A buck-boost circuit and voltage stress control method

Abstract

A buck-boost circuit and a voltage stress control method, the circuit includes a logic control circuit, a first switch tube, a second switch tube, an inductor, a resistor, a first capacitor, and a second capacitor, the input end of the logic control circuit is respectively coupled to the two ends of the resistor, the output end of the logic control circuit is respectively coupled to the first end of the first switch tube and the first end of the second switch tube, the first end of the resistor is respectively coupled to the first end of the first capacitor and the first end of the second capacitor, the second end of the resistor is coupled to the first end of the inductor, the second end of the inductor is respectively coupled to the second end of the first switch tube and the second end of the second switch tube, the third end of the first switch tube is coupled to the second end of the first capacitor, and the third end of the second switch tube is coupled to the second end of the second capacitor; the logic control circuit is used to reduce the switching frequency of the first switch tube and the second switch tube to the first frequency range or the second frequency range when the current value is greater than the first threshold value. The embodiment of the present application can reduce the circuit voltage stress.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of electronic circuits, and in particular to a buck-boost circuit and a voltage stress control method. Background Art

[0002] The buck-boost circuit is an important component of the distributed power supply of low-power modules for wireless communication equipment. The buck-boost circuit has three operating modes: continuous conduction mode (CCM), boundary conduction mode (BCM) and discontinuous conduction mode (DCM). When the buck-boost circuit is in the CCM mode, the reverse recovery problem of the body diode of the freewheeling tube will occur due to the presence of a body diode between the source and drain of the MOS tube. When the buck-boost circuit is in the BCM mode, the rectifier tube can be turned on at zero voltage to avoid the reverse recovery problem of the diode of the freewheeling tube.

[0003] For low-power module power supplies, the BUCK-BOOST circuit can work in BCM mode. However, when the load jumps, the current flowing through the inductor increases, so that the BUCK-BOOST circuit is in a short-term CCM mode, causing the body diode of the freewheeling tube to reverse recover and the voltage stress to exceed the standard, resulting in circuit instability. Therefore, how to improve the reliability of the BUCK-BOOST circuit is an urgent problem to be solved. Summary of the invention

[0004] The embodiment of the present application provides a buck-boost circuit and a voltage stress control method, which are used to optimize the reverse recovery problem of the body diode of the freewheeling tube caused by the BUCK-BOOST circuit entering a short CCM mode when the load suddenly changes when the BUCK-BOOST circuit operates in BCM mode, thereby reducing the circuit voltage stress and improving the circuit reliability.

[0005] A first aspect provides a BUCK-BOOST circuit, which may include: a logic control circuit, a first switch tube, a second switch tube, an inductor, a resistor, a first capacitor, and a second capacitor. The input end of the logic control circuit is respectively coupled to the two ends of the resistor, the output end of the logic control circuit is respectively coupled to the first end of the first switch tube and the first end of the second switch tube, the first end of the resistor is respectively coupled to the first end of the first capacitor and the first end of the second capacitor, the second end of the resistor is coupled to the first end of the inductor, the second end of the inductor is respectively coupled to the second end of the first switch tube and the second end of the second switch tube, the third end of the first switch tube is coupled to the second end of the first capacitor, and the third end of the second switch tube is coupled to the The first end of the first capacitor is coupled to the second end of the second capacitor, the two ends of the first capacitor are used as input ends of the buck-boost circuit, and the two ends of the second capacitor are used as output ends of the buck-boost circuit; the logic control circuit is used to detect the current value flowing through the resistor, and when the current value is greater than a first threshold, reduce the switching frequencies of the first switch tube and the second switch tube to a first frequency range or a second frequency range, the first frequency range is the frequency range of the buck-boost circuit working in the bcm, the second frequency range is the frequency range of the buck-boost circuit working in the dicm, and the first threshold is the value corresponding to the critical point frequency of the buck-boost circuit working in the ccm.

[0006] In the technical solution provided in the present application, when the load jumps, the logic control circuit uses frequency cutting (switching from CCM to BCM or DCM) to reduce the voltage stress problem caused by the reverse recovery of the freewheeling tube in the BUCK-BOOST circuit. Different from the prior art, a resonant branch is added in the CCM mode to reduce the voltage stress problem caused by the reverse recovery of the freewheeling tube in the BUCK-BOOST circuit. The embodiment of the present application can not only reduce the voltage stress problem caused by the reverse recovery of the freewheeling tube in the BUCK-BOOST circuit and improve the reliability of the circuit, but also save the hardware circuit corresponding to the resonant branch (1 MOS tube and its corresponding drive circuit, 1 diode and 1 inductor), thereby saving control resources. Under certain control resources, more power modules can be controlled to further achieve a power supply architecture with multi-channel output and partitioned power supply.

[0007] In a possible implementation, when the logic control circuit reduces the switching frequency of the first switch tube and the second switch tube to the second frequency range, the logic control circuit is also used to adjust the switching frequency of the first switch tube and the second switch tube to a target frequency, and the target frequency is a frequency within the first frequency range.

[0008] In the technical solution provided in the present application, since the circuit works best in the BCM mode, that is, the first switch tube can be turned on at zero voltage (zero voltage switch, ZVS) to reduce switching losses, and the second switch tube can be turned off at zero current to reduce reverse recovery losses. If the logic control circuit controls the switching frequency of the first switch tube and the second switch tube so that the circuit switches from CCM to DCM, then after frequency cutting, it enters a frequency conversion mode to find the BCM point, so that the working mode of the circuit slowly enters BCM from DCM, thereby improving the reliability of the circuit.

[0009] In a possible implementation, the logic control circuit is further configured to determine the target frequency according to the input voltage, the output voltage, and the current.

[0010] In the technical solution provided in the present application, the target frequency can be the optimal frequency when the BUCK-BOOST circuit operates in BCM. By determining the target frequency, the switching frequency of the first switch tube and the second switch tube is adjusted to the target frequency through the logic control circuit, so that the circuit operates in the optimal state and the reliability of the circuit is improved.

[0011] In a possible implementation, the logic control circuit is specifically used to detect a voltage value on the resistor, and obtain the current value according to the voltage value and a resistance value of the resistor.

[0012] In the technical solution provided in the present application, the input end of the logic control circuit is the voltage across the resistor. By converting the voltage into current, the switching frequency of the first switch tube and the second switch tube can be adjusted according to the current and the first threshold value, thereby improving the circuit reliability.

[0013] In a possible implementation, the BUCK-BOOST circuit further includes an amplifier circuit, and the input end of the logic control circuit is respectively coupled to two ends of the resistor through the amplifier circuit;

[0014] The amplifier circuit is used to amplify the voltage value to obtain a first voltage value;

[0015] The logic control circuit obtains the current value according to the first voltage value and the resistance value of the resistor.

[0016] In the technical solution provided in the present application, since the voltage across the resistor is small, the voltage value detected by the logic control circuit is small. Therefore, the voltage is amplified by the amplifier circuit and then sampled and converted into current. The switching frequencies of the first switch tube and the second switch tube are adjusted according to the current value and the first threshold value, thereby reducing the error.

[0017] In a possible implementation, the BUCK-BOOST circuit further includes a first isolation drive circuit and a second isolation drive circuit, and the output end of the logic control circuit is coupled to the first end of the first switch tube and the first end of the second switch tube through the first isolation drive circuit and the second isolation drive circuit respectively;

[0018] The first isolation driving circuit is used to receive a first control signal from the logic control circuit, and control the first switch tube to be turned on or off according to the first control signal;

[0019] The second isolation driving circuit is used to receive the second control signal of the logic control circuit and control the on or off of the second switch tube according to the second control signal.

[0020] In the technical solution provided in the present application, the logic control circuit is coupled to the first switch tube and the second switch tube respectively through the isolation drive circuit, and the isolation drive circuit can drive the switch tube according to the control signal output from the logic control circuit, thereby adjusting the switching frequency of the switch tube. The control signal can be a pulse width modulation (PWM) waveform signal.

[0021] In a possible implementation, the first switch tube and the second switch tube are one of a metal oxide semiconductor field-effect transistor (metal-oxide-semiconductor field-effect transistor, MOSFET tube), an insulated gate bipolar transistor (insulated gate bipolar transistor, IGBT), a gallium nitride field-effect transistor (Gallium Nitride Field-effect Transistor, GaN FET), and a triode.

[0022] In a second aspect, an embodiment of the present application provides a voltage stress control method, which can be applied to a BUCK-BOOST circuit. The BUCK-BOOST circuit may include a logic control circuit, a first switch tube, a second switch tube, an inductor, a resistor, a first capacitor and a second capacitor. The method may include: detecting a current value flowing through the resistor by the logic control circuit; when the current value is greater than a first threshold, reducing the switching frequency of the first switch tube and the second switch tube to a first frequency range or a second frequency range by the logic control circuit, the first frequency range being the frequency range in which the BUCK-BOOST circuit operates in BCM, the second frequency range being the frequency range in which the BUCK-BOOST circuit operates in DCM, and the first threshold being the value corresponding to the critical point frequency of the BUCK-BOOST circuit operating in CCM.

[0023] In the solution provided by the present invention, when the load jumps, the logic control circuit uses frequency cutting (switching from CCM to BCM or DCM) to reduce the voltage stress problem caused by the reverse recovery of the freewheeling tube in the BUCK-BOOST circuit. Different from the prior art, a resonant branch is added in the CCM mode to reduce the voltage stress problem caused by the reverse recovery of the freewheeling tube in the BUCK-BOOST circuit. The embodiment of the present application can not only reduce the voltage stress problem caused by the reverse recovery of the freewheeling tube in the BUCK-BOOST circuit and improve the reliability of the circuit, but also save the hardware circuit corresponding to the resonant branch (1 MOS tube and its corresponding drive circuit, 1 diode and 1 inductor), thereby saving control resources. Under certain control resources, more power modules can be controlled to further achieve a power supply architecture with multi-channel output and partitioned power supply.

[0024] It can be understood that the voltage stress control method described in the second aspect is applied to the buck-boost circuit of the first aspect, and the specific content corresponds to the content of the first aspect. The corresponding features of the second aspect and the beneficial effects achieved can refer to the description of the first aspect. To avoid repetition, the detailed description is appropriately omitted here.

[0025] In a possible implementation, when the logic control circuit reduces the switching frequency of the first switch tube and the second switch tube to the second frequency range, the method further includes: adjusting the switching frequency of the first switch tube and the second switch tube to a target frequency through the logic control circuit, and the target frequency is a frequency within the first frequency range.

[0026] In a possible implementation manner, the method further includes: determining the target frequency according to the input voltage, the output voltage, and the current by the logic control circuit.

[0027] In a possible implementation, detecting the current value flowing through the resistor by the logic control circuit includes: detecting the voltage value on the resistor by the logic control circuit, and obtaining the current value according to the voltage value and the resistance value of the resistor.

[0028] In a possible implementation, the BUCK-BOOST circuit further includes an amplifier circuit, and the method further includes: amplifying the voltage value by the amplifier circuit to obtain a first voltage value; and obtaining the current value according to the voltage value and the resistance value of the resistor includes: obtaining the current value according to the first voltage value and the resistance value of the resistor.

[0029] In a possible implementation, the BUCK-BOOST circuit also includes a first isolation drive circuit and a second isolation drive circuit, and the method also includes: receiving a first control signal of the logic control circuit through the first isolation drive circuit, and controlling the on or off of the first switch tube according to the first control signal; receiving a second control signal of the logic control circuit through the second isolation drive circuit, and controlling the on or off of the second switch tube according to the second control signal.

[0030] In a possible implementation manner, the first switch tube and the second switch tube are one of a MOS tube, an IGBT or a GaN FET, and a triode. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural diagram of a basic BUCK-BOOST circuit;

[0032] Figure 2 It is a waveform diagram of the inductor current of a basic BUCK-BOOST circuit working in CCM mode;

[0033] Figure 3 It is a schematic diagram of the structure of a BUCK-BOOST circuit with a resonant branch;

[0034] Figure 4 It is a waveform diagram of the inductor current when the load changes when the basic BUCK-BOOST circuit works in BCM mode;

[0035] Figure 5 It is a structural schematic diagram of a BUCK-BOOST circuit provided in an embodiment of the present application;

[0036] Figure 6 It is a waveform diagram of an inductor current after frequency cutting when a load jump occurs in a BUCK-BOOST circuit provided in an embodiment of the present application working in a BCM mode;

[0037] Figure 7 is a structural schematic diagram of another BUCK-BOOST circuit provided in an embodiment of the present application;

[0038] Figure 8 It is a flow chart of a voltage stress control method provided in an embodiment of the present application;

[0039] Fig. 9 It is a flow chart of another voltage stress control method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to describe the embodiments of the present application. The terms "first", "second", "third" and "fourth" in the specification and claims of the present application and the drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices. Mentioning "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The phrase does not necessarily refer to the same embodiment at various locations in the specification, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0041] In order to better understand a BUCK-BOOST circuit and a voltage stress control method provided by an embodiment of the present invention, the technical problems to be solved by the present application are further analyzed and proposed. The application scenario of the embodiment of the present application is described below.

[0042] With the rapid development of wireless communication equipment, especially the fifth generation mobile communication technology (5 th With the advent of 5G, in applications where the power amplifier in the radio remote unit (RRU) uses multi-channel output and partitioned power supply, the power brick is developing from a high-power (>1000W) module to multiple low-power (<400W) modules for energy saving.

[0043] There are two coexisting wireless communication power distribution methods: direct current-return common (DC-C) distribution and direct current-return isolate (DC-I) distribution. Among them, DC-I distribution is isolated distribution with single-point grounding, which meets the requirements of all distribution scenarios, but it is costly, large in size, and complex in circuit; DC-C distribution is multi-point grounding, with simplified filtering circuit, low cost, and small in size, but there is current on its ground wire, which may not meet the safety requirements of some markets.

[0044] At present, the DC-C power distribution method is one of the main power distribution methods for small power module power supplies, and the BUCK-BOOST circuit is an important part of the DC-C power distribution method. Therefore, the optimization of the BUCK-BOOST circuit has become an important direction for the distributed power supply of small power module power supplies for wireless communication equipment. The basic BUCK-BOOST circuit is a non-isolated DC conversion circuit whose output voltage can be lower or higher than the input voltage, but the polarity of its output voltage is opposite to the input voltage. The BUCK-BOOST circuit has three main operating modes, namely continuous conduction mode (CCM), discontinuous conduction mode (DCM) and boundary conduction mode (BCM). Among them, CCM: In a switching cycle, the inductor current never reaches 0, or the inductor never "resets", which means that the inductor flux never returns to 0 during the switching cycle, and when the power tube switch is closed, there is still current flowing in the coil. DCM: During the switching cycle, the inductor current always returns to 0, which means that the inductor is properly "reset", that is, when the power tube switch is closed, the inductor current is zero or less than zero. BCM: The controller monitors the inductor current and once it detects that the current is equal to 0, the power tube switch is immediately closed. The controller always waits for the inductor current to "reset" to activate the switch.

[0045] See also Figure 1 , Figure 1 This is a schematic diagram of the structure of a basic BUCK-BOOST circuit. Figure 1 As shown in the figure, the basic BUCK-BOOST circuit includes switch tube Q1, switch tube Q2, inductor L1, resistor Rs, filter capacitor C1, and filter capacitor C2. When Q1 is closed and Q2 is closed, L1 stores energy, and when Q1 is closed and Q2 is closed, L1 releases energy. Figure 2 , Figure 2 This is a waveform diagram of the inductor current of a basic BUCK-BOOST circuit working in CCM mode. Figure 2As shown in Figure 2, when the basic BUCK-BOOST circuit uses the CCM mode, the inductor current I L The waveform is always greater than zero.

[0046] When the basic BUCK-BOOST circuit operates in CCM mode, the body diode of the freewheeling tube (switch tube Q2) will have a reverse recovery problem. To solve the reverse recovery problem of the body diode of the freewheeling tube, an additional resonant freewheeling branch can be added to the basic BUCK-BOOST circuit. Figure 3 , Figure 3 This is a schematic diagram of the structure of a BUCK-BOOST circuit with a resonant branch. Figure 3 As shown, in Figure 1 Based on the circuit shown in the figure, a resonant branch is coupled between the two ends of the inductor L1, and the resonant branch includes a switch tube Q3, a diode D1 and an inductor L2. Figure 1 In the case where Q2 is turned off and Q1 is turned on, the reverse recovery voltage of Q2 is Vout+Vin. Figure 3 In the figure, before Q1 is turned on, the inductor current is at its lowest point, turning on Q3 in the resonant parallel branch. At this time, the forward current return path of L1 is changed from L1→Q2 to L1→L2→D1→Q3→L1. At this time, the reverse recovery voltage of Q2 is only Vout, so the reverse recovery of Q2 can be optimized.

[0047] For low-power module power supplies, the basic BUCK-BOOST circuit can work in BCM mode, which can make the rectifier tube (switch tube Q1) open at zero voltage and avoid the reverse recovery problem of the freewheeling tube. Figure 4 , Figure 4 This is a schematic diagram of the inductor current waveform when the load changes when the basic BUCK-BOOST circuit works in BCM mode. Figure 4 As shown, the basic BUCK-BOOST circuit works in BCM mode. When the load jumps, the inductor current I L A short CCM mode is generated, which will cause the body diode of the freewheeling tube to reverse recover and the voltage stress to exceed the standard, resulting in circuit instability.

[0048] If the BUCK-BOOST circuit operates in CCM mode and the diode of the freewheeling tube has reverse recovery problems, use the following Figure 3 The scheme described above is compared with Figure 1The basic BUCK-BOOST circuit shown requires an additional switch tube, a diode, and an inductor. In the application of low-power power bricks, this is a huge challenge for power bricks with high power density and small area. In addition, after splitting a high-power module into multiple low-power modules, more control resources are required, resulting in tight control resources, and the resonant branch also requires additional control resources and responsive drive, which further increases the area and increases the design difficulty, making it impossible to meet the requirements. Therefore, how to improve the reliability of the BUCK-BOOST circuit in the low-power module power supply is an urgent problem to be solved.

[0049] Therefore, the technical problems to be solved by the embodiments of the present application may include the following:

[0050] 1. For low-power module power supplies, use the basic BUCK-BOOST circuit to meet the requirements of small area and high power density; 2. When the basic BUCK-BOOST circuit works in BCM mode, it can optimize the reverse recovery of the freewheeling tube caused by entering the short CCM mode under sudden load changes, resulting in excessive voltage stress.

[0051] Based on the above, the present application provides a BUCK-BOOST circuit and a voltage stress control method, which can optimize the reverse recovery problem of the freewheeling tube caused by the BUCK-BOOST circuit entering a short CCM mode when the load suddenly changes when the BUCK-BOOST circuit works in the BCM mode, thereby improving the circuit reliability. The BUCK-BOOST circuit is described in detail below.

[0052] See also Figure 5 , Figure 5 is a schematic diagram of the structure of a BUCK-BOOST circuit provided in an embodiment of the present application. Figure 5 The BUCK-BOOST circuit shown in the figure can optimize the reverse recovery problem of the freewheeling tube caused by the BUCK-BOOST circuit entering the short-term CCM mode under the condition of sudden load change when the BUCK-BOOST circuit works in the BCM mode. Figure 5As shown, the BUCK-BOOST circuit may include a logic control circuit, a first switch tube Q1, a second switch tube Q2, an inductor L, a resistor Rs, a first capacitor C1, and a second capacitor C2. Wherein: the input end of the logic control circuit is respectively coupled to the two ends of the Rs, the output end of the logic control circuit is respectively coupled to the first end of Q1 and the first end of Q2, the first end of Rs is respectively coupled to the first end of C1 and the first end of C2, the second end of Rs is coupled to the first end of L, the second end of L is respectively coupled to the second end of Q1 and the second end of Q2, the third end of Q1 is coupled to the second end of C1, the third end of Q2 is coupled to the second end of C2, the two ends of C1 are used as the input ends of the BUCK-BOOST circuit, and the two ends of C2 are used as the output ends of the BUCK-BOOST circuit.

[0053] Wherein, the logic control circuit is used to detect the current value flowing through the Rs, and when the current value is greater than the first threshold value, the switching frequency of Q1 and Q2 is reduced to the first frequency range or the second frequency range, the first frequency range is the frequency range of the BUCK-BOOST circuit working in BCM, the second frequency range is the frequency range of the BUCK-BOOST circuit working in DCM, and the first threshold value is the value corresponding to the critical point frequency of the BUCK-BOOST circuit working in CCM, for example, the critical point frequency of CCM is 200kHz, and the first threshold value is the current value corresponding to 200kHz. When the BUCK-BOOST circuit works in BCM, during the process of sudden load increase, after reaching the threshold point, the switching frequency of Q1 and Q2 is reduced to the circuit working in BCM or DCM under heavy load by using the frequency cutting and frequency reduction method through the logic control circuit, so that the current flowing to L passes through zero in the negative direction, ensuring that the reverse stress of the freewheeling tube Q2 is small when commutating. This circuit adjusts the current valley by changing the frequency of the switching tube. It adopts the BCM control mode under both heavy load and light load, adjusts the current state when the freewheeling tube is turned off, and makes the current approach 0 during the commutation process from the freewheeling tube to the rectifier tube.

[0054] In one embodiment, see Figure 6 , Figure 6 1 is a schematic diagram of the waveform of the inductor current after the frequency is cut when the load jumps in a BUCK-BOOST circuit provided in an embodiment of the present application when the BUCK-BOOST circuit works in the BCM mode. Figure 6As shown, when the load suddenly increases, if the switching frequency of Q1 and Q2 drops to the second frequency range, that is, the BUCK-BOOST working mode is switched from CCM to DCM, first ensure that the reverse stress of the freewheeling tube Q2 is small during commutation. Then, the logic control circuit can also determine the target frequency according to the input voltage, output voltage and current flowing through the inductor. The target frequency can be the optimal frequency when the BUCK-BOOST works in BCM, and then continue to adjust the switching frequency of Q1 and Q2 to the target frequency. After switching to DCM, the circuit enters the mode of frequency conversion to find the BCM point, so that the working mode of the BUCK-BOOST can slowly enter the BCM mode from DCM.

[0055] In one embodiment, the logic control circuit detects the current value flowing through the Rs, and specifically, the voltage value on Rs is detected by the logic control circuit, and the current value flowing through Rs is obtained according to the voltage value and the resistance value of Rs. It should be noted that the method of sampling the inductor current value is not limited to sampling the resistor Rs, but can also be applied to other current sampling methods, such as copper sampling, current transformer sampling, coupled inductor sampling, etc. The sampled current value is also not limited to sampling the inductor current, but can also be applied to sampling other current values, such as output current, input current, etc. The embodiment of the present application does not limit the different sampling methods for each current value.

[0056] In one embodiment, see Figure 7 , Figure 7 is a schematic diagram of the structure of another BUCK-BOOST circuit provided in an embodiment of the present application. Figure 7 As shown, the BUCK-BOOST circuit may also include an amplifier circuit, and the input end of the logic control circuit is coupled to the two ends of the resistor respectively through the amplifier circuit. The amplifier circuit can be used to amplify the voltage value on Rs, and the logic control circuit then obtains the current value flowing through the Rs according to the amplified voltage value of Rs and the resistance value of Rs. Since the voltage value on Rs is not large, after the voltage value is amplified by the amplifier circuit, the error of the switching frequency of Q1 and Q2 controlled by the logic control circuit can be reduced, and the stability of the circuit can be improved. Optionally, the amplifier circuit may also be included in the logic control circuit, and the input end of the logic control circuit samples the voltage value of Rs, and after amplification by the amplifier circuit in the logic control circuit, the current value flowing through the Rs is obtained according to the amplified voltage value of Rs and the resistance value of Rs.

[0057] In one embodiment, Figure 7As shown, the BUCK-BOOST circuit may also include a first isolation drive circuit and a second isolation drive circuit, and the output end of the logic control circuit is coupled to the first end of the first switch tube and the first end of the second switch tube respectively through the first isolation drive circuit and the second isolation drive circuit. Wherein: the first isolation drive circuit can be used to receive the first control signal of the logic control circuit and control the on / off of Q1 according to the first control signal; the second isolation drive circuit can be used to receive the second control signal of the logic control circuit and control the on / off of Q2 according to the second control signal. Wherein, the control signal can be a PWM waveform signal.

[0058] It should be noted that the switch tube provided in the embodiment of the present application can be a metal oxide semiconductor field-effect transistor (metal-oxide-semiconductor field-effect transistor, MOSFET tube), an insulated gate bipolar transistor (insulated gate bipolar transistor, IGBT), a gallium nitride field-effect transistor (Gallium Nitride Field-effect Transistor, GaN FET), a triode, etc. The embodiment of the present application does not limit the type of the switch tube.

[0059] See also Figure 8 , Figure 8 is a flow chart of a voltage stress control method provided in an embodiment of the present application. The voltage stress control method is applied to a BUCK-BOOST circuit, such as Figure 5 As shown, the BUCK-BOOST circuit may include a logic control circuit, a first switch tube Q1, a second switch tube Q2, an inductor L, a resistor Rs, a first capacitor C1 and a second capacitor C2. Figure 8 As shown, the voltage stress control method may include steps S801 to S803, wherein step S803 is optional.

[0060] Step S801: Detect the current value flowing through the resistor through the logic control circuit.

[0061] Specifically, the logic control circuit can detect the voltage value on Rs, and obtain the current value according to the voltage value and the resistance value of Rs.

[0062] The BUCK-BOOST circuit may further include an amplifier circuit, which amplifies the voltage value on Rs and obtains the current value flowing through Rs according to the amplified voltage value of Rs and the resistance value of Rs through a logic control circuit.

[0063] Step S802: when the current value is greater than the first threshold, the switching frequency of the first switch tube and the second switch tube is reduced to the first frequency range or the second frequency range through the logic control circuit.

[0064] The first frequency range is the frequency range of the BUCK-BOOST circuit working in BCM, the second frequency range is the frequency range of the BUCK-BOOST circuit working in DCM, and the first threshold is the value corresponding to the critical point frequency of the BUCK-BOOST circuit working in CCM.

[0065] Step S803: When the logic control circuit reduces the switching frequencies of the first switch tube and the second switch tube to a second frequency range, the logic control circuit adjusts the switching frequencies of the first switch tube and the second switch tube to a target frequency.

[0066] When the load suddenly increases, if the switching frequency of Q1 and Q2 drops to the second frequency range, that is, the BUCK-BOOST working mode is switched from CCM to DCM, first ensure that the reverse stress of the freewheeling tube Q2 is small during commutation. Then, the target frequency can be determined according to the input voltage, output voltage and current flowing through the inductor through the logic control circuit. The target frequency can be the optimal frequency when the BUCK-BOOST works in BCM, and then the switching frequency of Q1 and Q2 is adjusted to the target frequency. After switching to DCM, the circuit enters the mode of frequency conversion to find the BCM point, so that the working mode of the BUCK-BOOST can slowly enter the BCM mode from DCM.

[0067] The BUCK-BOOST circuit may further include a first isolation drive circuit and a second isolation drive circuit. In one embodiment, the method may further include: receiving a first control signal from a logic control circuit through the first isolation drive circuit, and controlling the on or off of the first switch tube according to the first control signal; receiving a second control signal from the logic control circuit through the second isolation drive circuit, and controlling the on or off of the second switch tube according to the second control signal.

[0068] In one embodiment, the method may further include: when the current value is less than or equal to the first threshold, releasing the restriction on the switching frequency of Q1 and Q2 through the logic control circuit, allowing full-band frequency conversion, and continuing to maintain the circuit working in BCM.

[0069] The detailed description of each step in the above method can be found in the above Figure 5 The relevant description in will not be repeated here.

[0070] The voltage stress control method in the embodiment of the present application can trigger the frequency cutting process during the load increase process, Q1 realizes ZVS opening, reduces the switching loss, and realizes the BCM high-efficiency working mode. When Q2 is turned off, it is in the zero current or negative current state, which reduces the reverse recovery loss and the voltage stress generated by the reverse recovery, thereby improving the reliability of the circuit.

[0071] It should be noted that the voltage stress control method in the embodiment of the present application is not limited to the Buck-Boost circuit, but can also be applied to circuits of other BCM / DCM working modes, such as flyback circuits, resonant circuits, bridge circuits, boost circuits, buck circuits, etc.

[0072] Combination Figure 5 The buck-boost circuit and Figure 8 In one embodiment, the voltage stress control method is shown in FIG. Fig. 9 , Fig. 9 FIG. 1 is a flow chart of another voltage stress control method provided in an embodiment of the present application. Fig. 9 As shown in the figure, when the BUCK-BOOST circuit works in BCM, when the load changes and the current value flowing through Rs exceeds the current threshold I_off, the switching frequency of Q1 and Q2 is locked in the safe zone through the logic control circuit, for example, fs<200kHz, and the mode of frequency conversion to find the BCM point is entered in the safe zone. When the load decreases and the current value flowing through Rs is less than or equal to the current threshold I_off, the frequency limit is released through the logic control circuit, allowing full-band frequency conversion.

[0073] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made on the basis of the technical solution of the present invention should be included in the scope of protection of the present invention.

Claims

1. A buck-boost circuit, characterized in that: The circuit comprises a logic control circuit, a first switch tube, a second switch tube, an inductor, a resistor, a first capacitor and a second capacitor, wherein the input end of the logic control circuit is respectively coupled to the two ends of the resistor, the output end of the logic control circuit is respectively coupled to the first end of the first switch tube and the first end of the second switch tube, the first end of the resistor is respectively coupled to the first end of the first capacitor and the first end of the second capacitor, the second end of the resistor is coupled to the first end of the inductor, the second end of the inductor is respectively coupled to the second end of the first switch tube and the second end of the second switch tube, the third end of the first switch tube is coupled to the second end of the first capacitor, the third end of the second switch tube is coupled to the second end of the second capacitor, the two ends of the first capacitor are used as the input ends of the BUCK-BOOST circuit, and the two ends of the second capacitor are used as the output ends of the BUCK-BOOST circuit; The logic control circuit is used to detect the current value flowing through the resistor, and when the current value is greater than a first threshold value, reduce the switching frequency of the first switch tube and the second switch tube to a first frequency range or a second frequency range, the first frequency range is the frequency range of the buck-boost circuit working in a critical conduction mode BCM, the second frequency range is the frequency range of the buck-boost circuit working in a discontinuous conduction mode DCM, and the first threshold value is a value corresponding to the critical point frequency of the buck-boost circuit working in a continuous conduction mode CCM.

2. The BUCK-BOOST circuit according to claim 1, characterized in that: In the case where the logic control circuit reduces the switching frequencies of the first switch tube and the second switch tube to the second frequency range, the logic control circuit is further used to: The switching frequencies of the first switching tube and the second switching tube are adjusted to a target frequency, where the target frequency is a frequency within the first frequency range.

3. The BUCK-BOOST circuit according to claim 2, characterized in that: The logic control circuit is also used for: The target frequency is determined according to an input voltage, an output voltage, and a current flowing through the inductor.

4. The BUCK-BOOST circuit according to claim 1, characterized in that: The logic control circuit is specifically used for: The voltage value on the resistor is detected, and the current value is obtained according to the voltage value and the resistance value of the resistor.

5. The BUCK-BOOST circuit according to claim 4, characterized in that: The BUCK-BOOST circuit further includes an amplifier circuit, and the input end of the logic control circuit is respectively coupled to the two ends of the resistor through the amplifier circuit; The amplifier circuit is used to amplify the voltage value to obtain a first voltage value; The logic control circuit obtains the current value according to the first voltage value and the resistance value of the resistor.

6. The BUCK-BOOST circuit according to any one of claims 1 to 5, characterized in that: The BUCK-BOOST circuit further includes a first isolation driving circuit and a second isolation driving circuit, and the output end of the logic control circuit is coupled to the first end of the first switch tube and the first end of the second switch tube through the first isolation driving circuit and the second isolation driving circuit respectively; The first isolation driving circuit is used to receive a first control signal from the logic control circuit, and control the first switch tube to be turned on or off according to the first control signal; The second isolation driving circuit is used to receive the second control signal of the logic control circuit and control the on or off of the second switch tube according to the second control signal.

7. The BUCK-BOOST circuit according to claim 6, characterized in that: The first switch tube and the second switch tube are one of a metal oxide semiconductor field effect transistor MOS tube, an insulated gate bipolar transistor IGBT, a gallium nitride field effect transistor GaN FET or a triode.

8. A voltage stress control method, characterized in that: The method is applied to a buck-boost circuit, wherein the buck-boost circuit comprises a logic control circuit, a first switch tube, a second switch tube, an inductor, a resistor, a first capacitor, and a second capacitor. The input end of the logic control circuit is respectively coupled to the two ends of the resistor, the output end of the logic control circuit is respectively coupled to the first end of the first switch tube and the first end of the second switch tube, the first end of the resistor is respectively coupled to the first end of the first capacitor and the first end of the second capacitor, the second end of the resistor is coupled to the first end of the inductor, the second end of the inductor is respectively coupled to the second end of the first switch tube and the second end of the second switch tube, the third end of the first switch tube is coupled to the second end of the first capacitor, the third end of the second switch tube is coupled to the second end of the second capacitor, the two ends of the first capacitor are used as the input ends of the buck-boost circuit, and the two ends of the second capacitor are used as the output ends of the buck-boost circuit. The method comprises: Detecting the current value flowing through the resistor by the logic control circuit; When the current value is greater than a first threshold value, the switching frequencies of the first switch tube and the second switch tube are reduced to a first frequency range or a second frequency range through the logic control circuit, the first frequency range is a frequency range in which the BUCK-BOOST circuit operates in a critical conduction mode BCM, the second frequency range is a frequency range in which the BUCK-BOOST circuit operates in a discontinuous conduction mode DCM, and the first threshold value is a value corresponding to a critical point frequency in which the BUCK-BOOST circuit operates in a continuous conduction mode CCM.

9. The method according to claim 8, characterized in that In the case where the logic control circuit reduces the switching frequencies of the first switch tube and the second switch tube to the second frequency range, the method further includes: The switching frequencies of the first switch tube and the second switch tube are adjusted to a target frequency through the logic control circuit, and the target frequency is a frequency within the first frequency range.

10. The method according to claim 9, characterized in that The method further comprises: The target frequency is determined by the logic control circuit according to the input voltage, the output voltage, and the current flowing through the inductor.

11. The method according to claim 8, characterized in that The detecting the current value flowing through the resistor by the logic control circuit comprises: The voltage value on the resistor is detected by the logic control circuit, and the current value is obtained according to the voltage value and the resistance value of the resistor.

12. The method according to claim 11, characterized in that The BUCK-BOOST circuit further includes an amplifier circuit, and the method further includes: Amplifying the voltage value by the amplifier circuit to obtain a first voltage value; The obtaining the current value according to the voltage value and the resistance value of the resistor comprises: The current value is obtained according to the first voltage value and the resistance value of the resistor.

13. The method according to any one of claims 8 to 12, characterized in that: The BUCK-BOOST circuit further includes a first isolation driving circuit and a second isolation driving circuit, and the method further includes: receiving a first control signal from the logic control circuit through the first isolation drive circuit, and controlling the first switch tube to be turned on or off according to the first control signal; The second control signal of the logic control circuit is received through the second isolation driving circuit, and the conduction or closing of the second switch tube is controlled according to the second control signal.

14. The method according to claim 13, characterized in that The first switch tube and the second switch tube are one of a metal oxide semiconductor field effect transistor MOS tube, an insulated gate bipolar transistor IGBT, a gallium nitride field effect transistor GaNFET or a triode.

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