CN104202862A - Single-stage type LED drive power supply without electrolytic capacitor - Google Patents

Abstract

The invention discloses a single-stage type LED drive power supply without an electrolytic capacitor. The single-stage type LED drive power supply without the electrolytic capacitor is an AC/DC converter in essence, and the single-stage type LED drive power supply without the electrolytic capacitor is composed of an input filter rectification circuit, a fly-back primary switch circuit, an auxiliary winding full-bridge bidirectional circuit and a secondary rectification filter circuit. The single-stage type LED drive power supply without the electrolytic capacitor realizes the power factor correction through fixing the duty ratio of a main switch MOS tube Q1 and works in a current discontinuous mode to avoid the reverse recovery of a secondary diode QR; the main circuit thereof is a fly-back converter which is composed of the part 1, part 2 and part 4, an isolating transformer of the fly-back converter is provided with a winding, the auxiliary winding side uses a bidirectional power flow full-bridge converter to balance the instantaneous pulse difference between the input power and the output power, and the capacitance of an auxiliary energy storage capacitor is reduced through increasing the average voltage and voltage pulse of the auxiliary energy storage capacitor; the single-stage type LED drive power supply without the electrolytic capacitor removes double power frequency alternating current component of the output current, reduces the output filter capacitor capacitance and realizes the small volume and long service life, and the electrolytic capacitor can be substituted by a film capacitor; the output current of the LED drive power supply is constant current.

Description

A kind of single stage type no electrolytic capacitor LED driving power

Technical field:

The present invention relates to a kind of single stage type no electrolytic capacitor LED driving power, it belongs to especially LED driving power application of Switching Power Supply.

Background technology:

Along with the develop rapidly of human society, energy-consuming demand increases sharply, and energy crisis is day by day serious.Solve energy crisis and mainly contain two approach, one of approach is exploitation regenerative resource, reduces the dependence to traditional fossil energy; Another approach is to seek new power-saving technology, reduces the consumption of the energy, improves the utilization ratio of the energy.Wherein illumination is the importance that the mankind consume the energy, and traditional illuminating product is as incandescent lamp, fluorescent lamp, and high-pressure sodium lamps etc., exist the serious problems that power consumption rate is low.Therefore reduce the needed electric energy of illumination, will be conducive to reduce global energy consumption.In recent years, green energy conservation illumination has become the major issue that countries in the world are paid close attention to, also more and more urgent to the demand of new type light source.

LED (Light Emitting Diode) light-emitting diode relies on the advantages such as its clean and effective, light efficiency is high, the life-span is long, simulating nature light, within several years, has obtained high speed development at this, is widely used in various occasions.One of advantage that LED is very important is that useful life is very long, approximately 30,000～100,000 hours.Tradition LED driving power is 1 o'clock at input power factor, and its input current is to be the sine wave that phase place is identical with its input voltage, and therefore the form of its input power is sinusoidal square.And due to its constant voltage load characteristic and need constant current drive, therefore its power output is straight.So its driving power needs the storage capacitor that capacitance is very large to come balanced input power and power output, this storage capacitor adopts electrochemical capacitor more.And the life-span of electrochemical capacitor generally only has 5000 hours, the life-span of LED body has 100000 hours, and working life between the two differs greatly, and therefore electrochemical capacitor is the key factor in restriction LED driving power life-span.And electrochemical capacitor volume is larger, affect the further raising of driving power power density.For this reason, need to remove the electrochemical capacitor in LED driving power.

Summary of the invention:

The object of the present invention is to provide a kind of single stage type no electrolytic capacitor LED driving power, because LED driving power power is less, and output voltage is lower, adopt the anti exciting converter simple in structure main circuit as power factor correction, by increase an auxiliary winding on the isolating transformer of anti exciting converter, auxiliary winding side adopts to and fro flow of power full-bridge converter to carry out the poor of the instantaneous pulsation of balance input and output power, makes output filter capacitor can adopt the thin-film capacitor that capacitance is less.

The present invention adopts following technical scheme: a kind of single stage type no electrolytic capacitor LED driving power, it comprises input filter rectification circuit, the former limit of flyback switching circuit, auxiliary winding full-bridge two-way circuit, secondary current rectifying and wave filtering circuit and isolating transformer.

Further, isolating transformer T ₁formed by a former limit winding and two secondary windings, comprise isolating transformer T ₁former limit inductance L _mand leakage inductance;

The filter circuit of input filter rectification circuit 1 is by input filter inductance L ₁with input filter capacitor C ₁be connected in parallel on electrical network input two ends composition, the rectifying part of input filter rectification circuit 1 adopts four diode D ₁, D ₂, D ₃, D ₄the full-bridge of composition not control rectifying circuit is connected in parallel on filter circuit two ends;

The former limit of flyback switching circuit 2 is by isolating transformer T ₁the different name end of former limit winding and main switch metal-oxide-semiconductor Q ₁drain electrode be connected to form, main switch metal-oxide-semiconductor Q ₁comprise its parasitic diode and parasitic capacitance;

Auxiliary winding full-bridge two-way circuit 3 is by first, second auxiliary IGBT pipe Q _s1, Q _s2and first, second auxiliary MOS transistor Q _s3, Q _s4, first, second booster diode D _s1, D _s2and auxiliary energy storage capacitor C _bcomposition, wherein the first auxiliary IGBT pipe Q _s1with the first booster diode D _s1and the first auxiliary MOS transistor Q _s3series connection successively, the second auxiliary IGBT pipe Q _s2with the second booster diode D _s2and the second auxiliary MOS transistor Q _s4two brachium pontis parallel connections of composition after series connection successively, and be connected in parallel on isolating transformer T ₁second secondary winding two ends, isolating transformer T ₁the different name end of second secondary winding and first, second auxiliary IGBT pipe Q _s1, Q _s2collector electrode be connected, Same Name of Ends and first, second auxiliary MOS transistor Q _s3, Q _s4source class be connected, auxiliary energy storage capacitor C _bone end be connected in the first auxiliary IGBT pipe Q _s1with the first booster diode D _s1mid point, the other end is connected in the second auxiliary IGBT pipe Q _s2with the second booster diode D _s2mid point, first, second auxiliary IGBT pipe Q _s1, Q _s2each self-contained its parasitic capacitance, first, second auxiliary MOS transistor Q _s3, Q _s4each self-contained its parasitic diode and parasitic capacitance;

Secondary current rectifying and wave filtering circuit 4 is by rectifier diode D _r, rectification metal-oxide-semiconductor Q _rand output filter capacitor C ₂with output inductor L ₂composition, isolating transformer T ₁the different name end of first secondary winding is connected in rectifier diode D _ranode, rectifier diode D _rwith rectification metal-oxide-semiconductor Q _r, output inductor L ₂after series connection, be connected in the positive output end of LED load, isolating transformer T ₁the Same Name of Ends of first secondary winding is connected with the negative output terminal of LED load, output filter capacitor C ₂be parallel to rectification metal-oxide-semiconductor Q _rsource class and the negative output terminal of LED load between, rectification metal-oxide-semiconductor Q _rcomprise its parasitic diode and parasitic capacitance.

The present invention has following beneficial effect:

(1) adopt fixing main switch metal-oxide-semiconductor Q ₁mode realize power factor correction;

(2) converter is operated in discontinuous mode, has avoided the reverse recovery of secondary diode; The isolating transformer of anti exciting converter increases a winding, auxiliary winding side adopts to and fro flow of power full-bridge converter to carry out the poor of balance input and output power pulsations, reduce auxiliary capacitor capacitance size by the average voltage and the mains ripple that increase auxiliary energy storage electric capacity, remove the twice industrial frequency AC component of the drive current in LED driving power, reduce output filter capacitor capacitance size, make it replace electrochemical capacitor with thin-film capacitor, realize volume little, the long-life;

(3) auxiliary circuit increasing does not affect main circuit work, and auxiliary circuit is only processed the poor of input and output instantaneous power pulsation;

(4) output current of LED driving power is constant current, is applicable to need the LED driving power application scenario of constant current output.

Brief description of the drawings:

Fig. 1 is the structural representation of single stage type no electrolytic capacitor LED driving power of the present invention.

Fig. 2 is the main waveform schematic diagram of single stage type no electrolytic capacitor LED driving power.

Fig. 3-Fig. 7 is the equivalent circuit structure schematic diagram of each switch mode.

Main designation in above-mentioned accompanying drawing: v _in-line voltage; L ₁-input filter inductance; C ₁-input filter capacitor; D ₁, D ₂, D ₃, D ₄-diode; Q ₁-main switch metal-oxide-semiconductor; Q _s1the-the first auxiliary IGBT pipe; Q _s2the-the second auxiliary IGBT pipe; Q _s3the-the first auxiliary MOS transistor; Q _s4the-the second auxiliary MOS transistor; D _s1the-the first booster diode; D _s2the-the second booster diode; C _b-auxiliary energy storage electric capacity; T ₁-isolating transformer; D _r-rectifier diode; Q _r-rectification metal-oxide-semiconductor; C ₂-output filter capacitor; L ₂-output inductor; V _o-output voltage; I _o-output current; C _b-auxiliary energy storage electric capacity; p _in-input power; p _o-power output; p _ripit is poor that-input power and power output instantaneous power are pulsed; T _line-power frequency period; L _m-former limit inductance; i _s2electric current on-the second secondary winding; i _s1electric current on-first secondary winding; i _in-electrical network input current; i _p-transformer T ₁primary current; v _cb-auxiliary energy storage electric capacity both end voltage; v _aBvoltage between-A point and B point.

Embodiment:

Please refer to shown in Fig. 1, single stage type no electrolytic capacitor LED driving power of the present invention is made up of input filter rectification circuit 1, the former limit of flyback switching circuit 2, auxiliary winding full-bridge two-way circuit 3, secondary current rectifying and wave filtering circuit 4.Its main circuit is the anti exciting converter of 1,2,4 part compositions.

Isolating transformer T ₁formed by a former limit winding and two secondary windings, comprise former limit inductance (being produced by self-induction) and leakage inductance.The filter circuit of input filter rectification circuit 1 is by input filter inductance L ₁with input filter capacitor C ₁be connected in parallel on electrical network input two ends composition, rectifying part adopts four diode D ₁, D ₂, D ₃, D ₄the full-bridge of composition not control rectifying circuit is connected in parallel on filter circuit two ends.The former limit of flyback switching circuit 2 is by isolating transformer T ₁the different name end of former limit winding and main switch metal-oxide-semiconductor Q ₁drain electrode be connected to form.Main switch metal-oxide-semiconductor Q ₁comprise its parasitic diode and parasitic capacitance.The composition of auxiliary winding full-bridge two-way circuit 3 is, by the first auxiliary IGBT pipe Q _s1with the first booster diode D _s1and the first auxiliary MOS transistor Q _s3series connection successively, the second auxiliary IGBT pipe Q _s2with the second booster diode D _s2and the second auxiliary MOS transistor Q _s4two brachium pontis parallel connections of composition after series connection successively, and be connected in parallel on isolating transformer T ₁second secondary winding two ends.Isolating transformer T ₁the different name end of second secondary winding and first, second auxiliary IGBT pipe Q _s1, Q _s2collector electrode be connected, Same Name of Ends and first, second auxiliary MOS transistor Q _s3, Q _s4source class be connected.Auxiliary energy storage capacitor C _bone end be connected in the first auxiliary IGBT pipe Q _s1with the first booster diode D _s1mid point, the other end is connected in the second auxiliary IGBT pipe Q _s2with the second booster diode D _s2mid point.First, second auxiliary IGBT pipe Q _s1, Q _s2each self-contained its parasitic capacitance, first, second auxiliary MOS transistor Q _s3, Q _s4each self-contained its parasitic diode and parasitic capacitance.

Secondary current rectifying and wave filtering circuit 4 is by rectifier diode D _r, rectification metal-oxide-semiconductor Q _rand output filter capacitor C ₂with output inductor L ₂composition.Isolating transformer T ₁the different name end of first secondary winding is connected in rectifier diode D _ranode.Rectifier diode D _rwith rectification metal-oxide-semiconductor Q _r, output inductor L ₂after series connection, be connected in the positive output end of LED load.Isolating transformer T ₁the Same Name of Ends of first secondary winding is connected with the negative output terminal of LED load.Output filter capacitor C ₂be parallel to rectification metal-oxide-semiconductor Q _rsource class and the negative output terminal of LED load between.Rectification metal-oxide-semiconductor Q _rcomprise its parasitic diode and parasitic capacitance.

Electric main process is by input filter inductance L ₁with input filter capacitor C ₁the filter circuit of composition connects by diode D ₁, D ₂, D ₃, D ₄the rectifier bridge of composition, its anodal and isolating transformer T ₁the Same Name of Ends of former limit winding is connected.Isolating transformer T ₁the different name end of former limit winding connects main switch metal-oxide-semiconductor Q ₁drain electrode, main switch metal-oxide-semiconductor Q ₁source class be connected with rectifier bridge negative pole.

Auxiliary winding full-bridge two-way circuit 3 is by two auxiliary IGBT pipe Q _s1, Q _s2and two auxiliary MOS transistor Q _s3, Q _s4, two booster diode D _s1, D _s2and auxiliary energy storage capacitor C _bcomposition.Wherein auxiliary energy storage capacitor C _beffect be poor for the pulsation of balance input power and power output.

Isolating transformer T ₁secondary adopt rectifier diode D _rwith rectification metal-oxide-semiconductor Q _rrectification, by output filter capacitor C ₂with output inductor L ₂filtering.

Realize the basic skills of no electrolytic capacitor below in conjunction with the structure of Fig. 1 single stage type no electrolytic capacitor LED driving power and the main waveform schematic view illustrating single stage type no electrolytic capacitor LED driving power of Fig. 2 single stage type no electrolytic capacitor LED driving power.As seen from Figure 2, in the time that power factor is 1, input voltage is identical with input current phase place, and therefore input power is

$p_{\mathrm{in}}=v_{\mathrm{in}}\left(t\right)i_{\mathrm{in}}\left(t\right)=V_m\sin \mathrm{\ωt}\×I_m\sin \mathrm{\ωt}=\frac{V_m{I}_m(1-\cos 2\mathrm{\ωt})}{2}$

V in formula _mfor the effective value of electrical network input voltage, I _mfor the effective value of input current.

Due to the constant voltage load characteristic of LED, and need constant current to drive, therefore power output is straight, is designated as P _o.The efficiency of supposing converter is 100%, and Mean Input Power should equate with power output.Can obtain thus the poor of input power and the pulsation of power output instantaneous power

p _rip＝p _in(t)-P _o＝-P _ocos2ωt (2)

Instantaneous power on auxiliary energy storage electric capacity is equated with the difference of the instantaneous pulsation of input power power output, get final product the poor of balance input power and power output pulsation.At [T _line/ 8,3Tl _ine/ 8] in, auxiliary energy storage capacitor C _bthe energy absorbing is

$\mathrm{\ΔE}={\∫}_{\frac{T_{\mathrm{line}}}{8}}^{\frac{{3T}_{\mathrm{line}}}{8}}[p_{\mathrm{in}}\left(t\right)-p_o]\mathrm{dt}=\frac{P_o}{\mathrm{\ω}}--\left(3\right)$

Auxiliary energy storage electric capacity can also be expressed as at the energy absorbing during this period of time simultaneously

$\mathrm{\ΔE}=\frac{1}{2}{C}_b(V_{c\_\max }^2-V_{c\_\min }^2)---\left(4\right)$

Above two formulas are equal can draw auxiliary energy storage capacitor's capacity size, for

$C_b=\frac{2P_o}{\mathrm{\ω}(V_{c\_\max }^2-V_{c\_\min }^2)}=\frac{P_o}{\mathrm{\ω}\·{\mathrm{\ΔV}}_c\·V_{c\_\mathrm{av}}}---\left(5\right)$

Wherein ω is power frequency angular frequency, Δ V _cfor auxiliary energy storage capacitance voltage pulsating quantity, V _{c_av}for auxiliary energy storage capacitance voltage mean value.As can be seen from the above equation, by increasing Δ V _cand V _{c_av}can make the capacitance of auxiliary energy storage electric capacity significantly reduce.In the present invention, can increase Δ V by the turn ratio of adjusting second secondary winding and former limit winding _cand V _{c_av}, further reduce the size of auxiliary energy storage electric capacity, thereby can replace electrochemical capacitor with the less thin-film capacitor of capacitance.

Type of drive and each mode specific works principle of single stage type no electrolytic capacitor LED driving power are described below in conjunction with the main waveform schematic diagram of Fig. 2 and Fig. 3-7 each switch mode equivalent circuit structure schematic diagram.As shown in Figure 2, this converter mainly contains two mode of operations, is designated as Mode1 in the time that input instantaneous power is greater than output instantaneous power, is designated as Mode2 in the time that output instantaneous power is greater than input instantaneous power.In Mode1, in each switch periods, there are four kinds of switch mode, be respectively [t ₀, t ₁], [t ₁, t ₂], [t ₂, t ₃], [t ₃, t ₄].Below the working condition of each switch mode is made a concrete analysis of.

Before analyzing, make the following assumptions: 1. all switching tubes and diode are desirable device; 2. all inductance, electric capacity and isolating transformer are ideal element; 3. outputting inductance is enough large, can be similar to and think that output is a DC current source I _o, I _ofor output current; 4. because power frequency period is far longer than switch periods, in a switch periods, input voltage v _inapproximate regarding as constantly, is V _msin ω t; Auxiliary energy storage inductance C _bboth end voltage v _cbalso approximate regard as constant.

1. switch mode 1[t ₀, t ₁] (corresponding to Fig. 3)

At t ₀in the moment, open main switch metal-oxide-semiconductor Q ₁, isolating transformer T ₁the different name end of first secondary winding is negative voltage, secondary rectifier diode D _rreverse-biased cut-off, isolating transformer T ₁primary current i _pwith slope v _in/ L _mlinear rising, electric main is to former limit inductive energy storage.L _mfor the size of former limit inductance.Powered to the load by output filter capacitor and output inductor.Through D _yt _safter time, at t ₁moment is turn-offed main switch metal-oxide-semiconductor Q ₁.Wherein D _ymain switch metal-oxide-semiconductor Q ₁duty ratio, T _sit is switch periods.Isolating transformer T ₁the peak value of primary current is

$i_{p\_\mathrm{pk}}=\frac{V_m\left|\sin \mathrm{\ωt}\right|D_y}{L_m{f}_s}---\left(6\right)$

In a switch periods, the mean value of primary current is

$i_{p\_\mathrm{av}}=\frac{1}{2}{i}_{p\_\mathrm{pk}}{D}_y=\frac{V_m\left|\sin \mathrm{\ωt}\right|D_y^2}{2L_m{f}_s}---\left(7\right)$

In formula: f _sfor switching frequency; This shows in half power frequency period, if duty ratio D _yremain unchanged, input current average value is proportional to input voltage, therefore fixes main switch metal-oxide-semiconductor duty ratio, works in discontinuous current pattern and can automatically realize power factor correction.

2. switch mode 2[t ₁, t ₂] (corresponding to Fig. 4)

At t ₁moment is turn-offed main switch metal-oxide-semiconductor Q ₁after, open the first auxiliary IGBT pipe Q _s1with the second auxiliary MOS transistor Q _s4, the second auxiliary IGBT pipe D _s2also conducting, secondary rectification metal-oxide-semiconductor Q _rcut-off, former limit inductance L _menergy is to auxiliary energy storage capacitor C _bcharging, the current i of second secondary winding _s2linear decline.Powered to the load by output filter capacitor and output inductor.When former limit inductance L _mon energy be reduced to while just in time equaling in a switch periods output institute energy requirement, i.e. t ₂in the moment, turn-off the first auxiliary IGBT pipe Q _s1with the second auxiliary MOS transistor Q _s4.

3. switch mode 3[t ₂, t ₃] [corresponding to Fig. 5]

At t ₂moment is turn-offed the first auxiliary IGBT pipe Q _s1with the second auxiliary MOS transistor Q _s4after open secondary rectification MOS pipe Q _r, isolating transformer T ₁first secondary winding different name end is positive voltage, rectifier diode D _rconducting, former limit inductance L _mon Conversion of Energy be that electric field energy is to load and output capacitance C _oelectric discharge, isolating transformer T ₁first secondary winding on current i _s1linear decline, until drop to 0, i.e. t ₃time, this mode finishes.

4. switch mode 4[t ₃, t ₄] [corresponding to Fig. 6]

Isolating transformer T in this mode ₁on winding, electric current is zero, is interrupted mode, and all switching tubes and diode all end.Provide energy by output filter capacitor and output inductor for load.

In Mode2, in each switch periods, there are equally four kinds of switch mode, be respectively [t ₀, t ₁], [t ₁, t ₂], [t ₂, t ₃], [t ₃, t ₄].Wherein [t in Mode2 ₀, t ₁], [t ₁, t ₂], [t ₃, t ₄] [t in mode and Mode1 ₀, t ₁], [t ₁, t ₂], [t ₃, t ₄] mode operation principle is similar, do not repeat them here.

Make a concrete analysis of the switch mode 2[t in lower Mode2 below ₁, t ₂] operation principle of converter when [corresponding to Fig. 7].

At t ₁moment is turn-offed main switch metal-oxide-semiconductor Q ₁after, open the second auxiliary IGBT pipe Q _s2with the first auxiliary MOS transistor Q _s3, the first booster diode D _s1also conducting, secondary rectification metal-oxide-semiconductor Q _rcut-off, auxiliary energy storage capacitor C _bto isolating transformer T ₁former limit inductance L _mcharging, the current i of second secondary winding _s2linear rising.By output filter capacitor and output inductor to LED load supplying.When former limit inductance L _mon energy rise to while just in time equaling in a switch periods output institute energy requirement, i.e. t ₂in the moment, turn-off the second auxiliary IGBT pipe Q _s2with the first auxiliary MOS transistor Q _s3.

Can find out isolating transformer T ₁current i on first secondary winding _s1do not contain twice power frequency component, only contain switching frequency and higher harmonic components, can pass through less filter capacitor and filter inductance by high fdrequency component filtering, obtain straight output current.

Example of the present invention is as follows: input line voltage effective value: V _m=220V; Electrical network work frequency: f _line=50Hz; Output dc voltage: V _o=48V; Output current: I _o=0.7A; Isolating transformer T ₁former limit and first secondary winding no-load voltage ratio: 4; Isolating transformer T ₁former limit and second secondary winding no-load voltage ratio: 1; Former limit inductance: L _m=200uH; Main switch metal-oxide-semiconductor Q ₁, the first auxiliary MOS transistor Q _s3, the second auxiliary MOS transistor Q _s4: IXTP4N80P; The first auxiliary IGBT pipe Q _s1, the second auxiliary IGBT pipe Q _s2: SGP02N60; Secondary rectification metal-oxide-semiconductor Q _r: IRF630; The first booster diode D _s1, the second booster diode D _s2: US5J; Secondary rectifier diode D _r: MBRS3200; Auxiliary energy storage capacitor C _b: 4.7uF/400V; Input filter capacitor C ₁: 0.47uF/400V; Input filter inductance L ₁: 50uH; Output filter capacitor C ₂: 10uF/100V; Output inductor L ₂: 50uH; Switching frequency: f _s=200kHz.

The above is only the preferred embodiment of the present invention, it should be pointed out that for those skilled in the art, can also make under the premise without departing from the principles of the invention some improvement, and these improve and also should be considered as protection scope of the present invention.

Claims (2)

1. a single stage type no electrolytic capacitor LED driving power, is characterized in that: comprise input filter rectification circuit (1), the former limit of flyback switching circuit (2), auxiliary winding full-bridge two-way circuit (3), secondary current rectifying and wave filtering circuit (4) and isolating transformer (T ₁).

2. single stage type no electrolytic capacitor LED driving power as claimed in claim 1, is characterized in that: isolating transformer (T ₁) formed by a former limit winding and two secondary windings, comprise isolating transformer (T ₁) former limit inductance (L _m) and leakage inductance;

The filter circuit of input filter rectification circuit (1) is by input filter inductance (L ₁) and input filter capacitor (C ₁) being connected in parallel on electrical network input two ends composition, the rectifying part of input filter rectification circuit (1) adopts four diode (D ₁, D ₂, D ₃, D ₄) composition full-bridge not control rectifying circuit be connected in parallel on filter circuit two ends;

The former limit of flyback switching circuit (2) is by isolating transformer (T ₁) different name end and the main switch metal-oxide-semiconductor (Q of former limit winding ₁) drain electrode be connected to form, main switch metal-oxide-semiconductor (Q ₁) comprise its parasitic diode and parasitic capacitance;

Auxiliary winding full-bridge two-way circuit (3) is by first, second auxiliary IGBT pipe (Q _s1, Q _s2) and first, second auxiliary MOS transistor (Q _s3, Q _s4), first, second booster diode (D _s1, D _s2) and auxiliary energy storage electric capacity (C _b) composition, wherein the first auxiliary IGBT pipe (Q _s1) and the first booster diode (D _s1) and the first auxiliary MOS transistor (Q _s3) series connection successively, the second auxiliary IGBT pipe (Q _s2) and the second booster diode (D _s2) and the second auxiliary MOS transistor (Q _s4) after series connection, form two brachium pontis parallel connections successively, and be connected in parallel on isolating transformer (T ₁) second secondary winding two ends, isolating transformer (T ₁) different name end and first, second auxiliary IGBT pipe (Q of second secondary winding _s1), (Q _s2) collector electrode be connected, Same Name of Ends and first, second auxiliary MOS transistor (Q _s3, Q _s4) source class be connected, auxiliary energy storage electric capacity (C _b) one end be connected in the first auxiliary IGBT pipe (Q _s1) and the first booster diode (D _s1) mid point, the other end is connected in the second auxiliary IGBT pipe (Q _s2) and the second booster diode (D _s2) mid point, first, second auxiliary IGBT pipe (Q _s1, Q _s2) each self-contained its parasitic capacitance, first, second auxiliary MOS transistor (Q _s3, Q _s4) each self-contained its parasitic diode and parasitic capacitance;

Secondary current rectifying and wave filtering circuit (4) is by rectifier diode (D _r), rectification metal-oxide-semiconductor (Q _r) and output filter capacitor (C ₂) and output inductor (L ₂) composition, isolating transformer (T ₁) the different name end of first secondary winding is connected in rectifier diode (D _r) anode, rectifier diode (D _r) and rectification metal-oxide-semiconductor (Q _r), output inductor (L ₂) be connected in the positive output end of LED load, isolating transformer (T after series connection ₁) Same Name of Ends of first secondary winding is connected with the negative output terminal of LED load, output filter capacitor (C ₂) be parallel to rectification metal-oxide-semiconductor (Q _r) source class and the negative output terminal of LED load between, rectification metal-oxide-semiconductor (Q _r) comprise its parasitic diode and parasitic capacitance.