Switching Power Supply

Abstract

The present invention discloses a switching power supply, including a power stage circuit and a control circuit, wherein the control circuit is connected to the control end of the main switch tube of the power stage circuit to control the switching frequency and the peak value of the inductor current of the power stage circuit; the control circuit includes a peak current regulating circuit and a switching frequency regulating circuit, wherein the peak current regulating circuit receives a feedback signal and a corresponding reference signal, performs error processing on the feedback signal and the corresponding reference signal to obtain a compensation signal, and the compensation signal or a segmented compensation signal obtained according to the compensation signal is compared with a first sampling signal representing the inductor current flowing through the power stage circuit to obtain a first control signal; the switching frequency regulating circuit receives the compensation signal and obtains a second control signal according to the compensation signal. The present invention can improve the applicable range of the inductor and maintain the maximum output power stable in the case of magnetic interference or no interference.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a switching power supply. Background Art

[0002] The switching power supply can adopt a variety of topologies, including Buck circuit, Boost circuit, Flyback circuit, etc. The output power of the switching power supply can be adjusted by controlling the switching frequency, peak current and other information in the switching circuit.

[0003] like Figure 1 In the flyback switching power supply shown in the prior art, there may be a problem of external strong magnetic field interference in the application of the switching power supply. The external magnetic field interference will make the inductor more easily reach saturation, reduce the inductance of the inductor in the switching power supply, reduce the maximum peak current, thereby reducing the maximum output power of the switching power supply and affecting the normal operation of the switching power supply. In the prior art, when designing magnetic components such as inductors in switching power supplies, considering the problem of magnetic field interference, a large margin is often left, which not only increases the size of the switching power supply, but also increases the cost. In addition, even if there is no magnetic interference, if the application range of the inductor can be expanded, it is also conducive to reducing costs. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a switching power supply that improves the applicable range of inductance and maintains the stability of the maximum output power, so as to solve the technical problem of the prior art that the applicable range of inductance is limited under magnetic interference or without interference.

[0005] The technical solution of the present invention is to provide a switching power supply of the following structure, including a switching power supply, a power stage circuit and a control circuit, wherein the control circuit is connected to the control end of the main switch tube of the power stage circuit to control the switching frequency and the inductor current peak of the power stage circuit;

[0006] The control circuit includes a peak current regulation circuit and a switching frequency regulation circuit. The peak current regulation circuit receives a feedback signal and a corresponding reference signal, performs error processing on the feedback signal and the corresponding reference signal to obtain a compensation signal. The compensation signal or a segmented compensation signal obtained according to the compensation signal is compared with a first sampling signal representing the inductor current flowing through the power stage circuit to obtain a first control signal. The switching frequency regulation circuit receives the compensation signal and obtains a second control signal according to the compensation signal. The switching state of the main switch tube of the power stage circuit is controlled according to the first control signal and the second control signal.

[0007] Optionally, the switching frequency adjustment circuit converts the compensation signal into a first current signal, charges the capacitor in each switching cycle, compares the voltage on the capacitor with a first threshold, sets the switching frequency based on the comparison result between the two, and obtains the second control signal.

[0008] Optionally, the peak current regulation circuit includes a compensation signal adjustment circuit, which receives the compensation signal and performs segmented adjustment on the compensation signal to obtain the segmented compensation signal peak current.

[0009] Optionally, the maximum value of the segmented compensation signal is clamped at a second threshold value, and in the interval clamped at the second threshold value, the valley current of the power stage circuit is kept stable, and the switching frequency of the main switch tube increases with the increase of the compensation signal.

[0010] Optionally, the first control signal controls the main switch tube to be turned off, and the second control signal controls the main switch tube to be turned on.

[0011] Optionally, the switching frequency adjustment circuit includes a voltage-current conversion module, a first current mirror module and a first capacitor. The voltage-current conversion module receives the compensation signal and converts the compensation signal into a current signal characterizing the compensation signal. The first current mirror module receives the current signal characterizing the compensation signal, charges the first capacitor in each switching cycle, compares the voltage on the first capacitor with a first threshold, sets the switching frequency according to the comparison result between the two, and obtains the second control signal.

[0012] Optionally, the compensation signal adjustment circuit includes a multi-channel voltage-current conversion module, a second current mirror module and an impedance element, the input end of the multi-channel voltage-current conversion module receives the compensation signal, and the multi-channel voltage-current conversion module is also provided with a reference current. When the compensation signal is lower than the first reference, the voltage drop generated by the current after the reference current is mirrored by the second current mirror module on the impedance element is used as the first segment of the segmented compensation signal. When the compensation signal is greater than the first reference and less than the second reference, the voltage drop generated by the sum of the reference current and the current generated by one of the voltage-current conversion modules after the current is mirrored by the second current mirror module on the impedance element is used as the second segment of the segmented compensation signal. When the compensation signal is greater than the second reference, the current generated by the multi-channel voltage-current conversion module is clamped to a constant current, and the voltage drop generated by the current after the constant current is mirrored by the second current mirror module on the impedance element is used as the third segment of the segmented compensation signal. At this time, the segmented compensation signal is clamped at the second threshold.

[0013] Optionally, the inductor current at the time when the main switch tube is turned on is detected and compared with a third threshold value. When the inductor current is higher than the third threshold value, the turn-on time of the main switch tube in the next switching cycle is delayed until the inductor current drops to the third threshold value when the main switch tube is turned on.

[0014] Optionally, the switching power supply operates in a continuous conduction mode.

[0015] Optionally, the switching power supply operates in a discontinuous conduction mode or a continuous conduction mode.

[0016] Compared with the prior art, the present invention has the following advantages: in the peak current control mode, the regulation of energy transfer mainly depends on the control of the peak current and the switching frequency. Due to the limitation of the inductor, the increase of the peak current will be limited, especially in the case of magnetic interference, which will reduce the performance of the inductor and make the peak current unable to reach the threshold peak value. The present invention can maintain the stability of power by increasing the switching frequency, and keep the inductor current valley stable during the period. The present invention can improve the application range of the inductor in the case of magnetic interference or no interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of a switch circuit in the prior art;

[0018] Figure 2 A circuit schematic diagram of an embodiment of a control circuit of a switching power supply of the present invention;

[0019] Figure 3 A circuit schematic diagram of another embodiment of the control circuit of the switching power supply of the present invention;

[0020] Figure 4 A circuit structure diagram of a compensation signal adjustment circuit;

[0021] Figure 5 It is the working waveform diagram of the present invention;

[0022] Figure 6 This is a circuit schematic diagram of another embodiment of the control circuit of the switching power supply of the present invention. DETAILED DESCRIPTION

[0023] 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.

[0024] 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.

[0025] 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.

[0026] Figure 1 It is a flyback switching power supply of the prior art, and is also the basic topology on which the present invention is based. However, the flyback topology is adopted only for illustration, and the application of the present invention is not limited to the flyback topology. The primary side and the secondary side are isolated by an optocoupler, and the signal fed back from the secondary side to the primary side is output as a feedback signal VFB through the optocoupler. The feedback signal VFB represents the output current or output voltage information of the secondary side, and adjusts the switching state of the main power tube of the flyback switching power supply according to the feedback signal VFB. Based on the problems of the prior art, the technical solution of the present invention is aimed at the control circuit of the switching power supply, which is generally located in the primary side control circuit in the flyback switching power supply.

[0027] like Figure 2 As shown, the structural principle of the control circuit of the switching power supply of the present invention is illustrated. The switching power supply of the present invention includes a power stage circuit and a control circuit, and the control circuit is connected to the control end of the main switch tube of the power stage circuit to control the switching frequency and the peak value of the inductor current of the power stage circuit. The power stage circuit can adopt a topology structure such as Buck, Boost, Flyback, etc., and Flyback is used as an example for detailed description in this embodiment.

[0028] The control circuit includes a peak current regulation circuit and a switching frequency regulation circuit. The peak current regulation circuit receives a feedback signal VFB and a corresponding reference signal Vref, performs error processing on the feedback signal VFB and the corresponding reference signal Vref in an operational amplifier U01 to obtain a compensation signal Vcomp. The compensation signal Vcomp or a segmented compensation signal Vcomp2 obtained according to the compensation signal Vcomp is compared with a first sampling signal CS representing the inductor current flowing through the power stage circuit in a comparator U02 to obtain a first control signal Vctrl1. The switching frequency regulation circuit receives the compensation signal and obtains a second control signal Vctrl2 according to the compensation signal Vcomp. The switching state of the main switch tube M1 of the power stage circuit is controlled through an RS trigger according to the first control signal Vctrl1 and the second control signal Vctrl2.

[0029] The switching frequency adjustment circuit converts the compensation signal into a first current signal, charges the capacitor in each switching cycle, compares the voltage on the capacitor with the first threshold, sets the switching frequency according to the comparison result of the two, and obtains the second control signal. Specifically, the switching frequency adjustment circuit includes a voltage-current conversion module, a first current mirror module and a first capacitor C1, the voltage-current conversion module receives the compensation signal Vcomp, and converts the compensation signal Vcomp into a current signal I1 representing the compensation signal Vcomp, the first current mirror module receives the current signal I1 representing the compensation signal Vcomp, charges the first capacitor C1 in each switching cycle, and when the voltage on the first capacitor C1 reaches the threshold Vth1, the first capacitor C1 is discharged and reset, and the switching frequency is set according to the comparison result of the two, that is, the switching frequency is set according to the speed or time required for the voltage Vcomp3 on the first capacitor C1 to reach the first threshold Vth1, and the second control signal Vctrl2 is obtained. In this embodiment, the voltage-current conversion module includes a switch tube M3 and a resistor R4, wherein the control end of the switch tube M3 receives the compensation signal Vcomp, and the voltage drop of the resistor R4 is the difference between the compensation signal Vcomp and the gate-source voltage. Therefore, the current flowing through the resistor R4 is the difference between the compensation signal Vcomp and the gate-source voltage divided by the resistance value of the resistor R4. The first current mirror module can mirror the current in the same proportion, or set a proportional coefficient to mirror the current. Figure 4 As shown, the compensation signal Vcomp has a corresponding relationship with the switching frequency Fs. Therefore, a current signal consistent with the switching frequency Fs variation waveform can be obtained according to the compensation signal Vcomp. Figure 3 To understand this part, refer to the embodiments of the present invention.

[0030] like Figure 3 FIG. 1 is a diagram showing the structure principle of another embodiment of the control circuit of the switching power supply of the present invention. Figure 2The difference between the embodiments mainly lies in the technical solution of the switching frequency adjustment circuit. The switching frequency adjustment circuit includes a multi-channel voltage and current conversion module, a first current mirror module and a first capacitor C1. The multi-channel voltage and current conversion module receives the compensation signal Vcomp and converts the compensation signal Vcomp into a current signal I2. The first current mirror module receives the current signal I2 and charges the first capacitor C1 in each switching cycle. When the voltage on the first capacitor C1 reaches the threshold value Vth1 (compared by the comparator U03), the first capacitor C1 is discharged and reset. The switching frequency is set according to the comparison result of the two, that is, the switching frequency is set according to the speed or required time of the voltage on the first capacitor C1 reaching the first threshold value Vth1, and the second control signal Vctrl2 is obtained. In order to make the current signal I2 converted by the multi-channel voltage and current conversion module consistent with the waveform of the switching frequency Fs, the current signal I2 converted by the multi-channel voltage and current conversion module increases first, then remains unchanged, and then increases again as the compensation signal Vcomp increases.

[0031] like Figure 3 As shown, the multi-channel voltage-current conversion module includes three-channel voltage-current conversion modules, the first channel is a series structure of a switch tube M4 and a resistor R5, the second channel is a series structure of a switch tube M5 and a resistor R6, and the third channel is a series structure of a switch tube M6 and a resistor R7. Among them, the control end of the switch tube M4 receives the compensation signal Vcomp. The first regulating current IR1, the second regulating current IR2 and the second regulating current IR3 can be selectively provided on the first channel, the second channel and the third channel series structure as needed. The first regulating current IR1 is a forward current, and the second regulating current IR2 and the third regulating current IR3 can be reverse currents. The forward current refers to the current that can be mirrored by the first mirror module and charge the first capacitor, while the reverse current cannot, but can be used to offset the forward current generated by the channel.

[0032] When the compensation signal Vcomp is less than the first reference V1, the second and third paths do not work (can be achieved by disconnecting the switch), then only the first path generates current, and the generated current is (Vcomp-Vgs) / R5, where Vgs is the gate-source voltage of the switch tube M4. After superimposing the first regulating current IR1, the first regulating current IR1 can be a constant current source, and the total current is: (Vcomp-Vgs) / R5+IR1, and the first mirror module is used to achieve 1:1 current mirroring. Therefore, the charging current of the first capacitor C1 is (Vcomp-Vgs) / R5+IR1. At this time, the charging speed of the first capacitor C1 is the same as the change trend of Vcomp. When the compensation signal Vcomp is greater than the first reference V1 and less than the second reference V2, the first path does not work (can be achieved by disconnecting the switch), the control end of the switch tube M5 of the second path receives the first reference V1, and the second path may not be set with the second regulating current IR2. Therefore, the current generated by the second path is: (V1-Vgs) / R6. If it is set in the second regulating current IR2, it can be used to offset the current generated by Vgs. In this embodiment, the control end of the switch tube M6 of the third path receives the compensation signal Vcomp, and the forward current generated by the third path is (Vcomp-Vgs) / R7. After the third regulating current IR3 is superimposed, the total current is: (Vcomp-Vgs) / R7-IR3, where IR3=(V2-Vgs) / R7. It can be seen that in the interval where Vcomp is greater than the first reference V1 and less than the second reference V2, no current in the third path will be mirrored by the first mirror module to charge the first capacitor C1. When the compensation signal Vcomp is greater than the second reference V2, (Vcomp-Vgs) / R7 is greater than the third regulating current IR3, and the charging current of the first capacitor C1 increases with the increase of the compensation signal Vcomp.

[0033] like Figure 4 As shown, the circuit structure of the compensation signal adjustment circuit is illustrated. The peak current regulation circuit includes a compensation signal adjustment circuit, which receives the compensation signal Vcomp, and adjusts the compensation signal Vcomp in segments to obtain the segmented compensation signal Vcomp2. The maximum value of the segmented compensation signal is clamped at the second threshold value. In the interval clamped at the second threshold value (when the compensation signal Vcomp is greater than the second reference V2), the valley current of the power stage circuit is kept stable, and the switching frequency of the main switch tube increases with the increase of the compensation signal Vcomp. The first control signal Vctrl1 controls the main switch tube M1 to turn off, and the second control signal Vctrl2 controls the main switch tube M1 to turn on.

[0034] The compensation signal adjustment circuit includes a multi-channel voltage-current conversion module, a second current mirror module and an impedance element R8. The input end of the multi-channel voltage-current conversion module receives the compensation signal Vcomp. The multi-channel voltage-current conversion module is also provided with a reference current Iref. When the compensation signal Vcomp is lower than the first reference V1, the voltage drop generated by the current mirrored by the second current mirror module on the impedance element R8 is used as the first segment of the segment compensation signal Vcomp2. When the compensation signal Vcomp is greater than the first reference V1 and less than the second reference V2, the voltage drop generated by the sum of the reference current Iref and the current generated by one of the voltage-current conversion modules after the current mirrored by the second current mirror module on the impedance element R8 is used as the second segment of the segment compensation signal Vcomp2. When the compensation signal Vcomp is greater than the second reference V2, the current generated by the multi-channel voltage-current conversion module is clamped to a constant current, and the voltage drop generated by the current mirrored by the second current mirror module on the impedance element R8 is used as the third segment of the segment compensation signal Vcomp2. At this time, the segment compensation signal Vcomp2 is clamped at the second threshold value Vth2. Since the segmented compensation signal Vcomp2 is a reference to the peak current, the shape of the segmented compensation signal Vcomp is as follows: Figure 5The shape of the peak current Ip in. Whether each voltage-current conversion module is connected can be controlled by a switch. When the compensation signal Vcomp is lower than the first reference V1, the reference current Iref of the first path is connected, and the second path can also be connected at the same time, and the third path is disconnected. Since the reverse reference current Iref is set in the second path, when Vcomp is lower than the first reference V1, the path does not generate a circuit, or it can be considered that the generated current and the reverse reference current Iref offset each other; when Vcomp is greater than the first reference V1 and less than the second reference V2, the first path and the second path are connected at the same time, and the generated current is: Iref+(Vcomp-Vgs) / R9-Iref=(Vcomp-Vgs) / R9. During this period, the segmented compensation signal Vcomp2 increases with the increase of the compensation signal. When the compensation Vcomp is greater than the second reference V2, the first path and the second path are disconnected, and the third path is turned on. The current generated is: (V2-Vgs) / R10, that is, it is clamped to a constant current at this time. Taking the proportional coefficient of the second current mirror module as 1:1 as an example, during this period, the current flowing through the impedance element R8 is (V2-Vgs) / R10, and the voltage on the impedance element R8 is the impedance element (V2-Vgs) / R10*R8, which is the second threshold value. Among the above-mentioned paths, the first path is the reference current Iref, the second path is a series structure composed of a switch tube M6 and a resistor R9, and the second path is a series structure composed of a switch tube M7 and a resistor R10, and switches are set to control the on and off of each path. These switches can be controlled by the output of a comparator, and the comparator is used to determine the interval range of the compensation signal Vcomp. In the above embodiments, for the convenience of description and calculation, the resistance value of each path is equal by default, but the resistance size can be designed according to different needs.

[0035] like Figure 5 As shown, multiple working intervals of the present invention are illustrated. In these intervals, there is a corresponding relationship between the compensation signal Vcomp and the peak current Ip and the switching frequency Fs. When the compensation signal is lower than the first reference V1, the peak current Ip remains stable, and the switching frequency Fs increases with the increase of the compensation signal Vcomp. When the compensation signal is greater than the first reference V1 and less than the second reference V2, the switching frequency Fs remains stable, and the peak current Ip increases with the increase of the compensation signal Vcomp. Due to the possible problem of magnetic interference, it is difficult for the inductor current to increase when the compensation signal Vcomp is greater than the second reference V2. In order to maintain the maximum output power, this is achieved by increasing the switching frequency.

[0036] like Figure 6 As shown, it indicates that Figure 2On the basis of the embodiment of or 3, the judgment of the valley value is added. If the switching frequency Fs increases to a certain extent, in the continuous conduction mode (CCM), the inductor current may be kept at a high level, so that the circuit maintains a high power, the switching loss is also large, and higher requirements are placed on the performance and cost of the switch tube. Since in the flyback switching power supply, it is impossible to directly detect the current at the end of the freewheeling of the secondary side from the primary side, the current at the end of the freewheeling of the secondary side can only be judged by detecting the current at the time of the primary side conduction, and the two are almost equal under the conversion of the excitation current. The inductor current at the time of the main switch tube is detected and compared with the third threshold value Vth3. When the inductor current is higher than the third threshold value Vth3, the turn-on time of the main switch tube in the next switching cycle is delayed until the inductor current drops to the third threshold value Vth3 at the time of the main switch tube turning on. Therefore, in this embodiment, the comparator U04 is used to realize the comparison of the voltage VIv representing the current valley value with the third reference V3, and the third reference V3 represents the third threshold value Vth3. This embodiment further adds a conduction timing adjustment module, which adjusts the second control signal Vctrl2 by integrating the comparator U04 and the signal output by U04.

[0037] The switching power supply of the present invention is applicable to discontinuous conduction mode (DCM) and continuous conduction mode (CCM). In the CCM mode, it is generally necessary to increase the valley value judgment to prevent the frequency from being too high, which may cause the inductor current to remain high.

[0038] 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.

[0039] 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 switching power supply, comprising a power stage circuit and a control circuit, wherein the control circuit is connected to a control terminal of a main switch tube of the power stage circuit to control a switching frequency and an inductor current peak value of the power stage circuit, characterized in that: The control circuit includes a peak current regulating circuit and a switching frequency regulating circuit. The peak current regulating circuit receives a feedback signal and a corresponding reference signal, performs error processing on the feedback signal and the corresponding reference signal to obtain a compensation signal, compares a segmented compensation signal obtained according to the compensation signal with a first sampling signal representing the inductor current flowing through the power stage circuit, and obtains a first control signal; the switching frequency regulating circuit receives the compensation signal and obtains a second control signal according to the compensation signal; and controls the switching state of the main switch tube of the power stage circuit according to the first control signal and the second control signal; The peak current regulating circuit comprises a compensation signal adjusting circuit, which receives the compensation signal and performs segmented adjustment on the compensation signal to obtain the segmented compensation signal; The compensation signal adjustment circuit includes a multi-channel voltage-current conversion module, a second current mirror module and an impedance element. The input end of the multi-channel voltage-current conversion module receives the compensation signal. The multi-channel voltage-current conversion module is also provided with a reference current. When the compensation signal is lower than the first reference, the voltage drop generated by the current mirrored by the second current mirror module on the impedance element is used as the first segment of the segmented compensation signal. When the compensation signal is greater than the first reference and less than the second reference, the voltage drop generated by the sum of the reference current and the current generated by one of the voltage-current conversion modules after being mirrored by the second current mirror module on the impedance element is used as the second segment of the segmented compensation signal. When the compensation signal is greater than the second reference, the current generated by the multi-channel voltage-current conversion module is clamped to a constant current, and the voltage drop generated by the current mirrored by the second current mirror module on the impedance element is used as the third segment of the segmented compensation signal. At this time, the segmented compensation signal is clamped at the second threshold.

2. The switching power supply according to claim 1, characterized in that: The switching frequency adjustment circuit converts the compensation signal into a first current signal, charges the capacitor in each switching cycle, compares the voltage on the capacitor with the first threshold, sets the switching frequency according to the comparison result of the two, and obtains the second control signal.

3. The switching power supply according to claim 2, characterized in that: The maximum value of the segmented compensation signal is clamped at the second threshold value. In the interval clamped at the second threshold value, the valley current of the power stage circuit is kept stable, and the switching frequency of the main switch tube increases with the increase of the compensation signal.

4. The switching power supply according to any one of claims 1 to 3, characterized in that: The first control signal controls the main switch tube to be turned off, and the second control signal controls the main switch tube to be turned on.

5. The switching power supply according to claim 2, characterized in that: The switching frequency adjustment circuit includes a voltage-current conversion module, a first current mirror module and a first capacitor. The voltage-current conversion module receives the compensation signal and converts the compensation signal into a current signal representing the compensation signal. The first current mirror module receives the current signal representing the compensation signal, charges the first capacitor in each switching cycle, compares the voltage on the first capacitor with a first threshold, sets the switching frequency according to the comparison result of the two, and obtains the second control signal.

6. The switching power supply according to claim 3, characterized in that: The inductor current at the turn-on time of the main switch tube is detected and compared with a third threshold value. When the inductor current is higher than the third threshold value, the turn-on time of the main switch tube in the next switching cycle is delayed until the inductor current drops to the third threshold value at the turn-on time of the main switch tube.

7. The switching power supply according to claim 3 or 6, characterized in that: The switching power supply operates in a continuous conduction mode.

8. The switching power supply according to any one of claims 1-2, characterized in that: The switching power supply operates in a discontinuous conduction mode or a continuous conduction mode.

Images