CN112583280B

CN112583280B - Resonant converter

Info

Publication number: CN112583280B
Application number: CN202110207429.8A
Authority: CN
Inventors: 毛昭祺; 王纪周; 柯乃泉
Original assignee: Hangzhou Upowertek Power Supply Co ltd
Current assignee: Hangzhou Upowertek Power Supply Co ltd
Priority date: 2021-02-25
Filing date: 2021-02-25
Publication date: 2021-05-14
Anticipated expiration: 2041-02-25
Also published as: CN112583280A

Abstract

The invention discloses a resonant converter, and relates to the technical field of power electronics. The invention comprises a bridge circuit, a resonance circuit; a transformer T1: the resonant circuit 2 at least comprises a first capacitor Cr1, a second capacitor Cr2 and a clamping diode D2 which are connected in parallel, one end of the first capacitor Cr1 is connected in series with a second switch S3, and the first capacitor Cr1, the second capacitor Cr2 and the clamping diode D2 are respectively connected in series with the first clamping diode D1 and the resonant inductor Lr; a drive control circuit which supplies a drive signal Vg _ S3 to the second switch S3; the capacitance of the first capacitor Cr1 is far larger than that of the second capacitor Cr2, and the second clamping diode D2 and the first clamping diode D1 are reversely connected into the circuit. According to the invention, through the combined action of the second switching tube S3 and the clamping diodes D1 and D2 and through circuit control, a circuit is equivalent to a series resonant converter when the circuit is fully loaded, and the conversion efficiency is increased.

Description

Resonant converter

Technical Field

The invention belongs to the technical field of power electronics, and particularly relates to a resonant converter.

Background

The driving power supply with high power density, high efficiency and low cost is more competitive. Usually, the driving power source selects a resonant circuit to achieve the objectives of high power density and high efficiency. The resonant circuit can realize zero voltage switching-on of two or more switching tubes on the primary side and zero current switching-off of the secondary side rectifier diode, can reduce the switching loss of a power supply, and improves the efficiency and the power density of the power converter.

In the design of the resonant circuit of the power converter, if high-frequency operation can be adopted, the size of the transformer is greatly reduced, the power density is increased, the cost of passive devices is reduced, and the working efficiency is not reduced.

Fig. 6 is a diagram of an LLC resonant circuit provided in the prior art. The existing LLC resonant circuit converts an input power supply with an input voltage Vin into a form required by a load. However, in the prior art, in the normal operation region of the LLC resonant circuit, as the operating frequency increases, the gain of the resonant circuit decreases, and thus the output power decreases. It can be seen that the operating frequency of the existing LLC resonant circuit increases with the decrease of the load power, especially when the load is light, and the frequency is very high, and the curve is shown in fig. 7. Generally, the maximum operating frequency of the circuit needs to be limited, so that the full-load operating frequency cannot be greatly increased.

Therefore, how to change the operating mode of the resonant circuit to increase the full-load operating frequency and power density thereof is a technical problem that needs to be solved by those skilled in the art at present.

Disclosure of Invention

The invention aims to provide a resonant converter, which greatly improves full-load switching frequency and is beneficial to high-frequency and high-power density design by means of the combined action of a second switching tube S3 and clamping diodes D1 and D2 and the regulation of a resonant circuit through a drive control circuit.

In order to solve the technical problems, the invention is realized by the following technical scheme:

the invention is a resonant converter comprising:

a bridge circuit coupled to the input voltage Vin;

a resonant circuit coupled to the bridge circuit;

a transformer T1 coupled to the resonant circuit;

the resonant circuit at least comprises a first capacitor Cr1, a second capacitor Cr2 and a second clamping diode D2 which are connected in parallel, wherein one end of the first capacitor Cr1 is connected in series with a switch S3, the switch S3 is connected in parallel with a second capacitor Cr2, and the first capacitor Cr1, the second capacitor Cr2 and the second clamping diode D2 are respectively connected in series with the first clamping diode D1 and a resonant inductor Lr;

the drive control circuit is further included and is used for providing a drive signal Vg _ S3 for the switch S3;

the capacitance of the first capacitor Cr1 is much larger than that of the second capacitor Cr2, and the second clamping diode D2 and the first clamping diode D1 are reversely connected into the circuit.

Preferably, the bridge circuit is at least composed of a switch S1 and a switch S2, and the drive control circuit provides a drive signal Vg _ S1 to the switch S1 and a drive signal Vg _ S2 to the switch S2.

Preferably, the resonant circuit is driven by the switches S1, S2.

Preferably, the driving control circuit comprises a resistor Rfb, an operational amplifier Op1 and a comparator Comp1, wherein the positive input end of the operational amplifier Op1 is connected with a reference voltage Vref, the negative input end of the operational amplifier Op is connected with the resistor Rfb, the output end of the operational amplifier Op is connected with the positive input end of the comparator Comp1, the reverse input end of the comparator Comp1 is connected with a hysteresis voltage Vhyz, the hysteresis voltage Vhyz is connected with the reference voltage Vref, and the comparator Comp1 is used for comparing the voltage Vcomp output by the operational amplifier Op 1;

when the voltage Vcomp output by the operational amplifier Op1 rises to the sum of the hysteresis voltage Vhyz and the reference voltage Vref, the comparator Comp1 is configured to output the driving signal Vg _ S3 to the switch S3, the switch S3 is turned on, the switch S2 is turned on, and the switch S1 is turned off;

when the voltage Vcomp output from the operational amplifier Op1 drops to the reference voltage Vref, the comparator Comp1 is used to output the driving signal Vg _ S3 to the switch S3, the switch S3 is turned off, the switch S2 is turned off, and the switch S1 is turned on.

Preferably, the circuit further comprises a compensation capacitor Cfb, a voltage controlled oscillator VCO1, a voltage controlled oscillator VCO2, an inverter circuit and a symmetrical complementary driving circuit, two ends of the compensation capacitor Cfb are respectively connected to the inverting input end and the output end of the operational amplifier Op1, the output ends of the compensation capacitor Cfb and the operational amplifier Op1 are respectively connected to the voltage controlled oscillator VCO1 and the voltage controlled oscillator VCO2 which are arranged in parallel, the voltage controlled oscillator VCO1 is connected to the symmetrical complementary driving circuit through a switch Sa, and the voltage controlled oscillator VCO2 is connected to the symmetrical complementary driving circuit through a switch Sb;

when the voltage Vcomp output by the operational amplifier Op1 drops to the reference voltage Vref, the comparator Comp1 is configured to output a driving signal to the switch Sa, the switch Sa is turned on, and the switch Sb is turned off;

when the output voltage Vcomp output from the operational amplifier Op1 rises to the sum of the hysteresis voltage Vhyz and the reference voltage Vref, the comparator Comp1 is configured to output a driving signal to the switch Sb, the switch Sb is turned on, and the switch Sa is turned off.

Preferably, the symmetric complementary driving circuit outputs the driving signal Vg _ s1, and the duty ratios of the driving signal Vg _ s2 are 50% respectively.

Preferably, the switch S3 is one of an anti-series field effect transistor, a triode, and an insulated gate bipolar transistor.

Preferably, the output end of the transformer T1 is coupled to the output rectifying circuit DB1, and the output rectifying circuit DB1 is a center-tapped rectifying circuit, a voltage-doubler rectifying circuit or a full-bridge rectifying circuit.

The invention has the following beneficial effects:

according to the invention, through the combined action of the second switching tube S3 and the clamping diodes D1 and D2, the maximum frequency of the converter is limited within the second resonant frequency through circuit control.

The circuit is equivalent to a series resonant converter when the circuit is fully loaded, and has excellent conversion efficiency.

When the load is lighter, the working frequency of the switching tube can be reduced instead of being continuously increased, so that the service life of the switching tube is prolonged, compared with the existing LLC converter, the limitation on the highest frequency is reduced, the full-load switching frequency is favorably improved, and the high-frequency high-power density design is favorably realized.

Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a circuit diagram of a resonant converter of the present invention;

FIG. 2 is a driving control circuit diagram according to the present invention;

FIG. 3 is a line graph of load versus operating frequency Fs of the circuit;

FIG. 4 is a waveform diagram of a high load resonant converter;

FIG. 5 is a waveform diagram of a light-load resonant converter;

FIG. 6LLC resonant circuit diagram;

fig. 7 is a graph of operating frequency and current in the circuit diagram of fig. 6.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, the present invention is a resonant converter, including:

a bridge circuit 1 coupled to an input voltage Vin;

the bridge circuit 1 is composed of at least a switch S1 and a switch S2, wherein the switch S1 and the switch S2 are both switching triodes, that is, the on and off of the switch S1 and the switch S2 are drivable.

And a resonant circuit 2 coupled to the bridge circuit 1, wherein the resonant circuit 2 is driven by the switch S1 and the switch S2.

The primary side of a transformer T1 is coupled to the resonant circuit 2: the secondary side of the transformer T1 is coupled to an output rectifying circuit DB1, wherein the output rectifying circuit DB1 is a center-tapped rectifying circuit, a voltage doubler rectifying circuit or a full-bridge rectifying circuit.

Wherein:

the resonant circuit 2 at least comprises a first capacitor Cr1, a second capacitor Cr2 and a second clamping diode D2 which are connected in parallel, one end of the first capacitor Cr1 is connected in series with a switch S3, the switch S3 is connected in parallel with a second capacitor Cr2, and the first capacitor Cr1, the second capacitor Cr2 and the second clamping diode D2 are respectively connected in series with the first clamping diode D1 and the resonant inductor Lr.

The first capacitor Cr1, the second capacitor Cr2, and the second clamping diode D2 are respectively connected in series to the primary side of the transformer T1, wherein the second clamping diode D2 and the first clamping diode D1 are reversely connected to the circuit, and the connection directions of the clamping diodes are opposite to the current direction.

The switch S3 is one of a field effect transistor, a triode, and an insulated gate bipolar transistor connected in series in reverse.

In addition, the capacitance of the first capacitor Cr1 is much larger than that of the second capacitor Cr2, so when the switch S3 is always turned on, the total resonant capacitance is equal to Cr1+ Cr2, because the resonant capacitance is larger, the capacitor ripple voltage is smaller, and the first clamping diode D1 and the second clamping diode D2 are not turned on.

When the switch S3 is turned off all the time, the first capacitor Cr1 does not participate in the operation because the capacitance value of the resonant capacitor second capacitor Cr2 is small and the capacitor ripple voltage is large. When the voltage across the second capacitor Cr2 is greater than Vin, the first clamping diode D1 is turned on; when the voltage across the second capacitor Cr2 is less than 0, the second clamping diode D2 is turned on.

By controlling the on/off of the switch S3, the switch S1 and the switch S2, a stable output voltage can be obtained.

Further:

first resonance frequency:

the second resonance frequency:

third resonance frequency:

，

。

specifically, as shown in fig. 3:

when fully loaded, the switching frequency Fs approaches the first resonant frequency Fr1, and increases gradually as the load current decreases gradually. When the switching frequency Fs approaches the third resonant frequency Fr3, the switch S3 is turned off, Fs is set to Fr2, and the circuit enters a clamping mode of primary current limiting. As the load is further stepped down, the switching frequency Fs is also stepped down. Conversely, as the load increases gradually, the switching frequency Fs increases gradually to the second resonant frequency Fr2, the switch S3 is turned on, and Fs is set to Fr 3. Then, as the load is further increased, the switching frequency Fs is gradually decreased to be close to Fr 1.

And then the corresponding Kr value is adjusted and set, so that the circuit gain and frequency jump can be smoothed.

Along with the reduction of the load, the switching frequency cannot be greatly increased, the highest working frequency of the circuit is Fr2, the full-load working frequency can be greatly improved, and the high-frequency high-power density design is facilitated.

As shown in fig. 2, the driving control circuit 3 is further included, and supplies a driving signal Vg _ S3 to the switch S3, a driving signal Vg _ S1 to the switch S1, and a driving signal Vg _ S2 to the switch S2.

The on/off of the drive switch S3 is performed to obtain a stable output voltage V.

Specifically, the driving control circuit 3 includes a resistor Rfb, an operational amplifier Op1 and a comparator Comp1, wherein a positive input terminal of the operational amplifier Op1 is connected to the reference voltage Vref, a negative input terminal is connected to the resistor Rfb, an output terminal is connected to a positive input terminal of the comparator Comp1, a negative input terminal of the comparator Comp1 is connected to the hysteresis voltage Vhyz, the hysteresis voltage Vhyz is connected to the reference voltage Vref, and the comparator Comp1 is used for comparing the voltage Vcomp output by the operational amplifier Op 1.

When the voltage Vcomp output by the operational amplifier Op1 rises to the sum of the hysteresis voltage Vhyz and the reference voltage Vref, the comparator Comp1 is configured to output the driving signal Vg _ S3 to the switch S3, the switch S3 is turned on, and accordingly, the switch S2 is turned on and the switch S1 is turned off;

when the voltage Vcomp output from the operational amplifier Op1 drops to the reference voltage Vref, the comparator Comp1 is used to output the driving signal Vg _ S3 to the switch S3, the switch S3 is turned off, and accordingly, the switch S2 is turned off and the switch S1 is turned on.

Preferably, the states of the switch S2 and the switch S1 are automatically driven by the driving signal.

Correspondingly, the driving control circuit 3 further includes a compensation capacitor Cfb, a voltage-controlled oscillator VCO1, a voltage-controlled oscillator VCO2, a not gate circuit, and a symmetrical complementary driving circuit.

Operating characteristics of the voltage controlled oscillator VCO 1: the higher the input voltage, the higher the output frequency.

Operating characteristics of the voltage controlled oscillator VCO 2: the higher the input voltage, the lower the output frequency.

The frequency operating range of the VCO1 is Fr2 to 0, and the corresponding Vcomp voltage signal range is Vref to 0. The frequency operation range of the VCO2 is from Fr3 to Fr1, and the corresponding Vcomp voltage signal range is from Vref + Vhyz to the maximum limit value Vcomp _ max.

The output ends of the compensation capacitor Cfb and the operational amplifier Op1 are connected in parallel with the operational amplifier Op1, the output ends of the compensation capacitor Cfb and the operational amplifier Op1 are connected with a voltage-controlled oscillator VCO1 and a voltage-controlled oscillator VCO2 which are arranged in parallel with each other, the voltage-controlled oscillator VCO1 is connected to the symmetrical complementary driving circuit through a switch Sa, and the voltage-controlled oscillator VCO2 is connected to the symmetrical complementary driving circuit through a switch Sb.

When the voltage Vcomp output by the operational amplifier Op1 drops to the reference voltage Vref, the comparator Comp1 is configured to output a driving signal to the switch Sa, the switch Sa is turned on, the switch Sb is turned off, and the voltage controlled oscillator VCO1 operates;

when the voltage Vcomp output from the operational amplifier Op1 rises to the sum of the hysteresis voltage Vhyz and the reference voltage Vref, the comparator Comp1 is configured to output a driving signal to the switch Sb, the switch Sb is turned on, the switch Sa is turned off, and the voltage-controlled oscillator VCO2 operates instead of the voltage-controlled oscillator VCO 1.

Preferably, the symmetrical complementary driving circuit outputs symmetrical complementary driving signals with duty ratios of 50% to the switch S1 and the switch S2, respectively.

As shown in fig. 4, when the load is heavy, the switch S3 is always turned on, Cr1 participates in the resonant operation, and the circuit operation state approaches the series resonant converter, so as to ensure sufficient energy output.

As shown in fig. 5, when the load is light, the switch S3 is always turned off, Cr1 does not participate in resonant operation, D1 and D2 are alternatively clamped and turned on to feed part of energy back to the input, the converter operates in a clamp-on and off state, and the more light the load is, the more obvious the off is.

It should be noted that, in the above system embodiment, each included unit is only divided according to functional logic, but is not limited to the above division as long as the corresponding function can be implemented; in addition, specific names of the functional units are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present invention.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A resonant converter, comprising:

a bridge circuit (1) coupled to an input voltage (Vin);

a resonant circuit (2) coupled to the bridge circuit (1);

-a transformer (T1) coupled to the resonant circuit (2);

the resonant circuit (2) is characterized by at least comprising a first capacitor (Cr 1), a second capacitor (Cr 2) and a second clamping diode (D2) which are connected in parallel, wherein the first capacitor (Cr 1) is connected with a switch S3 in series, a branch of the first capacitor (Crl) which is connected with the switch S3 in series is connected with the second capacitor (Cr 2) and the second clamping diode (D2) in parallel respectively, one end of the first capacitor (Crl) is connected with one end of the switch S3, the other end of the switch S3 is connected with a cathode of the second clamping diode (D2), one end of a second capacitor (Cr 2) is connected with the anode of a first clamping diode (D1), the other end of the first capacitor (Crl), the anode of a second clamping diode (D2) and the other end of a second capacitor (Cr 2) are all connected with the cathode of the input power Vin, the cathode of the input power Vin is grounded, and the anode of a first clamping diode (Dl) is connected with the anode of the input power Vin;

the drive control circuit (3) is used for providing a drive signal Vg _ S3 to the switch S3;

the capacitance of the first capacitor (Cr 1) is far greater than that of the second capacitor (Cr 2), and the second clamping diode (D2) and the first clamping diode (D1) are reversely connected into the circuit;

the driving control circuit (3) comprises a resistor (Rfb), an operational amplifier (Op 1) and a comparator (Comp 1), wherein the positive input end of the operational amplifier (Op 1) is connected with a reference voltage (Vref), the negative input end of the operational amplifier (Op 1) is connected with the resistor (Rfb), the output end of the operational amplifier is connected with the positive input end of the comparator (Comp 1), the reverse input end of the comparator (Comp 1) is connected with a hysteresis voltage (Vhyz), the hysteresis voltage (Vhyz) is connected with the reference voltage (Vref), and the comparator (Comp 1) is used for comparing the voltage (Vcomp) output by the operational amplifier (Op 1);

when the voltage (Vcomp) output by the operational amplifier (Op 1) rises to the sum of the hysteresis voltage (Vhyz) and the reference voltage (Vref), the comparator (Comp 1) is configured to output the driving signal Vg _ S3 to the switch S3, the switch S3 is turned on, the switch S2 is turned on, and the switch S1 is turned off;

when the voltage (Vcomp) output from the operational amplifier (Op 1) drops to the reference voltage (Vref), the comparator (Comp 1) is used to output the driving signal Vg _ S3 to the switch S3, the switch S3 is turned off, the switch S2 is turned off, and the switch S1 is turned on.

2. A resonant converter according to claim 1, characterized in that the bridge circuit (1) is formed by at least a switch S1, a switch S2, and the drive control circuit (3) supplies a drive signal Vg _ S1 to the switch S1 and a drive signal Vg _ S2 to the switch S2.

3. A resonant converter according to claim 2, characterized in that the resonant circuit (2) is driven by the switches S1, S2.

4. The resonant converter according to claim 1, further comprising a compensation capacitor (Cfb), a voltage controlled oscillator VCO1, a voltage controlled oscillator VCO2, a not gate circuit and a symmetrical complementary driving circuit, wherein two terminals of the compensation capacitor (Cfb) are respectively connected to the inverting input terminal and the output terminal of the operational amplifier (Op 1), the output terminals of the compensation capacitor (Cfb) and the operational amplifier (Op 1) are respectively connected to the voltage controlled oscillator VCO1 and the voltage controlled oscillator VCO2 which are arranged in parallel, the voltage controlled oscillator VCO1 is connected to the symmetrical complementary driving circuit through a switch Sa, and the voltage controlled oscillator VCO2 is connected to the symmetrical complementary driving circuit through a switch Sb;

when the voltage (Vcomp) output by the operational amplifier (Op 1) drops to the reference voltage (Vref), the comparator (Comp 1) is used to output a driving signal to the switch Sa, the switch Sa is turned on, and the switch Sb is turned off;

when the voltage (Vcomp) output from the operational amplifier (Op 1) rises to the sum of the hysteresis voltage (Vhyz) and the reference voltage (Vref), the comparator (Comp 1) is used to output a driving signal to the switch Sb, the switch Sb is turned on, and the switch Sa is turned off.

5. The resonant converter according to claim 1, wherein the duty ratios of the output drive signal Vg _ s1 and the output drive signal Vg _ s2 of the symmetrical complementary drive circuit are 50% respectively.

6. A resonant converter according to claim 1, wherein the switch S3 is one of an anti-series fet, a triode, and an igbt.

7. A resonant converter according to claim 1, characterized in that the output of the transformer (T1) is coupled to an output rectifier circuit (DB 1), and the output rectifier circuit (DB 1) is one of a center-tapped rectifier circuit, a voltage doubler rectifier circuit or a full-bridge rectifier circuit.