CN206807823U - A kind of backlight LED drive circuit - Google Patents

A kind of backlight LED drive circuit Download PDF

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Publication number
CN206807823U
CN206807823U CN201720483110.7U CN201720483110U CN206807823U CN 206807823 U CN206807823 U CN 206807823U CN 201720483110 U CN201720483110 U CN 201720483110U CN 206807823 U CN206807823 U CN 206807823U
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China
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paths
leds
inductance
sustained diode
circuit
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刘雪山
梅军
郭强生
贾曜峰
周群
肖瑞
李学文
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Sichuan University
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Sichuan University
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Abstract

The utility model discloses a kind of backlight LED drive circuit, realizes stream and high efficiency light modulation.Wherein loop of power circuit is by power switch tube S1, main inductance Lm, sustained diodei(i=1,2 ... n), filter capacitor Ci(i=1,2 ... n), current sampling resistor Rs, resonant capacitance Cr(j)(i=1,2 ... n 1), resonant inductance Lr(k)(when n is even number, k=2,4 ... n/2, when n is odd number, k=3,5 ... (n 1)/2) composition.Control loop is made up of the part such as drive circuit, comparator, error amplifier and light adjusting controller, and i is controlled using voltage mode controlo1Size, io1It is controlled as Vref/Rs, by adjusting VrefSize realize pulse width light modulation and simulation dimming function.The utility model realizes stream and high efficiency light modulation, and control is simple, has voltage stress low and the characteristics of wide load operating range.

Description

A kind of backlight LED drive circuit
Technical field
It the utility model is related to LED sharing controls field, and in particular to a kind of backlight LED drive circuit.
Background technology
As one of green light source for most having development and application prospect, light emitting diode (LED) is with energy-saving and environmental protection long lifespan With control it is simple the features such as, be widely used in the occasions such as LCD backlight.LED belongs to spot light, in the application such as LED backlight, is Acquisition uniform luminous flux is, it is necessary to which plurality of LEDs is uniformly distributed.Plurality of LEDs, which is directly connected, will cause driving power voltage stress Height, poor reliability, thus more connected modes in parallel using LED strip, but accompanying problem is that need to carry out each paths of LEDs Sharing control.
LED, which flows, mainly two major class control methods：Active stream flows with passive.Active flow is had using switching tube etc. Source device and control circuit composition current regulator, realize the regulation of each branch road LED current.Active stream is generally divided into linearly Pattern flows to flow with switching mode.Linear model stream is the widely used method of small-power backlight electric power, but its efficiency compared with It is low；On-off mode, which flows, needs multiple inductance, multiple switch and multiple control loops, has the shortcomings that volume is big, cost is high.Nothing Source is flowed realizes that each branch current is balanced using only passive devices such as resistance, electric capacity, coupling inductances, has control simple special Point.It is not high and less efficient using the passive stream precision of resistance；Using the passive current share scheme volume of coupling inductance it is big, into This height.And there is the advantages of small volume, control circuit is simple using passive flow not only of capacitance charge equilibrium principle, also have The advantages of high efficiency and top adjustment precision.
The technical scheme of LED multi-path flow equalizings output is favorably realized with electric capacity charge balance theory in the prior art.Such as Fig. 1 institutes Show, it is the topological diagram that a kind of two-way exports LLCC resonance circuits.Main circuit primary side is half-bridge structure, the switch S of complementary drive1 And S2Produce square wave, the input as resonator.The resonant inductance L of primary sider, magnetizing inductance LmWith resonant capacitance CrForm resonance Structure, and with the stream electric capacity C of transformer secondary windings in seriesbAlso assist in resonance.So main circuit is the element resonances of LLCC tetra- Circuit.The two-way export structure that secondary rectifier bridge is made up of D1, D3 and D2, D4, it is every that a LED strip can be operated alone all the way. C1, C2 are output filter capacitor, due to two-way output for halfwave rectifier, it is necessary to which filter capacitor absorption current ripples, are provided for LED Constant electric current.According to the charge and discharge electric balance principle of electric capacity, CbTwo-way output can be made to realize automatic current equalizing.In addition, work as two-way When output voltage is unequal, CbIts voltage difference can also be undertaken.So that circuit is in the case where two output voltage differs greatly, Good stream effect can still be ensured.This LLCC resonance circuits can be not only used for the automatic current equalizing of two-way output, also This current equalizing structure can be extended to multiple-channel output, but can be only used for even number output branch road occasion, and this method needs are more Individual switch, and transformer is needed, volume is big, and cost is high, is not suitable for small size backlight LED driving applications.
Fig. 2 exports LED driver topology and its control loop, wherein switching tube S for a kind of traditional tunnel of single switch four1Shut-off When equivalent circuit it is as shown in Figure 3.From the figure 3, it may be seen that work as switching tube S1During shut-off, magnetizing inductance (Lm) electric current and resonant inductance (Lr) current-series, form the source-series ill circuit of electric current.If resonant inductance electric current is in S1It is zero during shut-off, resonant inductance Electric current will be excited inductive current by zero and force to be mutated to excitation inductance current peak value, and therefore, resonant inductance will produce higher Due to voltage spikes.Therefore, if allowing circuit normal work, it is necessary to plus absorbing circuit as shown in Figure 4.When output loading is lighter, open Close pipe S1Service time it is shorter.Switching tube S1After shut-off, due to resonant inductance (Lr) electric current will be excited by higher initial value Inductance (Lm) electric current pressure is reversely.Due to resonant inductance current break, S will be caused1It is upper to produce higher due to voltage spikes, and then lead Cause the steady operation of strong electromagnetic interference influence circuit.Therefore, even if plus absorbing circuit as shown in Figure 4, the circuit can not yet It is operated under lighter loading condition, so in the publication, author only analyzes S1Resonant inductance electric current is zero during shut-off Situation.That is, S1Service time be greater than resonance time and the circuit could normal work in the case where adding absorbing circuit. Its circuit stable state waveform is as shown in figure 5, as figure shows after adding absorbing circuit, S1Back-pressure due to voltage spikes be present.
Active flow adds active device and its control circuit formation current regulator in each LED strip.Current regulation Device can be divided into linear model and switching mode again.Switch mode current regulator adjusts each LED strip using DC/DC converters Electric current, can accurately control the electric current per all the way, it has efficient advantage.But have simultaneously with the increase of LED strip Source device also accordingly increases, and increases component complexity and the complexity of control.Linear model current regulator designs Simply, its equivalent to one active pull-up, and there is electric current to flow through all the time, therefore power attenuation is big, efficiency is low, is only used for Small-power occasion.
The as a rule passive circuit topology flowed and control are all more simple.Wherein flowed the most simply using resistance, The one big resistance of series connection in each LED strip, when the resistance of resistance is much larger than the equivalent resistance of LED strip, in each LED strip Electric current is roughly the same.But this method has substantial amounts of power attenuation on resistance, therefore this side is actually rarely employed Method.It is also fairly simple using the method for inductive, but the precision that the deviation of inductance value and coefficient of coup etc. all flows influence. With increasing for LED strip quantity, the quantity of coupling inductance is also a lot, adds the difficulty of design.And the LED strip of this method Even number can only be expanded to, there is certain limitation.Therefore this method is only used for LED strip negligible amounts and is even number Situation.There is the advantages of high-efficiency and low-cost using the passive stream of capacitor charge and discharge balance, be more than the comparison studied at present It is passive to flow measure.But current research is based on Half-bridge DC convertor mostly, Transformer Winding and switching tube are added Quantity, driver is set to become more complicated, it is also difficult to reach the requirement of miniaturization.
Utility model content
Technical problem to be solved in the utility model is to provide a kind of backlight LED drive circuit, realizes and flows and dim High efficiency backlight LED drive power, high efficiency, control are simple, have voltage stress low and the characteristics of wide load operating range.
In order to solve the above technical problems, the technical solution adopted in the utility model is：
A kind of backlight LED drive circuit, when n is even number, the loop of power circuit of n paths of LEDs driving powers has following structure：
By power switch tube S1, main inductance Lm, sustained diodei, filter capacitor Ci, resonant capacitance Cr(j)And resonant inductance Lr(k)Composition, wherein, i=1,2 ... n, j=1,2 ... n-1, k=2,4 ... n/2；
1st road to the 2nd paths of LEDs structure is：
Main inductance LmInput connects positive source；
Power switch tube S1One end is connected to main inductance LmOutput end, the other end are connected to power cathode；
Resonant capacitance Cr1One end is connected to main inductance LmOutput end, the other end are connected to sustained diode1Positive pole is also logical Cross resonant inductance Lr1It is connected to sustained diode2Negative pole；
Sustained diode1Negative pole connects the 1st paths of LEDs, and the 1st paths of LEDs is connected to power cathode, and the 1st paths of LEDs is parallel with filter Ripple electric capacity C1；
Sustained diode2Positive pole connects the 2nd paths of LEDs, and the 2nd paths of LEDs is connected to power cathode, and the 2nd paths of LEDs is parallel with filter Ripple electric capacity C2；
The n-2 paths of LEDs structure subsequently expanded is identical to the 2nd road connection mode with the 1st road；
When n is odd number, the loop of power circuit of n paths of LEDs driving powers has following structure：
By power switch tube S1, main inductance Lm, sustained diodei, filter capacitor Ci, current sampling resistor Rs, resonant capacitance Cr(j)With resonant inductance Lr(k)Composition, wherein, i=1,2 ... n, j=1,2 ... n-1, k=3,5 ... (n-1)/2；
1st road to the 3rd paths of LEDs structure is：
Main inductance LmInput connects positive source；
Power switch tube S1One end is connected to main inductance LmOutput end, the other end are connected to power cathode；
Resonant capacitance Cr1One end is connected to main inductance LmOutput end, the other end are connected to sustained diode1Positive pole is also logical Cross resonant inductance Lr1It is connected to sustained diode2Negative pole；
Sustained diode1Negative pole connects the 1st paths of LEDs, and the 1st paths of LEDs is connected to power cathode, and the 1st paths of LEDs is parallel with filter Ripple electric capacity C1；
Sustained diode2Positive pole connects the 2nd paths of LEDs, and the 2nd paths of LEDs is parallel with filter capacitor C2；
Main inductance LmOutput end, resonant capacitance Cr3, sustained diode3Positive pole is sequentially connected；Sustained diode3Negative pole connects The 3rd paths of LEDs is connect, the 3rd paths of LEDs is parallel with filter capacitor C3；
2nd road and the 3rd paths of LEDs are commonly connected to resonant capacitance Cr2One end, resonant capacitance Cr2Other end connection power supply is born Pole；
The n-3 paths of LEDs structure subsequently expanded is identical to the 3rd road connection mode with the 2nd road.
Further, in addition to control loop, the control loop include the drive circuit, comparator, mistake being sequentially connected Poor amplifier and light adjusting controller, the drive circuit are connected to power switch tube S1；I is controlled using voltage mode controlo1's Size, io1It is controlled as Vref/Rs, by adjusting VrefSize realize pulse width light modulation and simulation dimming function；Wherein, Rs For current sampling resistor, io1For the 1st paths of LEDs branch current, VrefFor reference voltage.
Compared with prior art, the beneficial effects of the utility model are：1) circuit should not exist in any operation mode and lead The mode of inducing current mutation or capacitance voltage mutation is sent a telegraph, otherwise circuit will produce infinitely great voltage stress or current stress； The mode of inductive current mutation is not present in the utility model, has the characteristics of low voltage stress and wide load operating range.2) it is electric Holding charge balance concept can realize that the average current being connected on the positive and negative branch road of electric capacity is equal, in order to ensure capacitance current does not occur Mutation, the positive and negative sense of current of electric capacity are required to be connected with inductance or resistance.And resistance loss is larger, connection inductance is a kind of high The solution of effect；Each branch road of the utility model flows the positive and negative sense of current of electric capacity and is respectively connected with inductance, therefore should with electric current The low and efficient feature of power.3) switch realizes that DC chopped-wave is simplest mode；The utility model is only with one Active switch, there is small volume, control the advantages of simple.
Brief description of the drawings
Fig. 1 is two-way output LLCC resonant circuit topology figures.
Fig. 2 is the tunnel of single switch four output topology and its control loop.
Equivalent modalities when Fig. 3 is switching tube shut-off.
Fig. 4 is voltage peak absorbing circuit.
Fig. 5 is that (S1 service times are less than resonance to the tunnel of resonant mode single switch four output Boost LED drive powers stable state waveform Time).
Fig. 6 is the topological sum control loop of n roads resonance LED drive power, and n is even number.
Fig. 7 is the topological sum control loop of n roads resonance LED drive power, and n is odd number.
Fig. 8 is the topological sum control loop output embodiment of 3 road resonance LED drive powers.
Fig. 9 is that 3 paths of LEDs driving power main inductances are operated in (CCM, ton>Tr/ 2) main oscillogram when.
Figure 10 is 3 paths of LEDs driving powers in (CCM, ton>Tr/ 2) t under0~t1The circuit equivalent figure of mode.
Figure 11 is 3 paths of LEDs driving powers in (CCM, ton>Tr/ 2) t under1~t2The circuit equivalent figure of mode.
Figure 12 is 3 paths of LEDs driving powers in (CCM, ton>Tr/ 2) t under2~t3The circuit equivalent figure of mode.
Figure 13 is that 3 paths of LEDs driving power main inductances are operated in (DCM, ton<Tr/ 2) main oscillogram when.
Figure 14 is 3 paths of LEDs driving powers in (DCM, ton<Tr/ 2) t under0~t1The circuit equivalent figure of mode.
Figure 15 is 3 paths of LEDs driving powers in (DCM, ton<Tr/ 2) t under1~t2The circuit equivalent figure of mode.
Figure 16 is 3 paths of LEDs driving powers in (DCM, ton<Tr/ 2) t under2~t3The circuit equivalent figure of mode.
Figure 17 is 3 paths of LEDs driving powers in (DCM, ton<Tr/ 2) t under3~t4The circuit equivalent figure of mode.
Figure 18 is 3 tunnels output embodiment.
Figure 19 is the dimming curve of 3 tunnels output embodiment.
Figure 20 is that 3 tunnels export embodiment in (CCM, ton>Tr/ 2) experimental result under.
Figure 21 is that 3 tunnels export embodiment in (DCM, ton<Tr/ 2) experimental result under.
Figure 22 is the start waveform of 3 tunnels output embodiment.
Figure 23 is the efficiency test result of 3 tunnels output embodiment.
Embodiment
The utility model is described in further detail with reference to the accompanying drawings and detailed description.
As shown in fig. 6, it is the loop of power circuit and control loop of n paths of LEDs driving powers.Wherein loop of power circuit is opened by power Close pipe S1, main inductance Lm, sustained diodei(i=1,2 ... n), filter capacitor Ci(i=1,2 ... n), current sampling resistor Rs, it is humorous Shake electric capacity Cr(j)(i=1,2 ... n-1), resonant inductance Lr(k)(when n is even number, k=2,4 ... n/2, when n is odd number, k=3, 5 ... (n-1)/2) composition.Control loop is made up of the part such as drive circuit, comparator, error amplifier and light adjusting controller, is adopted I is controlled with voltage mode controlo1Size, io1It is controlled as Vref/Rs, can be by adjusting VrefSize realize that pulse is wide Degree light modulation and simulation dimming function.
Its course of work of labor so that 3 tunnels export Fig. 8 as an example below.To simplify the analysis, hypothesis below is first made.
1) power switch tube S1, sustained diode1, D2, D3For ideal component；
2) filter capacitor C1, C2, C3Electric capacity it is sufficiently large, output voltage ripple can be ignored；
3) resonant capacitance Cr1, Cr2Size it is identical, Cr1=Cr2=Cr；
Fig. 9 show main oscillogram when 3 paths of LEDs driving power main inductances are operated in (CCM), shown in Figure 10 to Figure 12 For the circuit equivalent figure of corresponding 3 operation modes.
Principle Analysis：[the t of mode 10-t1]t0Moment switching tube turns on, main inductance LmThe voltage at both ends is Vin, therefore The electric current i at main inductance both endsLm(t) linear rise：
Diode D2Conducting, D1, D3Shut-off.Resonant inductance Lr1Series resonance occurs with two resonant capacitances.Therefore understand
WhereinFor the equiva lent impedance of resonance circuit,For the angular frequency of resonance circuit.
Work as iLr1(t) when resonance is to zero, diode D2Shut-off, mode 1 terminate.The duration of mode 1 is τ1=Tr/2。
[the t of mode 21-t2]t1Moment diode D2Shut-off, power switch pipe still turn on, main inductance LmStill linear rise.
In mode 2, fly-wheel diode is turned off, therefore the electric current of resonant inductance, and the electric current of resonant capacitance is zero.When Mode 2 terminates when switching tube turns off, and the duration of mode 2 is τ2=ton-Tr/ 2, wherein tonFor the ON time of switching tube.
[the t of mode 32-t3]t2Moment switching tube turns off, sustained diode2It is still off, D1, D3Conducting, when switching tube again During secondary conducting, mode 3 terminates, into next switch periods.The duration of mode 3 is τ3=Ts-ton。
Figure 13 show three paths of LEDs driving power main inductances and is operated in (DCM, ton<Tr/ 2) main oscillogram when, Figure 14 The circuit equivalent figure of corresponding four operation modes is shown to Figure 17.
There can not be inductance series connection (equivalent current is source-series) loop from circuit theory, in circuit and electric capacity is in parallel (equivalent voltage source in parallel) loop, otherwise inductive drop will produce very high due to voltage spikes or capacitance current will produce it is too high Current spike.Circuit shown in Fig. 2 has that inductance is connected (equivalent current is source-series), have impact on circuit normal work.
Analyzed more than, because the utility model circuit structure is different from Fig. 2, it was found from Fig. 9~17, work as switching tube S1During shut-off, the loop connected in the absence of magnetizing inductance with resonant inductance, excitation inductance current and resonance inductive current respectively with Respective loop individual flow, therefore, no matter magnetizing inductance is operated under CCM or DCM, also either ton>Tr/ 2 or ton< TrUnder/2, the utility model circuit can be very good work.The ill mode shown in Fig. 2 is not present in the utility model, therefore Absorbing circuit need not be increased, improve the efficiency and stability of circuit.Although in addition, equalizing-current network of the present utility model in the presence of Resonant inductance, but each output branch road still has good equal properties of flow.
LED drive circuit parameter is exported as embodiment using following 3 tunnel, as shown in figure 18.Input voltage vin=19V, output Each string LED voltage vo1=vo2=vo3=30V, export each string LED current io1=io2=io3=0.15A.Cr1=Cr2=220nF, Lm=33 μ H, Lr1=2.2 μ H, switching frequency fs=300kHz.Figure 19 give the utility model to should embodiment light modulation Curve.Figure 20 is the embodiment in (CCM, ton>Tr/ 2) experimental result under.Figure 21 is the embodiment in (DCM, ton<Tr/2) Under experimental result.From Figure 20 and Figure 21, any due to voltage spikes or electric current is not present in a utility model circuit waveform Spike.The start waveform of Figure 22 embodiments, each branch road LED current is rapidly reached stable state and realizes 152mA after start Stream.Figure 23 is 3 paths of LEDs driving power efficiency test results, and the utility model has efficient advantage.Table 1 gives The tunnel of utility model 3 exports stream experimental data of the embodiment under light-modulating mode, under various light modulation percentages, each branch road LED current, which realizes, preferably flows effect.
Table 1 dims and equal current test data
From experiment, Voltage and Current Spikes, wide loading range regulation, superior stream is not present in the utility model circuit Characteristic.Therefore in the LED driving applications that can be very good to be applied to such as wide loading range of backlight needs light modulation.

Claims (2)

  1. A kind of 1. backlight LED drive circuit, it is characterised in that
    When n is even number, the loop of power circuit of n paths of LEDs driving powers has following structure：
    By power switch tube S1, main inductance Lm, sustained diodei, filter capacitor Ci, resonant capacitance Cr(j)With resonant inductance Lr(k) Composition, wherein, i=1,2 ... n, j=1,2 ... n-1, k=2,4 ... n/2；
    1st road to the 2nd paths of LEDs structure is：
    Main inductance LmInput connects positive source；
    Power switch tube S1One end is connected to main inductance LmOutput end, the other end are connected to power cathode；
    Resonant capacitance Cr1One end is connected to main inductance LmOutput end, the other end are connected to sustained diode1Positive pole, also pass through resonance Inductance Lr1It is connected to sustained diode2Negative pole；
    Sustained diode1Negative pole connects the 1st paths of LEDs, and the 1st paths of LEDs is connected to power cathode, and the 1st paths of LEDs is parallel with filter capacitor C1；
    Sustained diode2Positive pole connects the 2nd paths of LEDs, and the 2nd paths of LEDs is connected to power cathode, and the 2nd paths of LEDs is parallel with filter capacitor C2；
    The n-2 paths of LEDs structure subsequently expanded is identical to the 2nd road connection mode with the 1st road；
    When n is odd number, the loop of power circuit of n paths of LEDs driving powers has following structure：
    By power switch tube S1, main inductance Lm, sustained diodei, filter capacitor Ci, current sampling resistor Rs, resonant capacitance Cr(j) With resonant inductance Lr(k)Composition, wherein, i=1,2 ... n, j=1,2 ... n-1, k=3,5 ... (n-1)/2；
    1st road to the 3rd paths of LEDs structure is：
    Main inductance LmInput connects positive source；
    Power switch tube S1One end is connected to main inductance LmOutput end, the other end are connected to power cathode；
    Resonant capacitance Cr1One end is connected to main inductance LmOutput end, the other end are connected to sustained diode1Positive pole, also pass through resonance Inductance Lr1It is connected to sustained diode2Negative pole；
    Sustained diode1Negative pole connects the 1st paths of LEDs, and the 1st paths of LEDs is connected to power cathode, and the 1st paths of LEDs is parallel with filter capacitor C1；
    Sustained diode2Positive pole connects the 2nd paths of LEDs, and the 2nd paths of LEDs is parallel with filter capacitor C2；
    Main inductance LmOutput end, resonant capacitance Cr3, sustained diode3Positive pole is sequentially connected；Sustained diode3Negative pole connection the 3rd Paths of LEDs, the 3rd paths of LEDs are parallel with filter capacitor C3；
    2nd road and the 3rd paths of LEDs are commonly connected to resonant capacitance Cr2One end, resonant capacitance Cr2The other end connects power cathode；
    The n-3 paths of LEDs structure subsequently expanded is identical to the 3rd road connection mode with the 2nd road.
  2. A kind of 2. backlight LED drive circuit as claimed in claim 1, it is characterised in that
    Also include control loop, the control loop includes drive circuit, comparator, error amplifier and the light modulation being sequentially connected Controller, the drive circuit are connected to power switch tube S1；I is controlled using voltage mode controlo1Size, io1It is controlled as Vref/Rs, by adjusting VrefSize realize pulse width light modulation and simulation dimming function；Wherein, RsFor current sampling resistor, io1For the 1st paths of LEDs branch current, VrefFor reference voltage.
CN201720483110.7U 2017-05-03 2017-05-03 A kind of backlight LED drive circuit Expired - Fee Related CN206807823U (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107105543A (en) * 2017-05-03 2017-08-29 四川大学 A kind of backlight LED drive circuit

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107105543A (en) * 2017-05-03 2017-08-29 四川大学 A kind of backlight LED drive circuit

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