CN101404447A - Soft switch BUCK converter and its design method - Google Patents

Abstract

The invention discloses a soft switching BUCK convertor and a design method thereof. A main switching tube and a filter inductance are in series connected on a cathode circuit between input power and load; a shut-in diode is connected between the junction of the tube and the inductance and an anode circuit; the main switching tube is in parallel connected with an auxiliary branch circuit formed by the series connection of an auxiliary switching tube, a fourth diode and a resonant inductance; and the main and the auxiliary switching tubes are respectively soft switches. The shut-in diode is in parallel connected with a series branch of a second capacitance and a second diode, a third diode is connected between the junction of the fourth diode and the auxiliary switching tube and the junction of the second diode and the second capacitance and the main switching tube is further connected with a first diode and a first capacitance in parallels. The main switching fulfills the start and shutoff of ZVS; the auxiliary switching tube realizes the start of ZCS and the shutoff of ZVS; the shut-in diode D5 fulfills the start of ZVS as well as the shutoff of ZVS and ZCS. The convertor is low in consumption, high in reliability and efficiency.

Description

Soft switch BUCK converter and method for designing thereof

Technical field

The present invention relates to a kind of DC/DC converter, relate in particular to a kind of soft switch BUCK (step-down) converter and method for designing thereof.

Background technology

Modern video display illumination needs artificial light sources simulating nature light source.Metal halide lamp (Metal halide is called for short the MH lamp) is a kind of high-voltage gas discharging light of novel efficient.The frequency spectrum of MH light is a kind of new type electro source of alternative natural daylight very near the frequency spectrum of sunlight.For production of film and TV, on-the-spot broadcasting provide convenience.The same with the high-voltage gas discharging light of other type, the MH light fixture has the electrical characteristic of negative increment impedance, between electrical network and lamp, needs to insert a ballast restriction electric current and just can make its steady operation.

At present the ballast that uses has two kinds of Inductive ballast and electric ballasts.Wherein, electric ballast be with PWM (Pulse Width Modulation, pulse-width modulation) type switch converters be the basis, output voltage and electric current are low frequency (less than 300Hz) square wave.Its major advantage is that noiseless covibration, peak power output grade are 18kW, no stroboscopic.Therefore, be subjected to using widely.

As shown in Figure 1, be the block diagram of MH electronic lamp ballast in the prior art, comprise DC/DC converter and DC/AC inverter.The major function of DC/DC converter is that the characteristic of its output voltage and electric current and the electrical characteristic of lamp are complementary, and guarantees the smooth start and the permanent power steady operation of lamp.DC/AC inverter output low frequency square-wave voltage and electric current drive the MH lamp.High-voltage trigger provides the trigger impulse of high frequency to make the gas in the lamp begin discharge, forms plasma.

The topological structure of DC/DC converter of the prior art comprises switch T, diode D, inductance L as shown in Figure 2.

There is following shortcoming at least in above-mentioned prior art:

What switch T adopted is hard switching, so its switching loss is big, diode D has very big reverse recovery current, and loss is big, reliability is low, efficient is low.

Summary of the invention

The purpose of this invention is to provide a kind of loss is low, reliability is high, efficient is high soft switch BUCK converter and method for designing thereof.

The objective of the invention is to be achieved through the following technical solutions:

Soft switch BUCK converter of the present invention, comprise direct-flow input end, dc output end, be provided with anodal circuit and negative pole circuit between described direct-flow input end and the dc output end, be in series with main switch and filter inductance on the described negative pole circuit, be connected with fly-wheel diode between the tie point of described main switch and filter inductance and the described anodal circuit, the negative electrode of described fly-wheel diode links to each other with described anodal circuit, described main switch is parallel with auxiliary branch, described auxiliary branch is in series with auxiliary switch, the 4th diode, resonant inductance, the negative electrode of described the 4th diode links to each other with described auxiliary switch, and described main switch and auxiliary switch are respectively soft switch.

The method for designing of above-mentioned soft switch BUCK converter of the present invention, described filter inductance is determined by following formula:

$L_m=\frac{V_{\mathrm{in}}{T}_s}{0.8I_o}{D}_{Z1}(1-D_{Z1})$

In the formula, V _InBe input voltage; D _Z1Duty ratio for main switch; Ts is a switch periods; I ₀Be load current.

As seen from the above technical solution provided by the invention, soft switch BUCK converter of the present invention and method for designing thereof, owing to be in series with main switch and filter inductance on the negative pole circuit, filter inductance passes through formula $L_m=\frac{V_{\mathrm{in}}{T}_s}{0.8I_o}{D}_{Z1}(1-D_{Z1})$ Determine, be connected with fly-wheel diode between the tie point of main switch and filter inductance and the anodal circuit, main switch also is parallel with auxiliary branch, and auxiliary branch is in series with auxiliary switch, the 4th diode, resonant inductance, and main switch and auxiliary switch are respectively soft switch.Loss is low, reliability is high, efficient is high.

Description of drawings

Fig. 1 is the calcspar of MH electronic lamp ballast in the prior art;

Fig. 2 is the topological structure of DC/DC converter in the prior art;

Fig. 3 is the topological structure of soft switch BUCK converter of the present invention;

Fig. 4 is main switch Z among the present invention ₁And auxiliary switch Z ₂Drive signal waveform figure;

Fig. 5 a is the equivalent circuit diagram of the working stage 1 of soft switch BUCK converter of the present invention;

Fig. 5 b is the equivalent circuit diagram of the working stage 2 of soft switch BUCK converter of the present invention;

Fig. 5 c is the equivalent circuit diagram of the working stage 3 of soft switch BUCK converter of the present invention;

Fig. 5 d is the equivalent circuit diagram of the working stage 4 of soft switch BUCK converter of the present invention;

Fig. 5 e is the equivalent circuit diagram of the working stage 5 of soft switch BUCK converter of the present invention;

Fig. 5 f is the equivalent circuit diagram of the working stage 6 of soft switch BUCK converter of the present invention;

Fig. 5 g is the equivalent circuit diagram of the working stage 7 of soft switch BUCK converter of the present invention;

Fig. 6 is the main oscillogram of each working stage of soft switch BUCK converter of the present invention;

Fig. 7 is Δ t among the present invention ₂(=t ₂-t ₁) with the graph of a relation of Lr;

Fig. 8 is Δ I among the present invention _LrWith L _rGraph of a relation.

Embodiment

Soft switch BUCK converter of the present invention, its preferable embodiment comprises direct-flow input end, dc output end as shown in Figure 3, is provided with anodal circuit and negative pole circuit between direct-flow input end and the dc output end, is in series with main switch Z on the negative pole circuit ₁With filter inductance L _m, main switch Z ₁With filter inductance L _mTie point and anodal circuit between be connected with sustained diode ₅, sustained diode ₅Negative electrode link to each other main switch Z with anodal circuit ₁Be parallel with auxiliary branch, auxiliary branch is in series with auxiliary switch Z ₂, the 4th diode D ₄, resonant inductance L _r, the 4th diode D ₄Negative electrode and auxiliary switch Z ₂Link to each other main switch Z ₁With auxiliary switch Z ₂Be respectively soft switch.

Sustained diode ₅Be parallel with second capacitor C ₂With the second diode D ₂Series arm, the second diode D ₂Negative electrode and sustained diode ₅Negative electrode link to each other second capacitor C ₂An end and the second diode D ₂Anode link to each other second capacitor C ₂The other end and sustained diode ₅Anode link to each other.

The 4th diode D ₄With auxiliary switch Z ₂The tie point and the second diode D ₂With second capacitor C ₂Tie point between be connected with the 3rd diode D ₃, the 3rd diode D ₃The negative electrode and the second diode D ₂Anode link to each other the 3rd diode D ₃Anode and the 4th diode D ₄Negative electrode link to each other.

Main switch Z ₁Can also be parallel with the first diode D ₁, the first diode D ₁Anode link to each other with the negative pole of direct-flow input end.Main switch Z ₁Can also be parallel with first capacitor C ₁

Filter inductance L _mCan be much larger than resonant inductance L _r

Fig. 3 is the topological diagram of the specific embodiment of soft switch BUCK converter of the present invention, in order to satisfy the requirement of MH lamp ballast, does not have output capacitance in the BUCK converter, as required, also can increase output capacitance, if add that its operation principle of output capacitance is constant.Among Fig. 3, L _mBe filter inductance, L _rBe resonant inductance, and L _m＞＞L _rZ ₁Be main switch, and Z ₂It is auxiliary switch; D ₅Be fly-wheel diode; R _LIt is the steady-state equivalent load of lamp.In a switch periods, Z ₁ON time be far longer than Z ₂ON time.In this topology, main switch Z ₁Realized that ZVS (zero voltage switch) opens and turn-offs; Auxiliary switch Z ₂Realized that ZCS (Zero Current Switch) opens, ZVS turn-offs; Sustained diode ₅Realized that ZVS unlatching, ZVS and ZCS turn-off.

As shown in Figure 4, be respectively main switch Z ₁With auxiliary switch Z ₂Drive signal waveform, the drive signal waveform from figure as can be known, auxiliary switch Z ₂Before main switch Z1 opens, open in advance, be main switch Z ₁Created the condition that ZVS opens.As main switch Z ₁During shutoff, because first capacitor C at its two ends ₁Capacity bigger, first capacitor C ₁The voltage at two ends is to rise slowly, therefore, and main switch Z ₁Realized the ZVS shutoff.Thereby lowered main switch Z ₁The switch power loss.Because resonant inductance L _rWith auxiliary switch Z ₂Series connection makes auxiliary switch Z ₂For ZCS opens, and suppressed sustained diode ₅Reverse recovery current, thereby sustained diode ₅Realized the ZCS shutoff.As auxiliary switch Z ₂During shutoff, second capacitor C ₂With the resonance inductance L _rSeries resonance takes place, and has realized auxiliary switch Z ₂ZVS turn-off and be sustained diode ₅ZVS open and to create conditions.Therefore auxiliary switch Z2 and sustained diode have been reduced ₅Switching loss.In a word, all power switchs in the topology of the present invention are soft switch entirely, so it has less switching loss.

Below operation principle of the present invention is done detailed description:

Process for simplifying the analysis, do following hypothesis:

(1) all switching tube and diodes all are desirable switches;

(2) all electric capacity and inductance all are desirable linear units;

(3) filter inductance L _m＞＞resonant inductance L _r

(4) filter inductance L _mEnough is big, and in a switch periods, its electric current remains unchanged substantially, like this filter inductance L _mWith load R _LCan regard an electric current as is I _oConstant-current source.

For the ease of analyzing, in a work period, the present invention can be divided into 7 kinds of on off states, and the equivalent circuit diagram of its each working stage is shown in Fig. 5 a-Fig. 5 g, and corresponding main waveform as shown in Figure 6.

(1) stage 1, [t ₀＜t＜t ₁]:

At t＜t ₀Constantly, main switch Z ₁With auxiliary switch Z ₂All be in off state, its equivalent electric circuit shown in Fig. 5 g, sustained diode ₅Conducting, and filter inductance L _mOn electric current be I _o, first capacitor C ₁End press and to be input voltage V _In, second capacitor C ₂End to press be zero.

At t=t ₀The time, auxiliary switch Z ₂Open, its equivalent electric circuit is shown in Fig. 5 a.According to equivalent electric circuit as can be known, auxiliary switch Z2 and sustained diode ₅On current expression be respectively:

$i_{\mathrm{Lr}}={\mathrm{<figure-callout\; id="2"\; label="i\; Z"\; filenames="A20081010181400134.png,A20081010181400141.png"\; state="\{\{state\}\}">i</figure-callout>}}_Z=\frac{V_{\mathrm{in}}}{L_r}(t-t_0)---\left(1\right)$

${\mathrm{<figure-callout\; id="5"\; label="i\; V\; D"\; filenames="A20081010181400142.png"\; state="\{\{state\}\}">i</figure-callout>}}_{V_D}=I_o-\frac{V_{\mathrm{in}}}{L_r}(t-t_0)---\left(2\right)$

Know by following formula, at t=t ₀Constantly, auxiliary switch Z ₂With the 4th diode D ₄Realized the ZCS unlatching; At t=t ₁Moment resonant inductance L _rElectric current reach I _o, the while sustained diode ₅The electric current linearity be reduced to zero, suppress sustained diode effectively ₅Reverse recovery current, realize soft recovery.

(2) stage 2, [t ₁＜t＜t ₂]:

At t=t ₁Constantly, resonant inductance L _rWith first capacitor C ₁The beginning parallel resonance, its equivalent electric circuit is shown in Fig. 5 b.Resonant inductance L _rThe electric current and first capacitor C ₁And sustained diode ₅The expression formula of terminal voltage be respectively:

$i_{\mathrm{Lr}}\left(t\right)=I_o+\frac{V_{\mathrm{in}}}{Z_p}\sin {\mathrm{\&omega;}}_1(t-t_1)---\left(3\right)$

$v_{C1}\left(t\right)=V_{\mathrm{in}}\cos {\mathrm{\&omega;}}_1(t-t_1)---\left(4\right)$

v _D5(t)＝V _in-V _incosω ₁(t-t ₁) (5)

In the formula, ${\mathrm{\&omega;}}_1=1/\sqrt{{\mathrm{<figure-callout\; id="1"\; label="L\; r\; C"\; filenames="A20081010181400123.png,A20081010181400132.png"\; state="\{\{state\}\}">L</figure-callout>}}_r{C}_{}{}_1},$ $Z_p=\sqrt{L_r/{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A20081010181400123.png,A20081010181400132.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}$

From (5) formula as can be known, sustained diode ₅Be that ZVS turn-offs.At t=t ₂Constantly, first capacitor C ₁On energy storage all transfer to resonant inductance L _r, i.e. first capacitor C ₁End to press be zero, resonant inductance L _rOn electric current reach maximum.Resonant inductance L _rOn current increment Δ I _LrEquation below satisfying:

$\frac{1}{2}{C}_1{\mathrm{<figure-callout\; id="1"\; label="V\; C"\; filenames="A20081010181400123.png,A20081010181400132.png"\; state="\{\{state\}\}">V</figure-callout>}}_{C_{}}^{{}_1}\left(t_1\right)=\frac{1}{2}{C}_1{V}_{\mathrm{in}}^2=\frac{1}{2}{L}_r\mathrm{\&Delta;}{I}_{\mathrm{Lr}}^2---\left(6\right)$

Can get current maxima on the resonant inductance Lr by (6) formula

Computing formula be:

$I_{\mathrm{Lr}\max }=I_o+\mathrm{\&Delta;}{I}_{\mathrm{Lr}}=I_o+\sqrt{C_1{V}_{\mathrm{in}}^2/L_r}---\left(7\right)$

(3) stage 3, [t ₂＜t＜t ₃]:

At t=t ₂Constantly, the first diode D ₁(its electric current is for ZVS opens $i_{{\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="A20081010181400123.png,A20081010181400132.png"\; state="\{\{state\}\}">D</figure-callout>}}_1}=I_{L_r\max }-I_0$ ), for the no-voltage unlatching of main switch Z1 creates conditions.Its equivalent electric circuit is shown in Fig. 5 c.Therefore, at t ₂＜t＜t ₃During this time, main switch Z ₁Can realize that ZVS opens.

(4) stage 4, [t ₃＜t＜t ₄]:

At t=t ₃Constantly, turn-off auxiliary switch Z ₂, resonant inductance L _rWith second capacitor C ₂By the 3rd diode D ₃With the 4th diode D ₄Beginning resonance, and the 3rd diode D ₃Be that ZVS opens, its equivalent electric circuit is shown in Fig. 5 d.According to equivalent electric circuit, can get following expression formula:

$i_{\mathrm{Lr}}\left(t\right)=I_{\mathrm{Lr}\max }\cos {\mathrm{\&omega;}}_2(t-t_3)---\left(8\right)$

$v_{C_2}\left(t\right)=Z_s{I}_{\mathrm{Lr}\max }\sin {\mathrm{\&omega;}}_2(t-t_3)---\left(9\right)$

$\frac{1}{2}{L}_r{\left(I_{\mathrm{Lr}\max }\right)}^2=\frac{1}{2}{C}_2{\mathrm{<figure-callout\; id="2"\; label="V\; C"\; filenames="A20081010181400134.png,A20081010181400141.png"\; state="\{\{state\}\}">V</figure-callout>}}_{C_{}}^{{}_2}=\frac{1}{2}{C}_2{V}_{\mathrm{in}}^2---\left(10\right)$

In the formula, ${\mathrm{\&omega;}}_2=1/\sqrt{{\mathrm{<figure-callout\; id="2"\; label="L\; r\; C"\; filenames="A20081010181400134.png,A20081010181400141.png"\; state="\{\{state\}\}">L</figure-callout>}}_r{C}_{}{}_2},$ $Z_s=\sqrt{L_r/{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="A20081010181400134.png,A20081010181400141.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}$

By equivalent electric circuit as can be known, second capacitor C ₂With auxiliary switch Z ₂Be in parallel, and second capacitor C ₂The voltage at two ends is slowly to rise, so auxiliary switch Z ₂Be that ZVS turn-offs.At t=t ₄Constantly, be stored in resonant inductance L _rOn energy fully transfer to second capacitor C ₂The 3rd diode D3 and the 4th diode D ₄Realized the ZCS shutoff.Ideal situation is that equation (10), i.e. second capacitor C are satisfied in the energy storage on the resonant inductance Lr ₂End press and to reach supply voltage V _In

(5) stage 5, [t ₄＜t＜t ₅]:

In this stage, identical with the operating state of DC/DC converter of the prior art, equivalent electric circuit is shown in Fig. 5 e.

(6) stage 6, [t ₅＜t＜t ₆]:

At t=t ₅Constantly, main switch Z ₁Turn-off.Output current begins to first capacitor C ₁Charging, its end are pressed slowly and are risen main switch Z ₁Realize that ZVS turn-offs, its equivalent circuit diagram is shown in Fig. 5 f.Work as V _{C1 (t)}+ M _{C2 (t)}=V _InThe time, the second diode D ₂Be that ZVS opens.Subsequently, first capacitor C ₁Charging, second capacitor C simultaneously ₂Discharge.At t=t ₆Constantly, V _{C1 (t6)}=V _InAnd V _{C2 (t6)}=0 o'clock, the second diode D ₂Realized the ZVS shutoff.

(7) stage 7, [t6＜t＜t7]:

At t=t ₆Constantly, second capacitor C ₂End to press be zero, sustained diode ₅Realized the ZVS unlatching, its equivalent electric circuit is shown in Fig. 5 g.In this stage, sustained diode 5 is identical with the working condition of DC/DC converter of the prior art.At t=t ₇Constantly, auxiliary switch Z ₂Open once more, begin to enter next switch periods circulation.

The method for designing of above-mentioned soft switch BUCK converter of the present invention, filter inductance can be determined by following formula:

$L_m=\frac{V_{\mathrm{in}}{T}_s}{0.8I_o}{D}_{Z1}(1-D_{Z1})$

In the formula, V _InBe input voltage; D _Z1Duty ratio for main switch; Ts is a switch periods; I ₀Be load current.

Resonant inductance can be determined by following formula:

$L_r=\frac{0.01D_{Z1}{T}_s{V}_{\mathrm{in}}}{I_o}.$

The value of first electric capacity calculates by following formula:

${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A20081010181400123.png,A20081010181400132.png"\; state="\{\{state\}\}">C</figure-callout>}}_1=\frac{L_r\mathrm{\&Delta;}{I}_{\mathrm{Lr}}^2}{V_{\mathrm{in}}^2}$ Or ${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A20081010181400123.png,A20081010181400132.png"\; state="\{\{state\}\}">C</figure-callout>}}_1=\frac{L_r\mathrm{\&Delta;}{I}_{\mathrm{Lm}}^2}{V_{\mathrm{in}}^2}$

In the formula, Δ I _LrRipple current for resonant inductance; Δ I _LmRipple current for filter inductance.

The value of second electric capacity calculates by following formula:

${\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="A20081010181400134.png,A20081010181400141.png"\; state="\{\{state\}\}">C</figure-callout>}}_2=\frac{L_r{\left(I_{\mathrm{Lr}\max }\right)}^2}{V_{\mathrm{in}}^2}$

In the formula, I _LrmaxMaximum current for resonant inductance.

Below method for designing of the present invention and step are done detailed description:

The technical indicator of the design of the specific embodiment of the invention is as follows: input voltage 275VDC, and output voltage 120VDC, the normal output current 50A of stable state, load 6kW MH lamp, its steady-state equivalent resistance is 2.4 ohm, the operating frequency of switch is 20kHz; Filter inductance is operated under CCM (continuous input current) condition.

Its The design process is as follows:

The first step, filter inductance L _mSelection:

After load MH lamp enters stable state, output voltage V _oWith equivalent load R _LRemain unchanged.Filter inductance is operated under the CCM condition, the duty ratio D of main switch Z1 _Z1=V _o/ V _In, filter inductance L _mOn ripple current Δ I _Lm,

$\mathrm{\&Delta;}{I}_{\mathrm{Lm}}=\frac{(V_{\mathrm{in}}-V_o)D_{Z1}{T}_s}{L_m}---\left(11\right)$

As filter inductance L _mWhen being operated in critical condition, Δ I _Lm=2I _o, the threshold inductance L of filter inductance Lm _OcExpression formula be

$L_{\mathrm{oc}}=\frac{V_{\mathrm{in}}{T}_s}{2I_o}{D}_{Z1}(1-D_{Z1})---\left(12\right)$

In side circuit, if want filter inductance L _mBe operated in CCM, then L _mWill be than threshold inductance L _OcBig slightly.If the ripple current on the filter inductance is too small, its loss also can correspondingly reduce, yet the volume of inductance and cost can increase; If the ripple current on the filter inductance is excessive, the volume of its inductance and cost all can reduce, however loss meeting increase, and the ripple current of excessive high frequency can damage the MH lamp.Weigh the advantages and disadvantages, generally press the ripple current on the following formula selection filter inductance on the engineering

ΔI _Lm≈0.8I _o (13)

Filter inductance L then _mComputing formula be

$L_m=\frac{V_{\mathrm{in}}{T}_s}{0.8I_o}{D}_{Z1}(1-D_{Z1})---\left(14\right)$

Second step, the selection of resonant inductance Lr:

As Fig. 7, shown in Figure 8, be respectively Δ t ₂(=t ₂-t ₁) and L _rGraph of relation and Δ I _LrWith L _rGraph of relation.

As can be seen from the figure if resonant inductance L _rValue excessive, Δ t ₂Time can be excessive, so just limited the operating frequency of switch.By stage 1 analysis as can be known, if resonant inductance L _rValue too small, resonant inductance L _rOn the speed that rises of electric current fast, be unfavorable for suppressing effectively sustained diode like this ₅Reverse recovery current.By stages 2 analysis as can be known, resonant inductance L _rValue too small, Δ I _LrCan be very big, can increase auxiliary switch Z like this ₂Conduction loss.In engineering design, generally select Δ t ₁(=t ₁-t ₀)=0.01D _Z1T _sCan calculate resonant inductance L according to equation (1) like this _rValue:

$L_r=\frac{V_{\mathrm{Lr}}\left(\mathrm{\&Delta;}{t}_1\right)}{i_{\mathrm{Lr}}\left(t_1\right)}=\frac{0.01D_{Z1}{T}_s{V}_{\mathrm{in}}}{I_o}---\left(15\right)$

Because in the circuit of reality, all components and parts are not desirable, so filter inductance L _mOn electric current at Z ₁Reduce during shutoff.So when Practical Calculation, can use filter inductance L _mThe minimum value of last electric current replaces the I in the equation (15) _o

The 3rd step, first capacitor C ₁With second capacitor C ₂Selection:

In order to make main switch Z ₁Under the ZVS condition, open, be stored in first capacitor C ₁On energy must all transfer to L in the stage 2 _r, so first capacitor C ₁Value and resonance inductance L _rValue satisfy equation (6), i.e. first capacitor C ₁Value can calculate by following formula:

${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A20081010181400123.png,A20081010181400132.png"\; state="\{\{state\}\}">C</figure-callout>}}_1=\frac{L_r\mathrm{\&Delta;}{I}_{\mathrm{Lr}}^2}{V_{\mathrm{in}}^2}=\frac{L_r\mathrm{\&Delta;}{I}_{\mathrm{Lm}}^2}{V_{\mathrm{in}}^2}---\left(16\right)$

Wherein general Δ I _Lr≈ Δ I _Lm

In like manner, in order to make sustained diode ₅Under the ZVS condition, open second capacitor C ₂Value and resonance inductance L _rValue satisfy equation (10), so, can calculate capacitor C ₂Value:

${\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="A20081010181400134.png,A20081010181400141.png"\; state="\{\{state\}\}">C</figure-callout>}}_2=\frac{L_r{\left(I_{\mathrm{Lr}\max }\right)}^2}{{\mathrm{<figure-callout\; id="2"\; label="V\; C"\; filenames="A20081010181400134.png,A20081010181400141.png"\; state="\{\{state\}\}">V</figure-callout>}}_{C_{}}^{{}_2}}=\frac{L_r{\left(I_{\mathrm{Lr}\max }\right)}^2}{V_{\mathrm{in}}^2}---\left(17\right)$

According to top discussion and rule, it is as follows that we calculate parameter: C ₁=42nF, C ₂=129.6nF, L _m=84.3uH, L _r=2.0uH.

Emulation and experimental result:

With Pspice10.0 novel circuit has been carried out emulation, parameter is as follows: C ₁=42nF, C ₂=129.6nF, L _m=84.3uH, L _r=2.0uH, V _In=275VDC, R _L=2.4 Ω, D _Z1=0.43, D _Z2T _s=1.2us (D _Z2Be the duty ratio of auxiliary switch Z2, T _sBe switch periods), frequency f _s=20kHz.From simulation result, can draw to draw a conclusion: (1) main switch Z ₁Be that ZVS opens and ZVS turn-offs; (2) auxiliary switch Z ₂Be that ZCS opens and ZVS turn-offs; (3) sustained diode ₅Be that ZVS unlatching and ZCS and ZVS turn-off.

Made an experimental prototype that power output is 6kW, main switch Z ₁The IGBT (insulated gate bipolar transistor, insulated gate bipolar transistor) that is GT80J101 by 4 models composes in parallel auxiliary switch Z ₂The IGBT that is GT80J101 by 2 models composes in parallel, diode D ₁, D ₂, D ₃, D ₄The diode that to be respectively a model be DSEI61-06, sustained diode ₅The diode that is DSEI61-06 by 2 models composes in parallel, the parameter designing that wattless component draws according to the 4th stage computational methods.When experimental prototype drives the MH lamp of 6kW, measured switching tube Z respectively ₁, Z ₂Drive signal voltage and the voltage between collector electrode and the emitter.Proved coming to the same thing of experiment measuring and emulation.And measured the efficient of novel circuit and whole electric ballast with power analyzer, experimental result shows: circuit of the present invention has very high efficient (about 96%), prior art is 85% with the gross efficiency of hard switching electric ballast, and gross efficiency of the present invention brings up to 93%.

All power switchs are soft switch among the present invention, have reduced switching loss greatly, and do not have extra voltage and current stress; Sustained diode ₅Reverse recovery current obtain good restraining, loss reduces, and has strengthened reliability.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.

Claims (10)

1, a kind of soft switch BUCK converter, comprise direct-flow input end, dc output end, be provided with anodal circuit and negative pole circuit between described direct-flow input end and the dc output end, it is characterized in that, be in series with main switch and filter inductance on the described negative pole circuit, be connected with fly-wheel diode between the tie point of described main switch and filter inductance and the described anodal circuit, the negative electrode of described fly-wheel diode links to each other with described anodal circuit, described main switch is parallel with auxiliary branch, described auxiliary branch is in series with auxiliary switch, the 4th diode, resonant inductance, the negative electrode of described the 4th diode links to each other with described auxiliary switch, and described main switch and auxiliary switch are respectively soft switch.

2, soft switch BUCK converter according to claim 1, it is characterized in that, described fly-wheel diode is parallel with the series arm of second electric capacity and second diode, the negative electrode of described second diode links to each other with the negative electrode of described fly-wheel diode, one end of described second electric capacity links to each other with the anode of described second diode, and the other end of described second electric capacity links to each other with the anode of described fly-wheel diode.

3, soft switch BUCK converter according to claim 2, it is characterized in that, be connected with the 3rd diode between the tie point of the tie point of described the 4th diode and auxiliary switch and described second diode and second electric capacity, the negative electrode of described the 3rd diode links to each other with the anode of described second diode, and the anode of described the 3rd diode links to each other with the negative electrode of described the 4th diode.

4, according to claim 1,2 or 3 described soft switch BUCK converters, it is characterized in that described main switch is parallel with first diode, the anode of described first diode links to each other with the negative pole of described direct-flow input end.

5, soft switch BUCK converter according to claim 4 is characterized in that, described main switch also is parallel with first electric capacity.

6, soft switch BUCK converter according to claim 1 is characterized in that, described filter inductance is much larger than described resonant inductance.

7, a kind of method for designing of each described soft switch BUCK converter of claim 1 to 6 is characterized in that, described filter inductance is determined by following formula:

$L_m=\frac{V_{\mathrm{in}}{T}_s}{0.8I_o}{D}_{Z1}(1-D_{Z1})$

In the formula, V _InBe input voltage; D _Z1Duty ratio for main switch; Ts is a switch periods; I ₀Be load current.

8, the method for designing of soft switch BUCK converter according to claim 7 is characterized in that, described resonant inductance is determined by following formula:

$L_r=\frac{0.01D_{Z1}{T}_s{V}_{\mathrm{in}}}{I_o}.$

9, the method for designing of soft switch BUCK converter according to claim 8 is characterized in that, the value of described first electric capacity calculates by following formula:

$C_1=\frac{L_r\mathrm{\&Delta;}{I}_{\mathrm{Lr}}^2}{V_{\mathrm{in}}^2}$ Or $C_1=\frac{L_r\mathrm{\&Delta;}{I}_{\mathrm{Lm}}^2}{V_{\mathrm{in}}^2}$

In the formula, Δ I _LrRipple current for resonant inductance; Δ I _LmRipple current for filter inductance.

10, the method for designing of soft switch BUCK converter according to claim 8 is characterized in that, the value of described second electric capacity calculates by following formula:

$C_2=\frac{L_r{\left(I_{\mathrm{Lr}\max }\right)}^2}{V_{\mathrm{in}}^2}$

In the formula, I _LrmaxMaximum current for resonant inductance.

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