A cascade circuit synchronous rectifier control method, control device and switching power supply

Abstract

The present invention discloses a control method, control device, and switching power supply for synchronous rectifiers in a cascade circuit. The control method includes: collecting the peak value of the inductor current, the valley value of the inductor current, and the total excitation and demagnetization time of the inductor current; comparing the valley value of the inductor current with a first threshold, comparing the peak value of the inductor current with a second threshold and a third threshold, and comparing the total excitation and demagnetization time of the inductor current with a fourth threshold and a fifth threshold; and determining when to turn on and off the drive of the secondary synchronous rectifier circuit based on the comparison results. The first threshold is used to determine when to turn off the drive of the secondary synchronous rectifier circuit in each cycle; the second and fourth thresholds are used to determine whether to stop driving the secondary synchronous rectifier circuit in the next cycle; and the third and fifth thresholds are used to determine whether to start driving the secondary synchronous rectifier circuit in the next cycle, with the second threshold being less than the third threshold and the fourth threshold being less than the fifth threshold. The present invention can improve the efficiency of the switching power supply.

Description

Technical Field

[0001] The present invention relates to the field of power supplies, and in particular to a control method, a control device and a switching power supply for a cascade circuit synchronous rectifier. Background Art

[0002] Buck-boost switching circuits convert input voltages to output voltages above, equal to, or below the input voltage, and can operate over a wide input voltage range. Due to their high safety and excellent efficiency, isolated buck-boost converters are widely used in intermediate bus power supplies within communication system power supply architectures, railway power supplies, and other fields.

[0003] Known isolated buck-boost converters usually adopt three-mode control: when the input voltage is greater than the output voltage of the previous stage buck-boost circuit, the previous stage buck-boost circuit operates in buck mode; when the input voltage is close to the output voltage of the previous stage buck-boost circuit, the previous stage buck-boost circuit operates in buck mode; when the input voltage is less than the output voltage of the previous stage buck-boost circuit, the previous stage buck-boost circuit operates in boost mode.

[0004] During the operation of an isolated buck-boost converter, if the current in the inductor is not fully released during the switching process, it belongs to the continuous current mode (CCM); if the current in the inductor is fully released and then recharged after a period of time, it belongs to the discontinuous current mode (DCM); if the current in the inductor is fully released and then immediately recharged, it belongs to the critical current mode (BCM).

[0005] In order to improve energy efficiency, synchronous rectification control is currently widely used, such as Figure 2 As shown, power tubes Q7 and Q8 are used as switches instead. Figure 1 For diodes D7 and D8 in the synchronous rectification circuit, complementary control is often used. Driver S8 for power transistor Q8 complements driver S5 for power transistor Q5, and driver S7 for power transistor Q7 complements driver S6 for power transistor Q6, improving efficiency under heavy loads. However, in scenarios where light load power consumption is high, it is necessary to promptly shut down the synchronous rectification circuit in DCM to prevent current backflow to the input side, thereby reducing power consumption under light no-load conditions. On the one hand, the control IC of the buck-boost isolation circuit is generally placed on the primary side, and can only collect information about the primary inductor current. On the other hand, the inductor current ripple of the buck-boost converter exhibits an inverted parabolic characteristic, with large currents on the edges and a small current in the middle. Currently, there is no effective method for achieving reliable control of the synchronous rectification circuit in an isolated buck-boost converter using the control IC on the primary side. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a synchronous rectification circuit control method, a control device and a switching power supply of a cascade circuit, which at least to a certain extent solve one of the technical problems existing in the prior art.

[0007] The main concept of the present invention is that the inductor current ripple amplitude of the isolated buck-boost converter changes greatly with the input voltage. When the difference between the input voltage and the output voltage is large, the inductor current ripple amplitude is large, and when the input voltage and the output voltage are close, the inductor current ripple amplitude is small. There are two difficulties in controlling its synchronous rectifier circuit: (1) how to effectively avoid current backflow under light load; (2) how to ensure that the synchronous rectifier circuit is put into operation as early as possible and the corresponding load current consistency when it is put into operation under different input and output voltages under the premise of ensuring no backflow. In addition to using the inductor current peak value and the inductor current valley value, the present invention also incorporates the total inductor current excitation and demagnetization time to determine when to turn on and off the drive of the secondary synchronous rectifier circuit, so as to achieve reliable shutdown of the synchronous rectifier circuit under light no-load, prevent current backflow, improve converter reliability, and at the same time improve the temperature rise of the synchronous rectifier circuit and improve efficiency.

[0008] As a first aspect of the present invention, an embodiment and technical solution of a synchronous rectification circuit control method of a cascade circuit is provided as follows:

[0009] A method for controlling synchronous rectifiers in a cascade circuit, wherein the cascade circuit includes a front-stage buck-boost circuit and a rear-stage isolated switch power supply circuit; the front-stage buck-boost circuit includes an inductor; the rear-stage isolated switch power supply circuit includes a primary-side switch circuit, a transformer, and a secondary-side synchronous rectifier circuit; wherein the control method includes:

[0010] Collect the peak value of the inductor current, the valley value of the inductor current and the total excitation and demagnetization time of the inductor current;

[0011] Comparing the valley value of the inductor current with a first threshold value, comparing the peak value of the inductor current with a second threshold value and a third threshold value respectively, and comparing the total excitation and demagnetization time of the inductor current with a fourth threshold value and a fifth threshold value respectively;

[0012] Determining when to turn on and off the drive of the secondary-side synchronous rectification circuit according to the comparison result;

[0013] Among them: the first threshold is used to determine when to shut down the drive of the secondary synchronous rectifier circuit in each cycle to avoid current backflow when the load is light; the second threshold and the fourth threshold are used to determine whether to no longer drive the secondary synchronous rectifier circuit in the next cycle, and the third threshold and the fifth threshold are used to determine whether to drive the secondary synchronous rectifier circuit in the next cycle, thereby improving the conversion efficiency of the cascade circuit under light no-load within the full input voltage range, and the second threshold is less than the third threshold, and the fourth threshold is less than the fifth threshold.

[0014] Furthermore, determining when to turn on and off the driving of the secondary-side synchronous rectification circuit according to the comparison result includes:

[0015] When the inductor current valley value is less than or equal to a first threshold, immediately turning off the driving of the secondary-side synchronous rectification circuit;

[0016] When the peak value of the inductor current is less than the second threshold value or the total excitation and demagnetization time of the inductor current is less than the fourth threshold value, the secondary synchronous rectification circuit is no longer driven in the next cycle;

[0017] When the peak value of the inductor current is greater than the third threshold and the total time of the inductor current excitation and demagnetization is greater than the fifth threshold, the secondary-side synchronous rectification circuit is driven in the next cycle.

[0018] Furthermore, under different operating conditions, the threshold value for determining when the secondary-side synchronous rectification circuit is turned on and off is configured as one of the following four combinations:

[0019] ① The first threshold is used to turn off the drive of the secondary synchronous rectifier circuit cycle by cycle, the second threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the third threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued;

[0020] ② The first threshold is used to turn off the drive of the secondary synchronous rectifier circuit cycle by cycle, the second threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the fifth threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued;

[0021] ③ The first threshold is used to turn off the drive of the secondary synchronous rectifier circuit cycle by cycle, the fourth threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the third threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued;

[0022] ④ The first threshold is used to shut down the drive of the secondary synchronous rectification circuit cycle by cycle, the fourth threshold is used as the threshold at which the drive of the secondary synchronous rectification circuit is not issued, and the fifth threshold is used as the threshold at which the drive of the secondary synchronous rectification circuit is issued.

[0023] Furthermore, under the operating condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is greater than a set value, when the load of the cascade circuit changes from light load to heavy load, the control timing is as follows:

[0024] When the load is light and the total excitation and demagnetization time of the inductor current is less than the fourth threshold, the secondary synchronous rectification circuit is not driven, and the converter operates in a diode rectification state;

[0025] As the load increases, when the total excitation and demagnetization time of the inductor current is greater than the fifth threshold, the secondary synchronous rectification circuit is driven normally in each cycle and is turned off when the valley value of the inductor current is equal to the first threshold;

[0026] As the load further increases, when the total excitation and demagnetization time of the inductor current is greater than the fifth threshold and the valley value of the inductor current is greater than the first threshold, the drive of the secondary synchronous rectification circuit is normally issued in each cycle and is turned off before the drive of the corresponding primary switching circuit is issued.

[0027] Furthermore, under the operating condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is greater than a set value, when the load of the cascade circuit changes from heavy load to light load, the control timing is as follows:

[0028] When the load is heavy, when the total excitation and demagnetization time of the inductor current is greater than the fifth threshold and the valley value of the inductor current is greater than the first threshold, the secondary synchronous rectification circuit is normally driven in each cycle and is turned off before the corresponding primary switching circuit is driven;

[0029] As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the secondary-side synchronous rectification circuit is driven normally in each cycle and is turned off when the inductor current valley value is equal to the first threshold value to prevent current backflow;

[0030] As the load further decreases, when the total excitation and demagnetization time of the inductor current is less than the fourth threshold, the secondary-side synchronous rectification circuit is not driven and enters the diode rectification mode.

[0031] Furthermore, under the operating condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is less than or equal to a set value, when the load of the cascade circuit changes from light load to heavy load, the control timing is as follows:

[0032] When the load is light and the peak value of the inductor current is less than the second threshold value, the secondary-side synchronous rectification circuit is not driven, and the converter operates in a diode rectification state;

[0033] As the load increases, when the peak value of the inductor current is greater than the third threshold value, the secondary-side synchronous rectification circuit is driven normally in each cycle and is turned off when the valley value of the inductor current is equal to the first threshold value;

[0034] As the load further increases, when the inductor current peak value is greater than the third threshold value and the inductor current valley value is greater than the first threshold value, the secondary synchronous rectification circuit is driven normally in each cycle and is turned off before the corresponding primary switching circuit is driven.

[0035] Furthermore, under the operating condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is less than or equal to a set value, when the load of the cascade circuit changes from heavy load to light load, the control timing is as follows:

[0036] When the load is heavy, when the inductor current peak value is greater than the third threshold value and the inductor current valley value is greater than the first threshold value, the secondary synchronous rectification circuit is normally driven in each cycle and is turned off before the corresponding primary switching circuit is driven;

[0037] As the load decreases, when the inductor current valley value is less than or equal to a first threshold value, the secondary-side synchronous rectification circuit is driven normally in each cycle and is turned off when the inductor current valley value is equal to the first threshold value;

[0038] As the load further decreases, when the peak value of the inductor current is less than the second threshold, the driving of the secondary-side synchronous rectification circuit is not issued.

[0039] As a second aspect of the present invention, an embodiment and technical solution of a synchronous rectification circuit control device of a cascade circuit is provided as follows:

[0040] A cascade circuit synchronous rectifier control device, the cascade circuit comprising a front-stage buck-boost circuit and a rear-stage isolated switch power supply circuit; the front-stage buck-boost circuit comprising an inductor; the rear-stage isolated switch power supply circuit comprising a primary-side switch circuit, a transformer, and a secondary-side synchronous rectifier circuit; wherein the control device comprises:

[0041] The acquisition module is used to collect the peak value of the inductor current, the valley value of the inductor current and the total excitation and demagnetization time of the inductor current;

[0042] a comparison module, configured to compare a valley value of the inductor current with a first threshold value, a peak value of the inductor current with a second threshold value and a third threshold value, and a total excitation and demagnetization time of the inductor current with a fourth threshold value and a fifth threshold value;

[0043] an execution module, configured to determine when to turn on and off the driving of the secondary-side synchronous rectification circuit according to the comparison result;

[0044] Among them: the first threshold is used to determine when to shut down the drive of the secondary synchronous rectifier circuit in each cycle to avoid current backflow when the load is light; the second threshold and the fourth threshold are used to determine whether to no longer drive the secondary synchronous rectifier circuit in the next cycle, and the third threshold and the fifth threshold are used to determine whether to drive the secondary synchronous rectifier circuit in the next cycle, thereby improving the conversion efficiency of the cascade circuit under light no-load within the full input voltage range, and the second threshold is less than the third threshold, and the fourth threshold is less than the fifth threshold.

[0045] As a third aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows:

[0046] A switching power supply includes a cascade circuit, the cascade circuit comprising: a front-stage buck-boost circuit and a rear-stage isolated switching power supply circuit; the front-stage buck-boost circuit includes an inductor; the rear-stage isolated switching power supply circuit includes a primary-side switching circuit, a transformer, and a secondary-side synchronous rectification circuit; wherein: the switching power supply also includes the cascade circuit synchronous rectifier tube control device described in any one of the second aspects above.

[0047] Preferably, the primary switching circuit is a push-pull circuit, a half-bridge circuit, a full-bridge circuit or an LLC circuit; the secondary synchronous rectification circuit is a half-wave rectification circuit, a full-wave rectification circuit, a full-bridge rectification circuit or a voltage doubler rectification circuit.

[0048] In addition to utilizing the inductor current peak and valley values, the present invention also incorporates the total inductor current magnetization and demagnetization time to determine when to turn on and off the secondary-side synchronous rectification circuit. This increase in control parameters increases the degree of freedom in optimizing the cascade circuit, which is beneficial for improving the overall performance and efficiency of the cascade circuit. The specific beneficial effects are analyzed as follows:

[0049] (1) The embodiment of the present invention uses the peak and valley values ​​of the inductor current and the excitation and demagnetization time information of the inductor current to jointly determine whether to drive the secondary synchronous rectification circuit in the next cycle. Through this composite control scheme, for converters such as isolated buck-boost converters with multiple operating modes, within the full input voltage range, the load corresponding to when the secondary synchronous rectification circuit starts working and the load corresponding to when it is not working are more consistent, which can effectively improve the temperature rise of the secondary synchronous rectification circuit;

[0050] (2) The first threshold value of the embodiment of the present invention is used to determine when the drive of the secondary-side synchronous rectification circuit is turned off in each cycle, thereby avoiding current backflow when the load is light. This allows the isolated buck-boost converter to reliably turn off the synchronous rectification circuit in the boost, buck-boost, and buck modes, thereby improving the reliability of the converter.

[0051] (3) In the embodiment of the present invention, the second threshold and the fourth threshold are used to determine whether to drive the secondary synchronous rectification circuit in the next cycle, that is, to switch to a diode rectification scheme under light no-load conditions, which can effectively improve the converter efficiency under light no-load conditions within the entire input voltage range. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 The figure is a schematic diagram of the diode rectification principle of the existing buck-boost cascade circuit;

[0053] Figure 2This is the power tube rectification principle diagram of the existing buck-boost cascade circuit;

[0054] Figure 3 This is a first schematic diagram of a cascade circuit applicable to the present invention;

[0055] Figure 4 This is a control flow chart of a method for controlling synchronous rectifiers in a cascade circuit according to the present invention;

[0056] FIG5(a) shows a first control timing sequence of the synchronous rectifier control method of the cascade circuit according to the present invention when the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is large;

[0057] FIG5( b ) is a second control timing sequence of the synchronous rectifier control method of the cascade circuit according to the present invention when the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-down circuit is large;

[0058] FIG6( a ) is a first control timing sequence of the synchronous rectifier control method of the cascade circuit according to the present invention when the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is small;

[0059] FIG6( b ) shows a second control timing sequence of the synchronous rectifier control method of the cascade circuit according to the present invention when the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-down circuit is small;

[0060] Figure 7 This is a principle block diagram of the cascade circuit synchronous rectifier control device of the present invention;

[0061] Figure 8 A second schematic diagram of a cascade circuit applicable to the present invention;

[0062] Figure 9 This is a third principle diagram of the cascade circuit applicable to the present invention. DETAILED DESCRIPTION

[0063] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0064] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0065] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate to describe the embodiments of the present application here. 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 necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0066] It should be understood that in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0067] In addition, the figures of this disclosure are merely schematic diagrams of the present disclosure and are not necessarily drawn to scale. Identical reference numbers in the figures denote identical or similar parts, and therefore repeated descriptions thereof will be omitted. Some of the blocks shown in the figures are functional entities that do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented using software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontrollers.

[0068] First embodiment

[0069] This embodiment provides a method for controlling synchronous rectifiers in a cascade circuit. Figure 3 This is a first schematic diagram of a cascade circuit applicable to the present invention, wherein the cascade circuit includes a front-stage buck-boost circuit and a rear-stage isolated switch power supply circuit; the front-stage buck-boost circuit includes an inductor; the rear-stage isolated switch power supply circuit includes a primary-side switch circuit, a transformer, and a secondary-side synchronous rectification circuit; Figure 4 This is a control flow chart of a control method for a cascade circuit synchronous rectifier tube according to the present invention, wherein the control method includes:

[0070] Collect the peak value of the inductor current, the valley value of the inductor current and the total excitation and demagnetization time of the inductor current;

[0071] Comparing the valley value of the inductor current with the first threshold, comparing the peak value of the inductor current with the second threshold and the third threshold respectively, and comparing the total excitation and demagnetization time of the inductor current with the fourth threshold and the fifth threshold respectively;

[0072] Determine when to turn on and off the driver of the secondary-side synchronous rectification circuit based on the comparison result;

[0073] Among them: the first threshold is used to determine when to shut down the drive of the secondary synchronous rectification circuit in each cycle to avoid current backflow when the load is light; the second threshold and the fourth threshold are used to determine whether to stop driving the secondary synchronous rectification circuit in the next cycle, and the third threshold and the fifth threshold are used to determine whether to drive the secondary synchronous rectification circuit in the next cycle, thereby improving the conversion efficiency of the cascade circuit under light no-load in the full input voltage range, and the second threshold is less than the third threshold, and the fourth threshold is less than the fifth threshold.

[0074] In addition to utilizing the inductor current peak and valley values, this embodiment also incorporates the total inductor current magnetization and demagnetization time to determine when to turn on and off the secondary-side synchronous rectification circuit. This increase in control parameters increases the degree of freedom in optimizing the cascade circuit, thereby improving the overall performance and efficiency of the cascade circuit.

[0075] Furthermore, determining when to turn on and off the driver of the secondary-side synchronous rectification circuit according to the comparison result includes:

[0076] When the inductor current valley value is less than or equal to the first threshold, the drive of the secondary-side synchronous rectification circuit is immediately turned off;

[0077] When the inductor current peak value is less than the second threshold value or the total inductor current excitation and demagnetization time is less than the fourth threshold value, the secondary synchronous rectification circuit is no longer driven in the next cycle;

[0078] When the peak value of the inductor current is greater than the third threshold and the total time of the inductor current excitation and demagnetization is greater than the fifth threshold, the secondary side synchronous rectification circuit is driven in the next cycle.

[0079] In this embodiment, based on the range of the input voltage Vin of the cascade circuit, the output voltage Vbus of the preceding buck-boost circuit, and the values ​​of the second, third, fourth, and fifth thresholds, there are only four combinations of thresholds for determining when to turn on and off the drive of the secondary-side synchronous rectification circuit:

[0080] ① The first threshold is used to turn off the drive of the secondary synchronous rectifier circuit cycle by cycle, the second threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the third threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued;

[0081] ② The first threshold is used to turn off the drive of the secondary synchronous rectifier circuit cycle by cycle, the second threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the fifth threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued;

[0082] ③ The first threshold is used to turn off the drive of the secondary synchronous rectifier circuit cycle by cycle, the fourth threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the third threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued;

[0083] ④ The first threshold is used to shut down the drive of the secondary synchronous rectifier circuit cycle by cycle, the fourth threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the fifth threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued.

[0084] In specific implementation, when the difference between the input voltage Vin of the cascade circuit and the output voltage Vbus of the preceding buck-boost circuit is large, the fourth threshold and the fifth threshold are used as the thresholds for controlling the driving of the secondary-side synchronous rectifier circuit to be not issued or issued; when the input voltage Vin of the cascade circuit is close to the output voltage Vbus of the preceding buck-boost circuit, the second threshold and the third threshold are used as the thresholds for controlling the driving of the secondary-side synchronous rectifier circuit to be not issued or issued.

[0085] The following describes the specific control process of the secondary-side synchronous rectification circuit based on the difference between the input voltage Vin of the cascade circuit and the output voltage Vbus of the preceding step-up / down circuit:

[0086] (1) When the difference between the input voltage Vin of the cascade circuit and the output voltage Vbus of the preceding step-up / down circuit is large, the inductor current ripple is large, the load corresponding to the fifth threshold is larger than the load corresponding to the third threshold, and the load corresponding to the fourth threshold is larger than the load corresponding to the second threshold.

[0087] When the load changes from light load to heavy load, the control timing of the secondary side synchronous rectification circuit is shown in Figure 5(a):

[0088] When the load is light and the total excitation and demagnetization time of the inductor current is less than the fourth threshold, the secondary synchronous rectification circuit is not driven and the converter operates in the diode rectification state.

[0089] As the load increases, when the total excitation and demagnetization time of the inductor current is greater than the fifth threshold, the drive of the secondary synchronous rectification circuit in each cycle is normally issued and turned off when the valley value of the inductor current is equal to the first threshold;

[0090] As the load increases further, when the total excitation and demagnetization time of the inductor current is greater than the fifth threshold and the inductor current valley is greater than the first threshold, the drive of the secondary synchronous rectification circuit in each cycle is normally issued and is turned off before the drive of the corresponding primary switching circuit is issued.

[0091] When the load changes from heavy load to light load, the control timing of the secondary side synchronous rectification circuit is shown in Figure 5(b):

[0092] When the load is heavy and the total excitation and demagnetization time of the inductor current is greater than the fifth threshold and the valley value of the inductor current is greater than the first threshold, the secondary synchronous rectification circuit is normally driven in each cycle and is turned off before the corresponding primary switching circuit is driven.

[0093] As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the secondary-side synchronous rectification circuit is driven normally in each cycle and is turned off when the inductor current valley value is equal to the first threshold value to prevent current backflow;

[0094] As the load further decreases, when the total excitation and demagnetization time of the inductor current is less than the fourth threshold, the secondary-side synchronous rectification circuit stops driving and enters the diode rectification mode.

[0095] (2) When the difference between the input voltage Vin of the isolated buck-boost converter and the output voltage Vbus of the preceding buck-boost circuit is small, the inductor current ripple is small, the load corresponding to the fourth threshold is smaller than the load corresponding to the second threshold, and the load corresponding to the fifth threshold is smaller than the load corresponding to the third threshold.

[0096] When the load changes from light load to heavy load, the control timing of the secondary side synchronous rectification circuit is shown in Figure 6(a):

[0097] When the load is light and the inductor current peak is less than the second threshold, the secondary synchronous rectification circuit does not drive and the converter operates in the diode rectification state.

[0098] As the load increases, when the inductor current peak value is greater than the third threshold value, the secondary-side synchronous rectification circuit is driven normally in each cycle and is turned off when the inductor current valley value is equal to the first threshold value;

[0099] As the load increases further, when the inductor current peak value is greater than the third threshold and the inductor current valley value is greater than the first threshold, the secondary synchronous rectification circuit is driven normally in each cycle and is turned off before the corresponding primary switching circuit is driven.

[0100] When the load changes from heavy load to light load, the control timing of the secondary side synchronous rectification circuit is shown in Figure 6(b):

[0101] When the load is heavy and the inductor current peak value is greater than the third threshold value and the inductor current valley value is greater than the first threshold value, the secondary synchronous rectification circuit is normally driven in each cycle and is turned off before the corresponding primary switching circuit is driven.

[0102] As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the secondary-side synchronous rectification circuit is driven normally in each cycle and is turned off when the inductor current valley value is equal to the first threshold value;

[0103] As the load further decreases, when the peak value of the inductor current is less than the second threshold, the driving of the secondary-side synchronous rectification circuit is stopped.

[0104] In particular, it should be noted that:

[0105] The above four threshold combinations are permutation and combination results. In actual application, only certain combinations may be included according to the different values ​​of the input voltage range, the second threshold, the third threshold, the fourth threshold and the fifth threshold.

[0106] Second embodiment

[0107] This embodiment provides a cascade circuit synchronous rectifier control device, the cascade circuit includes a front-stage buck-boost circuit and a rear-stage isolation switch power supply circuit; the front-stage buck-boost circuit includes an inductor; the rear-stage isolation switch power supply circuit includes a primary side switch circuit, a transformer and a secondary side synchronous rectifier circuit; the control device of this embodiment is as follows Figure 7 Shown, including:

[0108] The acquisition module is used to collect the peak value of the inductor current, the valley value of the inductor current and the total excitation and demagnetization time of the inductor current;

[0109] a comparison module, configured to compare a valley value of the inductor current with a first threshold value, a peak value of the inductor current with a second threshold value and a third threshold value, and a total excitation and demagnetization time of the inductor current with a fourth threshold value and a fifth threshold value;

[0110] An execution module, used for determining when to turn on and off the drive of the secondary-side synchronous rectification circuit according to the comparison result;

[0111] Among them: the first threshold is used to determine when to shut down the drive of the secondary synchronous rectification circuit in each cycle to avoid current backflow when the load is light; the second threshold and the fourth threshold are used to determine whether to stop driving the secondary synchronous rectification circuit in the next cycle, and the third threshold and the fifth threshold are used to determine whether to drive the secondary synchronous rectification circuit in the next cycle, thereby improving the conversion efficiency of the cascade circuit under light no-load in the full input voltage range, and the second threshold is less than the third threshold, and the fourth threshold is less than the fifth threshold.

[0112] The technical means adopted by the control device of this embodiment are consistent with the control method of the first embodiment, and have the same beneficial effects, so they are not described in detail.

[0113] In addition, the preferred technical means or further improved means of each step in the control method of the first embodiment can be extended to the corresponding units of this embodiment, and are not described one by one in this embodiment.

[0114] Third embodiment

[0115] This embodiment provides a switching power supply, including a cascade circuit, the cascade circuit including: a front-stage buck-boost circuit and a rear-stage isolated switching power supply circuit; the front-stage buck-boost circuit includes an inductor; the rear-stage isolated switching power supply circuit includes a primary-side switching circuit, a transformer and a secondary-side synchronous rectification circuit; its emphasis: the switching power supply also includes any cascade circuit synchronous rectifier tube control device of the second embodiment.

[0116] Since the switching power supply of this embodiment includes any one of the cascade circuit synchronous rectifier control devices of the second embodiment, the optimization freedom of the cascade circuit is increased, which is conducive to improving the overall performance and efficiency of the cascade circuit.

[0117] Furthermore, the primary side switching circuit is a push-pull circuit, a half-bridge circuit, a full-bridge circuit or an LLC circuit; the secondary side synchronous rectification circuit is a half-wave rectification circuit, a full-wave rectification circuit, a full-bridge rectification circuit or a voltage doubler rectification circuit. Figure 7 The second schematic diagram of the cascade circuit applicable to the present invention, Figure 8 This is a third principle diagram of the cascade circuit applicable to the present invention.

[0118] The following Figure 7 Taking an example, how the switching power supply of this embodiment is controlled is described in detail:

[0119] The input voltage Vin of the switching power supply is in the range of 9-36 VDC, the output voltage Vo is 12 VDC, the output voltage Vbus of the front-stage buck-boost circuit is 24 VDC, and the switching period is T.

[0120] Since the inductor current ripple of the isolated buck-boost converter shows an inverse parabola with the input voltage Vin,

[0121] When the input voltage Vin is between 0 and 24 V, there is an input voltage Vin1 at which the current Izcd2 is equal to the load current corresponding to the inductor excitation and demagnetization time K1*T. At this input voltage, the peak value of the inductor current is the second threshold value in the second embodiment, and the total excitation and demagnetization time of the inductor current is the fourth threshold value in the second embodiment. There is an input voltage Vin2 at which the current Izcd3 is equal to the load current corresponding to the excitation and demagnetization time K2*T. At this input voltage, the peak value of the inductor current is the third threshold value in the second embodiment, and the total excitation and demagnetization time of the inductor current is the fifth threshold value in the second embodiment.

[0122] When the input voltage Vin is between 24V and 36V: there is an input voltage Vin3, at which the current Izcd2 is equal to the load current corresponding to K1*T, the peak value of the inductor current at this input voltage is the second threshold value in the second embodiment, and the total excitation and demagnetization time of the inductor current is the fourth threshold value in the second embodiment; there is an input voltage Vin4, at which the current Izcd3 is equal to the load current corresponding to K2*T, the peak value of the inductor current at this input voltage is the third threshold value in the second embodiment, and the total excitation and demagnetization time of the inductor current is the fifth threshold value in the second embodiment;

[0123] Vin2<Vin1<Vin3<Vin4, K1 and K2 are constants, and the value range is 0<K1<K2≤1.

[0124] When Vin<Vin2, the load current corresponding to Izcd3 is smaller than the load current corresponding to K2*T, and the load current corresponding to Izcd2 is smaller than the load current corresponding to K1*T;

[0125] When Vin2<Vin<Vin1, the load current corresponding to Izcd2 is smaller than the load current corresponding to K1*T, and the load current corresponding to Izcd3 is larger than the load current corresponding to K2*T;

[0126] When Vin1<Vin<Vin3, the load current corresponding to Izcd2 is greater than the load current corresponding to K1*T, and the load current corresponding to Izcd3 is greater than the load current corresponding to K2*T;

[0127] When Vin3<Vin<Vin4, the load current corresponding to Izcd2 is smaller than the load current corresponding to K1*T, and the load current corresponding to Izcd3 is larger than the load current corresponding to K2*T;

[0128] Vin4<Vin, the load current corresponding to Izcd3 is smaller than the load current corresponding to K2*T, and the load current corresponding to Izcd2 is smaller than the load current corresponding to K1*T.

[0129] The following example illustrates the control method of the secondary-side synchronous rectification circuit, taking the input voltage Vin in the range of Vin1 < Vin < Vin3 and the load changing from heavy to light and from light to heavy as an example:

[0130] When the load changes from heavy to light, and the inductor current peak value is greater than Izcd3 under heavy load, the switches Q7 and Q8 are driven normally in each cycle. When the inductor current valley value is greater than Izcd1, the switches Q7 and Q8 are turned off according to the original timing sequence. The original timing sequence is that the drives of switches Q7 and Q6 complement each other, and the drives of switches Q8 and Q5 complement each other. When the load decreases further, the inductor current enters DCM mode. When the inductor current peak value is greater than Izcd2, the switches Q7 and Q8 are driven normally in each cycle. When the inductor current valley value is equal to Izcd1, the switches Q7 and Q8 are immediately turned off. As the load continues to decrease, when the inductor current peak value is detected to be less than Izcd2, the switches Q7 and Q8 are no longer driven.

[0131] When the load changes from light to heavy, when the load is light and the inductor current peak is less than Izcd3, the switches Q7 and Q8 are not driven. As the load increases, the inductor current peak is detected to be greater than Izcd3, and the switches Q7 and Q8 are driven. When the inductor current valley is detected to be equal to Izcd1, the switches Q7 and Q8 are turned off. When the load further increases and the inductor current enters CCM mode, when the inductor current peak is greater than Izcd3, the switches Q7 and Q8 are driven normally in each cycle. When the inductor current valley is greater than Izcd1, the switches Q7 and Q8 are turned off according to the original timing sequence. The original timing sequence is that the drives of the switches Q7 and Q6 complement each other, and the drives of the switches Q8 and Q5 complement each other.

[0132] The above embodiments should not be construed as limiting the present invention. The scope of protection of the present invention shall be determined by the scope defined in the claims. Persons skilled in the art will appreciate that equivalent substitutions, improvements, and modifications may be made without departing from the spirit and scope of the present invention. Such improvements and modifications shall also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling synchronous rectifiers in a cascade circuit, wherein the cascade circuit comprises a front-stage buck-boost circuit and a rear-stage isolated switch power supply circuit; the front-stage buck-boost circuit comprises an inductor; the rear-stage isolated switch power supply circuit comprises a primary-side switch circuit, a transformer, and a secondary-side synchronous rectifier circuit; characterized in that: The control method includes: Collect the peak value of the inductor current, the valley value of the inductor current and the total excitation and demagnetization time of the inductor current; Comparing the valley value of the inductor current with a first threshold value, comparing the peak value of the inductor current with a second threshold value and a third threshold value respectively, and comparing the total excitation and demagnetization time of the inductor current with a fourth threshold value and a fifth threshold value respectively; Determining when to turn on and off the drive of the secondary-side synchronous rectification circuit according to the comparison result; Wherein: the first threshold is used to determine when to shut down the drive of the secondary synchronous rectifier circuit in each cycle to avoid current backflow when the load is light; the second threshold and the fourth threshold are used to determine whether to stop driving the secondary synchronous rectifier circuit in the next cycle, and the third threshold and the fifth threshold are used to determine whether to drive the secondary synchronous rectifier circuit in the next cycle, thereby improving the conversion efficiency of the cascade circuit under light no-load conditions within the full input voltage range, and the second threshold is less than the third threshold, and the fourth threshold is less than the fifth threshold; The step of determining when to turn on and off the driving of the secondary-side synchronous rectification circuit according to the comparison result includes: When the inductor current valley value is less than or equal to a first threshold, immediately turning off the driving of the secondary-side synchronous rectification circuit; When the peak value of the inductor current is less than the second threshold value or the total excitation and demagnetization time of the inductor current is less than the fourth threshold value, the secondary synchronous rectification circuit is no longer driven in the next cycle; When the peak value of the inductor current is greater than a third threshold value and the total excitation and demagnetization time of the inductor current is greater than a fifth threshold value, driving the secondary-side synchronous rectification circuit in the next cycle; Under different operating conditions, the thresholds that determine when the secondary-side synchronous rectification circuit is turned on and off are configured as one of the following four combinations: ① The first threshold is used to turn off the drive of the secondary synchronous rectifier circuit cycle by cycle, the second threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the third threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued; ② The first threshold is used to turn off the drive of the secondary synchronous rectifier circuit cycle by cycle, the second threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the fifth threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued; ③ The first threshold is used to turn off the drive of the secondary synchronous rectifier circuit cycle by cycle, the fourth threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is not issued, and the third threshold is used as the threshold at which the drive of the secondary synchronous rectifier circuit is issued; ④ The first threshold is used to shut down the drive of the secondary synchronous rectification circuit cycle by cycle, the fourth threshold is used as the threshold at which the drive of the secondary synchronous rectification circuit is not issued, and the fifth threshold is used as the threshold at which the drive of the secondary synchronous rectification circuit is issued.

2. The method for controlling synchronous rectifiers in a cascade circuit according to claim 1, wherein: Under the operating condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is greater than the set value, when the load of the cascade circuit changes from light load to heavy load, the control timing is as follows: When the load is light and the total excitation and demagnetization time of the inductor current is less than the fourth threshold, the secondary synchronous rectification circuit is not driven, and the converter operates in a diode rectification state; As the load increases, when the total excitation and demagnetization time of the inductor current is greater than the fifth threshold, the secondary synchronous rectification circuit is driven normally in each cycle and is turned off when the valley value of the inductor current is equal to the first threshold; As the load further increases, when the total excitation and demagnetization time of the inductor current is greater than the fifth threshold and the valley value of the inductor current is greater than the first threshold, the drive of the secondary synchronous rectification circuit is normally issued in each cycle and is turned off before the drive of the corresponding primary switching circuit is issued.

3. The method for controlling synchronous rectifiers in a cascade circuit according to claim 1, wherein: Under the operating condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is greater than the set value, when the load of the cascade circuit changes from heavy load to light load, the control timing is as follows: When the load is heavy, when the total excitation and demagnetization time of the inductor current is greater than the fifth threshold and the valley value of the inductor current is greater than the first threshold, the secondary synchronous rectification circuit is normally driven in each cycle and is turned off before the corresponding primary switching circuit is driven; As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the secondary-side synchronous rectification circuit is driven normally in each cycle and is turned off when the inductor current valley value is equal to the first threshold value to prevent current backflow; As the load further decreases, when the total excitation and demagnetization time of the inductor current is less than the fourth threshold, the secondary-side synchronous rectification circuit is not driven and enters the diode rectification mode.

4. The method for controlling synchronous rectifiers in a cascade circuit according to claim 1, wherein: Under the operating condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is less than or equal to the set value, when the load of the cascade circuit changes from light load to heavy load, the control timing is as follows: When the load is light and the peak value of the inductor current is less than the second threshold value, the secondary-side synchronous rectification circuit is not driven, and the converter operates in a diode rectification state; As the load increases, when the peak value of the inductor current is greater than the third threshold value, the secondary-side synchronous rectification circuit is driven normally in each cycle and is turned off when the valley value of the inductor current is equal to the first threshold value; As the load further increases, when the inductor current peak value is greater than the third threshold value and the inductor current valley value is greater than the first threshold value, the secondary synchronous rectification circuit is driven normally in each cycle and is turned off before the corresponding primary switching circuit is driven.

5. The method for controlling synchronous rectifiers in a cascade circuit according to claim 1, wherein: Under the operating condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / down circuit is less than or equal to the set value, when the load of the cascade circuit changes from heavy load to light load, the control timing is as follows: When the load is heavy, when the inductor current peak value is greater than the third threshold value and the inductor current valley value is greater than the first threshold value, the secondary synchronous rectification circuit is normally driven in each cycle and is turned off before the corresponding primary switching circuit is driven; As the load decreases, when the inductor current valley value is less than or equal to a first threshold value, the secondary-side synchronous rectification circuit is driven normally in each cycle and is turned off when the inductor current valley value is equal to the first threshold value; As the load further decreases, when the peak value of the inductor current is less than the second threshold, the driving of the secondary-side synchronous rectification circuit is not issued.

6. A cascade circuit synchronous rectifier control device, the cascade circuit comprising a front-stage buck-boost circuit and a rear-stage isolated switch power supply circuit; the front-stage buck-boost circuit comprising an inductor; the rear-stage isolated switch power supply circuit comprising a primary-side switch circuit, a transformer, and a secondary-side synchronous rectifier circuit; characterized in that: The control device comprises: The acquisition module is used to collect the peak value of the inductor current, the valley value of the inductor current and the total excitation and demagnetization time of the inductor current; a comparison module, configured to compare a valley value of the inductor current with a first threshold value, a peak value of the inductor current with a second threshold value and a third threshold value, and a total excitation and demagnetization time of the inductor current with a fourth threshold value and a fifth threshold value; an execution module, configured to determine when to turn on and off the driving of the secondary-side synchronous rectification circuit according to the comparison result; Among them: the first threshold is used to determine when to shut down the drive of the secondary synchronous rectifier circuit in each cycle to avoid current backflow when the load is light; the second threshold and the fourth threshold are used to determine whether to no longer drive the secondary synchronous rectifier circuit in the next cycle, and the third threshold and the fifth threshold are used to determine whether to drive the secondary synchronous rectifier circuit in the next cycle, thereby improving the conversion efficiency of the cascade circuit under light no-load within the full input voltage range, and the second threshold is less than the third threshold, and the fourth threshold is less than the fifth threshold.

7. A switching power supply comprising a cascade circuit, the cascade circuit comprising: A front-stage buck-boost circuit and a rear-stage isolated switch power supply circuit; the front-stage buck-boost circuit includes an inductor; the rear-stage isolated switch power supply circuit includes a primary-side switch circuit, a transformer and a secondary-side synchronous rectification circuit; it is characterized in that: the switching power supply also includes the cascade circuit synchronous rectifier tube control device according to claim 6.

8. The switching power supply according to claim 7, characterized in that: The primary side switching circuit is a push-pull circuit, a half-bridge circuit, a full-bridge circuit or an LLC circuit; the secondary side synchronous rectification circuit is a half-wave rectification circuit, a full-wave rectification circuit, a full-bridge rectification circuit or a voltage doubler rectification circuit.

Images