High-precision isolation converter and control method thereof

Abstract

The invention relates to a high-precision isolation converter and a control method thereof, the isolation converter comprises a half-bridge switch circuit, when one switch tube of the half-bridge switch circuit is switched on, an excitation inductor, a resonant inductor, a resonant capacitor and the switch tube form a resonant network; the detection error amplification circuit obtains a first detection signal representing output voltage information by detecting a high-order end node voltage of a transformer primary winding, and obtains a compensation signal by performing error amplification on the first detection signal and a preset reference voltage. And the frequency and duty ratio modulation circuit obtains a switching control signal according to the compensation signal, the inductive current sampling signal and a preset frequency signal so as to control the switching action of the half-bridge switching circuit, thereby controlling the output signal of the isolation converter to be stable. Feedback control is carried out through output voltage detection, so that the output of the LLC isolation converter is stable and is not influenced by circuit parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and more specifically, to a high-precision isolation converter and a control method thereof. Background Art

[0002] In the power consumption fields such as new energy vehicles, new energy power generation and server power supply, different power levels of power electronic converters will involve multiple voltage bus levels. Usually, insulation isolation transmission is required between strong and weak electricity. With the development of the application of third-generation semiconductor materials, power electronic power levels require higher switching frequencies. The increase in the switching frequency of the third-generation semiconductor requires smaller parasitic parameters of the isolated power supply to avoid strong interference to the driver chip, isolated op amp and power devices. LLC flyback switching converter is a common topology of isolated converters. It includes a resonant network composed of resonant inductor, excitation inductor and resonant capacitor, so it is recorded as LLC flyback switching power supply. During the control process, its primary power tube can achieve zero voltage conduction, and the secondary rectifier tube can achieve zero current shutdown. The inductance required for resonance is small, and the leakage inductance energy can be utilized, so the parasitic parameters are smaller than other topologies. Therefore, LLC flyback switching converters are often used in isolated power supply scenarios for driver chips and isolated op amps.

[0003] However, if the existing LLC flyback switching converter is to achieve stable power supply to the load, it needs to add energy storage elements (transformer, inductor, capacitor, etc.) and components required for control signals to form a circuit to complete the power supply to the load. The existing LLC controller often adopts an open-loop control scheme. After the driver sets the switching frequency / transformer parameters / resonant cavity parameters / secondary rectifier diode, the output voltage is greatly affected by these parameter ranges, and the output voltage error is large, even up to several volts, affecting the accuracy and stability of the power supply.

[0004] The existing solutions cannot meet the existing control requirements. Therefore, it is necessary to provide an improved technical solution to overcome the above technical problems existing in the prior art. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a high-precision isolation converter and a control method thereof, so as to solve the technical problem that the isolation converter in the prior art cannot provide an output voltage accurately and stably.

[0006] Provided is a high-precision isolation converter, the isolation converter comprising a half-bridge switch circuit, an excitation inductor, a resonant inductor, and a resonant capacitor. When a switch tube of the half-bridge switch circuit is turned on, the excitation inductor, the resonant inductor, the resonant capacitor and the switch tube form a resonant network. The isolation converter comprises a controller and a transformer. The controller comprises a detection error amplifier circuit and a frequency modulation and duty cycle adjustment circuit. The detection error amplifier circuit detects the voltage of the high-end node of the primary winding of the transformer to obtain a first detection signal representing output voltage information, and obtains a compensation signal by performing error amplification between the first detection signal and a preset reference voltage. The frequency modulation and duty cycle adjustment circuit obtains a switch control signal according to the compensation signal and the preset frequency signal to control the switching action of the half-bridge switch circuit and control the output signal of the isolation converter to maintain stability.

[0007] Preferably, the resonant inductor and the resonant capacitor are connected in series, and the detection error amplification circuit detects the voltage of an intermediate node where the series branch is connected to the primary winding to obtain the first detection signal.

[0008] Preferably, during the conduction period of the upper switch tube or the conduction period of the lower switch tube of the half-bridge switch circuit, the detection error amplification circuit obtains the first detection signal, wherein the first detection signal is linearly correlated with the output voltage information.

[0009] Preferably, the controller further comprises a driving power circuit, wherein the driving power circuit receives a switch control signal for controlling the state of the half-bridge switch circuit to obtain a driving signal for driving the half-bridge switch circuit.

[0010] Preferably, the half-bridge switch circuit and the controller are integrated into one chip.

[0011] Preferably, the frequency modulation and duty cycle adjustment circuit includes a resonant frequency setting circuit and a switching frequency generating circuit. The resonant frequency setting circuit obtains a frequency signal of a set frequency value through a resistor external to the controller and transmits it to the switching frequency generating circuit. The switching frequency generating circuit receives the compensation signal and the frequency signal to generate the switching control signal and transmits it to the driving power circuit.

[0012] Preferably, the preset frequency signal includes a first frequency value and a second frequency value.

[0013] Preferably, the false detection error amplification circuit includes a first switch, a sampling and holding circuit and an error amplification circuit, the switching state of the first switch is consistent with the switching state of the upper switch tube of the half-bridge switching circuit; the sampling and holding circuit samples and holds the voltage signal at the high potential end of the primary winding when the first switch is turned on to obtain the first detection signal; the error amplification circuit receives the first detection signal and a preset reference voltage for error amplification to obtain the compensation signal.

[0014] Preferably, the preset reference voltage is set according to a resistor externally connected to the controller and is adjustable according to the output voltage of the isolation converter.

[0015] Preferably, the isolation converter is an LLC isolation converter.

[0016] Preferably, the controller further comprises a protection and alarm circuit, which receives circuit parameters to generate protection and alarm signals, wherein the circuit parameters comprise at least one of inductor current information, a first detection signal and chip temperature information.

[0017] In the second aspect, the present application also provides a control method for a high-precision isolation converter, wherein the isolation converter includes a half-bridge switching circuit, an excitation inductor, a resonant inductor, and a resonant capacitor. When a switch tube of the half-bridge switching circuit is turned on, the excitation inductor, the resonant inductor, the resonant capacitor and the switch tube constitute a resonant network, including the steps of: detecting the high-end node voltage of the primary winding of the transformer during the conduction period of the upper switch tube or the lower switch tube of the half-bridge switching circuit to obtain a first detection signal representing output voltage information; obtaining a compensation signal by amplifying the error between the first detection signal and a preset reference voltage; obtaining a switch control signal according to the compensation signal, the inductor current sampling signal and the preset frequency signal to control the switching action of the half-bridge switching circuit and control the output signal of the isolation converter to maintain stability.

[0018] Preferably, the preset frequency signal includes a first frequency value and a second frequency value.

[0019] Preferably, when the upper switch tube is turned on, the voltage signal at the high potential end of the primary winding is sampled and maintained to obtain the first detection signal; and the first detection signal and a preset reference voltage are error-amplified to obtain the compensation signal.

[0020] Preferably, the compensation signal and the preset frequency signal are received to generate the switch control signal; the switch control signal is used to obtain a drive signal through a drive circuit to drive the half-bridge switch circuit.

[0021] The high-precision isolation converter and control method thereof of the present invention are adopted. The isolation converter includes a half-bridge switch circuit, an excitation inductor, a resonant current, and a resonant capacitor. When a switch tube in the half-bridge switch circuit is turned on, the excitation inductor, the resonant inductor, the resonant capacitor and the switch tube form a resonant network. The detection error amplifier circuit detects the high-end node voltage of the primary winding of the transformer to obtain a first detection signal representing the output voltage information. The compensation signal is obtained by amplifying the error between the first detection signal and a preset reference voltage. The frequency modulation and duty cycle adjustment circuit obtains a switch control signal according to the compensation signal and the preset frequency signal to control the switching action of the half-bridge switch circuit, thereby controlling the output signal of the isolation converter to maintain stability. Through the output voltage detection and feedback control of the present invention, the output of the LLC isolation converter is stable, not affected by circuit parameters, with good feedback and high precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A circuit block diagram of an isolation converter according to the present invention;

[0023] Figure 2 Based on Figure 1 A circuit diagram of a controller in

[0024] Figure 3 Based on Figure 2 A circuit diagram of a frequency modulation and duty cycle modulation circuit;

[0025] Figure 4 Based on Figure 2 A circuit diagram of an implementation of a detection error amplification circuit;

[0026] Figure 5 Based on Figure 2 A circuit diagram of an implementation of a driving power circuit in;

[0027] Figure 6 FIG. 4 is a working waveform diagram according to the present invention. DETAILED DESCRIPTION

[0028] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made within the spirit and scope of the present invention.

[0029] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0030] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportion, and are only used for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention.

[0031] refer to Figure 1 A circuit block diagram of an isolation converter according to the present invention; Figure 2 Based on Figure 1 A circuit block diagram of a controller in the embodiment of the present invention, the isolation converter of the embodiment of the present invention is an LLC isolation converter, the isolation converter includes a half-bridge switch circuit, an excitation inductor, a resonant inductor, and a resonant capacitor. When one of the switch tubes in the half-bridge switch circuit is turned on, the excitation inductor, the resonant inductor, the resonant capacitor and the switch tube form a resonant network. For example, the half-bridge switch circuit includes a switch tube Q1 and a switch tube Q2. In this embodiment, the excitation inductor such as Lm is included in the primary winding of the transformer. When the switch tube Q1 is turned on, the resonant inductor Lr, the excitation inductor Lc, the resonant capacitor, the switch tube Q1 and the two input ends of the input voltage form a resonant network; when the switch tube Q2 is turned on, the excitation inductor Lr, the excitation inductor Lc, the resonant inductor Lr, the excitation inductor Lc, the resonant capacitor, and the switch tube Q2 form a resonant network. The LLC isolation converter receives an input voltage Vin, and converts it into a desired output voltage Vout output through the switching action of the half-bridge switch circuit to power the load.

[0032] Specifically, refer to Figure 2 As shown, the controller includes a detection error amplifier circuit, a frequency modulation duty cycle adjustment circuit and a driving power circuit. The detection error amplifier circuit detects the voltage of the high-end node of the primary winding of the transformer, such as the voltage of the W1 node, to obtain a first detection signal representing the output voltage information. Specifically, the resonant inductor Lr and the resonant capacitor Lc are connected in series, and the detection error amplifier circuit detects the voltage of the intermediate node connected between the series branch and the primary winding to obtain the first detection signal. After that, the compensation signal comp is obtained by error amplification of the first detection signal and the preset reference voltage Vref; the frequency modulation duty cycle adjustment circuit obtains a switch control signal according to the compensation signal comp and the preset frequency signal fr, and the driving power circuit receives the switch control signal Gate that controls the state of the half-bridge switch circuit to obtain a drive signal to drive the half-bridge switch circuit. Here, taking the example of the half-bridge switch circuit and the controller being integrated in one chip, the half-bridge switch circuit can be composed of transistors or switch tubes such as triodes.

[0033] Here, during the conduction period of the upper switch tube Q1 of the half-bridge switch circuit, the detection error amplifier circuit obtains the first detection signal, wherein the first detection signal is linearly related to the output voltage information. Here, when the switch tube Q1 is turned on, through the turns ratio relationship between the primary and secondary windings of the transformer, since the secondary winding of the transformer is associated with the output voltage, the high-end voltage of the primary winding can be obtained by calculation, and thus, the first detection signal and the output voltage information are also in a certain proportional relationship. Similarly, during the conduction period of the lower switch tube, the voltage sampled during the conduction time of the lower switch tube is a negative voltage, and then a positive voltage signal is obtained by voltage conversion. Specifically, refer to Figure 4 The false detection error amplifier circuit 200 includes a first switch 203, a sampling and holding circuit 202 and an error amplifier circuit EA1. The switching state of the first switch is consistent with the switching state of the upper switch tube Q1 of the half-bridge switch circuit. When the first switch is turned on, the sampling and holding circuit samples and holds the voltage signal at the high potential end of the primary winding to obtain the first detection signal. The error amplifier circuit receives the first detection signal and the preset reference voltage Vref for error amplification to obtain the compensation signal Comp. Here, the false detection error amplifier circuit 200 also includes an output voltage compensation reference establishment circuit 201, which is externally connected to a resistor to generate the preset reference voltage Vref. According to the resistance value of the resistor, the preset reference voltage Vref can be adjusted accordingly. If the resistance value of the resistor changes according to the output voltage, the preset reference voltage Vref can be adjusted according to the output voltage.

[0034] Specifically, refer to Figure 3 , as shown, the frequency modulation and duty cycle adjustment circuit 300 includes a resonant frequency setting circuit 302 and a switching frequency generation circuit 301. The resonant frequency setting circuit obtains a frequency signal fr of a set frequency value through a resistor outside the controller and transmits it to the switching frequency generation circuit. The switching frequency generation circuit receives the compensation signal Comp. The switching frequency generation circuit generates the switch control signal Gate according to the compensation signal and the frequency signal and transmits it to the driving power circuit. The preset frequency signal includes a first frequency value and a second frequency value. Among them, the preset frequency value is set according to the external resistor of the controller, and can also be adjusted according to the output voltage of the isolation converter. Specifically, the switching frequency generation circuit can adjust the working time of the main switch tube Q1 through the compensation signal to adjust the working frequency of the system so that the working frequency of the system is consistent with the frequency signal fr of the frequency value. Here, the frequency modulation and duty cycle adjustment circuit 300 can also receive the inductor current sampling signal Isense, and then adjust the duty cycle according to the inductor current sampling signal to achieve current overcurrent protection.

[0035] like Figure 5 As shown, the controller also includes a driving power circuit 100, which includes a driving circuit 101 and half-bridge switch circuits Q1 and Q2. The driving power circuit receives a switch control signal for controlling the state of the half-bridge switch circuit to obtain a driving signal to drive the half-bridge switch circuit. One power terminal of the switch tube Q1 is connected to the power supply voltage Vcc, and one power terminal of the other switch tube is connected to the reference ground terminal. The common node of the half-bridge switch circuits Q1 and Q2 is connected to the series branch of the resonant inductor and the resonant capacitor. The half-bridge switch circuit and the controller are integrated in one chip to make the circuit more integrated and optimize the volume.

[0036] In addition, the controller further includes a protection and alarm circuit, which receives circuit parameters to generate protection and alarm signals, wherein the circuit parameters include at least one of inductor current information, a first detection signal, and chip temperature information. The protection and alarm circuit can enable the controller to timely control the shutdown of the switch tube in an emergency to protect the safe operation of the controller.

[0037] refer to Figure 6 According to the working waveform diagram of the present invention, at time t1, the upper switch tube Q1 driving signal PWM_Q1 of the half-bridge switch circuit becomes a high effective state, the upper switch tube Q1 is turned on, the voltage VSW of the common node of the half-bridge switch circuit Q1 and Q2 also starts to rise, the resonant current Ir rises, and the excitation current ILm also rises, and the high-end voltage VW1 of the primary winding gradually rises to a stable value, which is associated with the output voltage information. At this time, the output voltage information is obtained through the detection of the error amplifier circuit, and fed back to the frequency modulation duty cycle circuit to control the duty cycle of the switch tube, so that the output voltage value is consistent with the preset reference voltage. Afterwards, at time t2, the resonant current Ir is equal to the excitation current ILm, and the current of the first diode D1 of the secondary side is reduced to zero, thereby realizing zero current shutdown ZCS. Until time t3, the resonant inductor Lr, the resonant capacitor Cr of the primary side and the excitation inductor of the first transformer T1 are connected in series to obtain a longer period of resonance. At time t3, the driving power circuit 100 drives the upper switch tube to turn off, and the resonant cavity current Ir is still positive, releasing the charge of the parasitic capacitance of the Vsw node so that Vsw is reduced to zero, until time t4 when the driving power circuit 100 drives the lower switch tube Q2 to turn on ZVS with zero voltage.

[0038] Through the above process, it can be known that the present application can realize zero current shutdown of the secondary side and zero voltage opening of the primary side, and can also realize the feedback of the output voltage information of the secondary side to the primary side, so as to accurately control the output voltage of the secondary side. For example, when the disturbance such as load change or supply voltage Vcc change enters the circuit, assuming that the output voltage Vout is higher than the preset value, the corresponding node voltage Vsw1 in the t1-t2 period is also higher than the set value, after passing through the sampling and holding circuit 202, the output compensation signal Comp of the first error amplifier EA1 begins to increase, and the gate signal frequency output by the switching frequency generating circuit 301 is positively correlated with the compensation signal Comp, that is, the higher the Gate signal frequency is. As is known to all, the LLC topology works normally in the inductive region, and the relationship between the output voltage Vout gain and the switching frequency is negatively correlated. The increase in the Gate signal frequency causes the output voltage Vo to decrease, so that under the disturbance that the output voltage Vout is higher than the set value, the closed-loop control output voltage Vout is adjusted down to the set value. Similarly, if the output voltage Vout is subjected to a reduced disturbance, the closed-loop regulation method is in a dual relationship with the above, which will not be elaborated here. Therefore, the control circuit can realize closed-loop control of the LLC topology isolated power supply.

[0039] Finally, the present application provides a control method for a high-precision isolation converter, wherein the isolation converter includes a half-bridge switching circuit, an excitation inductor, a resonant inductor, and a resonant capacitor. When a switch tube of the half-bridge switching circuit is turned on, the excitation inductor, the resonant inductor, the resonant capacitor and the switch tube constitute a resonant network, comprising the steps of:

[0040] During the conduction period of the upper switch tube of the half-bridge switch circuit, the high-end node voltage of the primary winding of the transformer is detected to obtain a first detection signal representing output voltage information; a compensation signal is obtained by amplifying the error between the first detection signal and a preset reference voltage; a switch control signal is obtained according to the compensation signal, the inductor current sampling signal and the preset frequency signal to control the switching action of the half-bridge switch circuit and control the output signal of the isolation converter to maintain stability.

[0041] Preferably, the preset frequency signal includes a first frequency value and a second frequency value.

[0042] Preferably, when the upper switch tube is turned on, the voltage signal at the high potential end of the primary winding is sampled and maintained to obtain the first detection signal; and the first detection signal and a preset reference voltage are error-amplified to obtain the compensation signal.

[0043] Preferably, the compensation signal and the inductor current sampling signal are received, a comparison signal is obtained by comparing the two, and the switch control signal is generated according to the comparison signal and the preset frequency signal; the switch control signal obtains a drive signal through a drive circuit to drive the half-bridge switch circuit.

[0044] In summary, through the output voltage detection and feedback control of the LLC isolation converter of the present invention, the output of the LLC isolation converter is stable, not affected by circuit parameters, has good feedback, high precision, and further improves work efficiency.

[0045] It should be noted that the specific implementation and corresponding illustrations given are merely a way of describing the implementation method of the present invention, and do not limit the specific structure of the implementation scheme of the present invention. Various changes or modifications can be made to these implementation schemes without departing from the principle and essence of the present invention, but these changes and modifications fall within the scope of protection of the present invention.

[0046] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0047] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A high-precision isolation converter, comprising a half-bridge switch circuit, an excitation inductor, a resonant inductor, and a resonant capacitor. When a switch tube of the half-bridge switch circuit is turned on, the excitation inductor, the resonant inductor, the resonant capacitor and the switch tube form a resonant network, characterized in that: The isolation converter includes a controller and a transformer, wherein the controller includes a detection error amplification circuit and a frequency modulation duty cycle adjustment circuit. The detection error amplification circuit detects the voltage of the high-end node of the primary winding of the transformer to obtain a first detection signal representing output voltage information, and obtains a compensation signal by performing error amplification on the first detection signal and a preset reference voltage; The frequency modulation and duty cycle adjustment circuit obtains a switch control signal according to the compensation signal and the preset frequency signal to control the switching action of the half-bridge switch circuit and control the output signal of the isolation converter to maintain stability.

2. The high-precision isolation converter according to claim 1, characterized in that: The resonant inductor and the resonant capacitor are connected in series, and the detection error amplification circuit detects the voltage of an intermediate node where the series branch is connected to the primary winding to obtain the first detection signal.

3. The high-precision isolation converter according to claim 1, characterized in that: During the conduction period of the upper switch tube of the half-bridge switch circuit or the conduction period of the lower switch tube of the half-bridge switch circuit, the detection error amplifying circuit obtains the first detection signal, Wherein, the first detection signal is linearly correlated with the output voltage information.

4. The high-precision isolation converter according to claim 1, characterized in that: The controller also includes a driving power circuit, The driving power circuit receives a switch control signal for controlling the state of the half-bridge switch circuit to obtain a driving signal to drive the half-bridge switch circuit.

5. The high-precision isolation converter according to claim 1, characterized in that: The half-bridge switch circuit and the controller are integrated into one chip.

6. The high-precision isolation converter according to claim 4, characterized in that: The frequency modulation and duty cycle adjustment circuit includes a resonant frequency setting circuit and a switching frequency generating circuit. The resonant frequency setting circuit obtains a frequency signal of a set frequency value through a resistor external to the controller, and transmits the signal to the switching frequency generating circuit. The switching frequency generating circuit generates the switching control signal according to the compensation signal and the frequency signal and transmits it to the driving power circuit.

7. The high-precision isolation converter according to claim 6, characterized in that: The preset frequency signal includes a first frequency value and a second frequency value.

8. The high-precision isolation converter according to claim 1, characterized in that: The misdetection error amplifier circuit includes a first switch, a sampling and holding circuit, and an error amplifier circuit. The switching state of the first switch is consistent with the switching state of the upper switch tube of the half-bridge switch circuit; The sampling and holding circuit samples and holds the voltage signal of the high potential end of the primary winding when the first switch is turned on, so as to obtain the first detection signal; The error amplifying circuit receives the first detection signal and a preset reference voltage to perform error amplification and obtain the compensation signal.

9. The high-precision isolation converter according to claim 1, characterized in that: The preset reference voltage is set according to a resistor externally connected to the controller and is adjustable according to the output voltage of the isolation converter.

10. The high-precision isolation converter according to claim 1, characterized in that: The isolation converter is an LLC isolation converter.

11. The high-precision isolation converter according to claim 1, characterized in that: The controller also includes a protection and alarm circuit, The protection and alarm circuit receives circuit parameters to generate protection and alarm signals. The circuit parameter includes at least one of inductor current information, a first detection signal and chip temperature information.

12. A control method for a high-precision isolation converter, wherein the isolation converter comprises a half-bridge switch circuit, an excitation inductor, a resonant inductor, and a resonant capacitor, wherein when a switch tube of the half-bridge switch circuit is turned on, the excitation inductor, the resonant inductor, the resonant capacitor and the switch tube form a resonant network, characterized in that: Includes steps: During the conduction period of the upper switch tube or the lower switch tube of the half-bridge switch circuit, the voltage of the high-end node of the primary winding of the transformer is detected to obtain a first detection signal representing output voltage information; A compensation signal is obtained by performing error amplification on the first detection signal and a preset reference voltage; A switch control signal is obtained according to the compensation signal, the inductor current sampling signal and the preset frequency signal to control the switching action of the half-bridge switch circuit and control the output signal of the isolation converter to maintain stability.

13. The control method of the high-precision isolation converter according to claim 12, characterized in that: The preset frequency signal includes a first frequency value and a second frequency value.

14. The control method of the high-precision isolation converter according to claim 12, characterized in that: When the upper switch tube is turned on, sampling and holding the voltage signal of the high potential end of the primary winding to obtain the first detection signal; The compensation signal is obtained by performing error amplification on the first detection signal and a preset reference voltage.

15. The control method of the high-precision isolation converter according to claim 12, characterized in that: Receiving the compensation signal and the preset frequency signal to generate the switch control signal; The switch control signal obtains a drive signal through a drive circuit to drive the half-bridge switch circuit.

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