CN107395022B

CN107395022B - Resonant switching converter and control method thereof

Info

Publication number: CN107395022B
Application number: CN201710614211.8A
Authority: CN
Inventors: 陈华捷; 谢小高
Original assignee: Hangzhou Silan Microelectronics Co Ltd
Current assignee: Hangzhou Silan Microelectronics Co Ltd
Priority date: 2017-07-25
Filing date: 2017-07-25
Publication date: 2023-08-08
Anticipated expiration: 2037-07-25
Also published as: CN107395022A

Abstract

The application discloses a resonant switching converter and a control method thereof. The resonant switching converter includes: the main circuit comprises a first transformer and a plurality of switching tubes connected with a primary winding of the first transformer, the switching tubes convert direct current voltage into square wave signals, the main circuit transmits the square wave signals from the primary winding of the first transformer to a secondary winding in a resonance mode so as to transmit electric energy, and the secondary winding is connected to an output end so as to supply power to a load; and a control circuit connected to the main circuit for obtaining the voltage sampling signal and the current sampling signal from the secondary side and generating driving signals of the plurality of switching tubes according to the voltage sampling signal and the current sampling signal, wherein the control circuit obtains the voltage sampling signal and the current sampling signal in a non-isolated manner and provides the driving signals to the plurality of switching tubes in an isolated manner. The resonant switching converter can eliminate an optocoupler, thereby simplifying a circuit structure and improving the stability and reliability of operation.

Description

Resonant switching converter and control method thereof

Technical Field

The present invention relates to power electronics, and more particularly, to a resonant switching converter and a control method thereof.

Background

The resonant switching converter is a power converter which adopts a switching tube to obtain square wave voltage and adopts a resonant circuit to carry out resonance so as to realize energy transmission. The LLC resonant converter comprises a third-order resonant network composed of LLC, and can realize the adjustment of load from full load to no load in a narrow frequency range. The LLC resonant converter has higher power density and fewer electronic components, has smooth current waveforms, is beneficial to improving electromagnetic interference, can realize zero-voltage switching (Zero Voltage Switching, ZVS) and zero-current switching (Zero Current Switching, ZCS) of a switching tube in the whole operation range, is beneficial to obtaining extremely high efficiency, and is widely applied.

Conventional LLC resonant converters typically employ a secondary side control method (Secondary Side Regulation, SSR). The secondary side circuit samples the output current signal and the output voltage signal, generates a feedback signal through the error amplifier, then transmits the feedback signal from the secondary side of the transformer to the primary side of the transformer through the optical coupler, and the primary side control chip controls the switching tube to be switched on or off according to the feedback signal transmitted by the optical coupler, so that the closed-loop regulation of the output voltage or the output current is realized.

Fig. 1 shows a schematic diagram of an SSR LLC half-bridge resonant converter according to the prior art. As shown, the resonant converter 100 includes a power factor correction circuit (PFC) 101, a square wave generation circuit 102, a resonant circuit 103, a rectifying circuit 104, an output capacitor Co, and an output current detection circuit Rsen. The resonant converter 100 receives an ac voltage Vac, rectifies the ac voltage Vac into a dc voltage by the PFC circuit 101, and inverts the dc voltage by the square wave generating circuit 102 to obtain a square wave voltage. The square wave voltage is input to the resonant circuit 103 to generate resonance. Energy is transferred from the primary side of transformer T1 to the secondary side of transformer T1 through resonant circuit 103. The load RL is supplied with power after rectification by the rectification circuit 104 and the filtering by the output capacitor Co. Meanwhile, the sampling and error amplifying circuit 107 samples the output current and output voltage, generates the compensation signal COMP internally, and generates the feedback signal VFB corresponding to the compensation signal COMP on the primary side through the optocoupler 106. The primary side control circuit 105 controls the switching on or off of the switching transistors Q1 and Q2 according to the feedback signal VFB, thereby realizing constant voltage output control or constant current output control.

However, the circuit structure of the SSR LLC resonant converter is complex, and the secondary side includes components such as the sampling and error amplifying circuit 107 and the optocoupler 106, so that the circuit cost is increased, the circuit area is increased, and the circuit reliability is reduced. The optocoupler 106 cannot operate in a high temperature environment and has a low frequency pole, so that the design difficulty of the SSR LLC resonant converter is increased, and the working stability and reliability are deteriorated.

Disclosure of Invention

In view of the above-described problems, an object of the present invention is to provide a novel resonant switching converter and a control method thereof, in which a control circuit directly acquires a sampling signal from a secondary side of a transformer and is used for primary side control, so that a circuit can be simplified and resonant operation stability and reliability can be improved.

According to a first aspect of the present invention, there is provided a resonant switching converter comprising: the main circuit comprises a first transformer and a plurality of switching tubes connected with a primary winding of the first transformer, the switching tubes convert direct current voltage into square wave signals, the main circuit transmits the square wave signals from the primary winding of the first transformer to a secondary winding in a resonance mode so as to transmit electric energy, and the secondary winding is connected to an output end so as to supply power to a load; and a control circuit connected to the main circuit for obtaining a voltage sampling signal representing an output voltage of the main circuit and a current sampling signal representing an output current of the main circuit from a secondary side, and generating driving signals of the plurality of switching tubes according to the voltage sampling signal and the current sampling signal, wherein the control circuit obtains the voltage sampling signal and the current sampling signal in a non-isolated manner, and supplies the driving signals to the plurality of switching tubes in an isolated manner.

Preferably, the main circuit comprises a current sampling resistor connected in series with the load, the control circuit being directly connected with the output terminal to obtain the voltage sampling signal, and with the current sampling resistor to obtain the current sampling signal.

Preferably, the control circuit includes: a first error amplifier for comparing the current sample signal with a first reference voltage to obtain a current error signal; a second error amplifier for comparing the voltage sample signal with a second reference voltage to obtain a voltage error signal; a selection module, coupled to the first error amplifier and the second error amplifier, for selecting one of the current error signal and the voltage error signal as a compensation signal; the control module is connected with the selection module and used for generating a switch control signal according to the compensation signal; and the driving module is connected with the control module and is used for receiving the switch control signals and generating driving signals of the switch tubes.

Preferably, the selecting module includes: a first diode having a cathode connected to an output terminal of the first error amplifier; and a second diode having a cathode connected to an output of the second error amplifier, wherein anodes of the first diode and the second diode are connected to each other to provide the compensation signal.

Preferably, the main circuit includes: the power factor correction circuit is used for rectifying and power factor correcting the alternating voltage to generate the direct voltage; the square wave signal generating circuit comprises a plurality of switching tubes, is connected with the power factor correction circuit and is used for converting direct current voltage into square wave signals; the resonance circuit is connected with the square wave signal generating circuit and is used for receiving the square wave signal in a resonance mode and transmitting the square wave signal from a primary winding to a secondary winding of the first transformer so as to transmit electric energy; the rectification circuit is connected with the secondary winding of the first transformer and is used for rectifying the received square wave signal into direct-current output voltage; and an output capacitor for filtering the output voltage.

Preferably, the plurality of switching tubes in the square wave signal generating circuit form a half bridge circuit or a full bridge circuit.

Preferably, the control circuit is configured to generate the first drive signal and the second drive signal.

Preferably, the method further comprises: and the isolation circuit is connected with the control circuit to receive the first driving signal and the second driving signal and is connected with the main circuit to provide driving signals of the switching tubes.

Preferably, the plurality of switching tubes include a first switching tube and a second switching tube that form a half bridge, the isolation circuit includes a second transformer having first to third windings, wherein the first switching tube and the second switching tube are sequentially connected in series between a power supply end of the direct current voltage and ground, a homonymous end of the first winding receives the first driving signal, a heteronymous end receives the second driving signal, the homonymous end of the second winding is connected to a control end of the first switching tube, the heteronymous end is connected to an intermediate node of the first switching tube and the second switching tube, and the heteronymous end of the third winding is connected to a control end of the second switching tube, and the homonymous end is grounded.

Preferably, the plurality of switching tubes include first to fourth switching tubes forming a full bridge, the isolation circuit includes a third transformer having first to fifth windings, wherein the first and second switching tubes are sequentially connected in series between a supply end of the dc voltage and a ground, the third and fourth switching tubes are sequentially connected in series between the supply end of the dc voltage and the ground, a homonymous end of the first winding receives the first driving signal, a homonymous end receives the second driving signal, a homonymous end of the second winding is connected to a control end of the first switching tube, a homonymous end is connected to intermediate nodes of the first and second switching tubes, a homonymous end of the third winding is connected to a control end of the second switching tube, a homonymous end of the fourth winding is connected to a control end of the third switching tube, a homonymous end of the fourth winding is connected to a homonymous end of the fourth switching tube, and a homonymous end of the fourth winding is connected to a control end of the fourth switching tube.

Preferably, the method further comprises: and the starting power supply circuit is used for generating a power supply voltage according to the alternating voltage when the system is started and supplying power to the control circuit.

Preferably, the start-up power supply circuit includes: a first capacitor and a second capacitor, wherein the first ends of the first capacitor and the second capacitor are used for receiving alternating voltage; a first rectifying diode, wherein a cathode of the first rectifying diode is connected to a second end of the first capacitor, and an anode of the first rectifying diode is connected to the second end of the second capacitor and grounded; and a second rectifying diode, an anode of the second rectifying diode is connected to a second end of the first capacitor, a cathode of the second rectifying diode provides the power supply voltage, wherein when the alternating voltage changes, the voltage between the first capacitor and the first end of the second capacitor changes periodically to generate current, and the first rectifying diode and the second rectifying diode rectify the current into direct current for power supply.

Preferably, the start-up power supply circuit includes: the first end of the first capacitor is used for receiving alternating voltage, and the first end of the second capacitor is grounded; a first rectifying diode, wherein a cathode of the first rectifying diode is connected to a second end of the first capacitor, and an anode of the first rectifying diode is connected to the second end of the second capacitor and grounded; and a second rectifying diode, an anode of the second rectifying diode is connected to a second end of the first capacitor, a cathode of the second rectifying diode provides the power supply voltage, wherein when the alternating voltage changes, the voltage between the first capacitor and the first end of the second capacitor changes periodically to generate current, and the first rectifying diode and the second rectifying diode rectify the current into direct current for power supply.

Preferably, the main circuit may operate in a current continuous mode, a current discontinuous mode or a current critical mode.

According to a second aspect of the present invention, there is provided a control method of a resonant switching converter, comprising: converting the direct current input voltage into square wave signals by adopting a plurality of switching tubes; the square wave signal is transferred from a primary winding of a first transformer to a secondary winding in a resonant manner to transfer electrical energy, the secondary winding being connected to an output to supply power to a load, wherein the method comprises obtaining a voltage sample signal and a current sample signal in a non-isolated manner, and providing the drive signal to the plurality of switching tubes in an isolated manner, wherein the voltage sample signal is used to characterize an output current provided to the load, and the voltage sample signal is used to characterize an output voltage provided to the load.

Preferably, the voltage sampling signal is obtained by directly connecting to the output terminal, and the current sampling signal is obtained by directly connecting to a current sampling resistor connected in series with the load.

Preferably, the step of generating the driving signals of the plurality of switching tubes includes: comparing the current sample signal with a first reference voltage to obtain a current error signal; comparing the voltage sample signal with a second reference voltage to obtain a voltage error signal; selecting one of the current error signal and the voltage error signal as a compensation signal; generating a switch control signal according to the compensation signal; and receiving the switch control signals and generating driving signals of the plurality of switching tubes.

Preferably, the driving signals of the plurality of switching tubes include: a first drive signal and a second drive signal.

Preferably, the plurality of switching tubes includes a first switching tube and a second switching tube that constitute a half bridge, and the control method further includes: and a second transformer is adopted to provide a first driving signal and a second driving signal for the first switching tube and the second switching tube in an isolated mode.

Preferably, the second transformer has first to third windings, wherein the first switching tube and the second switching tube are sequentially connected in series between a power supply end of the dc input voltage and ground, a homonymous end of the first winding receives the first driving signal, a heteronymous end receives the second driving signal, the homonymous end of the second winding is connected to a control end of the first switching tube, the heteronymous end is connected to an intermediate node of the first switching tube and the second switching tube, the heteronymous end of the third winding is connected to a control end of the second switching tube, and the homonymous end is grounded.

Preferably, the plurality of switching tubes includes first to fourth switching tubes constituting a full bridge, and the control method further includes: the first driving signal and the second driving signal are provided to the first to fourth switching tubes in an isolated manner using a third transformer.

Preferably, the third transformer has first to fifth windings, wherein the first switching tube and the second switching tube are sequentially connected in series between a power supply end of the dc input voltage and ground, the third switching tube and the fourth switching tube are sequentially connected in series between the power supply end of the dc input voltage and ground, a homonymous end of the first winding receives the first driving signal, a homonymous end receives the second driving signal, a homonymous end of the second winding is connected to a control end of the first switching tube, a heteronymous end is connected to an intermediate node of the first switching tube and the second switching tube, a heteronymous end of the third winding is connected to a control end of the second switching tube, a homonymous end of the fourth winding is connected to a control end of the third switching tube, a homonymous end is connected to an intermediate node of the third switching tube and the fourth switching tube, and a homonymous end of the fifth winding is connected to a control end of the fourth switching tube.

Preferably, the method further comprises: a supply voltage is generated at system start-up from the ac voltage for supplying power to the control circuits of the plurality of switches.

According to the resonant switching converter of this embodiment, the control circuit obtains the voltage sampling signal and the current sampling signal in a non-isolated manner, and generates a driving signal for driving the switching tubes on the primary side according to the comparison result of the two with the corresponding reference voltage, and then supplies the driving signals to the plurality of switching tubes in an isolated manner.

In a preferred embodiment, the feedback loop of the control circuit comprises a diode and a selection module configured to selectively communicate the output current and the sample number of the output voltage to the control module so that the resonant switching converter can provide a stable output current and/or output voltage.

In a further preferred embodiment, the resonant switching converter further comprises a start-up supply circuit. The starting power supply circuit is responsible for supplying power to the control circuit when the resonant switching converter is started.

In a further preferred embodiment, the power supply circuit comprises a first capacitor and a second capacitor, wherein the first capacitor and the second capacitor are connected between the primary side and the secondary side of the resonant converter, and the primary side power is transmitted to the secondary side by utilizing the principle that current flows in the capacitor when the voltage across the capacitor changes, so as to provide the power supply voltage.

In a further preferred embodiment, the rectifying circuit comprises a first diode and a second diode, which rectify the current flowing through the capacitor into a direct current, which powers the control circuit.

The control circuit directly acquires a current sampling signal and a voltage sampling signal from the secondary side of the resonant converter, so as to acquire a driving signal, and the driving signal is provided for a primary side switching tube of the resonant converter by adopting the isolation circuit, so that an amplifying circuit and an optocoupler of the sampling signal can be omitted, the circuit structure is simplified, and the stability and the reliability of work can be improved due to the fact that the optocoupler is removed.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the present invention with reference to the accompanying drawings, in which:

fig. 1 shows a simplified schematic diagram of an LLC resonant converter according to the prior art;

fig. 2 shows a schematic circuit diagram of a control circuit in an LLC resonant converter according to a first embodiment of the invention;

fig. 3 shows a schematic circuit diagram of an LLC resonant converter according to a second embodiment of the invention;

fig. 4 shows a schematic circuit diagram of an LLC resonant converter according to a third embodiment of the invention;

Fig. 5 shows a schematic circuit diagram of an LLC resonant converter according to a fourth embodiment of the invention.

Detailed Description

Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. The same reference numbers will be used throughout the drawings to refer to the same or like parts. For clarity, the various features of the drawings are not drawn to scale.

In the present application, a switching transistor is a transistor that operates in a switching mode to provide a current path, and includes one selected from a bipolar transistor or a field effect transistor. The first end and the second end of the switching tube are respectively a high potential end and a low potential end on a current path, and the control end is used for receiving a driving signal to control the switching tube to be turned on and off.

The invention will be further described with reference to the drawings and examples.

Fig. 2 shows a schematic circuit diagram of a control circuit in an LLC resonant converter according to a first embodiment of the invention. The control circuit 210 is configured to control on and off states of a switching tube of a primary side of the transformer according to a voltage sampling signal and a current sampling signal directly obtained from a secondary side of the transformer, thereby controlling energy transferred from the primary side winding to the secondary side winding of the transformer to maintain a constant output voltage and/or output current.

In this embodiment, the control circuit 210 includes an error amplifying module 211, a control module 212, and a driving module 213. The control circuit 210 has a first input terminal and a second input terminal respectively receiving the current sampling signal CS and the voltage sampling signal VS, and a first output terminal and a second output terminal respectively providing a first driving signal VG1 and a second driving signal VG2. The control circuit 210 may have a separate reference ground.

The error amplification module 211 includes a first error amplifier 214, a second error amplifier 215, a first reference voltage Vref1, a first reference voltage Vref2, and diodes D1 and D2. The positive input end of the first error amplifier 214 is connected to the first reference voltage Vref1, the negative input end of the error amplifier 214 receives the current sampling signal CS, and the current sampling signal CS is compared with the first reference voltage Vref1 to obtain a current error signal. The positive input end of the second error amplifier 215 is connected to the second reference voltage Vref2, the negative input end of the error amplifier 215 receives the voltage sampling signal VS, and the voltage sampling signal VS is compared with the second reference voltage Vref2 to obtain a voltage error signal. The current sampling signal CS is used to characterize the value of the output current of the resonant converter main circuit and the voltage sampling signal VS is used to characterize the value of the output voltage of the resonant converter main circuit.

Further, the output of error amplifier 214 is connected to the cathode of diode D1, and the output of error amplifier 215 is connected to the cathode of diode D2. The anode of the diode D1 is connected to the anode of the diode D2. Diodes D1 and D2 constitute a selection module for selecting one of the current error signal and the voltage error signal as the compensation signal COMP.

The control module 212 receives the compensation signal COMP generated by the error amplification module 211 and generates a switch control signal according to the compensation signal COMP.

The driving module 213 receives the switching control signal to generate a first driving signal VG1 and a second driving signal VG2 for driving the switching tube of the primary side.

According to the control circuit of this embodiment, the control module acquires the current sampling signal and the voltage sampling signal from the secondary side of the resonant converter, and generates a driving signal for driving the switching tube of the primary side according to the comparison result of the two with the corresponding reference voltage. The feedback loop of the control circuit comprises a selection module consisting of diodes D1 and D2 for selectively transmitting the sample numbers of the output current and the output voltage to the control module. The control circuit can omit an amplifying circuit and an optocoupler for sampling signals, so that the circuit structure is simplified, and the stability and the reliability of the work can be improved due to the fact that the optocoupler is removed.

Fig. 3 shows a schematic circuit diagram of an LLC resonant converter according to a second embodiment of the invention. The LLC resonant converter 200 includes a main circuit 220, an isolation circuit 230, a start-up supply circuit 240, and a control circuit 210 as shown in FIG. 2. In this resonant converter, the square wave signal generating circuit 102 includes switching transistors Q1 and Q2 constituting a half-bridge circuit. The main circuit 220 may operate in a current continuous mode, a current discontinuous mode, or a current critical mode.

The main circuit 220 of the LLC resonant converter 200 includes a PFC circuit 101, a square wave signal generating circuit 102, a resonant circuit 103, a rectifying circuit 104, an output capacitor Co, a load RL, and a current sampling resistor Rsen.

The PFC circuit 101 receives the ac voltage Vac, rectifies the ac voltage, and outputs a dc voltage after power factor correction.

In the square wave signal generating circuit 102, switching transistors Q1 and Q2 are connected in series between two output terminals of the PFC circuit 101. The first end of the switching tube Q1 is connected with the positive output end of the PFC circuit 101, the second end of the switching tube Q1 is connected with the first end of the switching tube Q2, and the second end of the switching tube Q2 is connected with the negative output end of the PFC circuit 101, namely grounded. The switching transistors Q1 and Q2 obtain the driving signals VG1 and VG2 from the control circuit 210, and are turned on or off under the control of the driving signals. During operation, the switching transistors Q1 and Q2 are alternately turned on and off, thereby converting the dc voltage into a square wave signal. The two output ends of the half-bridge circuit are respectively the intermediate nodes of the switching tubes Q1 and Q2 and the ground, and are used for providing the square wave signals.

The resonant circuit 103 includes a resonant inductance Lr, a resonant capacitance Cr, and a primary winding of the transformer T1. The transformer T1 comprises two windings, namely a primary winding and a secondary winding with a center tap. The first end of the resonant inductor Lr is connected with the intermediate node of the switching tubes Q1 and Q2, the second end of the resonant inductor Lr is connected with the homonymous end of the primary winding of the transformer T1, the heteronymous end of the primary winding of the transformer T1 is connected with the first end of the resonant capacitor Cr, and the second end of the resonant capacitor Cr is grounded.

The rectifier circuit 104 includes freewheeling diodes Dc1 and Dc2 connected to the secondary winding of the transformer T1. The homonymous end of the secondary winding of the transformer T1 is connected with the anode of the flywheel diode Dc1, the heteronymous end of the secondary winding of the transformer T1 is connected with the anode of the flywheel diode Dc2, and the middle tap of the secondary winding of the transformer T1 is grounded. The cathode of the freewheel diode Dc1 and the cathode of the freewheel diode Dc2 are connected to each other and commonly connected to the positive terminal of the output capacitor Co. The negative terminal of the output capacitor Co is connected with the output ground.

The load RL and the current sampling resistor Rsen are connected in series between the positive and negative terminals of the output capacitor Co. Although the current sampling resistor Rsen in this embodiment is a resistor, it will be appreciated by those skilled in the art that in alternative embodiments a similarly functioning current sensing element may be used in place of the current sampling resistor Rsen.

The control circuit 210 of the LLC resonant converter 200 is connected to the main circuit 220 for deriving a voltage sampling signal VS and a current sampling signal CS from the secondary side of the main circuit 220 and generating drive signals VG1 and VG2 for the primary side switching tubes of the main circuit 220 from both.

As shown in fig. 3, a first input terminal of the control circuit 210 is connected to a first terminal of a current sampling resistor Rsen in the main circuit 220, and receives a current sampling signal CS. A second input terminal of the control circuit 210 is connected to a positive terminal of an output capacitor Co in the main circuit 220, and a first output terminal and a second output terminal of the control circuit 210 receiving the voltage sampling signal VS are connected to the isolation circuit 230.

The isolation circuit 230 includes a transformer T2. The drive transformer T2 comprises three windings: n1, N2, N3. The homonymous terminal of the N1 winding is connected to a first output terminal of the control circuit 210, and the heteronymous terminal of the N1 winding is connected to a second output terminal of the control circuit 210. The homonymous end of the N2 winding is connected with the control end of the switching tube Q1 in the main circuit 220, and the heteronymous end of the N2 winding is connected with the second end of the switching tube Q1 in the main circuit 220. The synonym end of the N3 winding is connected to the control end of the switching tube Q2 in the main circuit 220, and the synonym end of the N3 winding is connected to the second end of the switching tube Q2 in the main circuit 220, i.e. to ground. The isolation circuit 230 isolates the drive signals VG1 and VG2 of the control circuit 210 to the input side of the main circuit 220 for driving the switching transistors Q1 and Q2 to operate.

The start-up power supply circuit 240 includes a capacitor Cs1, a capacitor Cs2, a diode Ds1, and a diode Ds2. The first ends of the capacitor Cs1 and the capacitor Cs2 are respectively connected with two ends of the input alternating voltage Vac, the second end of the capacitor Cs1 is connected to the cathode of the diode Ds1, the second end of the capacitor Cs2 is connected to the anode of the diode Ds1, and the second end of the capacitor Cs2 is grounded. The anode of the diode Ds2 is connected to the cathode of the diode Ds1, and the cathode of the diode Ds2 is connected to the power supply terminal VCC of the control circuit 210.

In this embodiment, the power supply principle of the start-up power supply circuit 240 is as follows: when the voltage between the first terminal of the capacitor Cs1 and the first terminal of the capacitor Cs2 changes, a current will flow in the capacitor Cs1 and the capacitor Cs2, and the current flowing in the capacitor Cs1 and the capacitor Cs2 is rectified into a direct current by the diode Ds1 and the diode Ds2, and then is supplied to the power supply terminal VCC of the control circuit 210. Therefore, according to the power supply principle of the power supply circuit 240, two arbitrary potential points on the primary side can be respectively connected to the first ends of the capacitor Cs1 and the capacitor Cs2 as long as the voltage between the two potential points changes periodically, so as to further realize power supply. In the LLC resonant converter 200 according to the second embodiment of the invention shown in fig. 3, when the input ac voltage Vac changes, the voltage change between the first terminal of the capacitor Cs1 and the first terminal of the capacitor Cs2 changes in ac, and an ac current flows through the capacitor Cs1 and the capacitor Cs2, and the ac current is rectified by the diode Ds1 and the diode Ds2 to supply power to VCC of the control circuit 210.

According to the LLC resonant converter of this embodiment, the control circuit acquires the current sampling signal and the voltage sampling signal from the secondary side of the resonant converter, and generates a drive signal for driving the switching tube of the primary side based on the comparison result of the two with the corresponding reference voltages. The feedback loop of the control circuit includes a selection module of diodes D1 and D2 for selectively transmitting the sampled signals of the output current and the output voltage to the control module so that the LLC resonant converter can provide a stable output current and/or output voltage. The control circuit directly obtains the driving signal according to the sampling signal of the secondary side, and the driving signal is provided for the primary side switching tube of the resonant converter by adopting the isolation circuit, so that an amplifying circuit and an optocoupler of the sampling signal can be omitted, the circuit structure is simplified, and the stability and the reliability of the work can be improved due to the fact that the optocoupler is removed.

Fig. 4 shows a schematic circuit diagram of an LLC resonant converter according to a third embodiment of the invention. The LLC resonant converter 300 includes a main circuit 320, an isolation circuit 230, a start-up supply circuit 340, and a control circuit 210 as shown in FIG. 2. Compared to the second embodiment shown in fig. 3, the LLC resonant converter 300 according to the third embodiment is different in that a current sampling resistor Rsen in the main circuit 320 is connected between the center tap of the secondary winding of the transformer T1 and ground.

The current signal CS sampled by the sampling circuit Rsen is a current signal which is output by the secondary winding of the transformer T1, rectified by the freewheeling diode Dc1 and the freewheeling diode Dc2, but not filtered by the output capacitor Co, and the average value of the current signal CS is equal to the output current, so the current signal CS can be used as an output current sampling signal. For the sake of brevity, the present description only shows the positions of the two sampling circuits Rsen as shown in fig. 3 and 4, but it should be understood by those skilled in the art that the sampling circuits Rsen may be placed at other positions on the secondary side of the transformer TI to obtain a current sampling signal related to the output current, and the claimed invention is directed to the claims of the present invention.

According to the LLC resonant converter 300 of the third embodiment, the first terminal of the capacitor Cs2 in the start-up supply circuit 340 is connected to ground. The working principle of the start-up power supply circuit 340 is as follows: when the input ac voltage Vac changes, the voltage between the first ends of the capacitor Cs1 and the capacitor Cs2 changes periodically, so as to realize power supply. It should be understood by those skilled in the art that there are other connection manners between the first ends of the capacitor Cs1 and the capacitor Cs2 in the start-up power supply circuit 340 and the primary side of the LLC resonant converter, and all circuits that implement power supply based on the operating principle of the start-up power supply circuit 340 are within the scope of the present invention, and the claims of the present invention are intended to be protected.

Other aspects of the LLC resonant converter according to the third embodiment are the same as those of the second embodiment, and will not be described again here.

Fig. 5 shows a schematic circuit diagram of an LLC resonant converter according to a fourth embodiment of the invention. The LLC resonant converter 400 includes a main circuit 420, an isolation circuit 430, a start-up supply circuit 240, and a control circuit 210 as shown in FIG. 2. In this resonant converter, the square wave signal generating circuit 202 includes switching transistors Q1 to Q4 constituting a full bridge circuit. The main circuit 420 may operate in a current continuous mode, a current discontinuous mode, or a current critical mode.

The main circuit 420 of the LLC resonant converter 400 includes the PFC circuit 101, the square wave signal generating circuit 202, the resonant circuit 103, the rectifying circuit 104, the output capacitor Co, the load RL, and the current sampling resistor Rsen.

In the square wave signal generating circuit 202, switching transistors Q1 and Q2 are connected in series between two output terminals of the PFC circuit 101, and switching transistors Q3 and Q4 are connected in series between two output terminals of the PFC circuit 101. The first end of the switching tube Q1 is connected with the positive output end of the PFC circuit 101, the second end of the switching tube Q1 is connected with the first end of the switching tube Q2, and the second end of the switching tube Q2 is connected with the negative output end of the PFC circuit 101, namely grounded. The first end of the switching tube Q3 is connected with the positive output end of the PFC circuit 101, the second end of the switching tube Q3 is connected with the first end of the switching tube Q4, and the second end of the switching tube Q4 is connected with the negative output end of the PFC circuit 101, namely grounded. The switching transistors Q1 to Q4 obtain driving signals VG1, VG2, VG1, respectively, from the control circuit 210, so as to be turned on or off under the control of the driving signals. In the working process, the switching tubes Q1 and Q2 are alternately switched on and off, the switching tubes Q3 and Q4 are alternately switched on and off, the switching tubes Q3 and Q1 are complementarily switched on, and the switching tubes Q4 and Q2 are complementarily switched on, so that direct-current voltage is converted into alternating-current signals. The two output ends of the full-bridge circuit are respectively the intermediate nodes of the switching tubes Q1 and Q2 and the intermediate nodes of the switching tubes Q3 and Q4, and are used for providing the alternating current signals.

The load RL and the current sampling resistor Rsen are connected in series between the positive and negative terminals of the output capacitor Co. Although the current sampling resistor Rsen in this embodiment is a resistor, it will be appreciated by those skilled in the art that in alternative embodiments a similarly functioning current sensing element may be used in place of the current sampling resistor Ren.

The control circuit 210 of the LLC resonant converter 400 is connected to the main circuit 420 for deriving a voltage sampling signal VS and a current sampling signal CS from the secondary side of the main circuit 420 and generating drive signals VG1 and VG2 for the primary side switching tubes of the main circuit 420 from both.

As shown in fig. 5, a first input terminal of the control circuit 210 is connected to a first terminal of a current sampling resistor Rsen in the main circuit 420, and receives a current sampling signal CS. A second input terminal of the control circuit 210 is connected to a positive terminal of the output capacitor Co in the main circuit 420, and a first output terminal and a second output terminal of the control circuit 210 receiving the voltage sampling signal VS are connected to the isolation circuit 430.

The isolation circuit 430 includes a transformer T3. The driving transformer T3 includes five windings: n1, N2, N3, N4, N5. The homonymous terminal of the N1 winding is connected to a first output terminal of the control circuit 210, and the heteronymous terminal of the N1 winding is connected to a second output terminal of the control circuit 210. The homonymous end of the N2 winding is connected with the control end of the switching tube Q1 in the main circuit 420, and the heteronymous end of the N2 winding is connected with the second end of the switching tube Q1 in the main circuit 420. The synonym end of the N3 winding is connected to the control end of the switching tube Q2 in the main circuit 420, and the synonym end of the N3 winding is connected to the second end of the switching tube Q2 in the main circuit 420, i.e. to ground. The synonym end of the N4 winding is connected with the control end of the switching tube Q3 in the main circuit 420, and the synonym end of the N4 winding is connected with the second end of the switching tube Q3 in the main circuit 420. The homonymous terminal of the N5 winding is connected to the control terminal of the switching tube Q4 in the main circuit 420, and the heteronymous terminal of the N5 winding is connected to the second terminal of the switching tube Q4 in the main circuit 420, i.e. to ground. The isolation circuit 430 isolates and transmits the driving signals VG1 and VG2 of the control circuit 210 to the input side of the main circuit 420 for driving the switching transistors Q1 to Q4 to operate.

The start-up power supply circuit 240 includes a capacitor Cs1, a capacitor Cs2, a diode Ds1, and a diode Ds2. The first ends of the capacitor Cs1 and the capacitor Cs2 are respectively connected with two ends of the input alternating voltage Vac, the second end of the capacitor Cs1 is connected to the cathode of the diode Ds1, the second end of the capacitor Cs2 is connected to the anode of the diode Ds1, and the second end of the capacitor Cs2 is grounded. The anode of the diode Ds2 is connected to the cathode of the diode Ds1, and the cathode of the diode Ds2 is connected to the power supply terminal VCC of the control circuit 210. When the input ac voltage Vac changes, an ac current flows through the capacitor Cs1 and the capacitor Cs2, and the ac current flows through the diode Ds1 and the diode Ds2 to be rectified and then supplied to VCC of the control circuit 210.

Embodiments in accordance with the present invention, as described above, 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 and various modifications as are suited to the particular use contemplated. The scope of the invention should be determined by the following claims.

Claims

1. A resonant switching converter comprising:

the main circuit comprises a first transformer and a plurality of switching tubes connected with a primary winding of the first transformer, the switching tubes convert direct-current voltage generated according to alternating-current voltage into square-wave signals, the main circuit transmits the square-wave signals from the primary winding of the first transformer to a secondary winding in a resonance mode so as to transmit electric energy, and the secondary winding is connected to an output end so as to supply power to a load;

the control circuit is connected with the main circuit and is used for obtaining a voltage sampling signal representing the output voltage of the main circuit and a current sampling signal representing the output current of the main circuit from the secondary side, and generating driving signals of the switching tubes according to the voltage sampling signal and the current sampling signal; and

a start-up power supply circuit for generating a power supply voltage according to the alternating voltage at the start-up of the system for supplying power to the control circuit,

wherein the control circuit obtains the voltage sampling signal and the current sampling signal in a non-isolated manner and supplies the driving signals to the plurality of switching tubes in an isolated manner,

the start-up supply circuit comprises a first capacitor and a second capacitor, and when the alternating voltage changes, the voltage between the first capacitor and the first end of the second capacitor changes periodically to generate current, and the start-up supply circuit further rectifies the current into direct current relative to the reference ground.

2. The resonant switching converter of claim 1, wherein the main circuit includes a current sampling resistor connected in series with the load, the control circuit being directly connected with the output to obtain the voltage sampling signal, and with the current sampling resistor to obtain the current sampling signal.

3. The resonant switching converter of claim 1, wherein the control circuit comprises:

a first error amplifier for comparing the current sample signal with a first reference voltage to obtain a current error signal;

a second error amplifier for comparing the voltage sample signal with a second reference voltage to obtain a voltage error signal;

a selection module, coupled to the first error amplifier and the second error amplifier, for selecting one of the current error signal and the voltage error signal as a compensation signal;

the control module is connected with the selection module and used for generating a switch control signal according to the compensation signal; and

and the driving module is connected with the control module and is used for receiving the switch control signals and generating driving signals of the switch tubes.

4. A resonant switching converter according to claim 3, wherein the selection module comprises:

a first diode having a cathode connected to an output terminal of the first error amplifier; and

a second diode having a cathode connected to the output of the second error amplifier,

wherein anodes of the first diode and the second diode are connected to each other to provide the compensation signal.

5. The resonant switching converter of claim 1, wherein the main circuit further comprises:

the power factor correction circuit is used for rectifying and power factor correcting the alternating voltage to generate the direct voltage;

the square wave signal generating circuit comprises a plurality of switching tubes, is connected with the power factor correction circuit and is used for converting the direct current voltage into a square wave signal;

the resonance circuit is connected with the square wave signal generating circuit and is used for receiving the square wave signal in a resonance mode and transmitting the square wave signal from a primary winding to a secondary winding of the first transformer so as to transmit electric energy;

the rectification circuit is connected with the secondary winding of the first transformer and is used for rectifying the received square wave signal into direct-current output voltage; and

And the output capacitor is used for filtering the output voltage.

6. The resonant switching converter of claim 5, wherein the plurality of switching tubes in the square wave signal generating circuit comprise a half bridge circuit or a full bridge circuit.

7. The resonant switching converter of claim 1, wherein the control circuit is configured to generate the first drive signal and the second drive signal.

8. The resonant switching converter of claim 7, further comprising: and the isolation circuit is connected with the control circuit to receive the first driving signal and the second driving signal and is connected with the main circuit to provide driving signals of the switching tubes.

9. The resonant switching converter of claim 8, wherein the plurality of switching tubes includes a first switching tube and a second switching tube constituting a half bridge, the isolation circuit includes a second transformer having first to third windings,

wherein the first switching tube and the second switching tube are sequentially connected in series between the power supply end of the direct-current voltage and the ground,

the homonymous end of the first winding receives the first driving signal, the heteronymous end receives the second driving signal,

The homonymous end of the second winding is connected to the control end of the first switching tube, the heteronymous end is connected to the intermediate nodes of the first switching tube and the second switching tube,

and the synonym end of the third winding is connected to the control end of the second switching tube, and the synonym end is grounded.

10. The resonant switching converter of claim 8, wherein the plurality of switching tubes includes first through fourth switching tubes constituting a full bridge, the isolation circuit includes a third transformer having first through fifth windings,

the third switching tube and the fourth switching tube are sequentially connected in series between the power supply end of the direct-current voltage and the ground,

the synonym end of the third winding is connected to the control end of the second switching tube, the synonym end is grounded,

The synonym end of the fourth winding is connected to the control end of the third switching tube, the synonym end is connected to the intermediate node of the third switching tube and the fourth switching tube,

and the homonymous end of the fifth winding is connected to the control end of the fourth switching tube, and the heteronymous end is grounded.

11. The resonant switching converter of claim 5, wherein the start-up supply circuit comprises:

a first capacitor and a second capacitor, wherein the first ends of the first capacitor and the second capacitor are used for receiving alternating voltage;

a first rectifying diode, wherein a cathode of the first rectifying diode is connected to a second end of the first capacitor, and an anode of the first rectifying diode is connected to the second end of the second capacitor and grounded; and

and the anode of the second rectifying diode is connected to the second end of the first capacitor, and the cathode of the second rectifying tube provides the power supply voltage.

12. The resonant switching converter of claim 5, wherein the start-up supply circuit comprises:

the first end of the first capacitor is used for receiving alternating voltage, and the first end of the second capacitor is grounded;

13. The resonant switching converter of claim 1, wherein the main circuit is operable in a current continuous mode, a current discontinuous mode, or a current critical mode.

14. A control method of a resonant switching converter, comprising:

when the system is started, a starting power supply circuit is adopted, and power supply voltage is generated according to alternating voltage and used for supplying power to a control circuit of the resonant switching converter;

converting a direct-current voltage generated according to an alternating-current voltage into a square wave signal by adopting a plurality of switching tubes, wherein the control circuit provides driving signals of the switching tubes;

transmitting said square wave signal from the primary winding of the first transformer to the secondary winding in a resonant manner, thereby transmitting electrical energy, said secondary winding being connected to the output terminal, thereby powering the load,

Wherein the method comprises obtaining a voltage sampling signal and a current sampling signal in a non-isolated manner, and providing the drive signals to the plurality of switching tubes in an isolated manner, wherein the voltage sampling signal is used for representing an output current provided to the load, the voltage sampling signal is used for representing an output voltage provided to the load,

15. The control method of claim 14, wherein the voltage sampling signal is obtained by directly connecting to the output terminal, and the current sampling signal is obtained by directly connecting to a current sampling resistor connected in series with the load.

16. The control method of claim 14, wherein generating the driving signals of the plurality of switching tubes comprises:

comparing the current sample signal with a first reference voltage to obtain a current error signal;

Comparing the voltage sample signal with a second reference voltage to obtain a voltage error signal;

selecting one of the current error signal and the voltage error signal as a compensation signal;

generating a switch control signal according to the compensation signal; and

and receiving the switch control signals and generating driving signals of the switch tubes.

17. The control method of claim 14, wherein the driving signals of the plurality of switching tubes comprise: a first drive signal and a second drive signal.

18. The control method according to claim 16, wherein the plurality of switching tubes includes a first switching tube and a second switching tube that constitute a half bridge, the control method further comprising:

and a second transformer is adopted to provide a first driving signal and a second driving signal for the first switching tube and the second switching tube in an isolated mode.

19. The control method according to claim 18, wherein the second transformer has first to third windings,

20. The control method according to claim 16, wherein the plurality of switching tubes includes first to fourth switching tubes constituting a full bridge, the control method further comprising:

the first driving signal and the second driving signal are provided to the first to fourth switching tubes in an isolated manner using a third transformer.

21. The control method according to claim 20, wherein the third transformer has first to fifth windings,