CN106028554A - LED driver, and controller and control method thereof - Google Patents

Abstract

The invention discloses an LED driver, and a controller and control method thereof. The control method comprises the following steps: establishing a database according to volt-ampere characteristics of LED loads with different structures; detecting output voltages and output currents of the LED driver; comparing the detected output voltages and the output currents with data in a database so as to determine the structures of the LED loads; and according to the determined load structures, adjusting the output currents of the LED driver to enable currents flowing through each string of LEDs to be smaller than a rated value.

Description

LED driver and controller thereof and control method

Technical field

The present invention relates to electronic circuit, particularly relate to LED driver and control method thereof.

Background technology

Due to specular removal and long-life, LED is considered as outstanding lighting source.In more than ten years of past, Its light efficiency improves constantly, cost rapid decrease.

One typical LED illumination scheme is made up of LED load and driver, and driver is according to loading condition May be multiple-channel output, it is also possible to export for single channel.In great majority application, LED load includes tens of LED, this is designed with beneficially luminous intensity distribution.

It is known that the electric current flowing through single LEDs must be smaller than its rated value to avoid it to damage because of overheated Bad.For multiple LED, need the electric current making to flow through LED identical and be less than rated value, the most beneficially luminous intensity distribution Design and ensure that the reliability of LED.In order to make the electric current flowing through LED identical, all LED strip are unified into A string is a simple solution.But, in the application that power is slightly larger, LED quantity is more, whole string Voltage may be the highest and optimization of to creep age distance, insulation and driver brings adverse effect.Therefore, LED load is frequently separated into many strings of parallel connection, forms array structure.Due to the deviation of components and parts, in array not Also differ with the C-V characteristic (V-I property) of string LED.Therefore in an array, a lot of strings may have The situation of electric current overrate exists, and this is likely to result in this string and damages.

A kind of existing way solving to cause each string electric current too high due to current-unbalance is to each string LED Electric current carries out current-sharing.As shown in Figure 1A, LED driver is AC/DC multiple-channel output constant pressure source, every a string LED All with a rear class adjustor (post regulator).This rear class adjustor can be active circuit (as Linear power supply or Switching Power Supply), can be passive circuit (such as resistance, electric capacity or coupling inductance).Due to The existence of rear class adjustor, the electric current flowing through each string can be balanced and be less than the rated value of LED.

Although the scheme of multiple-channel output current-sharing can solve well load internal current unbalanced and cross flow problem, But its circuit structure is more complicated, relatively costly, inefficient.Thus in actual applications, load is usually Being designed to the array module of only one of which binding post, driver is then designed without rear class and adjusts The single channel output constant current source of device, as shown in Figure 1B.

Generally, the constant current of driver output needs to be designed in proof load respectively to go here and there electric current and exists Being respectively less than the rated value of LED under stable state, this is considered the situation of driver and load matched.But In the case of load causes change due to aging or the impact of other factors, the electric current of some string may overflow Definite value so that the constant current of driver output is no longer appropriate for load, causes driver not mated with load. This situation may result in load and lost efficacy further, even works long hours in non-optimal state due to driver And shorten its life-span.

Summary of the invention

In order to solve the problems referred to above, the present invention proposes a kind of LED driver self-adapting load matching technique, makes The output electric current of driver can carry out self-adaptative adjustment according to support structures, to ensure in the load of array module Each string electric current is both less than rated value.

The control method of a kind of LED driver according to embodiments of the present invention, including: according to different structure The C-V characteristic of LED load sets up data base；The output voltage of detection LED driver and output electric current；Will inspection The output voltage measured and output electric current contrast with the data in data base, to judge the knot of LED load Structure；And the output electric current according to the support structures regulation LED driver judged, make to flow through every a string LED Electric current be respectively less than its rated value.

A kind of LED driver according to embodiments of the present invention, including: switch converters, input signal is turned It is changed to output voltage and output electric current to drive LED load；Memorizer, the LED load of record different structure C-V characteristic；Digitial controller, is coupled to switch converters and memorizer, detection output voltage and output Electric current, and the output voltage detected and output electric current are contrasted with the data in memorizer, to judge The structure of LED load, is then based on the support structures judged, regulates the output electric current of switch converters, Make to flow through and often go here and there the electric current of LED and be respectively less than rated value.

A kind of controller for LED driver according to embodiments of the present invention, wherein LED driver carries For output voltage with output electric current to drive LED load, this controller includes: memorizer, record difference knot The C-V characteristic of the LED load of structure；Digitial controller, is coupled to memorizer, detection output voltage and output Electric current, and the output voltage detected and output electric current are contrasted with the data in memorizer, to judge The structure of LED load, is then based on the support structures judged, produces output current reference level；And patrol Volume control circuit, is coupled to digitial controller to receive current reference level, according to exporting current reference level Produce control signal and export electric current with regulation, make the electric current flowing through every a string LED be respectively less than its rated value.

In an embodiment of the present invention, first data base is set up, so according to the C-V characteristic of different structure load Afterwards by output electric current and the voltage of detection LED driver, it is compared with database data, it is judged that negative Carry structure.Finally, Self Adaptive Control is realized according to the output electric current of support structures regulation LED driver. By such method, in the running of LED driver, even if load causes structure to be sent out due to fault Changing, LED driver output Adaptive matching can also load, thus improves the reliable of LED illumination System Property.

Accompanying drawing explanation

Figure 1A and Figure 1B is the schematic block diagram of existing LED driver；

Fig. 2 is the workflow diagram of the LED driver control method according to the embodiment of the present invention；

Fig. 3 is the schematic diagram of the LED driver 300 according to the embodiment of the present invention；

Fig. 4 illustrates the institute's likely support structures outside array-type LED load is except road and short circuit；

Fig. 5 illustrates C-V characteristic working curve and the stable state work of LED load structure according to embodiments of the present invention Make point and determine method；

Fig. 6 is the circuit theory diagrams of the LED driver 300A according to the embodiment of the present invention；

Fig. 7 A-7C is three kinds of exemplary LED load structures S_aA、S_aB、S_aC；

Fig. 8 illustrates LED load structure S according to embodiments of the present invention_aA、S_aB、S_aCC-V characteristic work song Line Curve_A、Curve_B、Curve_C；

Fig. 9 is the working waveform figure according to LED driver 300A shown in Fig. 6 of the embodiment of the present invention.

Detailed description of the invention

The specific embodiment of the present invention is described more fully below, it should be noted that the embodiments described herein is only used In illustration, it is not limited to the present invention.In the following description, thorough in order to provide the present invention Understand, elaborate a large amount of specific detail.It will be apparent, however, to one skilled in the art that, These specific detail need not be used to carry out the present invention.In other instances, in order to avoid obscuring the present invention, Do not specifically describe known circuit, material or method.

Throughout the specification, to " embodiment ", " embodiment ", " example " or " show Example " mention and meaning: combine this embodiment or special characteristic, structure or characteristic that example describes comprised In at least one embodiment of the invention.Therefore, each of entire disclosure local occur phrase " In one embodiment ", " in an embodiment ", " example " or " example " be not necessarily all referring to same Embodiment or example.Furthermore, it is possible to any suitable combination and/or sub-portfolio by specific feature, knot Structure or property combination are in one or more embodiments or example.Additionally, those of ordinary skill in the art should Understanding, accompanying drawing is provided to descriptive purpose provided herein, and accompanying drawing is not necessarily drawn to scale 's.Should be appreciated that it can be when claiming " element " " being connected to " or " coupled " to another element It is directly connected or coupled to another element or intermediary element can be there is.On the contrary, when claiming element " directly to connect Receive " or during " being directly coupled to " another element, there is not intermediary element.Identical reference instruction Identical element.Term "and/or" used herein includes appointing of one or more relevant project listed What and all combinations.

In LED illumination System, driver typically has two kinds of typical mismatch condition with load.One can be referred to as Static mismatch condition, i.e. driver have powered on and have not just mated with loading before machine.Such as, before powering on, load has A little LED have damaged, if driver is also to provide original output electric current, then both do not mate.Another kind of Can be referred to as dynamic mismatch situation, i.e. driver and power on after machine, support structures sudden change is caused driving with original Not mating of dynamic device output electric current.Usual this structural mutation is to be damaged by some LED in load or run During have the factor such as aging to cause caused by loose contact.There to be the array module of multi-string LED to load As a example by, in the case of driver constant output current, if wherein certain a string open circuit, then remaining string will undertake Bigger electric current, it is possible to overrate, shortens its life-span.Above two situation is the most right Reliability in LED illumination System all has negative effect, they be all the constant current exported by driver not Can be caused according to support structures change adjustment.

For make driver can automatically adjust output electric current to mate the load of different structure, the present invention proposes one Plant LED driver self-adapting load matching technique as shown in Figure 2, including: step S201, tie according to difference The C-V characteristic of structure load sets up data base；Step S202, the output voltage of detection LED driver and output Electric current；Step S203, it is right the output voltage detected and output electric current and the data in data base to be carried out Ratio, to judge to be coupled to the structure of the load of LED driver output；Step S204, negative according to judge Carry the output electric current of structure regulation LED driver, make the electric current flowing through every a string LED be respectively less than it specified Value.

Fig. 3 is the schematic diagram of the LED driver 300 according to the embodiment of the present invention.Wherein switch change-over Input signal is converted to output voltage v by device 301_oWith output electric current i_oTo drive LED load.Different structure The C-V characteristic of load with the form record of data base in memorizer 304.Digitial controller 303 detects defeated Go out voltage v_oWith output electric current i_o(such as, by potentiometer, sampling resistor and analog-digital converter etc.), And data detection obtained compare with the data of data base in memorizer 304, to judge LED load Structure.Subsequently, digitial controller 303 is based on the support structures judged, by logic control circuit 302 Regulation controls control signal DRV of switch converters 301, thus changes output electric current i_o, make to flow through and often go here and there The electric current of LED is respectively less than rated value I_rated, it is achieved LED driver mates with load.According to reality application Difference, outside memorizer 304 can be as shown in Figure 3 independent of digitial controller 303, it is also possible to numeral Controller 303 integrates.In some application-specific, logic control circuit 302 even can be saved Slightly, control signal DRV is directly produced by digitial controller 303.

For the array module load of the n of m row shown in Fig. 3 row, support structures matrix S can be used_arrayCome Represent its structure:

$S_{array}={\left[\begin{array}{cccc}{s}_{11}& s_{12}& ...& s_{1n}\\ s_{21}& s_{22}& ...& s_{2n}\\ \·& \·& & \·\\ \·& \·& ...& \·\\ \·& \·& & \·\\ s_{m1}& s_{m2}& ...& s_{mn}\end{array}\right]}_{m\×n}---\left(1\right)$

Wherein s_xy(x=1,2 ..., m, y=1,2 ..., n) represent in array and be positioned at the LED that xth row y arranges State, s_xy=0 represents this LED failure (open circuit or short circuit) and no longer luminous, s_xy=1 is just representing this LED Often work.As a example by m=2, n=2, matrixRepresent the LED short circuit of the 2nd row, the 2nd row, matrixRepresent the 2nd string open circuit.

According to the method for exhaustion, if the load of this m n array does not calculate the knot of whole load short circuits and open circuit Structure, its number of structures likely derived as shown in Figure 4, can be expressed as:

$TQ=C_{m+n}^n-1=\frac{(m+n)!}{m!n!}-1---\left(2\right)$

For a certain structure S_j, its C-V characteristic can be expressed as:

v_load=h_j(i_load) (3)

Wherein h_jIt it is structure S_jC-V characteristic function, i_loadAnd v_loadIt is respectively structure S_jElectric current and voltage, The specifications that its concrete data refer to LED calculate, it is also possible to obtain according to test.So, array The different structure of formula module load and the C-V characteristic of correspondence can be with point voltage each on curve, the shapes of electric current Formula is recorded in memorizer 304, forms data base.For the sake of directly perceived, the C-V characteristic of support structures is bent Line represents with patterned way in Fig. 5 at this.

For the load of different structure, its desired steady operation point, the namely output of LED driver Voltage x current is the most different.These steady operation points can also the form record of data in aforementioned data storehouse. As a example by Fig. 5, for the safety of a string LED every in proof load, flow through the electric current often gone here and there and not can exceed that single The rated value I of LED_rated.If the electric current flowing through pth string in all strings is maximum, as long as then ensureing this string electric current i_pLess than rated value I_rated?.For making full use of load, obtain the biggest luminous flux, can be by load Operating point (I_o, V_o) it is designed as making the electric current i of wherein pth string_pEqual to rated value I_rated。

Through above-mentioned steps, comprise support structures matrix corresponding to each support structures, VA characteristic curve with And the data base of steady operation point can be established.Subsequently, LED driver can be by detecting its output voltage v_o, electric current i_o, and it is contrasted with the data in data base, judge to be coupled to the negative of its outfan The structure carried, and provide according to the steady operation point of this structure and export electric current accordingly.

Accurately realize self-adapting load coupling premise is that the output voltage according to sampling, electric current judge Support structures.But in actual application, when just having powered on machine, due to LED driver output capacitance relatively Greatly, output voltage v_oIt is raised to stably typically require a period of time by above freezing.Within this time period, driver Exporting change is relatively big, thus sampling accuracy is difficult to ensure that, thus driver during this period in judge load knot Structure is the most difficult.In order to solve this problem, the work process of LED driver can be divided into two stages Start (run-up) stage and normal work (burn) stage, and startup stage make LED drive The output electric current i of device_oIncrementally increase with fixed step size, to realize the accurate detection to output voltage and electric current.

Due to high efficiency feature, LLC resonant converter is commonly used in LED driver.Below to use arteries and veins Rush as a example by the LLC resonant converter of frequency modulation(PFM) (pulse width modulation, PFM) the present invention Self-adapting load matching technique describe in detail.It will be appreciated by a person skilled in the art that this not uses In limiting the present invention, other suitable topological structure or control mode are equally applicable.

Fig. 6 gives the schematic diagram of LED driver 300A according to embodiments of the present invention, including the merit of prime Rate factor correcting (PFC) circuit and the LLC half bridge resonant of rear class.The resonator cavity of LLC resonant converter Comprise resonant capacitance Cr, resonant inductance Lr and magnetizing inductance Lm.Level V_irefAnd V_vrefIt is driver respectively Output electric current i_oWith output voltage v_oDatum, realize constant voltage, constant current control by Voltage loop and electric current loop System.

Microprogram control unit (MCU, micro control unit, such as single-chip microcomputer) is used as digitial controller, Its internal storage is used for storage loads structure related data.In the course of the work, the output electricity of driver Pressure v_oWith output electric current i_oBy analog-digital converter ADC1 and the ADC2 real-time sampling of MCU, and with in data base The VA characteristic curve contrast stored confirms support structures and corresponding steady operation point.Then, MCU provides corresponding datum V according to operating point_iref.Logic control circuit 302A is based on datum V_iref, by error amplifier OP_I therein, photoelectrical coupler and voltage controlled oscillator (voltage-controlled oscillator, VCO) controls the switching frequency of transistor M1, M2, from And regulate output electric current i_oAnd realize the Auto-matching of driver and load.

The work process of driver shown in Fig. 6 is described below in conjunction with Fig. 7-9.

Fig. 7 A-7C gives three kinds of LED load structures, wherein structures S_aAIt is a normal LED load, Structure S_aBAnd S_aCIt is to have a LED short circuit and the situation of open circuit respectively.The C-V characteristic assuming every LEDs is Identical, the most correspondingly the VA characteristic curve of three kinds of structures can be provided in fig. 8, be respectively Curve_A、Curve_BAnd Curve_C, its midpoint A, B, C are the steady operation that these three structure is corresponding respectively Point.LED load has structure S when driver just starts_aA.After entering normal work stage, it is positioned at xth The LED of row y row is short-circuited, and support structures is by S_aABecome S_aB, VA characteristic curve is also by Curve_A Become Curve_B.Seeing Fig. 9, the whole specific works process of driver is as follows:

[t0～t1]: driver powers on, output electric current is I_o1.Now the LLC resonant converter in driver with Maximum frequency operation is under intermittent mode (burst mode).Owing to [t0～t1] is for sampling long enough, drive MCU in dynamic device is able to detect that output voltage v_oWith output electric current i_o, and by the song in they and data base Line Curve_A、Curve_B、Curve_CCompare to judge support structures.In this example, owing to sampling obtains Output current/voltage (I_o1, V_o1) it is positioned at curve Curve_AOn, therefore driver judges support structures S_aAAnd select Select operating point A corresponding to this structure desired value as output.

[t1～t2]: output electric current i_oI is increased to a fixed step size Δ I_o1+ΔI。

[t2～t4]: the output electric current i of driver_oContinue to incrementally increase with fixed step size Δ I.Especially, exist [t2～the t3] time period, LLC resonant converter is entered continuous operation mode by burst pattern, and switching frequency is also Begin to decline.

[t4～t5]: the output electric current i of driver_oReach desired value I_oAAnd keep stable, V_oA、I_oARespectively For structure S_aAThe voltage and current value of corresponding operating point A.

[t5～t6]: in the t5 moment, owing to there being LED failure, support structures change, VA characteristic curve by Curve_ABecome Curve_B, output voltage v_oBy V_oABecome V_o2.In this stage, load may there is electric current not Balance and over-current phenomenon avoidance exist, for mismatch condition.

After [t6～] driver determines load change, by current reference level V_irefAdjust, make output desired value It is switched to VA characteristic curve Curve_BCorresponding operating point B, such driver is mated again with load.

Driver output electric current i_o[t0～the t4] stage incrementally increased with fixed step size is exactly alleged above opening The dynamic stage.Due to this control strategy, driver accurately can detect when just playing machine output voltage and Electric current, is conducive to accurately judging that support structures is to solve static mismatch condition.Startup stage persistent period take Certainly in sample rate, output capacitance capacitance and the power grade of driver.

It it is normal work stage after the t4 moment.After entering this stage, output voltage v_oWith output electric current i_oStill Sampled by MCU.If load changing, driver can automatically adjust output electric current and carry out matched load.

Forgoing describe the method setting up support structures data base, but in actual application, it is also contemplated that load The impact that C-V characteristic deviation and temperature cause.Formula (3) is the C-V characteristic expression formula of a support structures. Owing to the C-V characteristic of single LEDs of batch production is the most variant, historical facts or anecdotes border application Chinese style (3) is the most not Enough accurate.Another one impact is that the VA characteristic curve of load can change along with the change of temperature.Due to Both factors, in some embodiments, it is desirable to carry out school to the C-V characteristic of the support structures in data base Accurate.

In view of above-mentioned factor, formula (3) can increase bias term v_devWith load temperature T_load.Fig. 6 shows In example circuit, load temperature T_loadDetected by the MCU in driver.Revised formula (3) is expressed as:

|v_load-h_j(i_load,T_load)|≤v_jdev (4)

v_jdevValue come from the result of calculation of data in product description, or from big under same support structures The test result of amount load.This revised expression formula shows, to load C-V characteristic region generation in data base For original load VA characteristic curve.If measured output voltage electric current is in this region, then can determine whether For this support structures.This way also is adapted for software operation, this is because under the influence of measurement error, adopt The output voltage electric current of sample is just highly difficult on load VA characteristic curve, more reasonably routine processes Mode is under same electric current, it is judged that whether the voltage of sampling exceeds the scope of VA characteristic curve, super Go out, then it represents that for this support structures.

In theory, the C-V characteristic of all LED load structures can be calculated or be measured.Preferable In the case of, the support structures comprised in data base is the most, and driver can mate more load, and system is also More reliable.But have two factors can affect the support structures quantity stored in data base.First, according to Formula (2), the load that structure is the most complicated, i.e. m, n are the biggest, and the derived structure that load is comprised is the most, this May bring extremely complex calculating to setting up data base and measure work, more complicated structure is likely to meeting More structure is had to judge situation by accident.Second, there is a lot of support structures to have a strong impact on illuminating effect, unsuitable inadequate Use.Due to the two factor, data base can be reduced to only store important support structures.Must be strong Adjusting, even if the support structures of data base is through simplifying, driver also is able to an adaptive judgement part and bears Carrying structure, compared with the driver of traditional function without adaptive judgement, still improve illuminator can By property.

In LED application process, the reliability of LED driver and array load has with matching degree between the two Close.For there being the driver of fixing output electric current, when after the C-V characteristic change of load, load may be deposited In current imbalance and the phenomenon of off-rating, thus accelerator actuator and the damage of load.The present invention carries The self-adapting load matching technique gone out can make driver adapt to multiple support structures, improves the problems referred to above, carries High illumination scheme reliability.Although exemplary embodiment describing the present invention with reference to several, it is to be understood that, Term used is explanation and exemplary and nonrestrictive term.Owing to the present invention can be in a variety of forms It is embodied as the spirit without deviating from invention or essence, it should therefore be appreciated that above-described embodiment is not limited to any Aforesaid details, and should explain widely in the spirit and scope that appended claims are limited, therefore fall Enter the whole changes in claim or its equivalent scope and remodeling all should be appended claims and contained.

Claims (10)

1. a control method for LED driver, including:

The C-V characteristic of the LED load according to different structure sets up data base；

The output voltage of detection LED driver and output electric current；

The output voltage detected and output electric current are contrasted with the data in data base, to judge The structure of LED load；And

According to the output electric current of the support structures regulation LED driver judged, make to flow through every a string LED Electric current be respectively less than its rated value.

2. control method as claimed in claim 1, also includes:

Just play the stage of machine at LED driver, made the output electric current of LED driver progressively increase with fixed step size Greatly.

3. control method as claimed in claim 1, in wherein said data base, also record has different structure Load desired steady operation point, wherein according to the output electricity of the support structures regulation LED driver judged The step of stream includes: arrange the defeated of LED driver according to the steady operation point corresponding to the support structures judged Go out current reference level.

4. control method as claimed in claim 1, also includes:

The specifications of reference LED calculate, or obtain the C-V characteristic of different structure load according to test.

5. a LED driver, including:

Switch converters, is converted to output voltage and output electric current to drive LED load by input signal；

Memorizer, the C-V characteristic of the LED load of record different structure；

Digitial controller, is coupled to switch converters and memorizer, detection output voltage and output electric current, and The output voltage detected and output electric current are contrasted with the data in memorizer, to judge LED load Structure, be then based on the support structures judged, the output electric current of regulation switch converters, make to flow through and often go here and there The electric current of LED is respectively less than rated value.

6. LED driver as claimed in claim 5, wherein memorizer and digitial controller are integrated in one Rise.

7. LED driver as claimed in claim 5, wherein digitial controller is based on the load judged Structure produces output current reference level, and this LED driver also includes:

Logic control circuit, is coupled to digitial controller to receive current reference level, according to output electric current ginseng Examine level and produce control signal to control switch converters.

8. LED driver as claimed in claim 5, has wherein just played the stage of machine at LED driver, The output electric current of switch converters is controlled to fixed step size and incrementally increases.

9. LED driver as claimed in claim 5, in wherein said memorizer, also record has different knot Structure loads desired steady operation point, and digitial controller is according to the stable state work corresponding to the support structures judged Make point and the output current reference level of LED driver is set.

10., for a controller for LED driver, wherein LED driver provides output voltage and output Electric current is to drive LED load, and this controller includes:

Memorizer, the C-V characteristic of the LED load of record different structure；

Digitial controller, is coupled to memorizer, detection output voltage and output electric current, and defeated by detect Go out voltage and output electric current contrasts with the data in memorizer, to judge the structure of LED load, then base In the support structures judged, produce output current reference level；And

Logic control circuit, is coupled to digitial controller to receive current reference level, according to output electric current ginseng Examine level generation control signal and export electric current with regulation, make the electric current flowing through every a string LED be respectively less than it specified Value.