CN101894530A - Driving circuit and guard method thereof, light-emitting device and display equipment - Google Patents
Driving circuit and guard method thereof, light-emitting device and display equipment Download PDFInfo
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Abstract
In the driving circuit of the present invention, pulse-modulator (20) generates first pulse signal (S1) that its dutycycle is conditioned, and the detection voltage (Vs) of the electric state of the LED string (10) of feasible expression driven object is consistent with the reference voltage (Vref) of regulation.Be applied in first pulse signal (S1) on the primary coil (32) of pulse transformer (30).DC/DC transducer (40) comprises its conducting, ends the on-off element (42) that is controlled according to the last signal that produces of the secondary coil (34) of pulse transformer (30), will offer the anode of LED string (10) after input voltage (Vdc) voltage stabilizing.Thus, in led drive circuit, improve efficient.
Description
Technical field
The present invention relates to the Driving technique of light emitting diode.
Background technology
Backlight as liquid crystal board, replace CCFL (Cold Cathode Fluorescent Lamp in the past, cold-cathode fluorescence lamp) or EEFL (External Electrode Fluorescent Lamp, external electrode fluorescence lamp), use is seen the white light-emitting diode (being designated hereinafter simply as LED) with good characteristic from the viewpoint of long-life, low power consumption, wide colour gamut.
The prior art document:
Patent documentation:
(patent documentation 1): the spy opens the 2004-32875 communique
(patent documentation 2): the spy opens the 2002-252971 communique
(patent documentation 3): the spy opens the 2007-028784 communique
(patent documentation 4): the spy opens the 2007-173813 communique
(patent documentation 5): the spy opens the 2008-136293 communique
Summary of the invention
The problem that invention will solve
Fig. 1 is the block scheme of the structure of the general display equipment of expression.Smoothing circuit 202 carries out commercial ac voltage (100V) smoothly.Power-factor improvement (PFC:Power Factor Correction) circuit 204 is set in order to improve power factor, for example produces the DC voltage about 380V.Switching Power Supply (a DC/DC transducer) 206 DC voltage with 380V are depressurized to 24V.The voltage of the 24V of Sheng Chenging is used as the supply voltage of each piece of display equipment like this.
At the back side of liquid crystal board, the string that configuration is made of a plurality of light emitting diodes that are connected in series (below be designated as LED) (hereinafter referred to as LED string (string)) 210.In Fig. 1, only represent single LED string 210.The 2nd DC/DC transducer 208 is boost switching regulator (regulator), the DC voltage of 24V is boosted and produces driving voltage about 40～50V.This driving voltage is applied in the anode-side of LED string.Cathode side at LED string 210 is provided with constant-flow driver 212, and the drive current corresponding with luminosity offered LED string 210.The conducting of the controller 209 gauge tap element SW of the 2nd DC/DC transducer 208, the dutycycle of ending are so that the electric state of LED string 210 is near desired value.
In the system of Fig. 1, for driving LED, with the temporary transient step-down of commercial ac voltage and after boost, so need the voltage transformation of two-stage, become the main cause of degradation in efficiency.
Be in the electronic equipment of representative with the display equipment, need making primary side (thermal region) 214 of power supply and zone (cool region) 216 electrical isolations of primary side.In the system of Fig. 1, be the border with the primary coil and the secondary coil of the transformer of a DC/DC transducer, heat of dissociation zone HOT and cool region COLD.
In order in primary voltage transformation, 380V to be transformed to 40～50V, so the detection signal of representing the electric state of LED string 210 need be fed back to the controller 207 of a DC/DC transducer 206.But, in this case, because feedback line strides across thermal region HOT and cool region COLD, so violate the condition of electrical isolation.If photoelectrical coupler etc. is set on feedback line, then can assert electrical isolation, simultaneously detection signal is fed back to controller 207.But,, then produce the problem of the precision deterioration of feedback if use photoelectrical coupler.
1, the present invention finishes in this case, and one of illustrative purpose of its some mode provides the driving circuit with the high-level efficiency driving LED.
And the inventor studies led drive circuit, recognizes following problem.
Fig. 5 is the circuit diagram of the structure example of the general led drive circuit 300 of expression.Led drive circuit 300 has: power circuit 302, current driver 304, pulsed modulation light adjusting circuit 306, LED terminal 308, holding circuit 310.On LED terminal 308, be connected with the cathode terminal of the LED string of a plurality of LED that comprise driven object.Power circuit 302 offers driving voltage Vdrv on the anode of LED string 10.
On LED terminal 308, be connected with current driver 304.Current driver 304 produces the brightness corresponding driving electric current I drv with LED string 10, provides it to LED string 10.
Under the situation of led drive circuit 300 operate as normal, the current potential of LED terminal 308 remains near the voltage of regulation with being stabilized.But, produce fault and become open circuit at LED string 10, when perhaps terminal earth fault on the driving path of LED or power supply connected fault (below, these states are called abnormality), the current potential of LED terminal 308 (be also referred to as and detect voltage Vs) became and just often different values.Holding circuit 310 is by monitoring the detection voltage Vs of LED terminal 308, the abnormality of testing circuit, the protection processing of stipulating when generation is unusual.
Sometimes for the purpose of brightness (light modulation) of control LED, with the dutycycle corresponding to brightness make the drive current Idrv conducting of flowing through LED string 10, by (switch).Also being referred to as PWM drives.PWM light adjusting circuit 306 acts on current driver 304, according to pwm signal SPWM drive current Idrv is carried out switch.
Carrying out under the situation that PWM drives, drive current Idrv be cut off during, the current potential of LED terminal 308 is the same with abnormality, departs from the scope of regulation, so the difference of normal condition and abnormality is not given prominence to, hinders suitable circuit protection.
2, the present invention finishes in this state, and one of illustrative purpose of its some mode provides in the technology of LED being carried out positively carry out when PWM drives abnormality detection.
The means that are used to deal with problems
1, certain mode of the present invention relates to the driving circuit of light emitting diode.This driving circuit comprises: pulse-modulator, generate first pulse signal that its dutycycle is conditioned, and the detection voltage of the electric state of the light emitting diode of feasible expression driven object is consistent with the reference voltage of regulation; Pulse transformer comprises primary coil and secondary coil, has been applied in first pulse signal on this primary coil; And Switching Power Supply, comprise its conducting of signal controlling that produces on the secondary coil according to described pulse transformer, the on-off element that ends, will offer the first terminal of light emitting diode after the input voltage voltage stabilizing.
According to this mode, can heat of dissociation zone and cool region, use single DC/DC transducer driving LED simultaneously.
In certain mode, driving circuit also can also comprise: constant-current circuit is connected to second terminal of light emitting diode.Pulse-modulator also can be regulated the dutycycle of first pulse signal, makes the current potential of second terminal consistent with reference voltage.
Light emitting diode also can be a backlight liquid crystal display.Driving circuit also can also comprise: the PLL circuit, accept and the synchronous vertical synchronizing signal of view data that will on LCD, show, and with the vertical synchronizing signal multiplication, and clocking; And the dutycycle setup unit, by clock signal is counted, the pulse-modulated signal that has produced by pulsed modulation.Constant-current circuit also can make the drive current switch that flows through in the light emitting diode according to pulse-modulated signal.
At this moment, can be synchronous with view data, LED is carried out PWM drive.Therefore, for example under the situation that the frequency of vertical synchronizing signal has changed,, the Automatic Frequency ground of PWM is changed even do not carry out the processing of appending of software or hardware.
Driving circuit also can also comprise: smoothing circuit makes alternating voltage level and smooth; And power factor correction circuit, accept by smoothing circuit the voltage after level and smooth, generate the input voltage of Switching Power Supply.
Another mode of the present invention is a light-emitting device.This light-emitting device comprises: light emitting diode; And the driving circuit of above-mentioned one of them mode of driven for emitting lights diode.
Another mode of the present invention is a display equipment.This display equipment comprises: liquid crystal board; And as the above-mentioned light-emitting device that is configured in the back side of liquid crystal board backlight.
2, another mode of the present invention relates to the driving circuit of light emitting diode.Driving circuit comprises: current driver, be set at the cathode side on the current path of light emitting diode of driven object, and generate drive current; The pulsed modulation light adjusting circuit, the driving pulse that has generated by pulsed modulation makes the drive current conducting, ends according to this driving pulse; Abnormal detection circuit, the current potential of the cathode terminal of supervision light emitting diode generates the anomaly detection signal of being assert when detecting abnormality; And timer circuit, represent conducting with driving pulse, and anomaly detection signal has been identified as opportunity and the start time measures, when before anomaly detection signal is negated, having been passed through official hour, generate the guard signal of being assert.When driving circuit was assert at guard signal, the protection that puts rules into practice was handled.
According to this mode, because so that the drive current conducting of light emitting diode and detect unusual for condition is used for the time measurement of circuit protection, so can distinguish the cut-off state and the abnormality of drive current.And, after time measurement begins, under the state that anomaly detection signal has been assert, even the cut-off state that PWM drives, also continue and the continuation time measurement, positively detect unusual so can rely on the dutycycle of driving pulse as abnormality.
Timer circuit also can comprise: capacitor, and the current potential of one end is fixed; Charging circuit charges to capacitor; Discharge circuit discharges to capacitor; Trigger (flip-flop), when representing that conducting and anomaly detection signal are assert, driving pulse is set, when being negated, anomaly detection signal is reset, in SM set mode, make charging circuit activate (active), make the non-activation of discharge circuit, and in reset mode, make the non-activation of charging circuit, discharge circuit is activated; And comparer, the current potential of the other end of capacitor and the threshold voltage of regulation are compared, generate the guard signal that has with the corresponding level of comparative result.
And, make the combination arbitrarily or the textural element of the present invention of above textural element or show the result of phase double replacement between method, device, the system etc., also be effective as mode of the present invention.
The invention effect
According to certain mode of the present invention, driving LED expeditiously.And, according to alternate manner of the present invention, when LED being carried out the PWM driving, can positively detect unusual.
Description of drawings
Fig. 1 is the block scheme of the structure of the general display equipment of expression.
Fig. 2 is the circuit diagram of structure of the display equipment of expression first embodiment.
Fig. 3 is the circuit diagram of a part of structure of the led drive circuit of presentation graphs 2.
Fig. 4 is the timing diagram that a routine PWM of the circuit of presentation graphs 3 drives.
Fig. 5 is the circuit diagram of the structure example of the general led drive circuit of expression.
Fig. 6 is the circuit diagram of structure of the led drive circuit of expression second embodiment.
(a) of Fig. 7 and (b) be the timing diagram of an example of action of the led drive circuit of presentation graphs 6.
Label declaration
2... display equipment; 4... liquid crystal board; 6... liquid crystal driver; 8... it is backlight; 10...LED string; 20... pulse-modulator (voltage control unit); 22... error amplifier; 24... pulse-width modulator; 26... impact damper; 30... pulse transformer; 32... primary coil; 34... secondary coil; 40...DC/DC transducer (power circuit); 42... on-off element; 44... transformer; 46... primary coil; 48... secondary coil; D1... commutation diode; C1... output capacitor; 60... commercial ac power source; 62... smoothing circuit; 64... wave filter; 66...PFC circuit; 70... constant-current circuit; 72...PLL circuit; 74... light adjusting circuit; 100...LED driving circuit; 110...LED drive IC; S1... first pulse signal; S2... second pulse signal; 76...n bit counter; 78... register; 80... timer latch cicuit; 82... "AND" circuit; 84...SR trigger (flip-flop); 86... charging circuit; CCS1... constant current source; SW1... charge and use switch; 87... discharge circuit; 88... latch; CMP2... timer comparer; 40... power circuit; 50... holding circuit; CMP1... abnormal detection circuit; S1... anomaly detection signal; S2... guard signal; C10... first capacitor
Embodiment
Below, according to preferred embodiment with reference to description of drawings the present invention.Give identical label for identical or equal textural element, parts, the processing represented in each accompanying drawing, suitably the repetitive description thereof will be omitted.And embodiment is not used in and limits invention but illustration, the distinguishing characteristics of recording and narrating in the embodiment or its combination, the not necessarily feature of essence of the present invention or combination.
In this manual, so-called " state that components A is connected with part B " both comprised the physically direct-connected situation of components A and part B, also comprised the situation that components A and part B are connected indirectly via other parts that status of electrically connecting do not exerted an influence.
Equally, so-called " parts C is set at the state between components A and the part B ", except components A and parts C, perhaps outside part B and the direct-connected situation of parts C, also comprise situation about connecting indirectly via other parts that status of electrically connecting do not exerted an influence.
(first embodiment)
Fig. 2 is the circuit diagram of structure of the display equipment 2 of expression first embodiment.Display equipment 2 has: liquid crystal board 4, liquid crystal driver 6, backlight 8.
Liquid crystal board 4 has and is configured to rectangular a plurality of pixels.Each pixel is configured in the intersection point of a plurality of data lines and a plurality of sweep traces.Liquid crystal driver 6 accepts to be presented at the view data on the liquid crystal board 4.Liquid crystal driver 6 comprises: a plurality of data lines are applied the data driver of the driving voltage corresponding with brightness, and grid (gate) driver of selecting a plurality of sweep traces successively.
Dispose backlight 8 at the back side of liquid crystal board 4.Backlight 8 driving circuits 100 that have a plurality of LED strings 10 and be used to drive a plurality of LED strings 10.LED string 10 comprises a plurality of LED that are connected in series.
For each LED string 10 constant-current circuit 70 is set.Specifically, each constant-current circuit 70 is set between the cathode terminal and ground terminal of corresponding LED string 10.The electric current that light adjusting circuit 74 generates by control constant-current circuit 70, thereby the brightness of adjusting LED string 10.And light adjusting circuit 74 carries out switch motion by making constant-current circuit 70, LED string 10 is carried out PWM drive.Drive about PWM, in the back narration.
Pulse-modulator 20 generates the first pulse signal S1 according to the detection voltage Vs of the electric state of expression LED string 10.The dutycycle that pulse-modulator 20 is regulated the first pulse signal S1 makes that detection voltage Vs is consistent with the reference voltage V ref of regulation.As the electric state of LED string 10, example illustrates the voltage of the cathode terminal of LED string 10, the perhaps voltage of anode terminal.In Fig. 2, electric state is the voltage of cathode terminal, in other words, is the voltage between the two ends of constant-current circuit 70.
Pulse-modulator 20 comprises error amplifier 22 and pulse-width modulator 24.Error amplifier 22 has a plurality of reversed input terminals (-) and single normal phase input end (+).In a plurality of reversed input terminals (-), import the detection voltage Vs of electric state corresponding in a plurality of LED strings 10 of expression respectively.The reference voltage V ref of input regulation in normal phase input end (+) of error amplifier 22.Error amplifier 22 amplifies minimum detection voltage Vs of magnitude of voltage and the error of reference voltage V ref, generated error voltage Verr.Pulse-width modulator 24 generates the first pulse signal S1 that dutycycle changes according to error voltage Verr.For example, pulse-width modulator 24 comprise the oscillator that produces the wavy periodic voltage of triangular wave or sawtooth and utilize error voltage Verr to periodic voltage carry out amplitude limit comparer.And the structure of pulse-modulator 20 is not limited to the structure of Fig. 2, can utilize various technique known.
Commercial ac power source 60 produces the commercial ac voltage Vac of 50Hz or 60Hz.Smoothing circuit 62 for example is diode bridge (bridge), rectified AC voltage Vac.Voltage after smoothed is imported into DC/DC transducer 40 via pfc circuit 66.
DC/DC transducer 40 is so-called Switching Power Supplies, comprises on-off element 42, transformer 44, commutation diode D1, output capacitor C1.The topology of DC/DC transducer 40 is general topologys.One end of the primary coil 46 of transformer 44 is applied in the DC voltage (hereinafter referred to as input voltage Vdc) from about the 380V of pfc circuit 66 output.The other end at the primary coil 46 of transformer 44 is provided with on-off element 42.One end ground connection of secondary coil 48, the other end is connected with the anode of commutation diode D1.Output capacitor C1 is set between the negative electrode and ground terminal of commutation diode D1.
The output voltage V out of DC/DC transducer 40 is conditioned according to the dutycycle (conducting, the time scale of ending) of the switch of on-off element 42.Output voltage V out is applied in the anode of LED string 10.
Between the gate-to-source of on-off element 42, be connected with the secondary coil 34 of pulse transformer 30.Therefore, the conducting of on-off element 42, the second pulse signal S2 that ends according to generation in the secondary coil 34 of pulse transformer 30 are controlled.That is, on-off element 42 carries out switch according to the first pulse signal S1.
It more than is the structure of display equipment 2.Backlight 8 action then is described.If the user connects the power supply of display equipment 2, then provide DC voltage Vdc to DC/DC transducer 40.
DC/DC transducer 40 carries out switch motion according to the second pulse signal S2.Flow through the drive current Id that is generated by constant-current circuit 70 in LED string 10, its result produces voltage drop VLED on LED string 10.
Regulate the dutycycle of the first pulse signal S1, make that the negative electrode of LED string 10 is consistent with reference voltage V ref.Therefore, the output voltage V out of DC/DC transducer 40 is made Vout=VLED+Vref set up by voltage stabilizing.
It more than is backlight 8 action.
Backlight 8 according to Fig. 2 can make the voltage of the negative electrode of LED string 10, in other words makes the voltage between constant-current circuit 70 two ends consistent with reference voltage V ref.If the brownout between constant-current circuit 70 two ends, then can not generate the drive current Id of hope, have the brightness of the LED string 10 unsettled misgivings that become, but in the present embodiment, because the voltage between the two ends of assurance constant-current circuit 70 is so can positively generate drive current Id.
And, as the electric state of LED string 10, also can replace cathode voltage and feed back anode voltage.At this moment, compare with the situation that monitors cathode voltage, though see from the viewpoint of efficient poor slightly, with the same driving LED expeditiously of structure of Fig. 2.
Circuit shown in Figure 1 generates driving voltage Vout by two DC/DC transducers, and is relative with it, Fig. 2 backlight 8 in DC/DC transducer 40 be one.Therefore, can improve power efficiency significantly.
And, owing to thermal region HOT separates with pulse transformer 30 by transformer 44 with cool region COLD, so satisfy the Insulation Specification that electric product is required.The detection signal Vs of the electric state of expression LED string 10 is transformed in cool region COLD after the first pulse signal S1, is sent to thermal region HOT.Here, because the information of electric state is loaded on the pulse width of the first pulse signal S1, so compare with the situation that photoelectrical coupler etc. makes information be carried on the amplitude like that, can improve the resistance for noise, more positively the driving LED string 10.
Then, illustrate with backlight 8 PWM of embodiment and drive relevant feature.
In recent years, importing following technology, promptly use LED as situation backlight under, deep or light by according to the image that on liquid crystal board, shows, change brightness backlight (being called as Region control or local dim (dimming)) partly, thereby improve contrast.Local dimness is undertaken by the brightness of controlling a plurality of LED strings 10 independently.
Under the situation that drives the light modulation of implementing LED string 10 by PWM, worry to produce following problem.
On liquid crystal board, show based on image from the view data of outside and the synchronizing signal that accompanies with it.But, in general led drive circuit, independent oscillator is set, carry out PWM synchronously with clock signal and drive with the phase place irrelevant, frequency with view data.Like this, view data and light modulation backlight are asynchronous, can not obtain to improve the benefit of contrast.And, under the situation that the frequency (resolution) of view data has been changed, need be corresponding and frequency that change PWM in software formula ground drives with it.
Following feature is helpful to solving such problem.
Fig. 3 is the circuit diagram of a part of structure of the led drive circuit 100 of presentation graphs 2.PLL circuit 72 is accepted the vertical synchronizing signal VSYNC of frequency f in, and its multiplication is generated clock signal C K.PLL circuit 72 comprises so-called phase comparator and VCO (Voltage Controlled Oscillator, voltage controlled oscillator) and frequency divider.
Clock signal C K and vertical synchronizing signal VSYNC are synchronous, and frequency also correspondingly changes with it.
Each of 74 pairs of a plurality of constant-current circuits 70 of light adjusting circuit and being provided with, but for the purpose of simplifying the description, only represent one here.Light adjusting circuit 74 comprises n bit counter 76 and register 78.In register 78, store the corresponding count value C1 of brightness with corresponding constant-current circuit 70.This count value C1 upgrades according to the view data that shows on the liquid crystal board 4.
76 couples of clock signal C K of n bit counter count, generate have with register 78 in the pwm signal SPWM of the corresponding dutycycle of count value C1 of storage.
Fig. 4 is the timing diagram of the example that drives of the PWM of the circuit of presentation graphs 3.N bit counter 76 begins counting in the timing of the rising edge of vertical synchronizing signal VSYNC, count number is reached in the register 78 till the count value C1 of storage as conduction period Ton, afterwards, will until till the rising edge of next vertical synchronizing signal VSYNC as the off period between Toff.As an example, the timing diagram of Fig. 4 is represented the situation of n=8, C1=5.
According to the light adjusting system of Fig. 3, can regulate brightness backlight synchronously with view data.And, even under the situation that the resolution of view data has changed, also can follow this variation and Automatic Frequency ground that PWM is driven changes.
(second embodiment)
Fig. 6 is the circuit diagram of structure of the led drive circuit 100 of expression second embodiment.The light-emitting device integral body that comprises led drive circuit 100 and LED string 10 shown in Figure 6.This light-emitting device can utilize the various uses of utilizing LED as the illumination of backlight, the mobile phone of liquid crystal board or lighting device etc.The invention of second embodiment can be made up with first embodiment, perhaps separated utilization.
Led drive circuit 100 has power circuit 40 and LED drive IC 110, drives the LED string 10 that comprises a LED at least.Power circuit 40 for example comprises switching regulaor, charge pump circuit, one of them of linear regulator or their combination, generates driving LED string 10 needed driving voltage Vdrv, offers the anode of LED string 10.Though the structure of power circuit 40 does not limit especially, is made as Switching Power Supply here.The power circuit 40 of Fig. 6 is corresponding with the DC/DC transducer 40 of Fig. 2.
(1) thus FEEDBACK CONTROL power circuit 40 is regulated the function of driving voltage Vdrv
(2) thus the function of regulating the drive current Idrv control brightness of flowing through in the LED string 10
(3) detect abnormality, the function of holding circuit
About function 2, LED drive IC 110 has voltage control unit 20.The current potential (hereinafter referred to as detecting voltage Vs) of the LED terminal that voltage control unit 20 acceptance are connected with the negative electrode of LED string 10 is controlled power circuit 40 by feedback, makes that detection voltage Vs is consistent with the reference voltage V ref of regulation.By this FEEDBACK CONTROL, regulate the output voltage V drv of power circuit 40, make Vdrv=VLED+Vref set up.Voltage control unit 20 is corresponding with pulse-modulator 20 among Fig. 2.
At power circuit 40 is under the situation of switching regulaor, generates by voltage control unit 20 to have the pwm signal SWOUT with the corresponding dutycycle of error that detects voltage Vs with reference voltage V ref, provides it to power circuit 40.The switch inside element (not shown) of power circuit 40 is regulated driving voltage Vdrv by along with pwm signal SWOUT repeats conducting, ends.
About function 2, LED drive IC 110 has current driver (constant-current circuit of Fig. 2) 70 and PWM light adjusting circuit 74 (light adjusting circuit 74 of Fig. 2).Current driver 70 is set at the cathode side on the current path of LED string 10 of driven object.Current driver 70 generates and brightness corresponding driving electric current I drv, the electric current that flows through in the control LED string 10.To be called electric current light modulation (simulation light modulation) with the adjustment of the brightness of the big or small corresponding LED string 10 of drive current Idrv.
LED drive IC 110 is also carried out so-called PWM light modulation except the electric current light modulation.Specifically, make drive current timesharing ground carry out switch, regulate the time average of drive current Idrv, brightness is changed with dutycycle corresponding to brightness.
The driving pulse SPWM that PWM light adjusting circuit 74 has generated by pulsed modulation has and the corresponding dutycycle of brightness it.PWM light adjusting circuit 74 acts on current driver 70 according to driving pulse SPWM, thereby makes drive current Idrv conducting, end.In Fig. 6, be assigned between the high period of driving pulse SPWM between the light emission period of LED string 10 (conduction period Ton), be assigned between low period (Toff) between non-light emission period.
Then, circuit protection as the 3rd function is described.About defencive function, LED drive IC 110 has abnormal detection circuit CMP1, timer latch cicuit 80, holding circuit 50.
Abnormal detection circuit CMP1 monitors the current potential of the cathode terminal (LED terminal) of LED string 10, promptly detects voltage Vs and generates anomaly detection signal S1.Abnormal detection circuit CMP1 is judged to be abnormality at detection voltage Vs when the scope of stipulating breaks away from, and assert (assert) anomaly detection signal S1.Detect voltage Vs in being contained in the scope of regulation the time, anomaly detection signal S1 is negated (negate).
Abnormal detection circuit CMP1 for example also can be the comparer that relatively detects the first threshold voltage VTH1 of voltage Vs and regulation.Abnormal detection circuit CMP1 comprises in detection under the situation of open-circuit condition in path of LED string 10, wishes that first threshold voltage VTH1 is set at the value near ground voltage 0V lower than reference voltage V ref.At this moment, when abnormal detection circuit CMP1 is Vs＜VTH1, is judged to be abnormality and assert anomaly detection signal S1 (high level).
Timer latch cicuit 80 is represented conducting with driving pulse SPWM, and anomaly detection signal S1 is identified as opportunity and start time mensuration.After the beginning, if anomaly detection signal S1 has passed through official hour T1 before negating, then timer latch cicuit 80 is assert guard signal S2.
In order to realize this function, for example comprise: timer latch cicuit 80, "AND" circuit 82, set-reset flip-floop 84, charging circuit 86, discharge circuit 87, the first capacitor C10, timer comparator C MP2, latch 88.
Thereby the first terminal ground connection current potential of the first capacitor C10 is fixed.Charging circuit 86 constitutes changeable activation and non-activation, provides constant current Ic to the first capacitor C10 and charge under state of activation.For example, charging circuit 86 comprises: the constant current source CCS1 and the charging switch SW 1 that is arranged on its path that generate constant current Ic.Charging activates with switch SW 1 charging circuit 86 when conducting.
Discharge circuit 87 extracts electric current from the first capacitor C10 and discharges under state of activation.Discharge circuit 87 for example comprises second terminal and the switch SW 2 of the discharge between the ground terminal that is set at the first capacitor C10.Discharge circuit 87 activated when switch (SW2) conducting was used in discharge, and the current potential of second terminal of the first capacitor C10 (condenser voltage Vc) is initialized to earthing potential (0V).
"AND" circuit 82 generates the logic product of driving pulse SPWM and anomaly detection signal S1, outputs to set (set) terminal (S) of set-reset flip-floop 84.Be transfused to anomaly detection signal S1 in the reseting terminal of set-reset flip-floop 84 (inverted logic).
That is, set-reset flip-floop 84 is represented conducting at driving pulse SPWM, and anomaly detection signal S1 is set when being assert.And set-reset flip-floop 84 is reset when anomaly detection signal S1 is negated.
Set-reset flip-floop 84 makes charging circuit 86 activate under SM set mode, makes discharge circuit 87 non-activation.When set-reset flip-floop 84 was SM set mode, the first capacitor C10 was recharged with constant current Ic, so current potential (condenser voltage) Vc of second terminal of the first capacitor C10 rises in time.
Set-reset flip-floop 84 makes charging circuit 86 non-activation in reset mode, discharge circuit 87 is activated.When discharge circuit 87 activated, condenser voltage Vc was initialised.
Timer compares condenser voltage Vc and predetermined second threshold value voltage VTH2 with comparator C MP2, generates the guard signal S2 that has with the corresponding level of comparative result.Guard signal S2 is high level (identification) when Vc＞VTH2.Condenser voltage Vc provides by following formula: Vc=t * Ic/C10.Wherein, t is that C10 represents the capacitance of the first capacitor C10 from the elapsed time of charging beginning.
Therefore, guard signal S2 is assert when beginning from charging to pass through the stipulated time T1 that represents with following formula.
T1＝VTH2×C10/Ic
It more than is the structure of the led drive circuit 100 of Fig. 6.Its action then is described.
The (a) and (b) of Fig. 7 are timing diagrams of an example of action of the led drive circuit 100 of presentation graphs 6.In accordance with the order from top to bottom, expression driving pulse SPWM, anomaly detection signal S1, condenser voltage Vc, guard signal S2.
Sequential when (a) expression executive circuit of Fig. 7 is protected.At t0 sometime, drive signal SPWM is a high level, and LED string 10 is a conducting state.Under this state, when producing open-circuit condition on the path of LED string 10, the current potential Vs of LED terminal is reduced near the ground voltage (0V), and anomaly detection signal S1 is assert (high level).When anomaly detection signal S1 was assert, set-reset flip-floop 84 was set, and beginning is based on the charging of the first capacitor C1 of charging circuit 86.
At moment t2, driving pulse SPWM moves to low level, but this situation does not influence the state of set-reset flip-floop 84.That is, the charging based on charging circuit 86 continues.
At moment t3, condenser voltage Vc arrives the second threshold voltage VTH2.This situation represents that abnormality has continued more than t1 specified time limit.Assert that at moment t3 guard signal S2 (S2 ') execute protection is handled.
Afterwards, if remove and anomaly detection signal S1 is negated in moment t4 abnormality, then set-reset flip-floop 84 is reset, and condenser voltage Vc is initialised by discharge circuit 87.
(b) of Fig. 7 represents the sequential under the situation of the protection of executive circuit not.All (a) with Fig. 7 is identical till moment t3.In (b) of Fig. 7, begin to through the moment t4 ' before the stipulated time T1 from charging, anomaly detection signal S1 is negated.Therefore, condenser voltage Vc does not arrive the second threshold voltage VTH2, thus guard signal S2 (S2 ') do not assert that execute protection is not handled.
Like this, according to the led drive circuit 100 of embodiment, can go here and there 10 conduction period Ton at LED and produce abnormality, abnormality has continued to protect processing under the above situation of stipulated time T1 afterwards.In the continuing of abnormality, even driving pulse SPWM is a cut-off state, owing to do not remove the detection of abnormality, so even the pulse width variation of driving pulse SPWM also can not be subjected to it to influence the ground holding circuit.
Technology is investigated following situation as a comparison, promptly omits set-reset flip-floop 84, directly switches the activation of charging circuit 86 and discharge circuit 87, non-activation by the output signal of "AND" circuit 82.That is be that charging circuit 86 was for activating during conducting state (luminance) and anomaly detection signal S1 were assert, at LED string 10.
In this comparison techniques, after anomaly detection signal S1 was assert, when drive pulse signal SPWM became low level at once, although abnormality continues, charging circuit 86 also was non-activation, stop time measurement.That is, continued more than the stipulated time T1, also do not assert guard signal S2, also do not protected the situation of processing even produce abnormality.
In contrast,, can not rely on the pulse width (length of conduction period Ton) of driving pulse SPWM, apply circuit protection according to the led drive circuit 100 of embodiment.
According to embodiment the present invention has been described, but embodiment is only represented principle of the present invention, application, in embodiment, in the scope of the thought of the present invention that does not break away from the claim defined, the change of various deformation example or configuration is arranged certainly.
Claims (12)
1. a driving circuit is characterized in that, comprising:
Pulse-modulator generates first pulse signal that its dutycycle is conditioned, and the detection voltage of the electric state of the light emitting diode of feasible expression driven object is consistent with the reference voltage of regulation;
Pulse transformer comprises primary coil and secondary coil, has been applied in described first pulse signal on this primary coil; And
Switching Power Supply comprises its conducting of signal controlling that produces on the secondary coil according to described pulse transformer, the on-off element that ends, and will offer the first terminal of described light emitting diode after the input voltage voltage stabilizing.
2. driving circuit as claimed in claim 1 is characterized in that,
Also comprise:
Constant-current circuit is connected to second terminal of described light emitting diode,
Described pulse-modulator is regulated the dutycycle of described first pulse signal, makes that the current potential of described second terminal is consistent with described reference voltage.
3. driving circuit as claimed in claim 2 is characterized in that,
Described light emitting diode is a backlight liquid crystal display,
Described driving circuit also comprises:
The PLL circuit is accepted and the synchronous vertical synchronizing signal of view data that will show on described LCD, with described vertical synchronizing signal multiplication, and clocking; And
The dutycycle setup unit, by described clock signal is counted, the pulse-modulated signal that has produced by pulsed modulation,
Described constant-current circuit carries out switch according to described pulse-modulated signal to the drive current that flows through in described light emitting diode.
4. driving circuit as claimed in claim 3 is characterized in that, also comprises:
Smoothing circuit makes alternating voltage level and smooth; And
Power factor correction circuit is accepted by described smoothing circuit the voltage after level and smooth, generates the input voltage of described Switching Power Supply.
5. driving circuit as claimed in claim 2 is characterized in that,
Also comprise:
The pulsed modulation light adjusting circuit, the driving pulse that has generated by pulsed modulation makes drive current conducting that described constant-current circuit generates, ends according to this driving pulse;
Abnormal detection circuit monitors the current potential of second terminal of described light emitting diode to be created on the anomaly detection signal of being assert when detecting abnormality; And
Timer circuit is represented conducting with described driving pulse, and described anomaly detection signal has been identified as opportunity and the start time measures, when having been passed through official hour before described anomaly detection signal is negated, generates the guard signal of being assert,
When described guard signal was assert, the protection that puts rules into practice was handled.
6. driving circuit as claimed in claim 5 is characterized in that,
Described timer circuit comprises:
Capacitor, the current potential of one end is fixed;
Charging circuit charges to described capacitor;
Discharge circuit discharges to described capacitor;
Trigger, when representing that conducting and described anomaly detection signal are assert, described driving pulse is set, when being negated, described anomaly detection signal is reset, described charging circuit is activated, make the non-activation of described discharge circuit, and in reset mode, make the non-activation of described charging circuit, described discharge circuit is activated; And
Comparer compares the current potential of the other end of described capacitor and the threshold voltage of regulation, generates the described guard signal that has with the corresponding level of comparative result.
7. a light-emitting device is characterized in that, comprising:
Light emitting diode; And
Drive the driving circuit of any record of the claim 1 to 6 of described light emitting diode.
8. a display equipment is characterized in that, comprising:
Liquid crystal board; And
Light-emitting device as claim 7 record at the back side that is configured in described liquid crystal board backlight.
9. the driving circuit of a light emitting diode is characterized in that, comprising:
Current driver is set at the cathode side on the current path of light emitting diode of driven object, generates drive current;
The pulsed modulation light adjusting circuit, the driving pulse that has generated by pulsed modulation makes described drive current conducting, ends according to this driving pulse;
Abnormal detection circuit monitors the current potential of the cathode terminal of described light emitting diode, and generates the anomaly detection signal of being assert when detecting abnormality; And
Timer circuit is represented conducting with described driving pulse, and described anomaly detection signal has been identified as opportunity and the start time measures, when having been passed through official hour before described anomaly detection signal is negated, generates the guard signal of being assert,
When described guard signal was assert, the protection that puts rules into practice was handled.
10. driving circuit as claimed in claim 9 is characterized in that,
Described timer circuit comprises:
Capacitor, the current potential of one end is fixed;
Charging circuit charges to described capacitor;
Discharge circuit discharges to described capacitor;
Trigger, when representing that conducting and described anomaly detection signal are assert, described driving pulse is set, when being negated, described anomaly detection signal is reset, described charging circuit is activated, make the non-activation of described discharge circuit, and in reset mode, make the non-activation of described charging circuit, described discharge circuit is activated; And
Comparer compares the current potential of the other end of described capacitor and the threshold voltage of regulation, generates the described guard signal that has with the corresponding level of comparative result.
11. a light-emitting device is characterized in that, comprising:
Light emitting diode; And
Drive the claim 9 of described light emitting diode or the driving circuit of 10 records.
12. a guard method is characterized in that, comprising:
Generate drive current, and offer the step of the light emitting diode of driven object;
Generation by pulsed modulation driving pulse, the step that makes described drive current conducting, ends according to this driving pulse;
Monitor the current potential of the cathode terminal of described light emitting diode, when detecting abnormality, generate the step of the anomaly detection signal of being assert;
Represent conducting with described driving pulse, and described anomaly detection signal is identified as opportunity and the start time measures, when before described anomaly detection signal is negated, having been passed through official hour, generated the step of the guard signal of being assert; And
When described guard signal is assert, the step that the protection that puts rules into practice is handled.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2009120904 | 2009-05-19 | ||
| JP120904/09 | 2009-05-19 | ||
| JP2009123845 | 2009-05-22 | ||
| JP123845/09 | 2009-05-22 | ||
| JP2010068475A JP5600456B2 (en) | 2009-05-19 | 2010-03-24 | Light emitting diode drive circuit, light emitting device and display device using the same, and drive circuit protection method |
| JP068475/10 | 2010-03-24 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN101894530A true CN101894530A (en) | 2010-11-24 |
| CN101894530B CN101894530B (en) | 2015-05-06 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN201010179584.5A Active CN101894530B (en) | 2009-05-19 | 2010-05-17 | Driving circuit and protection method thereof, light-emitting device and display device |
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| CN104135789A (en) * | 2014-06-10 | 2014-11-05 | 矽力杰半导体技术(杭州)有限公司 | Primary-side controlled LED (Light Emitting Diode) driving method and driving circuit |
| CN108650747A (en) * | 2014-09-16 | 2018-10-12 | 株式会社小糸制作所 | Lamp circuit and the lamps apparatus for vehicle for using the lamp circuit |
| CN108650747B (en) * | 2014-09-16 | 2020-11-10 | 株式会社小糸制作所 | Lighting circuit and vehicle lamp using the same |
| CN109587869A (en) * | 2017-09-29 | 2019-04-05 | 东莞市高效电控有限公司 | Light emitting diode driving circuit and lighting device thereof |
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| CN109587869B (en) * | 2017-09-29 | 2021-07-23 | 东莞市高效电控有限公司 | Light emitting diode driving circuit and lighting device thereof |
| CN111326126A (en) * | 2020-04-16 | 2020-06-23 | 福州京东方光电科技有限公司 | Signal supply circuit, signal supply method and display device |
| CN111326126B (en) * | 2020-04-16 | 2022-03-25 | 福州京东方光电科技有限公司 | Signal supply circuit, signal supply method and display device |
| CN116189581A (en) * | 2023-04-27 | 2023-05-30 | 杭州视芯科技股份有限公司 | LED open circuit detection method and circuit, and LED driving method and circuit |
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