CN203387407U - LLC resonant converter light load control device - Google Patents

Abstract

The utility model provides a light-load control device for an LLC resonant converter, which belongs to the field of power conversion, and solves the problem of loss of soft switching environment of zero-voltage switches and zero-current switches. The device includes a controller, a frequency modulation module and a width adjustment module , the current detection unit and the voltage detection unit, the controller is also connected with a feedback compensation error amplifier, the voltage detection unit and the reference voltage power supply are respectively connected with the feedback compensation error amplifier, the current detection unit is connected with the controller, the controller is connected with a working module switching unit, frequency modulation The module and the width adjustment module are respectively connected to the controller and the switching unit of the working module. The switching unit of the working module is connected to the control terminal of the switching tube. The controller judges whether the LLC resonant converter is working under light load according to the error voltage signal and output current signal; , carry out frequency regulation control mode; in light load, carry out fixed frequency pulse width control mode. The device realizes soft switching environment and resonance parameter optimization in the full load range.

Description

LLC controlled resonant converter underload control device

Technical field

The utility model belongs to the power conversion field, relates to a kind of LLC controlled resonant converter underload control device.

Background technology

Along with the development of switch power technology, high efficiency and high power density become development trend.Therefore the LLC controlled resonant converter is applied and is given birth to also more and more extensive.The LLC controlled resonant converter realizes that in wider frequency range the no-voltage of primary side switching tube opens and secondary side rectifying tube zero-current switching.But, along with alleviating of load, in order to obtain identical DC current gain, the LLC controlled resonant converter need to improve switching frequency.The rising of switching frequency, increased switching loss on the one hand; On the other hand, also will cause the electric current of rectification side diode just not turn-off when there is no back to zero, the soft switch environment of Zero Current Switch is lost, and further increases switching loss.Simultaneously, underloading reduces quality factor of circuit Q value, and load variations can have a strong impact on voltage gain.Therefore, under LLC controlled resonant converter underloading, along with the increase of switching frequency, the efficiency of transducer will be affected, and compare its heavily loaded high efficiency, and the efficiency while being difficult to simultaneously take into account underloading improves.

Along with the requirements at the higher level to supply convertor efficiency, the LLC converter need to obtain higher light-load efficiency, prior art often adopts the control method of output sluggishness with comparison circuit, on-off switching tube control signal when output voltage is elevated to a certain higher limit, and converter enters idle condition; Produce switching tube frequency modulation(FM) control signal when output voltage is reduced to a certain lower limit, converter enters the operating state of power output.The method is only suitable in utmost point underload or holding state.Other light load efficiency improves strategy and also has the scheme that increases switching tube or diode auxiliary branch in the primary and secondary level, and the fixing PWM control program of duty ratio is also arranged.Loss when these schemes can make zero load or underload reduces, but realizes owing to increasing hardware in main circuit, and the reliability of circuit is brought to certain impact, and the efficiency while also being difficult to simultaneously take into account heavy duty improves.

Chinese patent literature discloses a kind of LLC controlled resonant converter control method and the device that application number is 200910221471.4, this device judges load condition by input switch pipe turn-on frequency, carry out respectively frequency conversion, adjust wide control according to load condition again, reduced to a certain extent circuit loss, but this frequency conversion adjusts wide control without any constraints, can make the switch tube zero voltage switch of LLC controlled resonant converter and the soft switch environment of rectifying tube Zero Current Switch lose, thereby make the cavity voltage gain uncertain.

Summary of the invention

There are the problems referred to above in the utility model for existing technology, a kind of LLC controlled resonant converter underload control device has been proposed, this device adopts underload frequency pulse width control surely, thereby realize soft switch environment and the resonance parameter optimization of full-load range, the efficiency of raising converter is light-load efficiency especially.

The utility model is realized by following technical proposal: a kind of LLC controlled resonant converter underload control device, it is characterized in that, this device comprises controller, for making controlled resonant converter be operated in the frequency modulation module under the frequency adjustment control model and determine the wide module of tune under frequency pulse width control pattern for controlled resonant converter is operated in, the output voltage signal of nursing one's health for the hardware circuit that detects respectively the LLC controlled resonant converter and voltage detection unit and the current detecting unit of output current signal, described controller also is connected with the feedback compensation error amplifier, described voltage detection unit and reference voltage power supply are connected respectively the input of feedback compensation error amplifier, described current detecting unit connects the input of controller, the output of described controller is connected with the operational module switch unit, described frequency modulation module is connected respectively controller and operational module switch unit with the wide module of tune, described operational module switch unit connects controlled resonant converter switch controlled end, the output current signal that the error voltage signal that the output voltage that described controller detects according to voltage detection unit is exported after the feedback compensation error amplifier and current detecting unit detect judges whether the LLC controlled resonant converter works in light-load state, if be not operated in underload, by the operational module switch unit, select the work of frequency modulation module, carry out the frequency adjustment control model, if be operated in underload, by the operational module switch unit, select to adjust wide module work, carry out determining frequency pulse width control pattern, realize the duty cycle adjustment voltage gain, and export corresponding switch controlled signal to the switch controlled end through the operational module switch unit.

LLC controlled resonant converter hardware circuit bussed supply voltage is direct voltage.Load control circuit comprises controller, voltage detection unit, current detecting unit, frequency modulation module and adjust wide module.Voltage detection unit gathers the direct current output loading voltage signal of LLC controlled resonant converter hardware circuit, send to the feedback compensation error amplifier, and compare with reference voltage, the error voltage signal after relatively sends to controller through the feedback compensation error amplifier.The controller output current signal that the received current detecting unit gathers simultaneously, controller is nominal load, loyal load or underload according to the error voltage signal received and output current signal judgement load, through the operational module switch unit, selects corresponding control model; If be operated in heavy duty or nominal load, by the operational module switch unit, select the work of frequency modulation module, carry out the frequency adjustment control model; If be operated in underload, by the operational module switch unit, select to adjust wide module work, carry out determining frequency pulse width control pattern, realize the duty cycle adjustment voltage gain, and export corresponding switch controlled signal to the switch controlled end through the operational module switch unit.

In above-mentioned LLC controlled resonant converter underload control device, the wide module of described tune for generation of fixed switching frequency and regulate change in duty cycle according to the controlled resonant converter output voltage signal determine the frequency pulse width signal.Here realized under the underload situation, the control signal that controlled resonant converter receives is the two-way pwm signal that same frequency, same duty cycle and sequential differ half switch periods.

In above-mentioned LLC controlled resonant converter underload control device, described in determining the processing of frequency pulse width control pattern cycle, fixed switching frequency is resonance frequency, and, according to different load output voltage voltage stabilizing requirements, calculates PWM duty ratio D.PWM is pulse-width regulated, and the frequency pulse width control pattern of determining in this method is the pulse-width regulated control mode that is fixed frequency.Here determine that fixed switching frequency and load output voltage stabilizing require the relation existed with PWM duty ratio D, have the effect of optimizing the resonant network parameter.

In above-mentioned LLC controlled resonant converter underload control device, described duty cycle range is

f wherein _rfor resonance frequency, i.e. fixed switching frequency, f _r2it is the second resonance frequency.When nominal load, proportion is regulated control model, and now switching frequency is at f _r2<f≤f _rinterior change.Here the duty ratio D excursion of determining underload resonant network voltage gain is connected with nominal load and makes the fixed frequency value more stable with heavy duty.

In above-mentioned LLC controlled resonant converter underload control device, described PWM duty ratio is for regulating the gain of controlled resonant converter interior resonance network voltage, and described underload resonant network voltage gain computing formula is $G_{\mathrm{ac}}=\frac{1-\cos \left(2\mathrm{\&pi;D}\right)}{2}.$

In above-mentioned LLC controlled resonant converter underload control device, switching in the Dead Time after a switch periods finishes of described frequency adjustment control model and fixed pulse width control pattern frequently carried out.Here realized the impact that is not subject to a switch periods in Dead Time of frequency adjustment control model and the switching of fixed pulse width control pattern frequently, it is more accurate to make to control.

In above-mentioned LLC controlled resonant converter underload control device, the symmetrical output form of the pipe of arm switch up and down of described controlled resonant converter.Here realized under the underload situation, the control signal that controlled resonant converter receives is the two-way pwm signal that same frequency, same duty cycle and sequential differ half switch periods.

In above-mentioned LLC controlled resonant converter underload control device, described resonant network parameter is high magnetizing inductance and the design of low resonant inductance.Conventional LLC controlled resonant converter adopts low magnetizing inductance design, and higher circulating current in the time of can causing transformer primary side underloading on the one hand, make again when the heavy duty resonance current is larger on the other hand, brings more conducting and switching loss.In the application, high magnetizing inductance design has certain benefit to optimizing transformer size and control circuit.

In above-mentioned LLC controlled resonant converter underload control device, described LLC controlled resonant converter underload control device is for the resonance type power converter of full-bridge, half-bridge or push-pull configuration.Here illustrate that this control device can apply in the LLC controlled resonant converter with number of different types.

Compared with prior art, this LLC controlled resonant converter underload control device has the following advantages:

1, this device and method of the utility model adopts underload frequency pulse width control surely, realizes soft switch environment and the resonance Parameters Optimal Design of full-load range, and the efficiency of raising controlled resonant converter is light-load efficiency especially.

2, this device and method of the utility model directly carries out the selection of mode of operation by voltage, the current condition of load.Simultaneously, the utility model has also explicitly pointed out the critical switching point of two kinds of mode of operations at nominal load resonance frequency place.Guarantee switch tube zero voltage switch in whole control procedure and the soft switch environment of rectifying tube Zero Current Switch, thereby effectively determine the cavity voltage gain.

The accompanying drawing explanation

Fig. 1 is the utility model circuit diagram;

Fig. 2 is control flow chart of the present utility model;

The crucial current waveform figure of the switch controlled signal resonant cavity that Fig. 3 adjusts wide module to produce while being the regulation and control of the utility model underload.T wherein _r=1/f _r, a=DT _r;

Fig. 4 is the utility model resonant cavity normalized gain performance diagram when determining frequency pulse width control pattern;

Fig. 5 is the utility model crucial electric current experimental waveform of resonant cavity figure when determining frequency pulse width control pattern.

Embodiment

Be below specific embodiment of the utility model, and by reference to the accompanying drawings the technical solution of the utility model be further described, but the utility model is not limited to these embodiment.

As Figure 1-5, this LLC controlled resonant converter underload control device comprises controller, for making controlled resonant converter be operated in the frequency modulation module under the frequency adjustment control model and determine the wide module of tune under frequency pulse width control pattern for controlled resonant converter is operated in, the output voltage signal of nursing one's health for the hardware circuit that detects respectively the LLC controlled resonant converter and voltage detection unit and the current detecting unit of output current signal, described controller also is connected with the feedback compensation error amplifier, described voltage detection unit and reference voltage power supply are connected respectively the input of feedback compensation error amplifier, described current detecting unit connects the input of controller, the output of described controller is connected with the operational module switch unit, described frequency modulation module is connected respectively controller and operational module switch unit with the wide module of tune, described operational module switch unit connects controlled resonant converter switch controlled end, the output current signal that the error voltage signal that the output voltage that described controller detects according to voltage detection unit is exported after the feedback compensation error amplifier and current detecting unit detect judges whether the LLC controlled resonant converter works in light-load state, if be not operated in underload, by the operational module switch unit, select the work of frequency modulation module, carry out the frequency adjustment control model, if be operated in underload, by the operational module switch unit, select to adjust wide module work, carry out determining frequency pulse width control pattern, realize the duty cycle adjustment voltage gain, and export corresponding switch controlled signal to the switch controlled end through the operational module switch unit.Described in determining the processing of frequency pulse width control pattern cycle, fixed switching frequency is resonance frequency, and, according to different load output voltage voltage stabilizing requirements, calculates PWM duty ratio D.PWM is pulse-width regulated, and the application's the frequency pulse width control pattern of determining is the pulse-width regulated control mode that is fixed frequency.Here determine that fixed switching frequency and load output voltage stabilizing require the relation existed with PWM duty ratio D, have the effect of optimizing the resonant network parameter.

The PWM duty ratio is for regulating the gain of controlled resonant converter interior resonance network voltage, and now, underload resonant network voltage gain computing formula is

the duty ratio D excursion of regulating underload resonant network voltage gain is f wherein _rfor fixed switching frequency, f _r2for the switch low-limit frequency under the frequency adjustment control model, i.e. the second resonance frequency.Controlled resonant converter interior resonance network works in the switching frequency f=f under nominal load _r, switching frequency f=f _rfor frequency adjustment control model and the fixed critical working point of pulse width control pattern frequently.Here the switching frequency under the nominal load operating state is the fixed switching frequency under the underload operating state, and as frequency adjustment control model and the fixed critical working point of pulse width control pattern frequently.Be convenient to optimize the resonant parameter of controlled resonant converter interior resonance network.Switching in the Dead Time after a switch periods finishes of frequency adjustment control model and fixed pulse width control pattern frequently carried out.

Adjust wide module to fix for generation of frequency and regulate change in duty cycle according to the controlled resonant converter output voltage signal determine frequency pulse width signal, the symmetrical output form of the pipe of arm switch up and down of described controlled resonant converter.

The utility model LLC controlled resonant converter underload control device is applicable to the resonance type power converter of full-bridge, half-bridge or push-pull configuration.Controlled resonant converter generally comprises electronic switch, the output of half-bridge or full bridge structure, armature winding or electromagnetic induction coil by resonant inductance, resonant capacitance and transformer are in series, and wherein resonant inductance can be integrated with transformer magnetic, or individualism.The LLC controlled resonant converter of selecting in the present embodiment be LLC half bridge resonant as shown in Figure 1, comprising: input direct voltage V _in, the squarer driven by switching tube Q1, switching tube Q2, by the series resonance capacitor C _r, series resonance inductor L _rwith the shunt excitation inductance L _mthe resonant network formed, the ideal transformer T that no-load voltage ratio is n:1:1, diode VD ₁, diode VD ₂the rectification circuit formed, filter capacitor C _oand load resistance R _o.Series resonance inductor L wherein _rcan be an independent component, also can be integrated with transformer T magnetic.Drawn the control signal control of switching tube Q1, switching tube Q2 and the Working mould block selection signal mode timing waveform in critical point in figure.Above-mentioned voltage detection unit, current detecting unit can consist of resistance, also can consist of Hall element or voltage, current transformer; Its middle controller, frequency modulation module, adjust wide module and Working mould block selection circuit can adopt analog circuit to realize, also can adopt digital circuit to realize, comprise the programmable controller with software operational capability.

As shown in Figure 1 and Figure 2, in figure, FM means the frequency adjustment control model, and PWM means solid frequency pulse-width regulated control model, and LLC controlled resonant converter hardware circuit bussed supply voltage is direct voltage.Load control circuit comprises controller, voltage detection unit, current detecting unit, frequency modulation module and adjust wide module.Voltage detection unit gathers the direct current output loading voltage signal of LLC controlled resonant converter hardware circuit, send to the feedback compensation error amplifier, and compare with reference voltage, the error voltage signal after relatively sends to controller through the feedback compensation error amplifier.The controller output current signal that the received current detecting unit gathers simultaneously, controller is nominal load, loyal load or underload according to the error voltage signal received and output current signal judgement load, through the operational module switch unit, selects corresponding control model; If be operated in heavy duty or nominal load, by the operational module switch unit, select the work of frequency modulation module, carry out the frequency adjustment control model; If be operated in underload, by the operational module switch unit, select to adjust wide module work, carry out determining frequency pulse width control pattern, realize the duty cycle adjustment voltage gain, and export corresponding switch controlled signal to the switch controlled end through the operational module switch unit.If select solid pulse width control pattern frequently, controller is in the period treatment of adjusting wide module, and fixed switching frequency is resonance frequency, and calculates the PWM duty ratio according to different load output voltages by the voltage gain formula of solid frequency pulse width control pattern; Controller is in the period treatment of frequency modulation module, and fixed duty cycle is that 1/2(ignores Dead Time), according to different load output voltages, the voltage gain formula by frequency modulation mode calculates switching frequency; Controller selects to adjust wide module or the work of frequency modulation module, output switch management and control signal processed according to loading condition.Controller, according to different error voltage values, is exchanged wide module and is carried out the duty ratio adjustment, thereby the voltage gain of regulating circuit makes the output loading voltage of LLC controlled resonant converter keep stable.Concrete adjustment process comprises:

When nominal load, proportion is regulated the frequency adjustment control model of gain, and switching frequency is at f _r2<f≤f _rinterior change, mean Q on the signal flow graph in the drawings ₁, Q ₂for Fig. 1 switching tube Q1 and driving signal corresponding to switching tube Q2.The driving signal Q of switching tube Q1 and switching tube Q2 ₁, Q ₂duty ratio is fixed as 1/2.The resonant network voltage gain is:

$G_{\mathrm{ac}}=1/\sqrt{{\{1+\frac{1}{K}[1-{\left(\frac{f_r}{f}\right)}^2\left]\right\}}^2+Q^2{(\frac{f}{f_r}-\frac{f_r}{f})}^2}$

Wherein $K=\frac{L_m}{L_r},$ $f_r=\frac{1}{2\mathrm{\&pi;}\sqrt{L_r{C}_r}},$ ${\mathrm{<figure-callout\; id="2"\; label="f\; r"\; filenames="HDA00003526818100011.png"\; state="\{\{state\}\}">f</figure-callout>}}_r=\frac{1}{2\mathrm{\&pi;}\sqrt{(L_r+L_m)C_r}},$ Quality factor $Q=\frac{{2\mathrm{\&pi;}}^3{f}_r{L}_r}{{8\mathrm{\&pi;}}^2{R}_o}.$ C in formula _rcapacitance, L for series resonance capacitor C r _rinductance value, L for series resonance inductor Lr _mfor the inductance value of magnetizing inductance Lm, the ratio that K is magnetizing inductance and resonant inductance.

When load lightens, adopt switching frequency to be fixed as f=f _rsolid frequency pulse width control pattern, carry out regulation voltage gain by PWM duty ratio D.Resonant network circuit gain computing formula is $G_{\mathrm{ac}}^{\&prime;}=\frac{1-\cos \left(2\mathrm{\&pi;D}\right)}{2},$ Wherein duty ratio D excursion is $1-\frac{f_r}{2{\mathrm{<figure-callout\; id="2"\; label="f\; r"\; filenames="HDA00003526818100011.png"\; state="\{\{state\}\}">f</figure-callout>}}_r}<D\&le;\frac{1}{2}.$

When the duty ratio pwm signal that is D removes to control LLC controlled resonant converter half-bridge switch pipe, by fourier decomposition, bussed supply direct voltage V _inthe fundametal compoment amplitude that is input to resonant network is:

and the fundametal compoment amplitude under traditional frequency adjustment control model is every half switch periods is T, load current I _oby resonance current i _crwith exciting current i _lmdifference through transformer coupled, obtain, meet:

i _owith i _crand i _lmthe area surrounded is directly proportional.During power output, exciting current i _lmbecause rectification side clamped kept constant linear change.Therefore, when load reduction, resonance current i _crmust reduce to adapt to this variation.Because switching frequency is fixed on f=f _r, do not change the impedance operator of resonant network, can adapt to resonance current i by PWM duty ratio D control inputs voltage _crreduce.

Can fully demonstrate the result that the utility model obtains according to above-mentioned analysis in Fig. 3,4,5, the operational modal analysis of carrying out solid frequency pulse-width regulated control model as Fig. 3 under light-load state is as follows:

In Fig. 3, can see, at t ₀constantly, drive signal Q ₂turn-off exciting current i _lmoppositely, start linear the rising, resonance current i _crby resonance frequency f _rrise, resonance current i _crexciting current i _lm, rectification side diode VD ₁conducting, output has obtained energy.Because the existence of duty ratio, now Q ₁drive signal not arrive;

At resonance current i _crt before zero passage ₁constantly, apply Q ₁drive signal; Because underload makes resonance current i _crlow during than nominal load, resonance current i _cr=exciting current i _lmoccur in the t arrived before the half period ₂constantly, now rectification side diode VD ₁cut-off, energy is cut off from the input stage to the output stage.Resonance current i _crwith exciting current i _lmserial connection, resonant network is pressed f _r2frequency resonance.See diode VD ₁for Zero Current Switch turn-offs;

At t ₃constantly, Q ₁the driving signal turn-offs, exciting current i _lmoppositely, start linear decline, resonance current i _crby resonance frequency f _rdescend, resonance current i _cr<exciting current i _lm, rectification side diode VD ₂the conducting rectification;

At i _crt before zero passage ₄constantly, apply Q ₂drive signal; Resonance current i _cr=exciting current i _lmoccur in the t arrived before the half period ₅constantly, now rectification side diode VD ₂cut-off, energy is cut off from the input stage to the output stage.Resonance current i _crwith exciting current i _lmserial connection, resonant network is pressed f _r2frequency resonance.Diode VD ₂for Zero Current Switch turn-offs;

At t ₆constantly, Q ₂the driving signal turn-offs, i _lmoppositely, enter next work period.

To sum up to the analysis of Fig. 3, can find out under light-load state and realize that by solid pulse-width regulated control model frequently the Zero Current Switch of rectification side diode turn-offs, if driving signal can guarantee to apply before the resonance current zero passage, the switch tube zero voltage switch turn-offs and also can realize, Gu the mould of pulse-width regulated control frequently realizes that the zero voltage switch shutoff is guaranteed by duty ratio D span.

Resonant network is designed under nominal load work in switching frequency f=f _r, this is also the critical working point that frequency modulation mode and fixed pulse width are regulated pattern.Frequency modulation mode and the solid switching of pulse-width regulated control model frequently are to carry out in the Dead Time after a switch periods finishes.Fixed pulse width adjusting pattern has the symmetrical drive form of the upper underarm same with frequency modulation mode.

The selection of operational module and the calculating of error voltage signal can adopt analog circuit or digital control PI algorithm.

Fig. 4 is resonant cavity normalized gain performance diagram while using solid pulse-width regulated control model frequently in the utility model embodiment.The selected parameter of curve is: L _r=46 μ H, L _m=1.38mH, C _r=55nF, Q=0.126, K=30.X-axis is duty ratio D, and Y-axis is the normalized voltage gain, switching frequency f=f in figure _r, by duty ratio minimum value D _mindetermine the minimum voltage gain G _min.D _mincan when design resonant network parameter, determine.As can be seen from the figure by this gain computing formula, can effectively determine the cavity voltage gain.Conventional frequency modulation mode can make quality factor of circuit change when load variations, cause circuit gain to change along with load, use underload gain characteristic curve as shown in Figure 4, can effectively improve above-mentioned impact, make circuit gain and load switch, controlled by duty ratio D.

Fig. 5 is used the crucial electric current experimental waveform of the solid resonant cavity of pulse-width regulated control model frequently figure in the utility model embodiment.Shown driving signal Q as schemed ₁for 5V/div, Q2 is 5V/div, the lower i of effect _crfor resonance current 500mA/div, switching tube Q ₁, switching tube Q ₂voltage and rectifier diode VD ₁, diode VD ₂electric current synthetic waveform figure, Fig. 5 has further verified the analysis of above-mentioned Fig. 3.Wherein X-axis is i _cr=0.As experimental results show that underload, figure adopt PWM duty ratio D to control voltage gain, make the LLC controlled resonant converter realize that the zero voltage switch of switching tube is turn-offed and the Zero Current Switch of rectifying tube turn-offs, mean that with ZVS zero voltage switch is turn-offed and the ZCS table is that Zero Current Switch turn-offs respectively in the drawings.As shown in Figure 5 drive signal Q in solid frequency pulse-width regulated control model ₁, Q ₂the lower resonance current i of effect _cr, rectifying tube VD ₁, VD ₂current waveform.Gu the pulse-width regulated control model makes converter realize ZCS when underloading frequently, as shown in Figure 5, Q ₁certain moment before driving signal to turn-off, i _vD2arrive 0 and realize zero-current switching, after this Q ₁turn-off resonance current i _crafter phase delay voltage, start oppositely to descend, i _vD1rise, at i _crbefore zero passage, Q ₂the driving signal arrives.Therefore, this pattern had both realized switching tube ZVS, had realized again rectifying tube ZCS.

Specific embodiment described herein is only to the explanation for example of the utility model spirit.The utility model person of ordinary skill in the field can make various modifications or supplements or adopt similar mode to substitute described specific embodiment, but can't depart from spirit of the present utility model or surmount the defined scope of appended claims.

Claims (10)

1. A light load control device for an LLC resonant converter, characterized in that the device includes a controller, a frequency modulation module for making the resonant converter work under the frequency regulation control mode and a frequency modulation module for making the resonant converter work at a fixed frequency Width adjustment module under pulse width control mode, a voltage detection unit and a current detection unit for respectively detecting the output voltage signal and output current signal of the LLC resonant converter, the controller is also connected with a feedback compensation error amplifier, and the voltage The detection unit and the reference voltage power supply are respectively connected to the input end of the feedback compensation error amplifier, the current detection unit is connected to the input end of the controller, the output end of the controller is connected to the working module switching unit, the frequency modulation module and the width adjustment module The controller and the switching unit of the working module are respectively connected, and the switching unit of the working module is connected to the control terminal of the switching tube of the resonant converter. 2. The LLC resonant converter light load control device according to claim 1, characterized in that, the controller detects the output voltage according to the output voltage detected by the voltage detection unit after the error voltage signal output by the feedback compensation error amplifier and the detection by the current detection unit The output current signal of the LLC resonant converter can be used to judge whether the LLC resonant converter is working in the light load state; if it is working in the light load state, the width adjustment module can be selected to work through the working module switching unit, and the constant frequency pulse width control mode can be used to realize the duty ratio to adjust the voltage gain. And the corresponding switching tube control signal is output to the switching tube control terminal through the working module switching unit. 3. The LLC resonant converter light load control device according to claim 2, characterized in that the width adjustment module is used to generate a fixed switching frequency and a constant frequency pulse that adjusts the duty cycle according to the output voltage signal of the resonant converter wide signal. 4. The LLC resonant converter light load control device according to claim 3, characterized in that, in the periodic processing of the fixed frequency pulse width control mode, the fixed switching frequency is the resonant frequency, and the output voltage is stable according to different loads. Voltage requirements, calculate the PWM duty cycle D. 5. LLC resonant converter light load control device according to claim 4, is characterized in that, described duty cycle range is

Among them, f _r is the resonant frequency, that is, a fixed switching frequency, and f _r2 is the second resonant frequency. 6. The LLC resonant converter light load control device according to claim 5, wherein the PWM duty cycle is used to adjust the resonant network voltage gain in the resonant converter, and the light load resonant network voltage gain calculation formula for 7. The LLC resonant converter light load control device according to any one of claims 1-6, wherein the switching between the frequency regulation control mode and the constant frequency pulse width control mode is performed after a switching cycle ends during the dead time. 8. The LLC resonant converter light load control device according to claim 7, characterized in that the upper and lower arm switching tubes of the resonant converter have a symmetrical output form. 9. The LLC resonant converter light load control device according to claim 8, characterized in that, the resonant network parameters of the LLC resonant converter are a large excitation inductance value and a small resonant inductance value. 10. The LLC resonant converter light load control device according to claim 9, characterized in that the LLC resonant converter light load control device is used for resonant power converters with full bridge, half bridge or push-pull structures.

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