CN102137524B - High-efficiency control method for balance-driving light-emitting diode (LED) - Google Patents

Abstract

The invention discloses a low-loss balance technology for balance-driving multiple light-emitting diodes (LED) or multiple direct current (DC) loads. According to the invention, based on the electromagnetic coupling principle of a transformer, dynamic quadergy is generated so as to balance multiple LED loads. The balanced network formed on the basis of the principle is applicable to different circuit topology structures; a common driving power supply is allowed to balance-drive multiple LED loads. The invention also discloses a combined LED drive circuit with power factor adjustment, and provides a low-cost practical scheme for LED backlight and illumination application.

Description

High efficiency LED balance drive control method

Background introduction

Field that the present invention belongs to

This patent is the invention belonged in light emitting diode (LED) drived control field, more particularly there is provided a kind of control mode of the LED multi-path of balance drive expeditiously.Relevant field describes

LED brings a revolutionary change to lighting field.Efficiency is high, and volume is little, and the life-span is long, pollution-free, easy light modulation, and the Mechanical Reliability come with solid luminescence characteristic, and the flexibility etc. of portability and design makes it become the optimal selection of luminescent device in a lot of fields.The back lighting of LCD display and general lighting are the two large fields wherein most with development potentiality.

Usually all adopt in the display backlight illumination of large-size and the general lighting application of relatively high power and organize LED strip more.Each LED strip is become by several to dozens of LED strip joint groups.Single led forward voltage drop is about 3.3 volts, so the operating voltage of LED strip is generally tens volts to one or two hectovolt.The way of many groups LED strip can ensure that whole light-emitting surface brightness is even on the one hand, and the single LED power simultaneously also due to common is limited, and high-power LED price costly.These LED strip can adopt often string power supply or multi-series and parallel connection utility power separately.Because often going here and there, independent power supply cost is higher, and great majority application all adopts multi-series and parallel to join the mode of utility power, as shown in Figure 1.

Forward conduction voltage drop due to LED has sizable discreteness, and the forward current voltage characteristic of LED is steeper exponential curve, when many strings are directly in parallel, each crosstalk fails to be convened for lack of a quorum and occurs larger difference to such an extent as to cause each string non-uniform light and cause the life-span inconsistent.Therefore need to add sharing control measure during multi-series and parallel connection.Way the most frequently used is at present the closed-loop control of linear adjusting circuit of connecting, as shown in Figure 1.MOSFET pipe Q1 in Fig. 1, Q2 ... waiting is regulable control element, R1, R2 ... Rk etc. are current measuring element.The current signal I_SNS1......I_SNSk etc. detected feeds back to error amplifier EA1, EA2 ... the input of EAk etc., and realize closed-loop control by comparing with reference signal IREF.The supply voltage of LED strip is controlled by current feedback signal by another loop.Control objectives keeps making the LED strip of maximum forward pressure drop maintain the minimum amount of voltage that of given electric current.Like this by regulable control pipe maintain each string LED electric current equal.And the light modulation of back light system is generally in pulse-width controlled mode, also namely control brightness by the dutycycle changing LED conducting.Each string LED is operated in identical dutycycle.

This way is in regulable control pipe top voltage consumption unnecessary in LED strip loop lower for forward voltage drop obviously.Therefore efficiency can be suffered a loss.And the power consumption on regulable control pipe causes device temperature to rise and corresponding cooling requirements, thus increase system cost and built-in temperature and reduce system reliability.From one of key factor that the efficiency of above-mentioned visible LED drive scheme is raising systematic function and reliability and reduction system cost.

When LED current is larger, the efficiency of Fig. 1 scheme and heat dissipation problem are just more outstanding.Usually an independent Switching Power Supply is used to power to every a string LED to overcome these shortcomings people.Although this way efficiency is high, power consumption is little, and cost is obviously higher.This is a critical problem in the application of mass product.

Summary of the present invention

In sum, object of the present invention is exactly many groups LED balance drive scheme that a kind of high-performance, high efficiency, circuit will be provided simple and with low cost.This programme breaches and traditional utilizes the linear tube pressure drop of regulable control pipe to the transient current balancing LED strip and the current control mode of powering one to one to LED strip by many group Switching Power Supplies, lossless balancing network is adopted to control to the balance realizing LED current, thus the efficiency of LED drive system is greatly enhanced, cost then greatly reduces.

Accompanying drawing explanation

Fig. 6 shows the exemplary circuit configuration using inverse-excitation type isolated converter and balance drive network of the present invention to drive many group LED.

Fig. 7 shows the function using single-stage inverse excitation type converter simultaneously to realize power factor regulation and isolated DC voltage current transformation, and realizes the exemplary circuit configuration of many group LED balance drives in conjunction with balance drive network of the present invention.

Fig. 8 shows the exemplary circuit configuration using buck (Buck) converter and transformer balance drive network to realize many group LED balancing runs.

Fig. 9 shows the another kind of exemplary circuit configuration using buck (Buck) converter and transformer balance drive network to realize many group LED balancing runs.

Figure 10 shows the exemplary circuit configuration that the power conversion circuit of several use transformer isolation and transformer balancing network of the present invention realize many group LED balance drives.

Figure 11 shows and uses transformer isolation conversion also that LED inverse parallel is even to form two-way LED strip, then realizes several exemplary circuit configuration of many group LED balance drives in conjunction with balancing network of the present invention.

Figure 12 shows another kind of rectifier bridge and the LED strip of using and combines and form two-way type LED structure and use transformer balancing network and transformer isolation conversion to carry out the exemplary circuit configuration of balance drive many groups LED.

Figure 13 shows the simplification circuit that the series diode of LED strip in Figure 11 and shunt capacitance are removed.

main element symbol and explanatory note

DC SUPPLY DC power supply IREF current control reference signal

PWM PWM dimmer pulse sequence I2 secondary windings loop current

VDC+ DC input voitage GND power supply ground end

D signal dutyfactor IDD drives total current

L inductance D1....Dk diode

SNB absorbing circuit BG1 rectifier bridge

CTRL control circuit VQD MOSFET source-drain voltage

TX1 main transformer TB1....TBk balancing transformer

AC+ ac input end AC-ac input end

Q1....Q4 main switch C1....Ck capacitor

N1 primary number of winding turns N2 transformer secondary output number of winding turns

LED1...LEDk LED strip CS, CL, CA capacitor

ILED1....ILEDk LED current SW half-bridge switch node

NP primary number of winding turns NS transformer secondary output number of winding turns

R1...Rk current sampling resistor EA1...EAk error amplifier

I_SNS...I_SNSK current feedback signal Q1..Qk regulable control pipe

The detailed description of invention

Fig. 2 is one group and carrys out the schematic diagram of balance drive multi-string LED with balancing transformer network.As shown in Fig. 2 (a), TB1, TB2.....TBk are balancing transformer, and the number of turns is the winding of N1 is armature winding, and the number of turns is the winding of N2 is then secondary windings.LED1, LED2......LEDk are the LED strip that multiple LED strip joint group becomes, and the LED number of often going here and there can from one to individual arbitrarily.The LED number of each string is usually equal in actual applications, even if but each string LED number is unequal, and balancing network of the present invention also can make the electric current flowing through each LED strip equal, and its operation principle is as described below:

As shown in Fig. 2 (a), be parallel to after the primary windings connected in series of each LED strip and corresponding balancing transformer between public input IDD and GND.The secondary windings of balancing transformer is then forward connected formation loop, its rule of forward connecting is that the electric current induced in each balancing transformer secondary windings flows by same direction in serial loop when electric current flows to corresponding LED strip by each armature winding of balancing transformer.Such circuit polarities relation schematically shows with arrow in Fig. 2 (a).

According to the general principle of transformer, when there being an electric current changed in time to flow through the primary coil of balancing transformer, the flux change caused by this electric current can induce induced voltage in its corresponding secondary coil.When as shown in Fig. 2 (a), polarity connects into loop to secondary coil, secondary induced voltage will form loop current in the loop.If ignore the exciting current part of transformer, then the primary current of each transformer and secondary current follow following relation: N1I _lED1=N2I2, N1I _lED2=N2I2............. NkI _lEDk=N2I2 [Eqn.1] I here _lED1, I _lED2... ... ..I _lEDkbeing respectively the electric current of the armature winding of each balancing transformer, is also the electric current of each corresponding LED strip; I2 is the loop current of secondary windings, is also the secondary winding current of each balancing transformer.From equation [Eqn.1] be not difficult release, as long as each balancing transformer adopts identical primary and secondary number of turns ratio, then they primary winding current can secondary loop lotus root cooperation with under autobalance, also namely: I _lED1=I _lED2=... ... ..=I _lEDk=N2/N1I2 [Eqn.2] is simultaneously because I _lED1+ I _lED2+ ... ... .+I _lEDk=I _dDthen I can be released further _lED1=I _lED2=... ...=I _lEDk=N2/N1I2=(1/k) I _dD[Eqn.3] it may be noted that above-mentioned relation formula and its equilibrium function are mainly applicable to following situation here: (1), electric current are not containing the continuous or interrupted AC wave shape of DC component, and (2), electric current are containing change waveform during DC component discontinuous.For the not so difficult understanding of the first situation, for second case, when change waveform is discontinuous when only having, transformer flux just can be made to have the process of reset, thus avoid the error caused by DC component accumulation.Fig. 3 describes and severally typical becomes waveform containing during DC component discontinuous.Here the waveform shown in Fig. 3 that requires emphasis is so that its principle to be described as example.Become waveform during in actual applications discontinuous and be not limited to type shown in Fig. 3.In addition, when the electric current of each LED strip needs to distribute in a given ratio, instead of whole equal time, also can realize by setting different number of turns ratios to each balancing transformer.Electric capacity C1 in parallel with LED strip in Fig. 2, C2 ... .CK, can with also can.When using shunt capacitance, the electric current of LED strip is smoother.With or do not affect the counterbalance effect of circuit without electric capacity.

Circuit described by Fig. 2 (b) is connected on the cathode terminal of LED strip balancing network, and the circuit in its operation principle and effect and Fig. 2 (a) is just the same.In order to the reasons such as easy-to-connect also can adopt, some balancing transformer is connected on cathode terminal in actual applications, and other are connected on the mixing connection of anode tap, as long as keep secondary winding current to flow in the loop unanimously.Here we are called 1 type balancing circuitry the balancing circuitry shown in Fig. 2 (a) He Fig. 2 (b); Fig. 2 (c) describes the structure of another kind of transformer balancing circuitry, and we are called 2 type balancing circuitrys here.The primary and secondary number of winding turns of balancing transformer TB1 is equal in such an embodiment, and presses each and LED strip series connection of polarity shown in figure.Primary and secondary current relationship described by same basis [Eqn.1], can draw the electric current I of two LED strip _lED1=I _lED2conclusion.This principle also can be generalized in the application more than two string LED by the mode of cascade.Fig. 2 (d) is depicted as driving 4 and goes here and there the example of LED.According to the general principle of [Eqn.1], the balancing transformer in this structure also can adopt the different primary and secondary number of turns to control the current ratio of two branch roads.In some applications, the hybrid combination that shown in Fig. 2 (a) and Fig. 2 (c), balancing network combines can also be adopted.Its operation principle still as previously mentioned.Here require emphasis Fig. 2 (c) and balancing circuitry Fig. 2 (d) Suo Shi is equally applicable to exchange or containing the discontinuous time varying current waveform of DC component.

Balance drive network shown in Fig. 2 is utilize the electromagnetic coupled principle of transformer in the winding of balancing transformer, automatically to produce correction voltage to keep the dynamic equilibrium of each paths of LEDs electric current in essence.Because this correction voltage is idle in essence, so except the conduction loss caused by winding D.C. resistance and a small amount of core loss, almost do not have other active loss, efficiency is more much higher than the conventional balanced drive circuit shown in Fig. 1.Simultaneously because LED strip has antistatic Zener diode inverse parallel usually, when wherein one group of LED strip open circuit or certain a string in indivedual LED short circuit time, the armature winding of balancing transformer can produce the balance that corresponding bucking voltage maintains LED current automatically, the problem that whole circuit still normally can work and there will not be local components and parts overheated, thus reliability is quite high.In addition, in circuit shown in Fig. 2 (a) and Fig. 2 (b), when LED strip occurs abnormal, particularly during certain a string LED open circuit, the secondary primary winding voltage of its corresponding balancing transformer can higher than normal value, if at this moment the voltage signal of secondary windings is fed back to failure detector circuit, then can monitor the failure condition of LED strip easily.Simultaneously because the primary and secondary winding of balancing transformer is mutually isolated, and the voltage of secondary windings can by the number of turns than the low voltage level controlled in safety, so whole failure detector circuit comprises integrated circuit component etc. wherein, device or the processing procedure of low-voltage low cost can be used.Thus provide one both simple and easy to do, solution with low cost again.

Figure 4 shows that and use boost type (Boost) translation circuit and 1 type balancing transformer network to realize the example of Single switch balance drive LED multi-path string.When switching tube Q1 conducting, the electric current of inductance L is by from the loop linear increase of VDC+ through L, Q1, R1 to GND, and energy storage in inductance, this period D1 ends, and balancing transformer no current passes through, and its magnetic flux reduces to zero.When Q1 turns off, the electric current of inductance L passes through from VDC+ through L, D1, and the series arm that each balancing transformer armature winding and LED strip form releases energy to the loop of GND, and makes LED luminous.In the process released energy, inductive current declines gradually.The balancing network be made up of TB1, TB2 ... .TBk in this course remains that the electric current of each LED strip is equal.The operating current waveform of this process is as shown in Fig. 3 (a) He Fig. 3 (b).Fig. 3 (a) be depicted as inductive current Q1 again conducting time decay to zero, the situation that also namely inductive current is discontinuous.Shown in Fig. 3 (b) then for inductive current Q1 again conducting time also do not decay to zero, the yet situation of i.e. continuous current mode.Because the magnetic flux of balancing transformer can ensure reset-to-zero in Q1 conduction period, no matter whether continuous current mode can ensure balance quality to this circuit.Electric capacity C1, C2......Ck of being in parallel with each LED strip in Fig. 4 can, do not affect counterbalance effect.

When operating current is larger, the diode D1 in Fig. 4 also can change switch mosfet pipe into reduce conduction loss, and circuit as shown in Figure 5.In Fig. 5 circuit, Q2 instead of the D1 in Fig. 4, its conducting and the turn-off time the same with the D1 in Fig. 4, also namely when Q1 conducting Q2 cut-off, inductance L carries out energy storage.And when Q1 ends, Q2 conducting, inductance L is released energy to LED by Q2.Balancing network in Fig. 4 and Fig. 5 also can adopt 2 type balancing networks shown in Fig. 2, or the hybrid network of 1 type and the combination of 2 types.Circuit shown in Fig. 4 and Fig. 5 can carry out light modulation by the pulse-width controlled of the Current Control of LED or service intermittent.The principle of batch (-type) pulse-width controlled light modulation makes whole drive circuit periodically work or stop by a frequency lower than converter operation switching frequency, and by regulating the mean flow rate of the dutycycle control LED of working time in each resting period.Each low frequency resting period comprises tens usually to a hundreds of map function frequency cycle.The electric current of LED can be controlled by the total current signal detected by R1, also can be controlled by the electric current of direct-detection LED strip.

In LED backlight system traditional at present, the input power of its drive circuit is mostly through the DC low-voltage of High voltage output after conversion from power factor regulation circuit (PFC), is generally 12V or 24V.LED drive circuit converts required drive current or voltage to the input of this DC low-voltage again.Because by multistage conversion, efficiency is naturally lower.If the High voltage output of pfc circuit is directly supplied LED drive circuit to convert the driving-energy of LED to, then can minus one-level electric energy transfer process, not only cost-saving but also raise the efficiency.But in doing so, because the requirement LED circuit of safety standard needs to isolate with input supply terminal usually.In this case, voltage up converting circuit can replace with inverse-excitation type translation circuit, and its typical circuit as shown in Figure 6.In circuit shown in Fig. 6, input voltage VDC+ is the High voltage output of pfc circuit, and balance drive network is still the same with Fig. 4 with Fig. 5, and energy conversion operation process is also similar with Fig. 4 Fig. 5.When switching tube Q1 conducting, armature winding (number of turns is the side of the NP) inductance of transformer carries out charging energy-storing by input power.When Q1 turns off, the energy storage of primary inductance is coupled to secondary by mutual inductance and is released energy to LED loop by D1.When not meeting electric capacity C1, C2........CK, the operating current waveform in LED loop is still as shown in Fig. 3 (a) He Fig. 3 (b).Fig. 3 (a) for Transformer Winding electric current Q1 again conducting time decayed to zero situation.Shown in Fig. 3 (b), situation is Transformer Winding electric current does not decay to zero situation when Q1 conducting.Equally, in Q1 conduction period, balancing transformer no current passes through, and magnetic-reset is to zero, so whether this circuit equally with Fig. 4, Fig. 5 circuit can ensure balance quality equally regardless of continuous current mode.It is noted herein that because the existence of transformer leakage inductance, need to add absorbing circuit at its primary return, absorb this part leakage inductance energy when Q1 turns off, thus prevent switching tube Q1 drain electrode end from occurring overvoltage phenomenon.Circuitry block SNB in Fig. 6 is absorbing circuit.This absorbing circuit can be passive network, also can be active circuit.Absorbing circuit as being connected across the two ends of transformer TX1 armature winding in Fig. 6, also can be able to be connected across between the drain electrode QD of switching tube and power supply ground GND.Circuit of reversed excitation in Fig. 6, except having electrical safety buffer action, also provides the flexibility of input and output voltage proportionate relationship simultaneously.The operating voltage of such LED strip can lower than, to equal or higher than input voltage VDC+, thus make range of application wider.Diode D1 in Fig. 6 also can change controllable type electronic switch into, such as MOSFET, realizes the operation of synchronous mode inverse-excitation converting and raises the efficiency further.In addition, Fig. 6 circuit is except using 1 type balancing network shown in figure, and 2 type balancing networks or 1 type and 2 type hybrid networks can use equally.Equally, the light modulation of LED or can regulate the dutycycle of service intermittent to realize by the electric current of control LED.

Circuit shown in Fig. 6 also slightly can do expansion and use same one-level inverse excitation type converter to complete the dual-use function of power factor adjustment and isolated DC conversion simultaneously.The circuit of expansion as shown in Figure 7.In circuit shown in Fig. 7, input adds rectifier bridge BG1 and filter capacitor CA.After BG1 rectification, all-wave sinuous pulsation waveform is become at VDC+, as shown in Figure 7 from the alternating voltage of ac input end AC+, AC-input.The capacitance of CA is generally selected smaller, mainly plays the high frequency noise of filtering caused by the high-frequency switching operation of Q1, but still the sinuous pulsation waveform after making VDC+ keep rectification.In the switching manipulation process of Q1, the switch control rule principle of Q1 makes the current signal by detected on R1, also namely holds the envelope of the current signal flowed into follow the sinuous pulsation waveform of VDC+ by VDC+.So also just make the sinusoidal waveform of electric current maintenance and the input voltage homophase inputted by ac input end, thus complete the function of power factor regulation.Current signal amplitude on the other hand detected by R1 then controls according to required LED current size.Such one-level flyback switching operation can realize comprising power factor regulation, the global function operation of DC-isolation conversion and output current control etc.The balancing network that the current balance type of each LED strip is also made up of balancing transformer TB1, the TB2.......TBk shown in Fig. 7 is automatically accomplished.

Transformer balance drive network of the present invention also can be applied in buck drive circuit.Figure 8 shows that a typical application example.Q1 is main switch in fig. 8, and when Q1 conducting, D1 is forced to cut-off, and input power VDC+ provide electric current by Q1 and L to LED, and the electric current simultaneously in inductance L also increases linearly over time.When Q1 turns off, the electric current in inductance L is discharged until current attenuation is to zero to LED by D1.Inductive current increase and decay process in the balancing network that is made up of TB1, TB2.......TBk remain that the electric current in each LED loop is equal, also i.e. I _lED1=I _lED2=... ... ..=I _lEDk=(1/k) I _dD.Here need to remind, in order to prevent continuous DC component accumulate caused by balance error, the electric current of inductance L should be operated in discrete state, also namely closes to have no progeny at Q1 and will wait until and make Q1 start next turn-on cycle again after the current attenuation of inductance L is to zero.The light modulation of same LED or can regulate the dutycycle of batch (-type) pulse-width controlled operation to realize by the electric current of control LED.

In circuit shown in Fig. 8, the source electrode of Q1 is floating, and when Q1 conducting, its source potential rises to the level of VDC+.Withstand voltage, complexity and the cost of drive circuit are in this case all higher.Shown in Fig. 9, circuit is placed near end Q1.Because the voltage drop on current sense resistor R1 is usually all very little, the source electrode closely current potential of Q1, drive singal can with ground end GND for reference point.Make the withstand voltage of drive circuit like this, complexity and cost decline all widely, can provide a kind of solution of more simply saving money.Shown in the operation principle of this circuit structure and performance and Fig. 8, circuit is just the same.Here repeat no more.

The way of similar above-mentioned buck drive circuit also can be generalized to from the High voltage output of pfc circuit or directly powers to the system architecture of LED drive circuit after exchanging input rectifying.This structure is the same with the flyback drive circuit of Fig. 6, Fig. 7, needs to use isolating transformer.Figure 10 describes the example of several circuit arrangement.Figure 10 (a) is depicted as positive activation type drive circuit, and Figure 10 (b) is half-bridge drive circuit, and Figure 10 (c) is push-pull driver circuit, and Figure 10 (d) is full bridge driving circuit.In figure, diode D1, D2 are rectifying device, power after the alternating voltage of transformer TX1 secondary windings is converted to direct current to LED network.These two diodes can replace realizing synchronous rectification to raise the efficiency further with MOSFET.The operating process of these circuit is the same with circuit shown in Fig. 8, and energy transferring carries out when elementary main switch conducting, and during main switch cut-off, inductive current is discharged dump energy to LED load by afterflow.Here need remind, and the circuit of reversed excitation shown in Fig. 6, Fig. 7 unlike, in circuit shown in Figure 10, the electric current of inductance L needs to be operated in discrete state, to prevent the balance error caused by continuous DC component.In addition, circuit shown in Fig. 8, Fig. 9 and Figure 10, except employing as illustrated in the drawing 1 type balancing network, also can adopt 2 type balancing networks, or the combined balance system network of 1 type and the combination of 2 types.The light modulation of LED can be realized by the electric current of control LED, also can realize with the pulse-width controlled operation of service intermittent.

When using PFC output or other high direct voltages directly to power, another kind of way of the present invention adopts antiparallel connection to form two-way LED strip occasionally LED, the symmetrical switch change-over circuit such as then use half-bridge, full-bridge or recommend is to drive these LED strip even, centre need not through rectification link, and its schematic circuit as shown in figure 11.Figure 11 (a) is depicted as half-bridge circuit, and in figure, 11 (b) is full-bridge circuit, and Figure 11 (c) is push-pull circuit.Here it is noted that symmetrical switch circuit is not limited to above-mentioned 3 kinds, shown in Fig. 9, help as just example the concept that invention is described.As shown in Figure 11, the connection of LED is that every two string inverse parallels become one group.Such as LED1A and LED1B inverse parallel becomes one group ..., LEDKA and LEDKB inverse parallel becomes one group.Under each group LED can be operated in AC signal situation like this.When voltage be upper just lower negative time, A group LED conducting, on the contrary when voltage be lower just going up bear time, B group LED conducting.So respectively organize LED can directly be connected on the secondary output end of transformer TX1 by balancing network and not need extra rectification link.For Figure 11 (a), as primary side Q1 and Q2 alternate conduction, its switch motion also makes A group and B group LED correspondingly conducting at the voltage that the secondary windings of TX1 produces.Flow through balancing transformer TB1 ... in this case., the electric current of the armature winding of TBk is alternating polarity, do not have the problem of magnetic-reset during balancing transformer work.Here note there is a Diode series at each LED strip circuit, its main cause is Zener diode and the LED inverse parallel that LED strip has antistatic usually, if there is no diode D1A, D1B.....DKA, DKB, then when LED strip bears backward voltage, Zener diode meeting conducting, thus make circuit cisco unity malfunction, after having had these series diodes, Zener diode would not conducting.In figure and electric capacity C1A, C1B.......CKA, CKB etc. of LED parallel connection in order to the electric current of level and smooth LED, also can and do not affect counterbalance effect.The electric capacity CL be in series with the secondary windings of TX1 can intercept the flip-flop in electric current, also can help the voltage differences balancing positive and negative two groups of LED simultaneously.Such as when the operating voltage of A group is higher than B group, electric capacity CL automatically can produce a left side in operation and bear right positive voltage to make the total current of A group and B group equal, and in A group and B group, respectively the current balance type of going here and there between LED is then realized by balancing transformer network.Inductance L in Figure 11 is used for reducing the peak current of secondary loop and resonant frequency.When transformer secondary output leakage inductance is less, circuit likely produces peak current and causes the higher-order of oscillation thus in On-off transition.When transformer secondary output leakage inductance is larger, inductance L can.Circuit shown in Figure 11, except adopting 1 type balancing network as shown in the figure, also can adopt 2 type balancing networks, or the combined balance system network of 1 type and the combination of 2 types.The light modulation of LED simultaneously can be realized by the electric current of control LED, or realizes with the operation of batch (-type) pulse-width controlled.

If LED strip does not have antiparallel Zener diode in circuit shown in Figure 11, LED strip would not conducting under backward voltage.In this case, if the oppositely resistance to of LED strip is pressed with enough surpluses, series diode D1A, D1B.....DKA, DKB etc. also can.At this moment shunt capacitance C1A, C1B.......CKA, CKB etc. also need to remove, otherwise can produce alternating current bypass effect.So circuit just simplifies many.In addition inductance L still can according to the secondary leakage inductance size of transformer decide with or need not.Balancing network is also the same with Figure 11 circuit with the scope of application of dimming mode.Circuit after simplification as shown in figure 13.

Another kind of low cost way of the present invention as depicted in fig. 12.In fig. 12, each LED strip is connected with a little rectifier bridge composition two-way LED structure.As shown in the figure, the anode of LED strip LED1, LED2.....LEDk is connected to the positive output end of equal rectifier bridge BG1, BG2....BGk, and the negative electrode of LED is connected to the negative output terminal of rectifier bridge.The ac input end of each rectifier bridge BG1, BG2....BGk is then the input port of two-way LED structure.The such two-way LED structure of single channel can be directly connected to the output of converter main transformer TX1 secondary windings.When the two-way LED structure driving multichannel such, the armature winding of corresponding in the input on every road and balancing network balancing transformer TB1, TB2....TBk is in series, and the branch road like this after series connection is parallel to the output of main transformer TX1 secondary windings again.Like this when the full-bridge circuit in the half-bridge circuit in Figure 12 (a), the push-pull circuit in Figure 12 (b) and Figure 12 (c) works, the alternation pressure produced at the secondary windings of main transformer TX1 can often organize rectifier bridge-LED combination by Direct driver, and keeps each string LED current equal by balancing transformer network.Series inductance L in Figure 12 is used for the operating current of level and smooth transformer secondary output winding, if the leakage inductance of TX1 secondary windings is enough large, inductance L also can.Except 1 type balancing network shown in Figure 12,2 type balancing networks or 1 type and 2 type combined balance system networks, be suitable for too.The light modulation of same LED can by the Current Control of LED, or the pulse-width controlled of cyclical intermission formula work realizes.The direct current input VDC+ of circuit shown in Figure 12 is the High voltage output of power factor regulating circuit (PFC) under most applicable cases, but also can be other any one dc source.

As is generally known full-bridge circuit can realize Sofe Switch operation usually, symmetrical half bridge and push-pull circuit cannot do Sofe Switch operation under normal conditions.But when circuit working is close to full dutycycle time, can be realized by the suitable selection symmetrical half bridge of circuit parameter and the Sofe Switch operation of push-pull circuit.For the half-bridge circuit in Figure 11 (a), when steady operation, the series capacitance of primary winding can set up the positive right negative voltage in the left side approximating (1/2) VDC+, when Q1 conducting Q2 ends, the primary winding current of transformer TX1 from top to bottom flows.But when Q1 turns off, if the electromagnetic energy of energy storage is enough large in TX1, the afterflow effect of its primary winding current can be shifted the earth potential of GND onto the current potential of half-bridge mid point SW and maintain continuation circulation by the parasitic diode of Q2, and its circulation flow path is through as shown in Figure 11 (a).At this moment Q2 source and drain voltage across poles is zero substantially.If make Q2 conducting in this case, circuit just achieves the Sofe Switch operation of no-voltage conducting, and switching loss and switch noise all can reduce widely.But will notice that TX1 primary current is when maintaining above-mentioned conducting situation, must overcome the voltage being equivalent to (1/2) VDC+ on electric capacity CS here, therefore decling phase is when fast.In this case, if the time turned off between Q2 conducting from Q1 is long, also when namely the dutycycle of PWM switching manipulation is smaller, then the electric current of TX1 armature winding can decay to zero before Q2 conducting, the parasitic diode cut-off of Q2, the current potential of half-bridge mid point SW rises, thus loses the condition of Zero-voltage soft switch operation.Therefore only have when circuit working is when close to full dutycycle, the time turned off between Q2 conducting from Q1 is enough short, just may realize Zero-voltage soft switch operation.This principle is equally also applicable to push-pull circuit.Based on this principle, the optimum operation scheme of the circuit of the present invention described in Figure 11 and Figure 12 allows change-over switch be operated in close to full dutycycle to realize Sofe Switch operation.The operating current of LED can be selected by circuit parameter, as the parameter of transformer TX1, the Selecting parameter of electric capacity CL and inductance L etc. makes it equal rated value when close full duty cycle operation, and the light modulation of LED is then realized by the pulse-width controlled operation of service intermittent.Such mode of operation is used in the circuit described in Figure 11 and Figure 12, in the LED drive circuit of particularly elementary use half-bridge or push-pull topology, can excellent and solution with low cost.

More than be described through object lesson to explain principle of the present invention, but in all senses, do not limit the range of application of principle of the present invention and other implementation methods of principle of the present invention.

Claims (11)

1. one kind utilizes transformer to balance the balancing circuitry structure of LED multi-path multi-channel DC load, it is characterized in that each balancing transformer has an armature winding and a secondary windings and gets identical number of turns ratio, the armature winding of each LED branch road or DC load branch road respectively with one corresponding balancing transformer is in series, each branch road that such series connection is formed is parallel-connected to common driver power port again, the secondary windings of each balancing transformer is connected in series composition closed circuit mutually, the electric current flow direction in the loop responded at each secondary windings when the connection polarity of each secondary windings in closed circuit makes the armature winding driving a current through each balancing transformer is consistent, the loop current of secondary windings makes the electric current flowing through each paths of LEDs or galvanic load equal by the electromagnetic balance effect between the primary and secondary winding of transformer in the course of the work.

2. circuit structure according to claim 1, it is characterized in that two windings of each balancing transformer are got the identical number of turns and are respectively in series with a LED branch road or DC load branch road, two branch roads that such series connection is formed are parallel-connected to common driver input port again, the polarity of two windings in being connected in series makes the magnetic flux produced when electric current flows into this two windings from public input cancel each other, make the electric current flowing through described LED or galvanic load equal by the electromagnetic balance effect between the primary and secondary winding of transformer in the course of the work, when LED branch road or load branch are more than two-way, above-mentioned balancing circuitry structure expands the LED or load branch that drive response by tandem type.

3. according to the arbitrary described circuit structure of claim 1 or 2, it is characterized in that driving balancing circuitry structure according to claim 1 or claim 2 with a non-isolated booster circuit, booster circuit is by a dc source, a main electronic switch, an inductance and a booster diode formed, one end of inductance receives the anode of dc source, the other end of inductance is connected with the anode of main electronic switch and the anode of booster diode, the negative terminal of main electronic switch is connected with the negative terminal of dc source, balancing circuitry structure according to claim 1 or claim 2 is received between the negative electrode of booster diode and the negative terminal of dc source, in operation the main electronic switch of booster circuit in each operation cycle conducting and cut-off once, when main electronic switch conducting, inductance carries out energy storage by input power, booster diode ends, the magnetic-reset of balancing transformer is to zero, when main electronic switch cut-off, the energy that inductance stores is powered to balancing circuitry structure by booster diode, the electric current of each LED branch road or DC load branch road keeps equal by the balanced action of balancing transformer, inductive current allows to be operated in continuous current mode or discontinuous current pattern in operation.

4. according to the arbitrary described circuit structure of claim 1 or 2, it is characterized in that driving balancing circuitry structure according to claim 1 or claim 2 with an inverse-excitation type translation circuit, inverse-excitation type translation circuit is by a dc source, a main electronic switch, a flyback transformer, formed with a commutation diode, during main electronic switch conducting, the primary winding inductance of flyback transformer carries out energy storage by input power, at this moment commutation diode cut-off, the magnetic flux reset-to-zero during this period of balancing transformer, when main electronic switch cut-off, the inductive energy that primary winding stores is coupled to armature winding and is powered to balancing circuitry structure by commutation diode, the electric current of each LED branch road or galvanic load branch keeps equal by the balanced action of balancing transformer.

5. according to the arbitrary described circuit structure of claim 1 or 2, it is characterized in that driving balancing circuitry structure according to claim 1 or claim 2 with a step-down conversion circuit, buck converter is by a direct-current input power supplying, a main electronic switch, an inductance, formed with a fly-wheel diode, the positive voltage terminal of main electronic switch is connected on input voltage anode, the negative electrode of the negative voltage side of main electronic switch and one end of inductance and fly-wheel diode is connected together, the anode of fly-wheel diode receives dc source negative terminal, multichannel balancing circuitry structure is connected on the other end and the dc source negative terminal of inductance, when main electronic switch conducting, electric current flows to multichannel balancing circuitry structure by inductance, when electronic switch ends, inductive current continues to power until electric current exhausts to multichannel balancing circuitry structure by fly-wheel diode, main electronic switch starts conducting again after inductive current exhausts, carry out the switching manipulation of next cycle.

6. circuit structure according to claim 5, it is characterized in that main electronic switch is connected on the negative terminal of dc source, when main electronic switch conducting, electric current flows to multichannel balancing circuitry structure by inductance, when electronic switch ends, inductive current continues to power until electric current exhausts to multichannel balancing circuitry structure by fly-wheel diode, and main electronic switch starts conducting again after inductive current exhausts, and carries out the switching manipulation of next cycle.

7. according to the arbitrary described circuit structure of claim 1 or 2, it is characterized in that using feed forward type translation circuit, half-bridge converter circuit, full-bridge type translation circuit, or push-pull type translation circuit drives the multichannel balancing circuitry structure described by claim 1 or claim 2, in the periodical operation process of converter electronic switch, when after electronic switch cut-off, the electric current of secondary filter inductance continues to power to multichannel balancing circuitry structure by afterflow, start again after the current attenuation of secondary filter inductance to zero is waited until in the conducting operation of electronic switch next time, make the magnetic flux of balancing transformer can reset-to-zero, to ensure effective balanced action.

8. according to the arbitrary described circuit structure of claim 1 or 2, it is characterized in that each LED branch road forms one two single-string LED inverse parallels can the AC LED branch road of conducting under positive and negative two polarity of voltages, combine with balancing transformer and form multichannel AC LED balancing circuitry structure, driving power uses half-bridge, full-bridge or push-pull symmetric form conversion switch drive above-mentioned multichannel AC LED balancing circuitry structure from the direct output AC voltage of the secondary windings of transformer, the not balance transformer when only having an AC LED branch road, two ports of transformer secondary output winding are directly received after this AC LED branch road and a capacitances in series.

9. circuit structure according to claim 8, it is characterized in that forming an AC LED branch road by a full-bridge rectifier and a LED strip, the anode tap of LED strip is connected with the positive output end of full-bridge rectifier, the cathode terminal of LED strip is connected with the negative output terminal of full-bridge rectifier, and two ac input ends of full-bridge rectifier are as two ports of this AC LED branch road.

10. circuit structure according to claim 8, it is characterized in that half-bridge, full-bridge and push-pull circuit that driving power uses realize Zero-voltage soft switch operation by the state be operated in close to full dutycycle, the brightness adjustment control of LED is realized by the dutycycle changing service intermittent.

11. circuit structures according to claim 10, it is characterized in that half-bridge, full-bridge and push-pull circuit that driving power uses realize Zero-voltage soft switch operation by the state be operated in close to full dutycycle, the brightness adjustment control of LED is realized by the dutycycle changing service intermittent.