying switch pulse to the grid voltage of MOSFET, this MOSFET can be used as switch and use.
When switch 13 was " conducting ", the electric current of supplying from DC current source Vin was sent to LED serial via inductor L.During this time, at inductor L cumlative energy.When switch 13 is " cutting out " (off) time, the energy power supply by being accumulated in inductor L is to LED serial 11.Regulate the power supply be supplied to LED serial 11 according to voltage detecting resistance R s, pulse width modulation drivers 12 is adjusted the dutycycle of the conducting of switches 13/close.
Fig. 4 B is the circuit diagram of the LED driving circuit example of known supercharging DC-to-DC converter (boost DC-DC converter).Shown in Fig. 4 B, in LED driving circuit, adopt known supercharging direct current to direct current transducer, inductor L and diode D are connected on the positive terminal of DC current source Vin, and capacitor C and LED serial 11 are connected in parallel to each other between the negative pole end of diode and DC current source Vin.Switch 13 and voltage detecting resistance R s are connected between the negative pole end of the connected node of inductor L and diode D and direct supply Vin.The magnitude of voltage that input is detected at voltage detecting resistance R s is to pulse width modulation drivers 12, according to the magnitude of voltage that detects, adjusts the dutycycle of the conducting of switch 13/close.Shown in Fig. 4 B, switch 13 can adopt MOSFET, and by adjusting its grid voltage, MOSFET can be used as switch and use.
When switch 13 " conducting ", cross inductor L and switch S from the current flowing of DC current source Vin supply, and store energy is in inductor L.When switch 13 " cut out ", the sum total stream that is accumulated among the DC current source Vin with the energy of inductor L was sent to LED serial 11 by diode D.Here, by smmothing capacitor (smoothing capacitor) C smooth voltage and be sent to LED serial 11, and its magnitude of voltage be greater than or be equal to input voltage vin.
In such LED driving circuit, the resistance value of adjusting voltage detecting resistor R s to be to revise the magnitude of voltage that is detected from voltage detecting resistance R s, adjusts the conducting of switch 13/close dutycycle whereby, and then controlled the brightness of light emitting diode.
U.S. Pat 20080002102 just proposes a kind of LED drive system of backlight module, it is by switched-mode power supply (the Switch Mode Power Supply of power source conversion backfeed loop, SMPS) AC-DC converter in (AC-DC converter) converts direct current to the alternating current with the outside, and direct current is converted to predetermined value with the DC-to-DC converter among the SMPS (DC-DC converter), whereby to drive the LED serial in the backlight module.
In addition, Jap.P. JP 2007013183 proposes a kind of to decide the LED driving circuit that current control method drives, its major technique is relatively more default internal reference voltage and the measured voltage of voltage detecting resistance of comparer (comparator) that is comprised with Pwm controller, and measure dutycycle (dutyratio) according to this comparative result by the controller that Pwm controller comprised, switch pulse (switch pulse) to MOSFET to export one in view of the above subsequently.
With reference to shown in Figure 5, the present invention also proposes a kind of LCD 100, and it comprises a LED drive system 110 and a LCD MODULE 180.This LED drive system 110 comprises aforesaid multiple tracks light modulation district 120, multiple tracks Heng Guang district 130, a plurality of pulse-length modulation driving circuit 160 and a fixed current supply unit 170.
When pulse-length modulation driving circuit 160 receives a brightness control signal 190 (for example when the brightness of user's desire adjustment LCD, LCD promptly can be produced and be risen a brightness control signal to the pulse-length modulation driving circuit), pulse-length modulation driving circuit 160 is according to the multiple tracks light modulation district 120 of these brightness control signal 190 output pulse width modulation signals to part, to adjust the brightness of first light emitting diode 142.
When pulse-length modulation driving circuit 160 is adjusted the brightness of first light emitting diode 142, decide current and power supply device 170 and still output current to a plurality of Heng Guang district 130 sustainedly and stably, so second light emitting diode 152 still can provide constant brightness.Therefore, first light emitting diode 142 and second light emitting diode 152 allocation ratio quantitatively can determine the minimum brightness of LCD 100 when light modulation.
For example, when the quantity ratio of first light emitting diode 142 and second light emitting diode 152 is 1: 1, and when first light emitting diode 142 being transferred to the darkest (also promptly closing first light emitting diode 142) by pulse-length modulation driving circuit 160, only remaining second light emitting diode 152 still continues luminous, so the time LCD 100 minimum brightness be 50%.
In addition, because the display brightness of LCD MODULE 180 is to provide by first light emitting diode 142 and second light emitting diode 152, therefore, above-mentioned light-adjusting module 140 can be by being staggered to adjust the display brightness of LCD MODULE 180 equably with permanent optical module 150.
Generally speaking, the LCD backlight that adopts above-mentioned light emitting diode comprises that according to the position of light source side-light type (edge-type) is backlight backlight with straight-down negative (direct-type).In the former, the side that light source is designed to strip and is configured in light guide plate (light guide plate) is to light shine on the panel of LCD.In the latter, surface source of light equates in fact with the size of panel of LCD, and is configured in the panel of LCD below so that light is shone directly on the panel of LCD.And the light emitting diode matrix that the present invention proposes quite is fit to be applied to the directly-down liquid crystal display.
Apparently, according to the description among the top embodiment, the present invention has many corrections and difference.Therefore need be understood in the scope of its additional claim item, except above-mentioned detailed description, the present invention can also implement in other embodiment widely.Above-mentioned is the preferred embodiments of the present invention only, is not in order to limit claim scope of the present invention; All other do not break away from the equivalence of being finished under the spirit disclosed in this invention and changes or modification, all should comprise within the scope of the appended claims.