A four-switch power conversion circuit and its control method

Abstract

The present application discloses a four-switch power conversion circuit and its control method. By sampling the inductor current information of the first switch, the time when the inductor current reaches the inductor current peak reference is obtained to obtain a first time signal. In the Buck operating state, when the first time signal reaches the highest time threshold, it switches to the Buck-Boost operating mode. After that, when the first time signal is lower than the lowest time threshold, it switches to the Boost operating mode. By comparing the first time signal for mode switching, on the one hand, the sampled signals are streamlined, and only the current information of the first switch needs to be sampled to control the switch state, avoiding the problem of sampling deviation. On the other hand, through the control scheme of the present application, the switching between modes is smoother and the stability of the output voltage is better.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and more particularly, to a four-switch power conversion circuit and a control method thereof. Background Art

[0002] The four-switch power conversion circuit can operate in a buck mode, a buck-boost mode, and a boost mode according to the relationship between the input voltage and the output voltage. Among them, the power stage circuit of the four-switch power conversion circuit includes four switching tubes and an inductor. The first switching tube and the second switching tube are connected between the input voltage and the ground, the third switching tube and the fourth switching tube are connected between the output voltage and the ground, and the inductor is connected between the intermediate node of the second switching tube and the third switching tube. Generally, the output of an error amplifier is used to limit the peak or valley value of the inductor current. During the switching process between different operating modes, the corresponding inductor current is adjusted accordingly by the change of the output of the error amplifier to make the system reach a stable state.

[0003] In the prior art, the switching between various operating modes is generally carried out according to the magnitude relationship between the input and output voltages. This switching method may result in poor switching smoothness and ripple in the output voltage. Therefore, it is necessary to improve the problems existing in the prior art. Summary of the Invention

[0004] In view of this, an object of the present invention is to provide a four-switch power conversion circuit and a control method thereof, so as to solve the technical problem that the output voltage generates ripple due to poor smoothness during the switching process existing in the prior art.

[0005] In the first aspect of the present invention, a four-switch power conversion circuit is provided, including a power stage circuit and a control circuit. The power stage circuit includes four switching tubes and an inductor. The first switching tube and the second switching tube are connected between the input voltage and the ground, the third switching tube and the fourth switching tube are connected between the output voltage and the ground. The inductor is connected between the intermediate node of the first switching tube and the second switching tube and the intermediate node of the third switching tube and the fourth switching tube. The control circuit includes a sampling circuit that samples the inductor current information of the first switching tube, obtains the time when the inductor current reaches the inductor current peak reference, and records it as the first time signal. The control circuit performs mode switching according to the magnitude relationship between the first time signal, the highest time threshold, and the lowest time threshold: in the buck mode, when the first time signal reaches the highest time threshold, it switches to the buck-boost mode, and then, when the first time signal is lower than the lowest time threshold, it switches to the boost mode.

[0006] Preferably, in the Buck - Boost operating mode, within one switching cycle, the turn - on process of the first to fourth switching transistors is as follows: the control circuit controls the first and third switching transistors to turn on, and then controls the second and fourth switching transistors to turn on, and then controls the first and fourth switching transistors to turn on.

[0007] Preferably, when the load of the power conversion circuit is in a light - load state, in the Buck - Boost operating mode, within one switching cycle, the turn - on process of the first to fourth switching transistors is as follows: the control circuit controls the first and third switching transistors to turn on, and then controls the second and fourth switching transistors to turn on.

[0008] Preferably, the highest time threshold is set as follows: when the input voltage is equal to the output voltage, the period time corresponding to the preset frequency is the highest time threshold; the lowest time threshold is set as: K1×the highest time threshold, where K1 is any coefficient between 0.8 and 1.

[0009] Preferably, the inductor current peak reference includes a first peak reference signal and a second peak reference signal, and the second peak reference signal is greater than the first peak reference signal; in the Buck operating mode and the Boost operating mode, the inductor current is compared with the first peak reference signal to obtain the turn - off signal of the current switching transistor; in the Buck - Boost operating mode, the inductor current is compared with the second peak reference signal to obtain the turn - off signal of the current switching transistor.

[0010] Preferably, the control circuit includes a reference generation circuit, and the reference generation circuit includes an error compensation circuit which obtains the first peak reference signal according to the output voltage and the output reference signal of the power conversion circuit; the reference generation circuit further includes an addition circuit which superimposes the first peak reference signal and the bias signal to obtain the second peak reference signal, and the bias signal is obtained according to the output voltage and the preset time signal.

[0011] Preferably, the control circuit includes a turn - off signal circuit, and the turn - off signal circuit includes a comparator group and a selection circuit. The comparator group receives the inductor current information, calculates the time when the inductor current reaches the inductor current peak reference to obtain the first time signal, and generates a first comparison signal to control the turn - off of the current working switching transistor when the inductor current reaches the inductor current peak reference. The selection circuit selects and outputs one of the first peak reference signal and the second peak reference signal based on the second output signal of the comparator group.

[0012] Preferably, the turn-off signal circuit includes a first comparator, a second comparator, and a third comparator. The first comparator receives the inductor current information and the inductor current peak reference to output a first comparison signal and a first time signal. The second comparator receives the first time signal and the highest time threshold to generate a second comparison signal. The third comparator receives the first time signal and the lowest time threshold to generate a third comparison signal. Among them, the second comparison signal and the third comparison signal serve as the second output signals of the comparator group.

[0013] Preferably, the second comparator includes a charge-discharge circuit and a comparator. The charge-discharge circuit charges a first capacitor through a first current source within the first time signal to obtain a first charging voltage. The comparator compares the first charging voltage with a first reference voltage and outputs the second comparison signal. Among them, the first reference voltage is the voltage obtained by charging the first capacitor through the first current source within the duration of the highest time threshold. When the first charging voltage reaches the first reference voltage, the second comparison signal is in an effective state.

[0014] Preferably, the second comparator includes a duration counting circuit and a comparison and logic circuit. The duration counting circuit records the duration of the first time signal in real time. The comparison and logic circuit compares whether the duration of the first time signal reaches the set duration of the highest time threshold. If it reaches, a pulse signal is output as the second comparison signal; otherwise, no pulse signal is output.

[0015] Preferably, the control circuit further includes a clock signal circuit. The clock signal circuit is used to output a clock signal to control the turn-off after the second switch tube and the fourth switch tube are conducted for a preset time. Among them, in the Buck or Boost operating mode, the duration of the preset time is a first duration. In the Buck-Boost operating mode, the duration of the preset time is a second duration, and the second duration is greater than the first duration.

[0016] Preferably, the control circuit further includes a zero-crossing detection circuit. The zero-crossing detection circuit detects the current information of the fourth switch tube to obtain a current detection signal, and controls the turn-off of the fourth switch tube according to whether the current detection signal crosses zero.

[0017] Second aspect, a control method for a four-switch power conversion circuit is provided. The four-switch power conversion circuit includes a power stage circuit and a control circuit. The power stage circuit includes four switching transistors and an inductor. The first switching transistor and the second switching transistor are connected between an input voltage and ground. The third switching transistor and the fourth switching transistor are connected between an output voltage and ground. The inductor is connected between an intermediate node of the first switching transistor and the second switching transistor and an intermediate node of the third switching transistor and the fourth switching transistor. The control method includes sampling the inductor current information of the first switching transistor, obtaining the time when the inductor current reaches an inductor current peak reference, and recording it as a first time signal; in the Buck operating mode, when the first time signal reaches a set highest time threshold, it switches to the Buck-Boost operating mode. In the Buck-Boost operating mode, when the first time signal is lower than a set lowest time threshold, it switches to the Boost operating mode.

[0018] Preferably, it is characterized in that the highest time threshold is set as: when the input voltage is equal to the output voltage, the period time corresponding to a preset frequency is the highest time threshold; the lowest time threshold is set as: K1 × the highest time threshold, where K1 is any coefficient between 0.8 and 1.

[0019] Preferably, the inductor current peak reference includes a first peak reference signal and a second peak reference signal, and the second peak reference signal is greater than the first peak reference signal. In the Buck operating mode and the Boost operating mode, the inductor current is compared with the first peak reference signal to obtain a turn-off signal of the current working switching transistor; in the Buck-Boost operating mode, the inductor current is compared with the second peak reference signal to obtain a turn-off signal of the current working switching transistor.

[0020] Preferably, after the second switching transistor and the fourth switching transistor are turned on for a preset time duration, they are controlled to turn off. Among them, in the Buck or Boost operating mode, the preset time duration is a first duration, and in the Buck-Boost operating mode, the preset time duration is a second duration, and the second duration is greater than the first duration.

[0021] By adopting the four-switch power conversion circuit and its control method of the present invention, the time when the inductor current reaches the inductor current peak reference is obtained by sampling the inductor current information of the first switch tube, so as to obtain a first time signal. In the Buck operating state, when the first time signal reaches the highest time threshold, it switches to the Buck-Boost operating mode. After that, when the first time signal is lower than the lowest time threshold, it switches to the Boost operating mode. The present application switches the mode by comparing the first time signal. On the one hand, the sampled signals are streamlined. Only the current information of the first switch tube needs to be sampled to obtain the state control of the switch, avoiding the information deviation caused by sampling signals of different nodes. On the other hand, the switching between various modes is smoother. For the case where the input voltage is different from the output voltage, it does not switch immediately, but switches according to the magnitude of the inductor current, making the switching process smoother and the stability of the output voltage better. Description of the Drawings

[0022] Figure 1 is the circuit block diagram of the four-switch power conversion circuit according to the present invention;

[0023] Figure 2 is a realization mode of the turn-off signal circuit according to the present invention;

[0024] Figure 3 is according to the present invention Figure 2 The first implementation mode of the second comparator in;

[0025] Figure 4 is according to the present invention Figure 2 The second implementation mode of the second comparator in;

[0026] Figure 5 is the working waveform according to the present invention Figure 1 ;

[0027] Figure 6 is the working waveform according to the present invention Figure 2 (in discontinuous mode). Detailed Embodiments

[0028] The following describes the preferred embodiments of the present invention in detail with reference to the drawings, but the present invention is not limited to these embodiments. The present invention covers any alternatives, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

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

[0030] The present invention will be described more specifically by way of example with reference to the accompanying drawings in the following paragraphs. It should be noted that the drawings are in relatively simplified forms and use non-precise scales, only for the purpose of facilitating and clearly assisting in explaining the embodiments of the present invention.

[0031] Figure 1 It is a circuit block diagram of a four-switch power conversion circuit according to the present invention. Figure 2 It is an implementation manner of the turn-off signal circuit according to the present invention. As Figure 1 shown, the four-switch power conversion circuit of the present invention includes a power stage circuit and a control circuit. The power stage circuit includes four switching transistors QA-QD and an inductor L. The first switching transistor QA and the second switching transistor QB are connected between the input voltage Vin and ground. The third switching transistor QC and the fourth switching transistor QD are connected between the output voltage and ground. The inductor L is connected between the intermediate node of the first and second switching transistors and the intermediate node of the third and fourth switching transistors. The control circuit is used to provide first to fourth control signals VQA-VQD to respectively control the conduction or turn-off of the first switching transistor QA, the second switching transistor QB, the third switching transistor QC, and the fourth switching transistor QD.

[0032] As Figure 1 shown, the control circuit includes a sampling circuit that samples the inductor current information of the first switching transistor QA. For example, the voltage VIsense represents the inductor circuit information, and the time when the inductor current reaches the inductor current peak reference is obtained and recorded as the first time signal T2. The control circuit performs mode switching according to the magnitude relationship between the first time signal T2 and the highest time threshold T2H and the lowest time threshold T2L: in the Buck operating mode, when the first time signal T2 reaches the highest time threshold T2H, it switches to the Buck-Boost operating mode. After that, when the first time signal T2H is lower than the lowest time threshold T2L, it switches to the Boost operating mode. Among them, the highest time threshold T2H is set as: when the input voltage Vin is equal to the output voltage Vo, the cycle time corresponding to the preset frequency, and this cycle time is set as the highest time threshold T2H. For example, when the preset frequency is f and the corresponding cycle time is T = the lowest time threshold T2L, then T2H = (Vin / Vo) × T. The lowest time threshold T2L is set as: K1 × the highest time threshold, where K1 is any coefficient between 0.8 and 1. Here, further, the highest time threshold T2 and the lowest time threshold T2L can be set to have a hysteresis value. Setting the hysteresis value can avoid the current operating mode from jumping back and forth near the threshold.

[0033] In an embodiment of the present invention, in the Buck-Boost operating mode, within one switching period, the turn-on processes of the first switch tube QA to the fourth switch tube QD are as follows: the control circuit controls the first switch tube QA and the third switch tube QC to turn on. After that, it controls the second switch tube QB and the fourth switch tube QD to turn on. Then, it controls the first switch tube QA and the fourth switch tube QD to turn on. After that, the control circuit controls the first switch tube QA and the third switch tube QC to turn on, and this cycle repeats. Here, those skilled in the art know that when the currently operating switch tube is conducting, the other switch tubes are in the off state.

[0034] In another embodiment, when the load of the power conversion circuit is in a light load state, in the Buck-Boost operating mode, within one switching period, the turn-on processes of the first switch tube to the fourth switch tube are as follows: the control circuit controls the first switch tube QA and the third switch tube QC to turn on. After that, it controls the second switch tube QB and the fourth switch tube QD to turn on. Then it controls the first switch tube QA and the third switch tube QC to turn on again, and this cycle repeats. In the case of its light load, the power loss of the switch can be reduced.

[0035] Through the above invention solution, when the desired output voltage is fixed, the change in the input voltage can cause the time for the inductor current to rise to the reference signal to change. By obtaining this rising time and based on the magnitude relationship between this time and the set time threshold, the switching of the operating mode is performed, and smooth switch control can be achieved, avoiding fluctuations in the output voltage.

[0036] Further, the inductor current peak reference includes a first peak reference signal Vc and a second peak reference signal Vc'. The second peak reference signal Vc' is greater than the first peak reference signal Vc'. In the Buck operating mode and the Boost operating mode, the inductor current is compared with the first peak reference signal Vc to obtain the turn-off signal of the current switch tube; in the Buck-Boost operating mode, the inductor current is compared with the second peak reference signal Vc' to obtain the turn-off signal of the current switch tube. Specifically, as Figure 1As shown, the control circuit includes a reference generation circuit, and the reference generation circuit includes an error compensation circuit, such as an EA and a capacitance compensation circuit, etc., which obtains a first peak reference signal Vc through error comparison and compensation processing based on the output voltage and the output reference signal error of the power conversion circuit; the reference generation circuit further includes an addition circuit, and the addition circuit superimposes the first peak reference signal and a bias signal ΔVc to obtain a second peak reference signal, and the bias signal is obtained based on the output voltage and a preset time signal. In the Buck-Boost operating mode, when the input voltage drops to a certain extent, the rising time of the inductor current is relatively long. Therefore, increasing the peak reference signal can increase the duty cycle of the switching transistor, thereby ensuring the stability of the output voltage.

[0037] As Figure 1 and Figure 2 As shown, the control circuit includes a turn-off signal circuit, and the turn-off signal circuit includes a comparator group and a selection circuit. The comparator group receives the inductor current information VIsense, calculates the time when the inductor current reaches the inductor current peak reference to obtain the first time signal T2, and generates a first comparison signal CMP when the inductor current reaches the inductor current peak reference to control the turn-off of the current working switching transistor. The selection circuit selects and outputs one of the first peak reference signal and the second peak reference signal based on the second output signal of the comparator group, and the output signal is denoted as Vx. As Figure 2 As shown, the turn-off signal circuit includes a first comparator, a second comparator, and a third comparator. The first comparator receives the inductor current information and the inductor current peak reference to output a first comparison signal and output a first time signal T2; the second comparator receives the first time signal T2 and the highest time threshold to generate a second comparison signal, and the third comparator receives the first time signal and the lowest time threshold to generate a third comparison signal. Here, the second comparison signal and the third comparison signal are used as the second output signal of the comparator group. Here, the selection circuit can be composed of two switching transistors. When the second output signal is valid, one switching transistor conducts to output the second peak reference signal. When the second output signal is invalid, the other switching transistor conducts to output the first peak reference signal. It can also be other logic circuits, not limited to this.

[0038] As Figure 3 According to the present invention Figure 2The first implementation of the second comparator in [description], the second comparator includes a charge-discharge circuit and a comparator. The charge-discharge circuit charges a first capacitor C1 through a first current source I1 within the first time signal T2 to obtain a first charging voltage V1. The comparator compares the first charging voltage with a first reference voltage Vref1 and outputs the second comparison signal. Wherein, the first reference voltage is the voltage obtained by charging the first capacitor with the first current source within the duration of the highest time threshold. When the first charging voltage reaches the first reference voltage, it indicates that T2 reaches the T2H time, and then the second comparison signal is in an effective state. When the second comparison signal is effective, the second output signal output by the comparator group is effective. At this time, the selection circuit selects the inductor current peak reference as the output signal for output.

[0039] Continue to refer to Figure 1 , the control circuit further includes a clock signal circuit, which is used to output a clock signal to control the turn-off after the second switch tube QB and the fourth switch tube QD are turned on for a preset time. Wherein, in the Buck or Boost working mode, the duration of the preset time is the first duration, and in the Buck-Boost working mode, the duration of the preset time is the second duration, and the second duration is greater than the first duration.

[0040] The working principle is introduced below in combination with Figure 5 and Figure 6 the waveform diagram shown: At the moment t0, the system enters the Buck working mode, and the first switch tube QA and the fourth switch tube QD are turned on. After that, the inductor current reaches the first peak reference, and the first switch tube QA and the fourth switch tube QD are turned off. The second switch tube QB and the fourth switch tube QD are turned on. At the moment t1, the clock of the clock signal arrives, and the second switch tube QB and the fourth switch tube QD are turned off. The second switch tube QB and the fourth switch tube QD are turned on. At the moment t2, the time T2 for the inductor current to rise reaches the highest time threshold T2H. At this time, the system switches to the Buck-Boost working mode, and the first switch tube QA and the third switch tube QC are turned on. After that, the inductor current reaches the second peak reference, and the first switch tube QA and the third switch tube QC are turned off. The second switch tube QB and the fourth switch tube QD are turned on. At the moment t1, the clock of the clock signal arrives, and the first switch tube QA and the fourth switch tube QD are turned off. During the Buck-Boost working mode process, as the input voltage decreases, during the conduction time of the first switch tube QA and the fourth switch tube QD, the inductor current will become smaller and smaller. As Figure 6 shown, during the stage of the first switch tube QA and the fourth switch tube QD, the inductor current changes from increasing to flat and finally to decreasing. As Figure 5As shown, at time t3, when the first time signal drops below the lowest time threshold, the system switches to the Boost operating mode. Thus, during the process of the input voltage changing, the smooth switching between various operating modes is completed.

[0041] In another embodiment, the second comparator includes a duration counting circuit and a comparison and logic circuit. The duration counting circuit records the duration of the first time signal in real time; the comparison and logic circuit compares whether the duration of the first time signal reaches the duration of the set highest time threshold. If it reaches, a pulse signal is output as the second comparison signal, otherwise no pulse signal is output. In this way, the comparison of the magnitudes of the first time signal and the highest time threshold can also be obtained.

[0042] It should be noted here that the implementation manner of the third comparator can be similar to that of the second comparator. It compares the first time signal and the lowest time threshold, and this function can be achieved by either a charge-discharge method or a counting method.

[0043] Preferably, the control circuit further includes a zero-crossing detection circuit. The zero-crossing detection circuit detects the current information of the fourth switching transistor to obtain a current detection signal Vsense, and controls the turning off of the fourth switching transistor according to whether the current detection signal crosses zero. Here, when the zero-crossing detection circuit detects that the inductor current crosses zero, the currently operating switching transistor is turned off to avoid the inductor current dropping to a negative current and affecting the efficiency of the system.

[0044] Finally, the present application provides a control method for a four-switch power conversion circuit. The four-switch power conversion circuit is the above-mentioned four-switch power conversion circuit structure, and the control method includes:

[0045] Sampling the inductor current information of the first switching transistor, obtaining the time when the inductor current reaches the inductor current peak reference, and recording it as the first time signal.

[0046] In the Buck operating mode, when the first time signal reaches the set highest time threshold, it switches to the Buck-Boost operating mode.

[0047] In the Buck-Boost operating mode, when the first time signal is lower than the set lowest time threshold, it switches to the Boost operating mode.

[0048] Wherein, the highest time threshold is set as: when the input voltage is equal to the output voltage, the period time corresponding to the preset frequency; the lowest time threshold is set as: K1 × the highest time threshold, and K1 is any coefficient between 0.8 and 1.

[0049] Wherein, the inductor current peak reference includes a first peak reference signal and a second peak reference signal, and the second peak reference signal is greater than the first peak reference signal. In the Buck operating mode and the Boost operating mode, the inductor current is compared with the first peak reference signal to obtain the turn-off signal of the current working switch tube; in the Buck-Boost operating mode, the inductor current is compared with the second peak reference signal to obtain the turn-off signal of the current working switch tube.

[0050] Through the four-switch power conversion circuit of the embodiment of the present invention, the control of the system is simple, the switching of the operating mode is smooth, the ripple is good, and the control accuracy of the system is high.

[0051] It should be supplementary noted that the specific embodiments and the corresponding legends given are only a way to describe the implementation method of the present invention, and do not limit the specific structure of the implementation scheme of the present invention. Without departing from the principle and essence of the present invention, various changes or modifications can be made to these implementation manners, but these changes and modifications all fall within the protection scope of the present invention.

[0052] Although the embodiments are described and elaborated separately above, for some common technologies, in the view of those of ordinary skill in the art, substitutions and integrations can be made between the embodiments. For the content not clearly recorded in one of the embodiments, reference can be made to the other embodiment with records.

[0053] The above-described embodiments do not constitute a limitation on the protection scope of the technical solution. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the above embodiments shall be included in the protection scope of the technical solution.

Claims

1. A four-switch power conversion circuit, comprising a power stage circuit and a control circuit, wherein the power stage circuit comprises four switch tubes and an inductor, wherein the first switch tube and the second switch tube are connected between an input voltage and ground, the third switch tube and the fourth switch tube are connected between an output voltage and ground, and the inductor is connected between an intermediate node between the first switch tube and the second switch tube and an intermediate node between the third switch tube and the fourth switch tube, characterized in that: The control circuit comprises: The sampling circuit samples the inductor current information of the first switch tube, obtains the time when the inductor current reaches the inductor current peak value reference, and records it as a first time signal, The control circuit switches the mode according to the magnitude relationship between the first time signal and the highest time threshold and the lowest time threshold: in the Buck working mode, when the first time signal reaches the highest time threshold, it switches to the Buck-Boost working mode; thereafter, when the first time signal is lower than the lowest time threshold, it switches to the Boost working mode. The maximum time threshold is set as follows: when the input voltage is equal to the output voltage, the cycle time corresponding to the preset frequency is the maximum time threshold; the minimum time threshold is set as follows: K1×the maximum time threshold, where K1 is any coefficient between 0.8 and 1.

2. The four-switch power conversion circuit according to claim 1, characterized in that: In the Buck-Boost working mode, within a switching cycle, the turn-on process of the first switch tube to the fourth switch tube is: the control circuit controls the first switch tube and the third switch tube to be turned on, and then controls the second switch tube and the fourth switch tube to be turned on, and then controls the first switch tube and the fourth switch tube to be turned on.

3. The four-switch power conversion circuit according to claim 2, characterized in that: When the load of the power conversion circuit is in a light load state, the power conversion circuit is in a Buck-Boost working mode. Within a switching cycle, the turn-on process of the first switch tube to the fourth switch tube is: the control circuit controls the first switch tube and the third switch tube to be turned on, and then controls the second switch tube and the fourth switch tube to be turned on.

4. The four-switch power conversion circuit according to claim 1, characterized in that: The inductor current peak reference includes a first peak reference signal and a second peak reference signal, wherein the second peak reference signal is greater than the first peak reference signal. In the Buck working mode and the Boost working mode, the inductor current is compared with the first peak reference signal to obtain a shutdown signal of the current switch tube; In the Buck-Boost working mode, the inductor current is compared with the second peak reference signal to obtain a turn-off signal of the current switch tube.

5. The four-switch power conversion circuit according to claim 4, characterized in that: The control circuit includes a reference generation circuit, The reference generation circuit includes an error compensation circuit, which obtains a first peak reference signal according to the output voltage of the power conversion circuit and the output reference signal; The reference generation circuit further includes an adding circuit, which superimposes the first peak reference signal and the bias signal to obtain a second peak reference signal. The bias signal is obtained according to the output voltage and a preset time signal.

6. The four-switch power conversion circuit according to claim 4, characterized in that: The control circuit includes a shutdown signal circuit, The shutdown signal circuit includes a comparator group and a selection circuit, The comparator group receives the inductor current information, calculates the time when the inductor current reaches the inductor current peak reference to obtain the first time signal, and generates a first comparison signal when the inductor current reaches the inductor current peak reference to control the shutdown of the currently working switch tube. The selection circuit selects one of the first peak reference signal and the second peak reference signal for output according to the second output signal of the comparator group.

7. The four-switch power conversion circuit according to claim 6, characterized in that: The shutdown signal circuit includes a first comparator, a second comparator and a third comparator, The first comparator receives the inductor current information and the inductor current peak reference to output a first comparison signal and a first time signal; The second comparator receives the first time signal and the highest time threshold to generate a second comparison signal; The third comparator receives the first time signal and the lowest time threshold to generate a third comparison signal; The second comparison signal and the third comparison signal serve as second output signals of the comparator group.

8. The four-switch power conversion circuit according to claim 7, characterized in that: The second comparator includes a charge and discharge circuit and a comparator, The charging and discharging circuit charges the first capacitor through the first current source within the first time signal to obtain a first charging voltage. The comparator compares the first charging voltage with a first reference voltage and outputs the second comparison signal, wherein the first reference voltage is a voltage obtained when the first current source charges the first capacitor within the duration of the highest time threshold, When the first charging voltage reaches the first reference voltage, the second comparison signal is in a valid state.

9. The four-switch power conversion circuit according to claim 7, characterized in that: The second comparator includes a time length counting circuit and a comparison and logic circuit. The duration counting circuit records the duration of the first time signal in real time; The comparison and logic circuit compares whether the duration of the first time signal reaches the duration of the set highest time threshold, and if so, outputs a pulse signal as the second comparison signal, otherwise, does not output a pulse signal.

10. The four-switch power conversion circuit according to claim 4, characterized in that: The control circuit also includes a clock signal circuit, The clock signal circuit is used to output a clock signal to control the second switch tube and the fourth switch tube to turn off after the second switch tube and the fourth switch tube are turned on for a preset time. Among them, in the Buck or Boost working mode, the duration of the preset time is a first duration, and in the Buck-Boost working mode, the duration of the preset time is a second duration, and the second duration is greater than the first duration.

11. The four-switch power conversion circuit according to claim 1, characterized in that: The control circuit also includes a zero-crossing detection circuit, The zero-crossing detection circuit detects the current information of the fourth switch tube to obtain a current detection signal. The fourth switch tube is controlled to be turned off according to whether the current detection signal passes through zero.

12. A control method for a four-switch power conversion circuit, the four-switch power conversion circuit comprising a power stage circuit and a control circuit, the power stage circuit comprising four switch tubes and an inductor, the first switch tube and the second switch tube are connected between an input voltage and ground, the third switch tube and the fourth switch tube are connected between an output voltage and ground, the inductor is connected between an intermediate node between the first switch tube and the second switch tube and an intermediate node between the third switch tube and the fourth switch tube, characterized in that: The control method comprises: sampling the inductor current information of the first switch tube, obtaining the time when the inductor current reaches the inductor current peak value reference, and recording it as a first time signal, In Buck working mode, when the first time signal reaches the set maximum time threshold, it switches to Buck-Boost working mode. In the Buck-Boost working mode, when the first time signal is lower than the set minimum time threshold, it switches to the Boost working mode. The maximum time threshold is set as follows: when the input voltage is equal to the output voltage, the cycle time corresponding to the preset frequency is the maximum time threshold; The minimum time threshold is set to: K1×the maximum time threshold, where K1 is any coefficient between 0.8 and 1.

13. The control method of the four-switch power conversion circuit according to claim 12, characterized in that: The inductor current peak reference includes a first peak reference signal and a second peak reference signal, wherein the second peak reference signal is greater than the first peak reference signal. In the Buck working mode and the Boost working mode, the inductor current is compared with the first peak reference signal to obtain a shutdown signal of the currently working switch tube; In the Buck-Boost working mode, the inductor current is compared with the second peak reference signal to obtain a turn-off signal of the currently working switch tube.

14. The control method of the four-switch power conversion circuit according to claim 12, characterized in that: After the second switch tube and the fourth switch tube are turned on for a preset time, they are controlled to be turned off. Among them, in the Buck or Boost working mode, the duration of the preset time is a first duration, and in the Buck-Boost working mode, the duration of the preset time is a second duration, and the second duration is greater than the first duration.

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