CN101969267A - Megahertz full-bridge soft-switching converter - Google Patents

Abstract

The invention provides a full-bridge soft-switching power supply structure with fixed working frequency. The full-bridge soft-switching power supply structure comprises a full-bridge switch, an LLC high frequency resonance circuit and a synchronizing rectifier circuit. A symmetrical bi-polarity control mode is adopted. The LLC high frequency resonance circuit is improved on the basis of the traditional series or parallel LC resonant converter, absorbs the advantages of the blocking function of a resonant capacitor of the series resonant converter and that resonant tank current is changed together with the load and the efficiency is high when the load is light, and simultaneously has the characteristic that a parallel resonant converter can work under the idle condition and has low requirement on the pulsating current of a filter capacitor, so the LLC high frequency resonance circuit is an ideal resonant converter topology.

Description

A kind of megahertz level full bridge soft switch converter

Technical field

The present invention relates to a kind of DC/DC converter, especially a kind of full bridge soft switch converter of fixed switching frequency.

Background technology

Since nearly half a century, the technological progress of Switching Power Supply and three mileages of development experience: 1. power device replaces the common power transistor with power field effect transistor and igbt; 2. the application of high frequency chemical control system The Application of Technology and soft switch technique; 3. the application of switch power supply system integrated technology.Modern high frequency switch power technology is a kind of power electronic technology with fastest developing speed, most widely used.

Now, new processor, memory body, DSP or the ASIC that releases of each generation, their power supply requirement trend is more low-work voltage, higher electric current, more speed.The challenge that system designer will be faced is when will deal with the low-voltage of quantity surge, more will deal with transient response faster, improves the efficient of overall power system, improves the power density of modular power source, thereby occupies plate space of planes still less.

Power density is power-weight ratio or power to volume ratio both, is the important indicator that characterizes the Switching Power Supply miniaturization, and the lifting of power density means that product has higher efficiency of transmission in miniaturization.The power density of present domestic main flow Switching Power Supply product is last hectowatt/cubic inch, just develop towards higher direction at present, power density doubles, and will reduce power supply product shared area on the circuit version greatly, improve the service efficiency of plank, save cost.

In order to realize the Switching Power Supply high power density, must improve the operating frequency of DC/DC transducer, thereby reduce the volume and weight of energy-storage travelling wave tube in the circuit.From 1980, improve switching frequency and become the effective means that reduces the Switching Power Supply size, also improved the dynamic property of Switching Power Supply simultaneously.Present 200～50KHz has become the standard switch frequency of the following Switching Power Supply of output 100W.The small power supply switching frequency of the special manufacturing that has has reached megahertz, but product is few, and technology is immature.

The raising of switching frequency is accompanied by the increase of switching loss.The appearance of soft switch technique makes high frequency switch power become possibility.According to the annexation of load and resonant circuit, existing controlled resonant converter soft switch technique can be divided into series resonant converter, parallel resonance converter, and both series parallel resonance converters that combination generated.Harmonic technology in this patent is to improve in above-mentioned soft switch technique.

(1) series resonant converter:

The series resonant converter advantage has: 1, series resonance electric capacity plays every straight effect, avoids high frequency transformer saturated; 2, the resonant groove path electric current is with the lightening and reduce of load, so efficient is higher during underloading.But series resonant converter is under underloading or no-load condition, and output voltage is non-adjustable, exports dc filter capacitor simultaneously and need bear bigger current pulsation.

(2) parallel resonance converter:

Parallel resonance converter advantage has: 1, converter can be worked to zero load, because output voltage is relevant with switching frequency all the time; 2, because output adopts big filter inductance, little to the current pulsation current requirements of filter capacitor, be applicable to the occasion of low output voltage, big output current.But its resonant groove path electric current of parallel resonance converter is basic and the load weight is irrelevant, so on-state loss relative fixed of switching tube, the efficient of converter when underloading is lower, is only applicable to the narrower relative constant occasion with the load of rated power place of output voltage range.

(3) series parallel resonance converter:

The series parallel resonance converter: combine the characteristic of series resonant converter and parallel resonance converter, advantage has: 1, when load when being specified, converter presents the characteristic of series resonant converter; 2, the characteristic of deflection parallel resonance converter when load lightens, its resonant groove path electric current can change with the variation of load, thereby high efficiency, simultaneously can be at the regulated in wider range output voltage by the by-pass cock frequency.But the former limit of the transformer of series parallel resonance converter leakage inductance can't be participated in resonance, causes the transformer voltage electric current to have bigger phase difference, causes reactive current increase in the resonant tank, and on-state loss also increases.

Summary of the invention

The objective of the invention is to overcome the deficiencies in the prior art, a kind of megahertz level full bridge soft switch converter is provided, is a kind of based on full-bridge switch, LLC resonance, efficient, high power density, reaction fast, the DC/DC power source design of cleaning.

According to technical scheme provided by the invention, described megahertz level full bridge soft switch converter comprises: the left arm mid point of full-bridge soft-switching links to each other by the end of the same name that electric capacity connects the former limit of transformer, and the right arm mid point of full-bridge soft-switching links to each other with the backward end on the former limit of transformer; The drain terminal of the 5th field effect transistor connects the end of the same name of transformer secondary, the source end of the 5th field effect transistor connects positive output, the drain terminal of the 6th field effect transistor connects the backward end of transformer secondary, the source end of the 6th field effect transistor connects positive output, filter capacitor one end connects positive output, the other end connects earth terminal, the centre tap earth terminal of transformer secondary; Described transformer is a flat surface transformer.

Described full-bridge soft-switching is made of first～the 4th field effect transistor and corresponding parasitic diode, and wherein first field effect transistor, second field effect transistor constitute left arm, and the 3rd field effect transistor, the 4th field effect transistor constitute right arm; Electric capacity connects the node between first field effect transistor and second field effect transistor, and the backward end on the former limit of transformer connects the node between the 3rd field effect transistor and the 4th field effect transistor.

Described full-bridge soft-switching input voltage is 48V, and switching frequency is f _s∈ [1MHz, 2MHz]; Former limit of transformer (Ta) and secondary turn ratio n ∈ [1,20], the ratio of transformer (Ta) former limit leakage inductance and magnetizing inductance $A=\frac{L_r}{L_M}\∈[\frac{1}{6},\frac{1}{48}];$

The resonant network value:

The former limit of transformer leakage inductance $L_r=\frac{{4n}^2{R}_o}{{\mathrm{\π}}^3{f}_s}$

The former limit of transformer magnetizing inductance $L_M=\frac{{4\mathrm{An}}^2{R}_o}{{\mathrm{\π}}^3{f}_s}$

The resonant capacitance value $C_r=\frac{\mathrm{\π}}{{16\mathrm{An}}^2{R}_o{f}_s};$

Wherein, Lr is the former limit of transformer (Ta) leakage inductance, L _MBe the former limit of transformer (Ta) magnetizing inductance, R _oBe load resistance.

As preferably, described full-bridge soft-switching frequency f _s=1.6 megahertzes, output voltage are 9.6V; Former limit of transformer (Ta) and secondary turn ratio equal 5; The resonant network value is L _r=200nH, L _M=2uH, C _r=49nF; Wherein, Lr is the former limit of a transformer leakage inductance, L _MBe the former limit of transformer magnetizing inductance, Cr is the resonant capacitance value.

Advantage of the present invention is: the bipolarity control mode that adopts symmetry.The LLC controlled resonant converter is that improvement produces on the basis of traditional serial or parallel connection LC controlled resonant converter, it had both absorbed changing with the load weight every straight effect and resonance mesh current that the series resonant converter resonant capacitance is played, efficient advantage of higher during underloading; Simultaneously had the parallel resonance converter again concurrently and can be operated under the idle condition, the characteristics little to the current pulsation current requirements of filter capacitor, the influence that the parasitic parameter that makes full use of device has simultaneously reduced EMI allows smaller volume improve power density simultaneously.The patented product makes the mains switch frequency reach the megahertz order of magnitude, and response speed is 2 delicate, and every cubic inch of power of power density can reach 400 watts, is a kind of more satisfactory controlled resonant converter topology.

Description of drawings

Fig. 1 is the equivalent circuit diagram of Fig. 6.

Fig. 2 is the equivalent parallel circuit diagram of Fig. 1.

Fig. 3 is the equivalent series circuit diagram of Fig. 2.

Fig. 4 is Fig. 2 circuit input and output voltage gain oscillogram.

Fig. 5 is a megahertz full-bridge LLC circuit transmission efficient oscillogram.

Fig. 6 megahertz level full bridge soft switch converter circuit theory diagrams.

Embodiment

In order to make purpose of the present invention, technical scheme and advantage clearer, the present invention is described in detail below in conjunction with accompanying drawing and example.

As shown in Figure 6, megahertz level full bridge soft switch converter of the present invention comprises: the left arm mid point A of full-bridge soft-switching links to each other by the end of the same name that capacitor C r connects the former limit of transformer Ta, and the right arm mid point B of full-bridge soft-switching links to each other with the backward end on the former limit of transformer Ta; The drain terminal of the 5th field effect transistor S1 connects the end of the same name of transformer Ta secondary, the source end of the 5th field effect transistor S1 connects positive output, the drain terminal of the 6th field effect transistor S2 connects the backward end of transformer Ta secondary, the source end of the 6th field effect transistor S2 connects positive output, filter capacitor Cf one end connects positive output, the other end connects earth terminal, the centre tap earth terminal of transformer Ta secondary; Described transformer Ta is a flat surface transformer.

Described full-bridge soft-switching is made of first～the 4th field effect transistor T1, T2, T3, T4 and corresponding parasitic diode D1, D2, D3, D4, wherein the first field effect transistor T1, the second field effect transistor T2 constitute left arm, the 3rd field effect transistor T3, the 4th field effect transistor T4 constitute right arm, adopt the bipolarity control mode; Capacitor C r connects the node A between the first field effect transistor T1 and the second field effect transistor T2, and the backward end on the former limit of transformer Ta connects the Node B between the 3rd field effect transistor T3 and the 4th field effect transistor T4.About the detailed explanation of full-bridge soft-switching, see " principle of Switching Power Supply and design " revised edition, Zhang Songzan, Cai Xuansan write, in September, 2004, Electronic Industry Press; The 363rd page to 365 pages.

For the circuit that the further instruction embodiment of the invention provides, now describe its operation principle and derivation in detail in conjunction with Fig. 1 to Fig. 5.Derivation institute description scope mainly is a full-bridge LLC resonance portion, and synchronous rectification part does not elaborate, therefore with the circuit diagram equivalence for as shown in Figure 1.

Megahertz full-bridge LLC series resonant converter equivalent electric circuit and Mathematical Modeling are set up:

Full-bridge LLC series resonant converter circuit as shown in Figure 1, its equivalent parallel circuit as shown in Figure 2.When converter operated in resonance frequency, it is sinusoidal wave that resonance current is approximately.And in one-period.Resonance current is to L _MDischarge and recharge, therefore, magnetizing current is approximately triangular wave.Remove the switching tube part, ignore Dead Time simultaneously, the duty ratio of supposing two pipes is 50%, and so, the input signal of resonant circuit is the square wave of 0～Vs.A, the voltage of B point-to-point transmission is U when preceding half period 0～Ts/2 _AB=V _IN, U during Ts/2 during half period in the back～Ts _AB=-V _INSo A, the fundametal compoment between B is

$V_{f1\left(t\right)}=\frac{4}{\mathrm{\π}}{V}_{\mathrm{IN}}\sin \left(w_{s}t\right)---\left(1\right)$

The effective value of fundametal compoment is

Peak value is

The equivalent load impedance of primary is:

$R_{\mathrm{eq}}=\frac{{8\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">n</figure-callout>}}^2}{{\mathrm{\&pi;}}^2}{R}_o---\left(2\right)$

Fig. 3 is the equivalent circuit diagram of Fig. 2, is about to parallel connection and converts series connection to.Wherein:

${L_M}^{\&prime;}=\frac{R_{\mathrm{eq}}^2}{{\mathrm{<figure-callout\; id="2"\; label="R\; eq"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{eq}}^{}+L_M}{L}_M=\frac{Q_P^2}{{\mathrm{<figure-callout\; id="2"\; label="Q\; P"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">Q</figure-callout>}}_P^{}+1}{L}_M,---\left(3\right)$

${R_{\mathrm{eq}}}^{\&prime;}=\frac{L_M^2}{{\mathrm{<figure-callout\; id="2"\; label="R\; eq"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{eq}}^{}+L_M^2}{R}_{\mathrm{eq}}=\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="Q\; P"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">Q</figure-callout>}}_P^{}+1}{R}_{\mathrm{eq}}---\left(4\right)$

$Q_P=\frac{R_{\mathrm{eq}}}{L_M}---\left(5\right)$

Order Then have: $L=L_r+L_M=L_r(1+\frac{1}{A})=L_M(1+A)---\left(6\right)$

Order again $w_{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="HSA00000283238000011.png,HSA00000283238000021.png"\; state="\{\{state\}\}">r</figure-callout>}1}=\frac{1}{\sqrt{L_r{C}_r}}---\left(7\right)$

${\mathrm{<figure-callout\; id="2"\; label="w\; r"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">w</figure-callout>}}_r=\frac{1}{\sqrt{(L_r+L_M)C_r}}---\left(8\right)$

${\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0=\sqrt{\frac{L_r+L_M}{C_r}}---\left(9\right)$

$Q_L=\frac{{\mathrm{<figure-callout\; id="0"\; label="R\; eq\; Z"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{eq}}}{Z_{}}=\frac{R_{\mathrm{eq}}}{w_{r2}(L_r+L_M)}=w_{r2}{C}_r{R}_{\mathrm{eq}}---\left(10\right)$

In Fig. 2, from V _{F1 (t)}The equiva lent impedance of seeing of turning right is:

$Z=\frac{1}{{\mathrm{jw}}_s{C}_r}+{\mathrm{jw}}_s{L}_r+\frac{{\mathrm{jw}}_s{L}_M{R}_{\mathrm{eq}}}{{\mathrm{jw}}_s{L}_M+R_{\mathrm{eq}}}---\left(11\right)$

Through getting after the arrangement: $Z=\frac{R_{\mathrm{eq}}\left\{(1+A)\right[1-{\left(\frac{w_{r2}}{w_s}\right)}^2]+j\frac{1}{Q_L}[\frac{w_s}{w_{r2}}\frac{\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HSA00000283238000011.png,HSA00000283238000021.png"\; state="\{\{state\}\}">A</figure-callout>}}{1+A}-\frac{w_{r2}}{w_s}\left]\right\}}{1-j(1+A)Q_L\frac{w_{r2}}{w_s}}---\left(12\right)$

Among Fig. 2, output voltage V ' ₀With V _{F1 (t)}Ratio be: $\frac{{\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">V</figure-callout>}}_0^{\&prime;}}{V_{f1\left(t\right)}}=\frac{R_{\mathrm{eq}}\left|\right|{\mathrm{jw}}_s{L}_M}{Z}---\left(13\right)$

$A_v=\frac{{\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">V</figure-callout>}}_0^{\&prime;}}{V_{f1\left(t\right)}}=\frac{V_{R_{\mathrm{eq}}\left(\mathrm{rms}\right)}}{V_{f1\left(\mathrm{rms}\right)}}=\frac{1}{(1+A)[1-{\left(\frac{w_{r2}}{w_s}\right)}^2]+j\frac{1}{Q_L}[\frac{w_s}{w_{r2}}\left(\frac{\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HSA00000283238000011.png,HSA00000283238000021.png"\; state="\{\{state\}\}">A</figure-callout>}}{1+A}\right)-\frac{w_{r2}}{w_s}]}---\left(14\right)$

Its modulus size equals: $\left|\right|A_v\left|\right|=\frac{1}{\sqrt{{(1+A)}^2{[1-{\left(\frac{w_{r2}}{w_s}\right)}^2]}^2+\frac{1}{{Q_L}^2}{[\frac{w_s}{w_{r2}}\left(\frac{\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HSA00000283238000011.png,HSA00000283238000021.png"\; state="\{\{state\}\}">A</figure-callout>}}{1+A}\right)-\frac{w_{r2}}{w_s}]}^2}}---\left(15\right)$

Know by formula (15): if A _v=1, then have: $w_s=\sqrt{\frac{1}{L_r{C}_r}}---\left(16\right)$

Obtaining waveform as shown in Figure 4 by formula (15), is to meet at a bit in 1 o'clock at yield value all as seen.

Megahertz full-bridge LLC series resonant converter input and output voltage gain A _vChange with frequency change.Along with load increases (is Q _LValue increases), the pairing frequency of characteristic curve peak value increases gradually.When the switching angle frequency

The time, gain A _vIrrelevant with the load size, be constantly equal to 1, meet at A as shown in Figure 4 _v=1 place.Work as A _v＞1 o'clock, converter was the characteristic of boosting; Work as A _v＜1 o'clock, converter was a dropping voltage characteristic.

This patent is to utilize gain to equal the full-bridge LLC series resonant converter circuit of fixed switching frequency of 1 o'clock characteristics design.

The energy efficiency parameter designing:

By shown in Figure 2: power output is: $P_{R_{\mathrm{eq}}}=\frac{{\left(2\sqrt{2}{A}_V{V}_{\mathrm{in}}\right)}^2}{{\mathrm{\&pi;}}^2{R}_{\mathrm{eq}}}---\left(17\right)$

Energy loss is: $P_r=\frac{16r{\left(A_V{V}_{\mathrm{in}}\right)}^2[1+{(1+A)}^2{Q}_L^2{\left(\frac{w_{r2}}{w_2}\right)}^2]}{2{\mathrm{\&pi;}}^2{R_{\mathrm{eq}}}^2}---\left(18\right)$

Wherein: $r=r_{\mathrm{ds}}+r_{\mathrm{cr}}+r_{\mathrm{Lr}}+r_{L_M^{\&prime;}}---\left(19\right)$

Efficient is: $\mathrm{\&eta;}=\frac{P_{R_{\mathrm{eq}}}}{P_{R_{\mathrm{eq}}}+P_r}=\frac{1}{1+\frac{r}{Z_0}[\frac{1}{Q_L}+{(1+A)}^2{\left(\frac{w_{r2}}{w_s}\right)}^2{Q}_L]}---\left(20\right)$

Order

: $Q_L=\frac{\left(\frac{w_s}{w_{r2}}\right)}{1+A}---\left(21\right)$ Obtain efficient with Q by formula (20) _LChanging, promptly is the curve chart of parameter with load variations, and as shown in Figure 5, its efficient is at Q _LBetween 1.4 to 5, all reached more than 94%.

Megahertz full-bridge LLC circuit parameter design:

According to above analysis, it is 48V that the present invention designs the full-bridge soft-switching input voltage, and switching frequency is f _s∈ [1MHz, 2MHz]; Former limit of transformer (Ta) and secondary turn ratio n ∈ [1,20], the ratio of transformer (Ta) former limit leakage inductance and magnetizing inductance $A=\frac{L_r}{L_M}\&Element;[\frac{1}{6},\frac{1}{48}];$

The resonant network value:

The former limit of transformer (Ta) leakage inductance $L_r=\frac{{4n}^2{R}_o}{{\mathrm{\&pi;}}^3{f}_s}$

The former limit of transformer (Ta) magnetizing inductance $L_M=\frac{{4\mathrm{An}}^2{R}_o}{{\mathrm{\&pi;}}^3{f}_s}$

The resonant capacitance value $C_r=\frac{\mathrm{\&pi;}}{{16\mathrm{An}}^2{R}_o{f}_s};$

R wherein _oBe load resistance.

One group of preferred design parameter is as follows:

Design objective: input voltage is: V _In=48V; Output voltage is: V _o=9.6V; The output loading scope is: R _oChanging its efficient in=0.45 Ω～1.65 Ω can both reach more than 94%; Switching frequency is designed to: f _s=1.6MHz;

1 is selected according to the minimax gain of resonant network: $A=\frac{L_r}{L_M}=\frac{1}{10}.$

2 transformer turn ratio: $n=N_P/N_S=\frac{V_{\mathrm{in}}}{V_o}=5.$

3 equivalent load impedances: $R_{\mathrm{eq}}=\frac{{8\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HSA00000283238000021.png,HSA00000283238000022.png"\; state="\{\{state\}\}">n</figure-callout>}}^2}{{\mathrm{\&pi;}}^2}{R}_o\&Element;[9.12\mathrm{\&Omega;}~81.1\mathrm{\&Omega;}].$

4 resonant networks: A _v=1 necessary and sufficient condition: Shift onto and consider that surplus chooses L by top _r=200nH, L _M=2uH, C _r=49nF.

To sum up, the present invention has the following advantages:

(1) in existing Switching Power Supply, electromagnetic component occupies the very most of of system bulk such as filter inductance, transformer etc., and the diffusion parasitic parameter can produce very big impact to the operation characteristic of system, and then affects the efficient of system. And the design of this patent all uses the leakage inductance of transformer and magnetizing inductance to replace series resonance inductor and parallel resonant inductor, reach the integrated purpose of magnetic, greatly reduce the volume of converter, reduce parasitic parameter to the adverse effect of converter, the electromagnetic compatibility problem when high frequency is with smaller.

(2) traditional switching power converters secondary rectifying tube majority is firmly open-minded, exists serious reverse recovery loss; And the secondary rectifying tube is to be operated in the discontinuous current state in fr1＞fs＞fr2 frequency range in this patent, Zero Current Switch, and reverse recovery loss has been overcome, so loss is smaller, can greatly improve exchanger efficiency.

(3) the LLC circuit uses fixed switching frequency in this patent, utilizes gain to be constantly equal to 1 this characteristic, makes output voltage not because the variation of load changes, and has solved the problem that needs backfeed loop regulation output voltage in traditional destructing, has reduced the control difficulty. Because controlled resonant converter works in the megahertz frequency range, main switch adopts MOSFET, and MOSFET is suitable for and works in ZVS. Wherein primary switch all is operated in ZVT (ZVS) condition. And secondary diode can adopt Zero Current Switch (ZCS) work, does not have reverse recovery loss.

Claims (4)

1. megahertz level full bridge soft switch converter, it is characterized in that: the left arm mid point (A) that comprises full-bridge soft-switching links to each other by the end of the same name that electric capacity (Cr) connects the former limit of transformer (Ta), and the right arm mid point (B) of full-bridge soft-switching links to each other with the backward end on the former limit of transformer (Ta); The drain terminal of the 5th field effect transistor (S1) connects the end of the same name of transformer (Ta) secondary, the source end of the 5th field effect transistor (S1) connects positive output, the drain terminal of the 6th field effect transistor (S2) connects the backward end of transformer (Ta) secondary, the source end of the 6th field effect transistor (S2) connects positive output, filter capacitor (Cf) end connects positive output, the other end connects earth terminal, the centre tap earth terminal of transformer (Ta) secondary; Described transformer (Ta) is a flat surface transformer.

2. megahertz level full bridge soft switch converter according to claim 1, it is characterized in that: described full-bridge soft-switching is made of first～the 4th field effect transistor (T1, T2, T3, T4) and corresponding parasitic diode (D1, D2, D3, D4), wherein first field effect transistor (T1), second field effect transistor (T2) constitute left arm, and the 3rd field effect transistor (T3), the 4th field effect transistor (T4) constitute right arm; Electric capacity (Cr) connects the node (A) between first field effect transistor (T1) and second field effect transistor (T2), and the backward end on the former limit of transformer (Ta) connects the node (B) between the 3rd field effect transistor (T3) and the 4th field effect transistor (T4).

3. megahertz level full bridge soft switch converter according to claim 1, it is characterized in that: described full-bridge soft-switching input voltage is 48V, switching frequency is f _s∈ [1MHz, 2MHz]; Former limit of transformer (Ta) and secondary turn ratio n ∈ [1,20], the ratio of transformer (Ta) former limit leakage inductance and magnetizing inductance $A=\frac{L_r}{L_M}\&Element;[\frac{1}{6},\frac{1}{48}];$

The resonant network value:

The former limit of transformer (Ta) leakage inductance $L_r=\frac{{4n}^2{R}_o}{{\mathrm{\&pi;}}^3{f}_s}$

The former limit of transformer (Ta) magnetizing inductance $L_M=\frac{{4\mathrm{An}}^2{R}_o}{{\mathrm{\&pi;}}^3{f}_s}$

The resonant capacitance value $C_r=\frac{\mathrm{\&pi;}}{{16\mathrm{An}}^2{R}_o{f}_s};$

R wherein _oBe load resistance.

4. as megahertz level full bridge soft switch converter as described in the claim 3, it is characterized in that: described full-bridge soft-switching frequency f _s=1.6 megahertzes, output voltage are 9.6V; Former limit of transformer (Ta) and secondary turn ratio equal 5; The resonant network value is L _r=200nH, L _M=2uH, C _r=49nF; Wherein, Lr is the former limit of a transformer leakage inductance, L _MBe the former limit of transformer magnetizing inductance, Cr is the resonant capacitance value.

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