CN101894530B - Driving circuit and protection method thereof, light-emitting device and display device - Google Patents
Driving circuit and protection method thereof, light-emitting device and display device Download PDFInfo
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Abstract
In a driving circuit of the invention, a pulse modulator (20) generates a first pulse signal (S1) with a regulated dutyfactor, such that a detection voltage (Vs) representing an electrical state of a LED string (10) of a drive object is identical to a reference voltage (Vref). A primary coil (32) of a pulse transformer (30) is subjected to the first pulse signal (S1). A DC.DC converter (40) contains a switch element (42) controlled to switch on/off according to a signal generated by a secondary coil (34) of the pulse transformer (30) and stabilizes an input voltage (Vdc) to supply to an anode of the LED string (10). Thereby, the efficiency of a LED driving circuit is improved.
Description
Technical field
The present invention relates to the Driving technique of light emitting diode.
Background technology
As the backlight of 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 the white light-emitting diode (hereinafter referred to as LED) viewed from the viewpoint of long-life, low power consumption, wide colour gamut with good characteristic.
Prior art document:
Patent documentation:
(patent documentation 1): JP 2004-32875 publication
(patent documentation 2): JP 2002-252971 publication
(patent documentation 3): JP 2007-028784 publication
(patent documentation 4): JP 2007-173813 publication
(patent documentation 5): JP 2008-136293 publication
Summary of the invention
The problem that invention will solve
Fig. 1 is the block scheme of the structure representing general display equipment.Smoothing circuit 202 is by smoothing for commercial ac voltage (100V).Power-factor improvement (PFC:Power Factor Correction) circuit 204 is set in order to improve power factor, such as, produces the DC voltage of about 380V.The DC voltage of 380V is depressurized to 24V by Switching Power Supply (a DC/DC transducer) 206.The voltage of the 24V of such generation is used as the supply voltage of each piece of display equipment.
At the back side of liquid crystal board, configure the string (hereinafter referred to as LED strip (string)) 210 be made up of the multiple light emitting diodes (being designated as LED below) be connected in series.In FIG, single LED strip 210 is only represented.2nd DC/DC transducer 208 is boost switching regulator (regulator), the dc voltage boost of 24V is produced the driving voltage of about 40 ~ 50V.This driving voltage is applied in the anode-side of LED strip.Constant-flow driver 212 is set at the cathode side of LED strip 210, the drive current corresponding with luminosity is supplied to LED strip 210.The conducting of controller 209 gauge tap element SW of the 2nd DC/DC transducer 208, the dutycycle of cut-off, to make the electric state of LED strip 210 close to desired value.
In the system of fig. 1, in order to driving LED, temporary transient for commercial ac voltage step-down is being boosted afterwards, so need the voltage transformation of two-stage, is becoming the main cause of degradation in efficiency.
In the electronic equipment taking display equipment as representative, need to make the primary side (thermal region) 214 of power supply and region (cool region) 216 electrical isolation of primary side.In the system of fig. 1, with the primary coil of the transformer of a DC/DC transducer and secondary coil for border, heat of dissociation region HOT and cool region COLD.
In order to 380V being transformed to 40 ~ 50V in primary voltage transformation, so need the controller 207 detection signal of the electric state representing LED strip 210 being fed back to 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 arrange photoelectrical coupler etc. on feedback line, then can assert electrical isolation, detection signal be fed back to controller 207 simultaneously.But, if use photoelectrical coupler, then produce the problem of the deteriorated accuracy of feedback.
1, the present invention completes in this case, and one of illustrative object of its some mode is to provide with the driving circuit of high-level efficiency driving LED.
And the present inventor studies LED drive circuit, recognize following problem.
Fig. 5 is the circuit diagram of the structure example representing general LED drive circuit 300.LED drive circuit 300 has: power circuit 302, current driver 304, pulsed modulation light adjusting circuit 306, LED terminal 308, protection circuit 310.LED terminal 308 is connected with the cathode terminal of the LED strip of the multiple LED comprising driven object.Driving voltage Vdrv is supplied to the anode of LED strip 10 by power circuit 302.
LED terminal 308 is connected with current driver 304.Current driver 304 produces the drive current Idrv corresponding to the brightness of LED strip 10, provides it to LED strip 10.
When LED drive circuit 300 normally works, the current potential of LED terminal 308 is stably retained near the voltage of regulation.But, produce fault in LED strip 10 and become open circuit, or it is (following that the terminal ground fault on the driving path of LED or power supply connect fault, these states are called abnormality) time, the current potential (also referred to as detection voltage Vs) of LED terminal 308 becomes the value different from time normal.Protection circuit 310, by monitoring the detection voltage Vs of LED terminal 308, the abnormality of testing circuit, carries out the conservation treatment specified when producing abnormal.
Sometimes for the object of the brightness (light modulation) of control LED, make with the dutycycle corresponding to brightness drive current Idrv conducting, the cut-off (switch) of flowing through LED strip 10.Also be referred to as PWM to drive.PWM light adjusting circuit 306 acts on current driver 304, carries out switch according to pwm signal SPWM to drive current Idrv.
When carrying out PWM driving, during drive current Idrv is cut off, 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 completes in a state in which, and one of illustrative object of its some mode is to provide the technology of positively carrying out abnormality detection when carrying out PWM to LED and driving.
For the means of dealing with problems
1, certain mode of the present invention relates to the driving circuit of light emitting diode.This driving circuit comprises: pulse-modulator, generates the first pulse signal that its dutycycle is conditioned, and makes the detection voltage of the electric state of the light emitting diode representing driven object consistent with the reference voltage of regulation; Pulse transformer, comprises primary coil and secondary coil, and this primary coil has been applied in the first pulse signal; And Switching Power Supply, comprise the on-off element that the signal that the secondary coil according to described pulse transformer produces controls its conducting, cut-off, the first terminal of light emitting diode will be supplied to after input voltage voltage stabilizing.
According to which, can heat of dissociation region and cool region, simultaneously by single DC/DC transducer driving LED.
In certain mode, driving circuit also can also comprise: constant-current circuit, is connected to the second terminal of light emitting diode.Pulse-modulator also can regulate the dutycycle of the first pulse signal, makes the current potential of the second terminal consistent with reference voltage.
Light emitting diode also can be the backlight of liquid crystal display.Driving circuit also can also comprise: PLL circuit, accepts the vertical synchronizing signal synchronous with the view data that will show on a liquid crystal display, vertical synchronizing signal is doubled, and clocking; And dutycycle setup unit, by counting clock signal, produce the pulse-modulated signal be pulse modulation.Constant-current circuit also according to pulse-modulated signal, can make the drive current switch flow through in light emitting diode.
At this moment, can be synchronous with view data, PWM driving is carried out to LED.Therefore, such as, when the frequency of vertical synchronizing signal changes, even if do not carry out the process added of software or hardware, the frequency of PWM also can be made automatically to change.
Driving circuit also can also comprise: smoothing circuit, makes alternating voltage level and smooth; And power factor correction circuit, accept the voltage after by smoothing circuit smoothes, generate the input voltage of Switching Power Supply.
Another mode of the present invention is light-emitting device.This light-emitting device comprises: light emitting diode; And the driving circuit of one of them mode above-mentioned of driving light emitting diode.
Another mode of the present invention is display equipment.This display equipment comprises: liquid crystal board; And the above-mentioned light-emitting device at the back side of liquid crystal board is configured in as backlight.
2, another mode of the present invention relates to the driving circuit of light emitting diode.Driving circuit comprises: current driver, is arranged on the cathode side on the current path of the light emitting diode of driven object, generates drive current; Pulsed modulation light adjusting circuit, generates the driving pulse be pulse modulation, makes drive current conducting, cut-off according to this driving pulse; Abnormal detection circuit, monitors the current potential of the cathode terminal of light emitting diode, generates the anomaly detection signal be identified when abnormality being detected; And timer circuit, represent conducting with driving pulse, and anomaly detection signal is identified as opportunity and start time measures, when have passed through official hour before anomaly detection signal is denied, generates the guard signal be identified.Driving circuit when guard signal is identified, the conservation treatment put rules into practice.
According to which, due to so that light emitting diode drive current conducting and detect and abnormal carry out for circuit protection time measurement, so cut-off state and the abnormality of drive current can be distinguished for condition.And, after time measurement starts, under the state that anomaly detection signal has been identified, even the cut-off state that PWM drives, also continue as abnormality and continue time measurement, so the dutycycle of driving pulse can not relied on and positively detect exception.
Timer circuit also can comprise: capacitor, and the current potential of its one end is fixed; Charging circuit, charges to capacitor; Discharge circuit, to discharging capacitors; Trigger (flip-flop), be set when driving pulse represents conducting and anomaly detection signal is identified, be reset when anomaly detection signal is denied, in SM set mode, make charging circuit activate (active), make discharge circuit inactive, and in reset mode, make charging circuit inactive, discharge circuit is activated; And comparer, the current potential of the other end of capacitor and the threshold voltage of regulation are compared, generates the guard signal with the level corresponding to comparative result.
And making the arbitrary combination of above textural element or textural element of the present invention or show the result of phase double replacement between method, device, system etc., is also effective as mode of the present invention.
Invention effect
According to certain mode of the present invention, can driving LED expeditiously.And, according to alternate manner of the present invention, when carrying out PWM to LED and driving, positively exception can be detected.
Accompanying drawing explanation
Fig. 1 is the block scheme of the structure representing general display equipment.
Fig. 2 is the circuit diagram of the structure of the display equipment representing the first embodiment.
Fig. 3 is the circuit diagram of a part for the structure of the LED drive circuit representing Fig. 2.
Fig. 4 is the timing diagram that a routine PWM of the circuit representing Fig. 3 drives.
Fig. 5 is the circuit diagram of the structure example representing general LED drive circuit.
Fig. 6 is the circuit diagram of the structure of the LED drive circuit representing the second embodiment.
(a) and (b) of Fig. 7 is the timing diagram of an example of the action of the LED drive circuit representing Fig. 6.
Label declaration
2... display equipment, 4... liquid crystal board, 6... liquid crystal driver, 8... backlight, 10...LED go here and there, 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... the first pulse signal, S2... the second pulse signal, 76...n bit counter, 78... register, 80... timer latch cicuit, 82... "AND" circuit, 84...SR (flip-flop) is triggered, 86... charging circuit, CCS1... constant current source, SW1... charging switch, 87... discharge circuit, 88... latch, CMP2... timer comparer, 40... power circuit, 50... protection circuit, CMP1... abnormal detection circuit, S1... anomaly detection signal, S2... guard signal, C10... the first capacitor
Embodiment
Below, according to preferred embodiment with reference to accompanying drawing, the present invention being described.Give identical label for the identical or equal textural element represented in each accompanying drawing, parts, process, suitably the repetitive description thereof will be omitted.And embodiment is not used in and limits invention but illustrate, the distinguishing characteristics described in 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 ", had both comprised the situation that components A is physically directly connected with part B, had also comprised the situation that components A is connected via other parts do not had an impact to status of electrically connecting indirectly with part B.
Equally, so-called " parts C is arranged on the state between components A and part B ", except components A and parts C, or outside part B and parts C situation about being directly connected, also comprise situation about indirectly connecting via other parts do not had an impact to status of electrically connecting.
(the first embodiment)
Fig. 2 is the circuit diagram of the structure of the display equipment 2 representing the 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 multiple pixels.Each pixel is configured in the intersection point of multiple data line and multiple sweep trace.Liquid crystal driver 6 accepts the view data that will be presented on liquid crystal board 4.Liquid crystal driver 6 comprises: the data driver multiple data line being applied to the driving voltage corresponding with brightness, and selects grid (gate) driver of multiple sweep trace successively.
In the back side of liquid crystal board 4 configuration backlight 8.Backlight 8 has multiple LED strip 10 and for driving the driving circuit 100 of multiple LED strip 10.LED strip 10 comprises the multiple LED be connected in series.
LED drive circuit 100 has: LED drive IC 110, pulse transformer 30, DC/DC transducer 40, wave filter 64 and pfc circuit 66.
LED drive IC 110 comprises pulse-modulator 20, impact damper 26, multiple constant-current circuit 70, PLL circuit 72 and light adjusting circuit 74, is integrated on a semiconductor substrate.
Constant-current circuit 70 is arranged for each LED strip 10.Specifically, between each constant-current circuit 70 cathode terminal of being arranged on corresponding LED strip 10 and ground terminal.The electric current that light adjusting circuit 74 generates by controlling constant-current circuit 70, thus the brightness regulating LED strip 10.And light adjusting circuit 74 carries out switch motion by making constant-current circuit 70, carries out PWM driving to LED strip 10.Drive about PWM, describe later.
Pulse-modulator 20 generates the first pulse signal S1 according to the detection voltage Vs of the electric state representing LED strip 10.Pulse-modulator 20 regulates the dutycycle of the first pulse signal S1, makes to detect voltage Vs consistent with the reference voltage V ref of regulation.As the electric state of LED strip 10, exemplify the voltage of the cathode terminal of LED strip 10, or the voltage of anode terminal.In fig. 2, electric state is the voltage of cathode terminal, in other words, be constant-current circuit 70 two ends between voltage.
Pulse-modulator 20 comprises error amplifier 22 and pulse-width modulator 24.Error amplifier 22 has multiple reversed input terminal (-) and single non-inverting input terminal (+).In multiple reversed input terminal (-), input represents the detection voltage Vs of the electric state of corresponding in multiple LED strip 10 respectively.The reference voltage V ref of input regulation in the non-inverting input terminal (+) of error amplifier 22.Error amplifier 22 amplifies the error of magnitude of voltage minimum detection voltage Vs and reference voltage V ref, generates error voltage Verr.Pulse-width modulator 24 generates the first pulse signal S1 that dutycycle changes according to error voltage Verr.Such as, pulse-width modulator 24 comprises the oscillator producing triangular wave or the wavy periodic voltage of 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, various known technology can be utilized.
Pulse transformer 30 comprises primary coil 32 and secondary coil 34.One end ground connection of primary coil 32, the other end is applied in the first pulse signal S1 via impact damper 26.The second pulse signal S2 corresponding to the first pulse signal S1 is produced in secondary coil 34.
Commercial ac power source 60 produces the commercial ac voltage Vac of 50Hz or 60Hz.Smoothing circuit 62 is such as diode bridge (bridge), rectified AC voltage Vac.DC/DC transducer 40 is imported into via pfc circuit 66 by the voltage after level and smooth.
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) of about the 380V exported from pfc circuit 66.At the other end of the primary coil 46 of transformer 44, on-off element 42 is set.One end ground connection of secondary coil 48, the other end is connected with the anode of commutation diode D1.Between the negative electrode that output capacitor C1 is arranged on commutation diode D1 and ground terminal.
The output voltage Vout of DC/DC transducer 40 is conditioned according to the dutycycle (time scale of conducting, cut-off) of the switch of on-off element 42.Output voltage Vout is applied in the anode of LED strip 10.
Between the gate-to-source of on-off element 42, be connected with the secondary coil 34 of pulse transformer 30.Therefore, on-off element 42 conducting, end according to pulse transformer 30 secondary coil 34 in the second pulse signal S2 of producing be controlled.That is, on-off element 42 carries out switch according to the first pulse signal S1.
It is more than the structure of display equipment 2.The action of backlight 8 is then described.If 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.In LED strip 10, flow through the drive current Id generated by constant-current circuit 70, its result, LED strip 10 produces voltage drop VLED.
Regulate the dutycycle of the first pulse signal S1, make the negative electrode of LED strip 10 consistent with reference voltage V ref.Therefore, the output voltage Vout of DC/DC transducer 40, by voltage stabilizing, makes Vout=VLED+Vref set up.
It is more than the action of backlight 8.
According to the backlight 8 of Fig. 2, the voltage of the negative electrode of LED strip 10 can be made, in other words make 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, the brightness that there is LED strip 10 becomes unstable misgivings, but in the present embodiment, due to ensure constant-current circuit 70 two ends between voltage, so can positively generate drive current Id.
And, as the electric state of LED strip 10, also can replace cathode voltage and feed back anode voltage.At this moment, compared with monitoring the situation of cathode voltage, although slightly poor viewed from the viewpoint of efficiency, the same with the structure of Fig. 2 can driving LED expeditiously.
Circuit shown in Fig. 1 generates driving voltage Vout by two DC/DC transducers, and corresponding thereto, in the backlight 8 of Fig. 2, DC/DC transducer 40 is one.Therefore, power efficiency can be improved significantly.
And, because thermal region HOT and cool region COLD are separated, so meet the Insulation Specification required electric product by transformer 44 and pulse transformer 30.After representing that the detection signal Vs of the electric state of LED strip 10 is transformed to the first pulse signal S1 in cool region COLD, be sent to thermal region HOT.Here, because the information of electric state is loaded in the pulse width of the first pulse signal S1, so compared with the situation making information be carried on amplitude like that with photoelectrical coupler etc., the resistance for noise can be improved, can more positively driving LED string 10.
Then, illustrate and drive relevant feature with the PWM of the backlight 8 of embodiment.
In recent years, importing following technology, namely when using LED as backlight, deep or light by according to the image that shows on liquid crystal board, change the brightness (being called as Region control or local dim (dimming)) of backlight partly, thus improve contrast.Local is dim is undertaken by the brightness controlling multiple LED strip 10 independently.
When being driven the light modulation implementing LED strip 10 by PWM, worry to produce following problem.
Liquid crystal board shows based on the view data from outside and the image of synchronizing signal that accompanies with it.But, in general LED drive circuit, independent oscillator is set, with have have nothing to do with view data phase place, frequency clock signal synchronization to carry out PWM driving.Like this, the light modulation of view data and backlight is asynchronous, can not obtain the benefit improving contrast.And, when the frequency (resolution) of view data is changed, need corresponding with it and software type ground changes the frequency that PWM drives.
Following feature is helpful to solving such problem.
Fig. 3 is the circuit diagram of a part for the structure of the LED drive circuit 100 representing Fig. 2.PLL circuit 72 accepts the vertical synchronizing signal VSYNC of frequency f in, is doubled and generated clock signal CK.PLL circuit 72 comprises so-called phase comparator and VCO (Voltage Controlled Oscillator, voltage controlled oscillator) and frequency divider.
Clock signal C K is synchronous with vertical synchronizing signal VSYNC, and frequency also correspondingly changes with it.
Light adjusting circuit 74 to multiple constant-current circuit 70 each and arrange, but here for the purpose of simplifying the description, only represent one.Light adjusting circuit 74 comprises n-bit counter 76 and register 78.The count value C1 corresponding to the brightness of corresponding constant-current circuit 70 is stored in register 78.This count value C1 upgrades according to the view data of display on liquid crystal board 4.
N-bit counter 76 couples of clock signal C K count, and generate the pwm signal SPWM with the dutycycle corresponding to the count value C1 stored in register 78.
Fig. 4 is the timing diagram of the example that the PWM of the circuit representing Fig. 3 drives.N-bit counter 76 starts counting in the timing of the rising edge of vertical synchronizing signal VSYNC, as conduction period Ton till count number being reached the count value C1 stored in register 78, afterwards, using till the rising edge of next vertical synchronizing signal VSYNC as Toff between the off period.As an example, the timing diagram of Fig. 4 represents the situation of n=8, C1=5.
According to the light adjusting system of Fig. 3, can be synchronous with view data and regulate the brightness of backlight.And, even if when the resolution of view data changes, also this change can be followed and the frequency that PWM is driven automatically changes.
(the second embodiment)
Fig. 6 is the circuit diagram of the structure of the LED drive circuit 100 representing the second embodiment.The light-emitting device entirety comprising LED drive circuit 100 and LED strip 10 shown in Figure 6.This light-emitting device can utilize the various uses utilizing LED as the backlight of liquid crystal board, the illumination of mobile phone or lighting device etc.The invention of the second embodiment can be combined with the first embodiment, or separated utilization.
LED drive circuit 100 has power circuit 40 and LED drive IC 110, drives the LED strip 10 at least comprising a LED.Power circuit 40 such as comprises the combination of one of them or they of switching regulaor, charge pump circuit, linear regulator, generates the driving voltage Vdrv required for driving LED string 10, is supplied to the anode of LED strip 10.Although the structure of power circuit 40 is not particularly limited, be set to Switching Power Supply here.The power circuit 40 of Fig. 6 is corresponding with the DC/DC transducer 40 of Fig. 2.
LED drive IC 110 mainly has following three functions.
(1) FEEDBACK CONTROL power circuit 40 thus regulate the function of driving voltage Vdrv
(2) regulate in LED strip 10 the drive current Idrv flow through thus control the function of brightness
(3) abnormality is detected, the function of protection circuit
About function 2, LED drive IC 110, there is voltage control unit 20.Voltage control unit 20 accepts the current potential (hereinafter referred to as detecting voltage Vs) of the LED terminal be connected with the negative electrode of LED strip 10, controls power circuit 40 by feedback, makes to detect voltage Vs consistent with the reference voltage V ref of regulation.By this FEEDBACK CONTROL, regulate the output voltage Vdrv of power circuit 40, Vdrv=VLED+Vref is set up.Voltage control unit 20 is corresponding with the pulse-modulator 20 in Fig. 2.
When power circuit 40 is switching regulaor, is generated the pwm signal SWOUT with the dutycycle corresponding with the error detecting voltage Vs to reference voltage V ref by voltage control unit 20, provide it to power circuit 40.The on-off element (not shown) of the inside of power circuit 40, by repeating conducting, cut-off along with pwm signal SWOUT, regulates driving voltage Vdrv.
About function 2, LED drive IC 110, there is 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 arranged on the cathode side on the current path of the LED strip 10 of driven object.Current driver 70 generates the drive current Idrv corresponding to brightness, controls the electric current flow through in LED strip 10.The adjustment of the brightness of the LED strip 10 corresponding with the size of drive current Idrv is called electric current light modulation (simulation light modulation).
LED drive IC 110, except electric current light modulation, also carries out so-called PWM light modulation.Specifically, carry out switch with making drive current timesharing with the dutycycle corresponding to brightness, regulate the time average of drive current Idrv, brightness is changed.
PWM light adjusting circuit 74 generates the driving pulse SPWM be pulse modulation, and makes it have the dutycycle corresponding to brightness.PWM light adjusting circuit 74 acts on current driver 70 according to driving pulse SPWM, thus makes drive current Idrv conducting, cut-off.In figure 6, between the light emission period being assigned to LED strip 10 between the high period of driving pulse SPWM (conduction period Ton), during being assigned to non-luminescent between low period (Toff).
LED drive IC 110 can the light modulation of dual-purpose electric current and PWM light modulation, by the brightness optimization of LED strip 10.
Then, the circuit protection as the 3rd function is described.About defencive function, LED drive IC 110 has abnormal detection circuit CMP1, timer latch cicuit 80, protection circuit 50.
Abnormal detection circuit CMP1 monitors the current potential of the cathode terminal (LED terminal) of LED strip 10, namely detects voltage Vs and generates anomaly detection signal S1.Abnormal detection circuit CMP1 is judged to be abnormality when detecting the scope of voltage Vs from regulation and departing from, and assert (assert) anomaly detection signal S1.When detection voltage Vs is in the scope being contained in regulation, anomaly detection signal S1 is denied (negate).
Abnormal detection circuit CMP1 also can be such as the comparer comparing the first threshold voltage VTH1 detecting voltage Vs and regulation.Abnormal detection circuit CMP1, when detection comprises the open-circuit condition in the path of LED strip 10, wishes that first threshold voltage VTH1 is set as the value close to 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 represents conducting with driving pulse SPWM, and anomaly detection signal S1 is identified as opportunity and start time measures.After beginning, if anomaly detection signal S1 have passed through official hour T1 before being denied, then timer latch cicuit 80 assert guard signal S2.
In order to realize this function, such as, comprise: timer latch cicuit 80, "AND" circuit 82, set-reset flip-floop 84, charging circuit 86, discharge circuit 87, first capacitor C10, timer comparer CMP2, latch 88.
The first terminal ground connection of the first capacitor C10 thus current potential are fixed.Charging circuit 86 is configured to changeable activation and inactive, provides constant current Ic in active state and charge to the first capacitor C10.Such as, charging circuit 86 comprises: the constant current source CCS1 generating constant current Ic and the charging interrupteur SW 1 be arranged on its path.Charging interrupteur SW 1 charging circuit 86 when conducting activates.
Discharge circuit 87 extracts electric current from the first capacitor C10 in active state and discharges.Discharge circuit 87 such as comprises the electric discharge interrupteur SW 2 between the second terminal and ground terminal being arranged on the first capacitor C10.During electric discharge switch (SW2) conducting, discharge circuit 87 activates, and the current potential (condenser voltage Vc) of second terminal of the first capacitor C10 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.Anomaly detection signal S1 is transfused in the reseting terminal (inverted logic) of set-reset flip-floop 84.
That is, set-reset flip-floop 84 represents conducting at driving pulse SPWM, and is set when anomaly detection signal S1 is identified.And set-reset flip-floop 84 is reset when anomaly detection signal S1 is denied.
Set-reset flip-floop 84 makes charging circuit 86 activate under SM set mode, makes discharge circuit 87 inactive.When set-reset flip-floop 84 is SM set mode, the first capacitor C10 is charged 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 inactive in reset mode, and discharge circuit 87 is activated.When discharge circuit 87 activates, condenser voltage Vc is initialised.
The Second Threshold voltage VTH2 of condenser voltage Vc and regulation compares by timer comparer CMP2, generates the guard signal S2 with the level corresponding to comparative result.Guard signal S2 is high level (identification) when Vc > VTH2.Condenser voltage Vc is provided by following formula: Vc=t × Ic/C10.Wherein, t is the elapsed time from charging, and C10 represents the capacitance of the first capacitor C10.
Therefore, guard signal S2 is being identified through the stipulated time T1 represented with following formula from charging.
T1＝VTH2×C10/Ic
Latch 88 latch up protection signal S2.Protection circuit 50 accepts the guard signal S2 ' be latched.When guard signal S2 ' is identified, when namely abnormality only continues official hour T1, the conservation treatment that protection circuit 50 puts rules into practice.So-called conservation treatment, such as, be the shutoff of power circuit 40 or constant-current circuit 70 etc., be not particularly limited.
It is more than the structure of the LED drive circuit 100 of Fig. 6.Its action is then described.
(a), (b) of Fig. 7 is the timing diagram of an example of the action of the LED drive circuit 100 representing Fig. 6.In accordance with the order from top to bottom, driving pulse SPWM, anomaly detection signal S1, condenser voltage Vc, guard signal S2 is represented.
Sequential when (a) of Fig. 7 represents that executive circuit is protected.Be high level at t0, drive singal SPWM sometime, LED strip 10 is conducting state.In this condition, when the path of LED strip 10 produces open-circuit condition, the current potential Vs of LED terminal is reduced near ground voltage (0V), and anomaly detection signal S1 is identified (high level).When anomaly detection signal S1 is identified, set-reset flip-floop 84 is set, and starts the charging of the first capacitor C1 based on charging circuit 86.
At moment t2, driving pulse SPWM moves to low level, but this situation does not affect 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 Second Threshold voltage VTH2.This situation represents that abnormality continue for more than t1 specified time limit.Be identified at moment t3 guard signal S2 (S2 '), carry out protection.
Afterwards, if anomaly detection signal S1 is denied in the releasing of 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 sequential when not executive circuit protection.All identical with (a) of Fig. 7 to moment t3.In (b) of Fig. 7, to the moment t4 ' before stipulated time T1 from charging, anomaly detection signal S1 is denied.Therefore, condenser voltage Vc does not arrive Second Threshold voltage VTH2, thus guard signal S2 (S2 ') be not identified, do not carry out protection.
Like this, according to the LED drive circuit 100 of embodiment, abnormality can be produced at the conduction period Ton of LED strip 10, when abnormality continue for stipulated time more than T1 afterwards, carry out conservation treatment.Abnormality continue in, even if driving pulse SPWM is cut-off state, owing to not removing the detection of abnormality, even if so the pulse width variation of driving pulse SPWM, also can not by its affect protection circuit.
As comparison techniques, following situation is investigated, namely omit set-reset flip-floop 84, directly switched the activation, inactive of charging circuit 86 and discharge circuit 87 by the output signal of "AND" circuit 82.That is, during LED strip 10 is conducting state (luminance) and anomaly detection signal S1 is identified, charging circuit 86 is for activating.
In this comparison techniques, after anomaly detection signal S1 is identified, when drive pulse signal SPWM becomes low level at once, although abnormality continues, charging circuit 86 is also inactive, stop time measurement.That is, even if produce abnormality continue for stipulated time more than T1, do not assert guard signal S2 yet, do not carry out the situation of conservation treatment yet.
In contrast, according to the LED drive circuit 100 of embodiment, the pulse width (length of conduction period Ton) of driving pulse SPWM can not relied on, apply circuit protection.
The present invention is described according to embodiment, but embodiment only represents principle of the present invention, application, in embodiments, in the scope of thought of the present invention not departing from claim defined, certainly can there is the change of various deformation example or configuration.
Claims (10)
1. a driving circuit, comprising:
Pulse-modulator, generates the first pulse signal that its dutycycle is conditioned, and makes the detection voltage of the electric state of the light emitting diode representing driven object consistent with the reference voltage of regulation;
Switching Power Supply, will be supplied to the first terminal of described light emitting diode after input voltage voltage stabilizing; And
Constant-current circuit, is connected to the second terminal of described light emitting diode,
Described pulse-modulator regulates the dutycycle of described first pulse signal, makes the current potential of described second terminal consistent with described reference voltage,
The feature of described driving circuit is,
Described light emitting diode is the backlight of liquid crystal display,
Described driving circuit also comprises:
Pulse transformer, comprises primary coil and secondary coil, this primary coil has been applied in described first pulse signal;
PLL circuit, accepts the vertical synchronizing signal synchronous with the view data that will show in described liquid crystal display, described vertical synchronizing signal is doubled, and clocking; And
Dutycycle setup unit, by counting described clock signal, produces the pulse-modulated signal be pulse modulation,
Described Switching Power Supply comprises the on-off element that the signal that the secondary coil according to described pulse transformer produces controls its conducting, cut-off,
Described constant-current circuit, according to described pulse-modulated signal, carries out switch to the drive current flow through in described light emitting diode.
2. driving circuit as claimed in claim 1, is characterized in that, also comprise:
Smoothing circuit, makes alternating voltage level and smooth; And
Power factor correction circuit, accepts the voltage after by described smoothing circuit smoothes, generates the input voltage of described Switching Power Supply.
3. a driving circuit, comprising:
Pulse-modulator, generates the first pulse signal that its dutycycle is conditioned, and makes the detection voltage of the electric state of the light emitting diode representing driven object consistent with the reference voltage of regulation;
Switching Power Supply, will be supplied to the first terminal of described light emitting diode after input voltage voltage stabilizing; And
Constant-current circuit, is connected to the second terminal of described light emitting diode,
Described pulse-modulator regulates the dutycycle of described first pulse signal, makes the current potential of described second terminal consistent with described reference voltage,
The feature of described driving circuit is, described driving circuit also comprises:
Pulse transformer, comprises primary coil and secondary coil, this primary coil has been applied in described first pulse signal;
Pulsed modulation light adjusting circuit, generates the driving pulse that has been pulse modulation, the drive current conducting described constant-current circuit being generated according to this driving pulse, cut-off;
Abnormal detection circuit, monitors the current potential of the second terminal of described light emitting diode, is created on the anomaly detection signal be identified when abnormality being detected; And
Timer circuit, represents conducting with described driving pulse, and described anomaly detection signal has been identified as opportunity and start time measures, and when have passed through official hour before described anomaly detection signal is denied, generates the guard signal be identified,
Described Switching Power Supply comprises the on-off element that the signal that the secondary coil according to described pulse transformer produces controls its conducting, cut-off, when described guard signal is identified, and the conservation treatment put rules into practice.
4. driving circuit as claimed in claim 3, is characterized in that,
Described timer circuit comprises:
Capacitor, the current potential of its one end is fixed;
Charging circuit, charges to described capacitor;
Discharge circuit, to described discharging capacitors;
Trigger, be set when described driving pulse represents conducting and described anomaly detection signal is identified, be reset when described anomaly detection signal is denied, in SM set mode, make described charging circuit activate, make described discharge circuit inactive, and in reset mode, make described charging circuit inactive, 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 with the level corresponding to comparative result.
5. a light-emitting device, comprising:
Light emitting diode,
The feature of described light-emitting device is, described light-emitting device also comprises:
Drive the driving circuit that any one of the Claims 1-4 of described light emitting diode is recorded.
6. a display equipment, comprising:
Liquid crystal board,
The feature of described display equipment is, described display equipment also comprises:
The light-emitting device that the claim 5 being configured in the back side of described liquid crystal board as backlight is recorded.
7. a driving circuit for light emitting diode, is characterized in that, comprising:
Current driver, is arranged on the cathode side on the current path of the light emitting diode of driven object, generates drive current;
Pulsed modulation light adjusting circuit, generates the driving pulse be pulse modulation, makes described drive current conducting, cut-off 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 be identified when abnormality being detected; And
Timer circuit, represents conducting with described driving pulse, and described anomaly detection signal has been identified as opportunity and start time measures, and when have passed through official hour before described anomaly detection signal is denied, generates the guard signal be identified,
When described guard signal is identified, the conservation treatment put rules into practice.
8. driving circuit as claimed in claim 7, is characterized in that,
Described timer circuit comprises:
Capacitor, the current potential of its one end is fixed;
Charging circuit, charges to described capacitor;
Discharge circuit, to described discharging capacitors;
Trigger, be set when described driving pulse represents conducting and described anomaly detection signal is identified, be reset when described anomaly detection signal is denied, in SM set mode, make described charging circuit activate, make described discharge circuit inactive, and in reset mode, make described charging circuit inactive, 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 with the level corresponding to comparative result.
9. a light-emitting device, comprising:
Light emitting diode,
The feature of described light-emitting device is, described light-emitting device also comprises:
Drive the driving circuit that the claim 7 or 8 of described light emitting diode is recorded.
10. a guard method, is characterized in that, comprising:
Generate drive current, and be supplied to the step of the light emitting diode of driven object;
Generate the driving pulse be pulse modulation, make the step of described drive current conducting, cut-off according to this driving pulse;
Monitoring the current potential of the cathode terminal of described light emitting diode, generating the step of the anomaly detection signal be identified when abnormality being detected;
Represent conducting with described driving pulse, and described anomaly detection signal is identified as opportunity and start time measures, when have passed through official hour before described anomaly detection signal is denied, generates the step of the guard signal be identified; And
When described guard signal is identified, the step of the conservation treatment put rules into practice.
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 |
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| CN101894530A CN101894530A (en) | 2010-11-24 |
| CN101894530B true CN101894530B (en) | 2015-05-06 |
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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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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP5835663B2 (en) * | 2011-11-10 | 2015-12-24 | 東芝ライテック株式会社 | Lighting power supply and lighting device |
| CN102542981A (en) * | 2011-12-14 | 2012-07-04 | 深圳市华星光电技术有限公司 | Driving circuit and method of light-emitting diode and displaying device applied by same |
| CN103687139A (en) * | 2012-09-07 | 2014-03-26 | 铱宝电子（苏州）有限公司 | LED drive device |
| CN104968522B (en) * | 2013-01-25 | 2018-10-12 | 金泰克斯公司 | The driving circuit of photoelectricity rear-view mirror system |
| CN104010404B (en) * | 2013-02-22 | 2016-09-28 | 普诚科技股份有限公司 | Light emitting diode drive device |
| EP2830395B1 (en) * | 2013-07-24 | 2017-09-13 | Dialog Semiconductor GmbH | Mains switch event detection for LED assemblies |
| CN103826344A (en) * | 2014-02-08 | 2014-05-28 | 黄焕珠 | Charging and digital dimming type LED desk lamp |
| CN104135789B (en) * | 2014-06-10 | 2017-02-01 | 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 |
| DE102015217712B4 (en) * | 2014-09-16 | 2017-01-19 | Koito Manufacturing Co., Ltd. | Lighting circuit and vehicle lamp having such |
| TWI656809B (en) * | 2017-09-29 | 2019-04-11 | 大陸商東莞市高效電控有限公司 | Light-emitting diode driving circuit and lighting device thereof |
| 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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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4052998B2 (en) * | 2003-11-25 | 2008-02-27 | シャープ株式会社 | Power supply circuit and electronic device using the same |
| KR101100881B1 (en) * | 2004-11-04 | 2012-01-02 | 삼성전자주식회사 | Driving device of light source for display device and display device |
| KR100917623B1 (en) * | 2006-02-13 | 2009-09-17 | 삼성전자주식회사 | LED Driving Apparatus |
| US7675245B2 (en) * | 2007-01-04 | 2010-03-09 | Allegro Microsystems, Inc. | Electronic circuit for driving a diode load |
| JP4932517B2 (en) * | 2007-02-08 | 2012-05-16 | Ｎｅｃディスプレイソリューションズ株式会社 | Image display device and frequency adjustment method thereof |
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