CN105392234A - Multipath current-sharing output LED (Light-Emitting Diode) driving power supply and dimming method - Google Patents

Abstract

The invention relates to a multipath current-sharing output LED (Light-Emitting Diode) driving power supply and a dimming method. The driving power supply comprises a switching network module, an LCL-nT type resonance network, a rectification network and a load unit, which are orderly connected with each other; the switching network comprises a first bridge arm and a second bridge arm which are connected in parallel, wherein the second bridge arm is used as a phase shift bridge arm and used for realizing wide-range lighting control; and the load unit comprises n paths of current-sharing output LED loads. The multipath current-sharing output LED driving power supply and the dimming method provided by the invention can realize constant and balanced output current under multiple paths of different LED lamp voltages, and have the characteristics of being simple in circuit structure, good in constant-current characteristic and high in current sharing accuracy, etc.

Description

The LED drive power that a kind of multi-path flow equalizing exports and light-dimming method

Technical field

The present invention relates to LED drive power field, the LED drive power of particularly a kind of multi-path flow equalizing output and light-dimming method.

Background technology

LED is as forth generation electric light source, and the advantage such as long service life, light efficiency are high owing to having, energy-saving and environmental protection is progressively subject to the favor of people, becomes the focus of lighting field.The LED driver of high efficient and reliable is then the key ensureing LED steady operation.Because LED has nonlinear voltage-current characteristic and negative temperature characteristic coefficient feature, therefore LED adopts constant current to drive to ensure the constant of its luminosity usually.

Because single LEDs power is less, for meet illumination requirement usually needs light plurality of LEDs simultaneously.This just needs to adopt series-parallel connection method to be combined by plurality of LEDs.For ensureing that LED luminance is consistent, these LED strip have joined and have been used as load by the simplest method exactly, when adopting this structure, although circuit structure is simple, and without equal flow problem, but whole circuit will be caused to work when one of them LED damages, and when power output is larger, the voltage exported also can be very high, is unfavorable for the safety ensureing circuit.Therefore usually adopt the series-parallel mixed structure of LED multi-path for the LED that power is larger, adopt this structure easily to realize high-power output, reliability is also higher.But due to the characteristic of LED negative temperature coefficient and the discreteness of conduction voltage drop, even if the pressure drop on each string LED is equal, electric current in each LED strip also has larger difference, cause the luminous intensity of each paths of LEDs different, even produce overcurrent, therefore need to adopt current-sharing measure to realize flowing through the equilibrium of each LED strip electric current.Current-sharing measure is active current-sharing and passive current-sharing two kinds usually.Active current share scheme, all there is relatively independent constant-current control circuit in each branch road, therefore current-sharing is effective, but need to use more components and parts, and cost is higher, and control circuit is also relatively complicated.Passive current share scheme utilizes the passive devices such as electric capacity, transformer (coupling inductance), magnetic amplifier to realize the current-sharing of multiple-channel output, and have circuit structure simple, cost is lower, and efficiency is advantages of higher comparatively.

Along with promoting the use of of LED, also more and more extensive to the needs of LED dimmer application.LED light modulation can energy savings, regulates spatial vision effect, can also extend the useful life of LED simultaneously, improves the reliability of LED.

Summary of the invention

In view of this, the object of the invention is the LED drive power and the light-dimming method that propose the output of a kind of multi-path flow equalizing, circuit structure is simple, and constant-current characteristics is good, and current-sharing precision is high, achieves the level and smooth brightness adjustment control to LED simultaneously.

Circuit of the present invention adopts following scheme to realize: the LED drive power that a kind of multi-path flow equalizing exports, and comprises the switching network module, LCL-nT type resonant network, commutated network and the LED load unit that are connected successively; Wherein said switching network comprises two the first brachium pontis be in parallel and the second brachium pontis, and wherein the second brachium pontis is as phase shift brachium pontis, and in order to realize wide region brightness adjustment control, described load unit comprises the LED load that the current-sharing of n road exports.

Further, described LCL-nT type resonant network comprises capacitance C _s1, capacitance C _s2, resonant inductance L _r1, resonant inductance L _r2, resonant capacitance C _r, and n inductance L _k1to L _kn; Described capacitance C _s1one end, capacitance C _s2one end be connected to the mid point of two brachium pontis in described switching network, described capacitance C respectively _s1the other end, capacitance C _s2the other end be connected to described resonant inductance L respectively _r1one end, resonant inductance L _r2one end, described resonant inductance L _r1the other end, resonant inductance L _r2the other end is connected and is connected to described resonant capacitance C _rone end, described resonant capacitance C _rthe other end be connected to one of them parallel connected end of two brachium pontis in described switching network, a described n inductance L _k1to L _knbe connected in parallel on described resonant capacitance C respectively respectively with after n transformer series _rtwo ends.

Further, described commutated network comprises 2n rectifier diode, the anode of a described 2n rectifier diode is connected with the Same Name of Ends of n transformer secondary of described LCL-nT type resonant network, different name end respectively, and two rectifier diodes be wherein connected with the secondary of the n-th transformer are D _n1, D _n2; The secondary of a described n transformer is connected to the load of n paths of LEDs respectively after rectifies.

Preferably, when circuit working is in constant current frequency, the current effective value in the load of described n paths of LEDs is:

$I_O=\left|\frac{8\left(\frac{n_1}{n_2}\right){\mathrm{\ω}}_0{C}_s{U}_{dc}}{{\mathrm{\π}}^2\[{{\mathrm{\ω}}_0}^4{L}_k{L}_r{C}_r{C}_s-{{\mathrm{\ω}}_0}^2(L_k{C}_r+2L_k{C}_s+L_r{C}_s)+n\]}\right|;$

Wherein, U _dcthe effective value of input direct voltage, L _r1=L _r2=L _r, C _s1=C _s2=C _s, L _k1=L _k2==L _kn=L _k, n ₁, n ₂be respectively n the transformer primary secondary number of turn.

Light-dimming method of the present invention adopts following scheme: the light-dimming method of the LED drive power that a kind of multi-path flow equalizing as described above exports specifically comprises the following steps:

Step S1: obtain the asynchronous ac equivalent circuit figure of two-phase sequential, comprise two branch roads in parallel, the first branch road comprises the equivalent source of series connection capacitance C _s1, resonant inductance L _r1, the second branch road comprises the equivalent source of series connection capacitance C _s2, resonant inductance L _r2; Two branch roads of described parallel connection and described resonant capacitance C _rparallel connection, described resonant capacitance C _rone end and L _k1to L _knequivalent inductance L _kone end be connected, described resonant capacitance C _rthe other end be connected with one end of equivalent load Z, described equivalent inductance L _kthe other end be connected with the other end of described equivalent load Z;

${\stackrel{\·}{U}}_1=U_{m}sin\left({\mathrm{\ω}}_{0}t\right)$

Step S2: establish wherein U _mfor the amplitude of LCL-nT type resonant network input voltage fundametal compoment, and

Step S3: the electric current obtained on equivalent load Z is:

The effective value obtaining output current is:

Wherein, A be only with described capacitance C _s1, capacitance C _s2, equivalent source equivalent source resonant inductance L _r1, resonant inductance L _r2, resonant capacitance C _r, equivalent inductance L _krelevant parameter;

Step S4: change described phase shift brachium pontis phase place, namely change at [0, π] size, make the output current I of circuit _ofrom being fully loaded with smooth change to zero, namely make the level and smooth light modulation of circuit realiration gamut.

Compared with prior art, the present invention has following beneficial effect:

1, the present invention is directed to high-power LED illumination application scenario propose a kind of two be in parallel LCL-nT type multi-path flow equalizing export controlled resonant converter topological structure, can be implemented in the constant and balanced of multichannel different LED modulating voltage Xia Ge road output current, have that circuit structure is simple, constant-current characteristics good and current-sharing precision high.

2, the present invention is in parallel on the basis of LCL-nT type controlled resonant converter two, propose a kind of phase shift brightness adjustment control strategy, be in parallel one in brachium pontis as phase shift light modulation brachium pontis using two, the output current of converter is regulated by the phase shifting angle changing two brachium pontis, achieve the level and smooth brightness adjustment control to LED, there is the advantages such as light modulation precision is high, dimming scope is wide.

Accompanying drawing explanation

Fig. 1 is schematic block circuit diagram of the present invention.

Fig. 2 is the work wave schematic diagram of each state of converter of the present invention.

Fig. 3 is LCL-nT type controlled resonant converter ac equivalent circuit of the present invention.

The relation curve of output current and operating frequency when Fig. 4 is load of the present invention difference.

Fig. 5 is n road of the present invention transformers connected in parallel equivalent electric circuit.

Fig. 6 is the asynchronous ac equivalent circuit figure of two-phase sequential of the present invention.

Fig. 7 is the present invention output current I during change _ochange curve.

Embodiment

Below in conjunction with drawings and Examples, the present invention will be further described.

As shown in Figure 1, present embodiments provide the LED drive power that a kind of multi-path flow equalizing exports, comprise the switching network module, LCL-nT type resonant network, commutated network and the LED load unit that are connected successively; Wherein said switching network comprises two the first brachium pontis be in parallel and the second brachium pontis, and wherein the second brachium pontis is as phase shift brachium pontis, and in order to realize wide region brightness adjustment control, described load unit comprises the LED load that the current-sharing of n road exports.

In the present embodiment, described LCL-nT type resonant network comprises capacitance C _s1, capacitance C _s2, resonant inductance L _r1, resonant inductance L _r2, resonant capacitance C _r, and n inductance L _k1to L _kn; Described capacitance C _s1one end, capacitance C _s2one end be connected to the mid point of two brachium pontis in described switching network, described capacitance C respectively _s1the other end, capacitance C _s2the other end be connected to described resonant inductance L respectively _r1one end, resonant inductance L _r2one end, described resonant inductance L _r1the other end, resonant inductance L _r2the other end is connected and is connected to described resonant capacitance C _rone end, described resonant capacitance C _rthe other end be connected to one of them parallel connected end of two brachium pontis in described switching network, a described n inductance L _k1to L _knbe connected in parallel on described resonant capacitance C respectively respectively with after n transformer series _rtwo ends.

In the present embodiment, described commutated network comprises 2n rectifier diode, the anode of a described 2n rectifier diode is connected with the Same Name of Ends of n transformer secondary of described LCL-nT type resonant network, different name end respectively, and two rectifier diodes be wherein connected with the secondary of the n-th transformer are D _n1, D _n2; The secondary of a described n transformer is connected to the load of n paths of LEDs respectively after rectifies.

Especially, in the present embodiment, when in converter two be in parallel the drive singal of brachium pontis identical time, work wave is as shown in Figure 2.The course of work can be divided into 6 states, as follows to each state analysis: u in figure _gsbe two driving voltage waveform being in parallel LCL-nT type multiple-channel output controlled resonant converter, the complementary signal fixing by a pair Dead Time forms, and drive singal Q1 is the drive waveforms of upper pipe S1, and drive singal Q2 is the drive waveforms of lower pipe S2; u _dS2for the half-bridge midpoint voltage of inversion module, namely descend the voltage of pipe S2 drain electrode, source electrode; i _dfor flowing through the electric current of switching tube, wherein i _d1for flowing through the electric current of upper pipe S1, i _d2for flowing through the electric current of lower pipe S2; i _lrfor flowing through resonant inductance L _relectric current; i _dfor flowing through the electric current of secondary side diode, wherein i _dn1for flowing through diode D _n1electric current, i _dn2for flowing through diode D _n2electric current; i _tpfor flowing through the electric current of transformer primary side.Below each operating state is analyzed:

1) t ₀< t < t ₁: t=t ₀time, switching tube S2 conducting, capacitance C _sthe voltage at two ends is added in the input of resonant tank.After S2 conducting in very short a period of time, resonant inductance L _relectric current complete oppositely; Flow through inductance L _kcurrent i _lKwith the current i flowing through transformer primary side _tpdirection all do not change, secondary rectifier diode D _n2conducting, D _n1cut-off; This stage is due to i _lKthe rate of decay compare i _tpwant slow, so the current i on magnetizing inductance _mincrease gradually, and work as i _tpwhen being reduced to zero, i _mincrease to maximum, circuit enters next stage.

2) t ₁< t < t ₂: t=t ₁time, primary side current of transformer i _tpdrop to 0 and start oppositely, the electric current of transformer secondary is thereupon reverse, rectifier diode D _n2turn off because bearing back-pressure, D _n1conducting thereupon, realize direct current and export, and electric current wherein rises to maximum gradually, this stage switch network is still S2 and is in on-state, continues by C _sthe voltage at two ends provides voltage to resonant tank; I in this stage _lK, i _tpreduce gradually under the effect of reverse voltage, at t ₂moment intersects at a point, i.e. i _mbe reduced to zero, now circuit enters next stage.

3) t ₂< t < t ₃: t=t ₂time, switching tube S2 turns off, resonant inductance L _ron current i _lrdirection is constant, the current i on switching tube S2 _d2direction is constant, the current i on S1 _d1oppositely, illustrate that the parasitic capacitance of S2 starts charging, the parasitic capacitance of S1 starts electric discharge, and after a period of time, the terminal voltage of S2 rises to maximum V _d, namely the terminal voltage of S1 parasitic capacitance is by resonance current i _lrreverse charging is to zero, and i _lrnow be less than 0, therefore i _d1for flowing through the electric current of the parasitic diode of S1, therefore to achieve no-voltage open-minded for S1;

4) t ₃< t < t ₄: t=t ₃time, switching tube S1 is open-minded, and input voltage is added in the input of resonant tank, resonant inductance L _rcurrent i _lrwith the current i on switching tube S1 _d1direction changes within very short time.Now i _lKand i _tpdirection be still oppositely, so the rectifier bridge of secondary is still D _n1conducting; Due to i _tpthe speed of reverse reduction is faster, so transformer magnetizing current i _mcontinue oppositely to increase, work as i _tpwhen being oppositely reduced to zero, i _mincrease to reverse maximum, circuit enters next stage.

5) t ₄< t < t ₅: t=t ₄time, switching tube S1 continues conducting, primary side current of transformer i _tpincrease to 0 and start oppositely, the electric current of transformer secondary is thereupon reverse, rectifier diode D _n1turn off, D _n2open-minded, and electric current wherein rises to maximum gradually; I in this stage _lK, i _tpincrease gradually under the effect of forward voltage, at t ₅moment intersects at a point, i.e. i _mbe increased to zero, now circuit enters next stage.

6) t ₅< t < t ₆: t=t ₅time, switching tube S1 turns off, resonant inductance L _rthe sense of current constant, the sense of current of switching tube S1 is constant, and reverse electric current appears in S2, and show that the parasitic capacitance of S1 starts charging, the parasitic capacitance of S2 starts electric discharge, and after a period of time, the voltage at S2 two ends is by resonance current i _lrreverse charging is to zero, and i _lrnow be greater than 0, therefore i _d2for flowing through the electric current of the body diode of S2, open for S2 realizes no-voltage the condition of creating.

T ₁-t ₆be two complete cycles being in parallel LCL-T type multiple-channel output controlled resonant converter.

In the present embodiment, suppose that primary current only has fundametal compoment to transmit energy to secondary, ignore the effect of other harmonic components, and C in resonant network _s1=C _s2=C _s, L _r1=L _r2=L _r, L _k1=L _k2==L _kn=L _k, L _m1=L _m2==L _mn=L _mand Z ₁=Z ₂==Z _n=Z, obtains LCL-nT type resonant network ac equivalent circuit as shown in Figure 3 thus.

In Fig. 3, U is the fundametal compoment effective value of resonant tank input voltage, U _outthe fundametal compoment effective value of equivalence to the output voltage of transformer primary side, L _r, L _k, C _rbe respectively resonant inductance and resonant capacitance, C _sfor capacitance, L _mfor static exciter inductance, Z is load equivalent resistance, supposes that the component parameters of each road parallel connection is consistent, then has in formula, n ₁, n ₂be respectively n the transformer primary secondary number of turn, U _dcit is the effective value of input direct voltage.

According to the current effective value that Fig. 3 can obtain on equivalent load Z/n be:

$I_{Zn}=\frac{2{\mathrm{nUX}}_{Lm}{X}_{Cr}}{AZ+jB}$

A＝(X _Lr+X _Cs)(X _Lm+X _Lk+nX _Cr)+2X _Cr(X _Lm+X _Lk)

B＝X _Lm[(X _Lr+X _Cs)(X _Lk+nX _Cr)+2X _LkX _Cr](1)

Known when A identically vanishing, when input voltage is fixed, the size of load current only with capacitance C _s, resonant inductance L _r, L _kwith resonant capacitance C _rrelating to parameters, and to have nothing to do with the size of load.Then have:

ω ₀ ⁴(L _m+L _k)L _rC _rC _s-ω ₀ ²[(L _m+L _k)(C _r+2C _S)+nL _rC _s]+n＝0(2)

When circuit working is in constant current frequency, the current effective value in described n road load is:

$I_O=\left|\frac{8\left(\frac{n_1}{n_2}\right){\mathrm{\&omega;}}_0{C}_s{U}_{dc}}{{\mathrm{\&pi;}}^2\&lsqb;{{\mathrm{\&omega;}}_0}^4{L}_r{C}_r{C}_s-{{\mathrm{\&omega;}}_0}^2({\mathrm{LC}}_r+2L_k{C}_s+L_r{C}_s)+n\&rsqb;}\right|---\left(3\right);$

Wherein, U _dcthe effective value of input direct voltage, L _r1=L _r2=L _r, C _s1=C _s2=C _s, L _k1=L _k2==L _kn=L _k, n ₁, n ₂be respectively n the transformer primary secondary number of turn.

As shown in Figure 4, when load resistance is respectively 10 Ω, when 20 Ω, 30 Ω, 40 Ω, 50 Ω, output current with frequency change curve as shown in Figure 4, can find out constant current operation frequency place and near the frequency band of certain limit, load resistance changes to 50 Ω from 10 Ω, and its output current is almost equal, circuit working, within the scope of this band frequency, all can realize constant current and drive.

In the present embodiment, additionally provide current-sharing specificity analysis, as shown in Figure 5, be n road Parallel opertation equivalent electric circuit, the equivalent inpnt voltage in Parallel opertation loop is suppose that in the output of n road, maximum equivalent output current is minimum equivalent output current is maximum equal stream error is ξ, and the maximum unbalanced degree of load is δ (namely when load imbalance degree is maximum, Zb=δ Za, wherein δ>=1).

As Qu Ge road resonant inductance L _k1, L _k2... L _knequal, each road static exciter inductance L _m1, L _m2... L _mnall equal, when load impedance Z does not wait, in branch road, minimum and maximum equivalent current is respectively:

${\stackrel{\&CenterDot;}{I}}_a=\frac{{\stackrel{\&CenterDot;}{U}}_{Cr}}{{\mathrm{jX}}_{Lk}+Z_a//{\mathrm{jX}}_{Lm}}\&CenterDot;\frac{{\mathrm{jX}}_{Lm}}{Z_a+{\mathrm{jX}}_{Lm}}=\frac{{\stackrel{\&CenterDot;}{U}}_{Cr}}{Z_a(1+\frac{X_{Lk}}{X_{Lm}})+{\mathrm{jX}}_{Lk}}---\left(4\right)$

${\stackrel{\&CenterDot;}{I}}_b=\frac{{\stackrel{\&CenterDot;}{U}}_{Cr}}{{\mathrm{jX}}_{Lk}+z_b//{\mathrm{jX}}_{Lm}}\&CenterDot;\frac{{\mathrm{jX}}_{Lm}}{Z_b+{\mathrm{jX}}_{Lm}}=\frac{{\stackrel{\&CenterDot;}{U}}_{Cr}}{Z_b(1+\frac{X_{Lk}}{X_{Lm}})+{\mathrm{jX}}_{Lk}}---\left(5\right)$

Then in each branch road, the equal stream error of maximum output current is

$\frac{\left|{\stackrel{\&CenterDot;}{I}}_a\right|-\left|{\stackrel{\&CenterDot;}{I}}_b\right|}{\left|{\stackrel{\&CenterDot;}{I}}_a\right|}\&le;\mathrm{\&xi;}---\left(6\right)$

Can be obtained by formula (4), formula (5), formula (6)

$Z_b\&le;\mathrm{\&delta;}\sqrt{\frac{\&lsqb;1-{(1-\mathrm{\&xi;})}^2\&rsqb;X_{Lk}^2}{\&lsqb;{(1-\mathrm{\&xi;})}^2{\mathrm{\&delta;}}^2-1\&rsqb;{(1+\frac{X_{Lk}}{X_{Lm}})}^2}}---\left(7\right)$

Wherein, Z _bfor the maximum equivalent load that can allow when circuit meets equal stream error.

From formula (7), the equal stream error of output current is only relevant with the unbalanced degree of load, the unbalanced degree of load is larger, then the equal stream error of output current is larger, if but choose load in setting range, export equal stream error and just can control in the scope of maximum equal stream error ξ.

The light-dimming method that the present embodiment additionally provides the LED drive power that a kind of multi-path flow equalizing as described above exports specifically comprises the following steps:

Step S1: obtain the asynchronous ac equivalent circuit figure of two-phase sequential, as shown in Figure 6, comprise two branch roads in parallel, the first branch road comprises the equivalent source of series connection capacitance C _s1, resonant inductance L _r1, the second branch road comprises the equivalent source of series connection capacitance C _s2, resonant inductance L _r2; Two branch roads of described parallel connection and described resonant capacitance C _rparallel connection, described resonant capacitance C _rone end and L _k1to L _knequivalent inductance L _kone end be connected, described resonant capacitance C _rthe other end be connected with one end of equivalent load Z, described equivalent inductance L _kthe other end be connected with the other end of described equivalent load Z;

${\stackrel{\&CenterDot;}{U}}_1=U_{m}sin\left({\mathrm{\&omega;}}_{0}t\right)$

Step S2: establish wherein U _mfor the amplitude of LCL-nT type resonant network input voltage fundametal compoment, and

Step S3: the electric current obtained on equivalent load Z is:

The effective value obtaining output current is:

Wherein, A be only with described capacitance C _s1, capacitance C _s2, equivalent source equivalent source resonant inductance L _r1, resonant inductance L _r2, resonant capacitance C _r, equivalent inductance L _krelevant parameter;

Step S4: change described phase shift brachium pontis phase place, namely change at [0, π] size, make the output current I of circuit _ofrom being fully loaded with smooth change to zero, namely make the level and smooth light modulation of circuit realiration gamut.Obtain output current value I and phase shifting angle between graph of relation, as shown in Figure 7.As can be seen from the figure, when when changing between [0, π], output current I _ochange to zero from being fully loaded with, and the change curve of electric current is level and smooth substantially, circuit can realize the level and smooth light modulation of gamut.

The foregoing is only preferred embodiment of the present invention, all equalizations done according to the present patent application the scope of the claims change and modify, and all should belong to covering scope of the present invention.

Claims (5)

1. a LED drive power for multi-path flow equalizing output, is characterized in that: comprise the switching network module, LCL-nT type resonant network, commutated network and the LED load unit that are connected successively; Wherein said switching network comprises two the first brachium pontis be in parallel and the second brachium pontis, and wherein the second brachium pontis is as phase shift brachium pontis, and in order to realize wide region brightness adjustment control, described load unit comprises the LED load that the current-sharing of n road exports.

2. the LED drive power of a kind of multi-path flow equalizing output according to claim 1, is characterized in that: described LCL-nT type resonant network comprises capacitance C _s1, capacitance C _s2, resonant inductance L _r1, resonant inductance L _r2, resonant capacitance C _r, and n inductance L _k1to L _kn; Described capacitance C _s1one end, capacitance C _s2one end be connected to the mid point of two brachium pontis in described switching network, described capacitance C respectively _s1the other end, capacitance C _s2the other end be connected to described resonant inductance L respectively _r1one end, resonant inductance L _r2one end, described resonant inductance L _r1the other end, resonant inductance L _r2the other end is connected and is connected to described resonant capacitance C _rone end, described resonant capacitance C _rthe other end be connected to one of them parallel connected end of two brachium pontis in described switching network, a described n inductance L _k1to L _knbe connected in parallel on described resonant capacitance C respectively respectively with after n transformer series _rtwo ends.

3. the LED drive power of a kind of multi-path flow equalizing output according to claim 1, it is characterized in that: described commutated network comprises 2n rectifier diode, the anode of a described 2n rectifier diode is connected with the Same Name of Ends of n transformer secondary of described LCL-nT type resonant network, different name end respectively, and two rectifier diodes be wherein connected with the secondary of the n-th transformer are D _n1, D _n2; The secondary of a described n transformer is connected to the load of n paths of LEDs respectively after rectifies.

4. the LED drive power that the multi-path flow equalizing described in any one claim according to claim 1,2 or 3 exports, is characterized in that: when circuit working is in constant current frequency, the current effective value in the load of described n paths of LEDs is:

$I_O=\left|\frac{8\left(\frac{n_1}{n_2}\right){\mathrm{\&omega;}}_0{C}_s{U}_{dc}}{{\mathrm{\&pi;}}^2\&lsqb;{{\mathrm{\&omega;}}_0}^4{L}_k{L}_r{C}_r{C}_s-{{\mathrm{\&omega;}}_0}^2(L_k{C}_r+2L_k{C}_s+{\mathrm{nL}}_r{C}_s)+n\&rsqb;}\right|;$

Wherein, U _dcthe effective value of input direct voltage, L _r1=L _r2=L _r, C _s1=C _s2=C _s, L _k1=L _k2==L _kn=L _k, n ₁, n ₂be respectively n the transformer primary secondary number of turn.

5. a light-dimming method for the LED drive power that the multi-path flow equalizing as described in claim 1,2 or 3 exports, is characterized in that comprising the following steps:

Step S1: obtain the asynchronous ac equivalent circuit figure of two-phase sequential, comprise two branch roads in parallel, the first branch road comprises the equivalent source of series connection capacitance C _s1, resonant inductance L _r1, the second branch road comprises the equivalent source of series connection capacitance C _s2, resonant inductance L _r2; Two branch roads of described parallel connection and described resonant capacitance C _rparallel connection, described resonant capacitance C _rone end and L _k1to L _knequivalent inductance L _kone end be connected, described resonant capacitance C _rthe other end be connected with one end of equivalent load Z, described equivalent inductance L _kthe other end be connected with the other end of described equivalent load Z;

${\stackrel{\&CenterDot;}{U}}_1=U_{m}sin\left({\mathrm{\&omega;}}_{0}t\right)$

Step S2: establish wherein U _mfor the amplitude of LCL-nT type resonant network input voltage fundametal compoment, and

Step S3: the electric current obtained on equivalent load Z is:

The effective value obtaining output current is:

Wherein, A be only with described capacitance C _s1, capacitance C _s2, equivalent source equivalent source resonant inductance L _r1, resonant inductance L _r2, resonant capacitance C _r, equivalent inductance L _krelevant parameter;

Step S4: change described phase shift brachium pontis phase place, namely change at [0, π] size, make the output current I of circuit _ofrom being fully loaded with smooth change to zero, namely make the level and smooth light modulation of circuit realiration gamut.