Cascade circuit synchronous rectifier tube control method, control device and switching power supply

Abstract

The invention discloses a cascade circuit synchronous rectifier tube control method, a control device and a switching power supply. The control method comprises the following steps: acquiring a peak value of an inductive current, a valley value of the inductive current and total excitation demagnetization time of the inductive current; the valley value of the inductive current is compared with a first threshold value, the peak value of the inductive current is compared with a second threshold value and a third threshold value, and the total excitation demagnetization time of the inductive current is compared with a fourth threshold value and a fifth threshold value; determining when the driving of the secondary side synchronous rectification circuit is switched on or switched off according to the comparison result; wherein the first threshold value is used for determining when to turn off the driving of the secondary side synchronous rectification circuit in each period; the second threshold value and the fourth threshold value are used for determining that the drive of the secondary side synchronous rectification circuit is not sent out in the next period, the third threshold value and the fifth threshold value are used for determining that the drive of the secondary side synchronous rectification circuit is sent out in the next period, the second threshold value is smaller than the third threshold value, and the fourth threshold value is smaller than the fifth threshold value. The efficiency of the switching power supply can be improved.

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] The buck-boost switching circuit can convert the input voltage into an output voltage higher, equal to or lower than the input voltage, and can operate within a wide range of input voltage variations. Isolated buck-boost converters are widely used in the fields of intermediate bus power supplies and railway power supplies in the power supply architecture of communication systems due to their high safety and excellent efficiency.

[0003] The known isolated buck-boost converter usually adopts 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 the 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 the buck-boost 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 the boost mode.

[0004] During the operation of the 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 charged again after a period of time, it belongs to the discontinuous current mode (DCM); if the current in the inductor is fully released and then charged immediately, 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. The driver S8 of power tube Q8 is complementary to the driver S5 of power tube Q5, and the driver S7 of power tube Q7 is complementary to the driver S6 of power tube Q6, so as to improve the efficiency under heavy load. However, in scenarios where light load power consumption requirements are high, it is necessary to shut down the synchronous rectification circuit in time under DCM to prevent current from flowing back to the input side to reduce power consumption under light no-load. On the one hand, the control IC of the buck-boost isolation circuit is generally placed on the primary side, and can only collect the primary side inductor current information; on the other hand, the inductor current ripple of the buck-boost converter presents an inverse parabola feature with large sides and small middle. There is currently no better way for the control IC to achieve reliable control of the synchronous rectification circuit on the isolated buck-boost converter 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 solve one of the technical problems existing in the prior art to a certain extent.

[0007] The main idea of ​​the present invention is that the amplitude of the inductor current ripple 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 amplitude of the inductor current ripple is large, and when the input voltage and the output voltage are close, the amplitude of the inductor current ripple is small. There are two difficulties in controlling the synchronous rectification circuit: (1) how to effectively avoid current backflow under light load; (2) how to achieve the consistency of the corresponding load current when the synchronous rectification circuit is put into operation as early as possible and 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 adds the total time of inductor current excitation and demagnetization to determine when the drive of the secondary synchronous rectification circuit is turned on and off, so as to achieve reliable shutdown of the synchronous rectification circuit under light no-load, prevent current backflow, improve the reliability of the converter, and at the same time improve the temperature rise of the synchronous rectification circuit and improve efficiency.

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

[0009] A method for controlling a synchronous rectifier tube 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 switch circuit, a transformer and a secondary synchronous rectifier circuit; wherein the control method comprises:

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

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

[0013] Among them: the first threshold is used to determine when the drive of the secondary synchronous rectification circuit is turned off 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 drive 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.

[0014] Further, determining when to turn on and off the driving of the secondary 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 value, immediately shutting down the drive 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 synchronous rectification circuit is driven in the next cycle.

[0018] Furthermore, under different working conditions, the threshold value for determining when the driver of the secondary 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 rectification circuit cycle by cycle, the second threshold is used as the threshold at which the drive of the secondary synchronous rectification circuit is not issued, and the third threshold is used as the threshold at which the drive of the secondary synchronous rectification circuit is issued;

[0020] ② The first threshold is used to turn off the drive of the secondary synchronous rectification circuit cycle by cycle, the second 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;

[0021] ③ The first threshold is used to turn off 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 third threshold is used as the threshold at which the drive of the secondary synchronous rectification 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 condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-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] The load is light, when the total excitation and demagnetization time of the inductor current is less than the fourth threshold value, the drive of the secondary synchronous rectification circuit is not issued, and the converter works in the 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 driving of the secondary synchronous rectification circuit is normally issued 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 inductor current valley 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 condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-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 value and the valley value of the inductor current is greater than the first threshold value, 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 switch circuit is issued;

[0029] As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the secondary 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, so as 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 synchronous rectification circuit is not driven and enters the diode rectification mode.

[0031] Furthermore, under the condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-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:

[0032] The load is light, when the inductor current peak value is less than the second threshold value, the secondary synchronous rectification circuit is not driven, and the converter works 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 driving of the secondary synchronous rectification circuit is normally issued 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 drive of the secondary synchronous rectification circuit is normally issued in each cycle and is turned off before the drive of the corresponding primary switch circuit is issued.

[0035] Furthermore, under the condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-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:

[0036] 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 drive of the secondary synchronous rectification circuit is normally issued in each cycle and is turned off before the drive of the corresponding primary switch circuit is issued;

[0037] As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the secondary 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 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 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 switch circuit, a transformer and a secondary synchronous rectifier circuit; wherein the control device includes:

[0041] The acquisition module is used to acquire 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, used for comparing the valley value of the inductor current with the first threshold value, comparing the peak value of the inductor current with the second threshold value and the third threshold value respectively, and comparing the total excitation and demagnetization time of the inductor current with the fourth threshold value and the fifth threshold value respectively;

[0043] An execution module, used for determining 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 the drive of the secondary synchronous rectification circuit is turned off 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 drive 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.

[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, wherein the cascade circuit includes: 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 value and the inductor current valley value, the embodiment of the present invention also adds the total inductor current excitation and demagnetization time to determine when the drive of the secondary synchronous rectification circuit is turned on and off. The increase in control parameters increases the degree of freedom of optimization of the cascade circuit, which is beneficial to 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 inductor current peak and valley values ​​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 a converter such as an isolated buck-boost converter with multiple working 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 synchronous rectification circuit is turned off in each cycle, so as to avoid current backflow when the load is light, so that the isolated buck-boost converter can realize reliable shutdown of the synchronous rectification circuit in the boost, buck-boost and buck modes, thereby improving the reliability of the converter;

[0051] (3) The second threshold and the fourth threshold of the embodiment of the present invention 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 full input voltage range. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is the principle diagram of diode rectification of the existing buck-boost cascade circuit;

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

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

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

[0056] FIG5(a) is a first control timing sequence of the synchronous rectifier control method of the cascade circuit of 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;

[0057] FIG5( b ) is a second control timing of the synchronous rectifier control method of the cascade circuit of 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 of the synchronous rectifier control method of the cascade circuit of 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;

[0059] FIG6( b ) is a second control timing of the synchronous rectifier control method of the cascade circuit of 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 It is a principle block diagram of the synchronous rectifier control device of the cascade circuit of the present invention;

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

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

[0063] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0064] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present 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, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising 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 equipment.

[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 drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0068] First embodiment

[0069] This embodiment provides a method for controlling a synchronous rectifier tube in a cascade circuit. Figure 3 The first schematic diagram of the 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 switch circuit, a transformer and a secondary synchronous rectification circuit; Figure 4 The control flow chart of the control method of the cascade circuit synchronous rectifier tube of 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 value, comparing the peak value of the inductor current with the second threshold value and the third threshold value respectively, and comparing the total excitation and demagnetization time of the inductor current with the fourth threshold value and the fifth threshold value respectively;

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

[0073] Among them: the first threshold is used to determine when the drive of the secondary synchronous rectification circuit is turned off 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 drive 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 value and the inductor current valley value, this embodiment also adds the total inductor current excitation and demagnetization time to determine when the drive of the secondary synchronous rectification circuit is turned on and off. The increase in control parameters increases the optimization freedom of the cascade circuit, which is beneficial to improving the overall performance and efficiency of the cascade circuit.

[0075] Further, 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 value, the drive of the secondary-side synchronous rectification circuit is immediately turned off;

[0077] When the peak value of the inductor current is less than the second threshold value or the total time of the inductor current excitation and demagnetization 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 synchronous rectification circuit is driven in the next cycle.

[0079] In this embodiment, according to the range of the input voltage Vin of the cascade circuit, the output voltage Vbus of the preceding step-up / step-down circuit, and the values ​​of the second threshold, the third threshold, the fourth threshold, and the fifth threshold, the thresholds for determining when the drive of the secondary synchronous rectification circuit is turned on and off have only the following four combinations:

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

[0081] ② The first threshold is used to turn off the drive of the secondary synchronous rectification circuit cycle by cycle, the second 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;

[0082] ③ The first threshold is used to turn off 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 third threshold is used as the threshold at which the drive of the secondary synchronous rectification circuit is issued;

[0083] 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.

[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 relatively large, the fourth threshold and the fifth threshold are used as the thresholds for controlling the driving of the secondary-side synchronous rectifier circuit not to be emitted or to be emitted; 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 not to be emitted or to be emitted.

[0085] The specific control process of the secondary synchronous rectification circuit is described below according to the difference between the input voltage Vin of the cascade circuit and the output voltage Vbus of the previous step-up and step-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 drive of the secondary synchronous rectification circuit is not issued, and the converter works 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, 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 switch circuit is issued;

[0093] As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the secondary synchronous rectification circuit is normally driven 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 drive of the secondary synchronous rectification circuit is not issued, and the diode rectification mode is entered.

[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 value is less than the second threshold value, the secondary synchronous rectification circuit does not drive and the converter works 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 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 further increases, 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 drive of the secondary synchronous rectification circuit is normally issued in each cycle and is turned off before the drive of the corresponding primary switch circuit is issued.

[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, 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 drive of the secondary synchronous rectification circuit is normally issued in each cycle and is turned off before the drive of the corresponding primary switch circuit is issued;

[0102] As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the drive of the secondary synchronous rectification circuit in each cycle is normally issued 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 not issued.

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

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

[0106] Second embodiment

[0107] The present 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 switch circuit, a transformer and a secondary synchronous rectifier circuit; the control device of the present embodiment is as follows Figure 7 As shown, including:

[0108] The acquisition module is used to acquire 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, used for comparing the valley value of the inductor current with the first threshold value, comparing the peak value of the inductor current with the second threshold value and the third threshold value respectively, and comparing the total excitation and demagnetization time of the inductor current with the fourth threshold value and the fifth threshold value respectively;

[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 the drive of the secondary synchronous rectification circuit is turned off 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 drive 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 correspond to and are consistent with the control method of the first embodiment, and have the same beneficial effects, so they will not be 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 this embodiment will not describe them one by one.

[0114] Third embodiment

[0115] The present 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 switching circuit, a transformer and a secondary synchronous rectification circuit; the switching power supply also includes any one of the cascade circuit synchronous rectifier tube control devices in 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] Further, 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, Figure 7 The second schematic diagram of the cascade circuit applicable to the present invention, Figure 8 This is a third principle diagram of a cascade circuit applicable to the present invention.

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

[0119] The input voltage Vin of the switching power supply ranges from 9 to 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 along with the input voltage Vin,

[0121] When the input voltage Vin is 0-24V: there is an input voltage Vin1, under which the current Izcd2 is equal to the load current corresponding to the inductor excitation and demagnetization time K1*T, the peak value of the inductor current under 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 Vin2, under which the current Izcd3 is equal to the load current corresponding to the excitation and demagnetization time K2*T, the peak value of the inductor current under 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;

[0122] When the input voltage Vin is 24V-36V: there is an input voltage Vin3, under which the current Izcd2 is equal to the load current corresponding to K1*T, the peak value of the inductor current under 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 a Vin4, under which the current Izcd3 is equal to the load current corresponding to K2*T, under which 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;

[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 less than the load current corresponding to K2*T, and the load current corresponding to Izcd2 is less than the load current corresponding to K1*T;

[0125] When Vin2<Vin<Vin1, the load current corresponding to Izcd2 is less 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;

[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 less 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;

[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 takes the input voltage Vin in the range of Vin1<Vin<Vin3, and the load changes from heavy to light and from light to heavy as an example to illustrate the control method of the secondary side synchronous rectification circuit:

[0130] When the load changes from heavy to light, and the peak value of the inductor current is greater than Izcd3 when the load is heavy, the drive of the switch tubes Q7 and Q8 is normally issued in each cycle. When the inductor current valley value is greater than Izcd1, the drive of the switch tubes Q7 and Q8 is turned off according to the original timing. The original timing is that the drive of the switch tubes Q7 and Q6 is complementary, and the drive of the switch tubes Q8 and Q5 is complementary; when the load is further reduced, the inductor current enters the DCM mode, and it is detected that the inductor current peak value is greater than Izcd2. The drive of the switch tubes Q7 and Q8 is normally issued in each cycle. When it is detected that the inductor current valley value is equal to Izcd1, the drive of the switch tubes Q7 and Q8 is immediately turned off; as the load continues to decrease, when it is detected that the inductor current peak value is less than Izcd2, the drive of the switch tubes Q7 and Q8 is no longer issued;

[0131] When the load changes from light to heavy, when the load is light and the inductor current peak is less than Izcd3, the drive of the switch tubes Q7 and Q8 is not issued; as the load increases, it is detected that the inductor current peak is greater than Izcd3, the drive of the switch tubes Q7 and Q8 is issued, and the switch tubes Q7 and Q8 are turned off when it is detected that the inductor current valley is equal to Izcd1; when the load further increases, the inductor current enters the CCM mode, and when the inductor current peak is greater than Izcd3, the drive of the switch tubes Q7 and Q8 is issued normally in each cycle, and when the inductor current valley is greater than Izcd1, the drive of the switch tubes Q7 and Q8 is turned off according to the original timing, and the original timing is that the drive of the switch tube Q7 is complementary to the drive of the switch tube Q6, and the drive of the switch tube Q8 is complementary to the drive of the switch tube Q5.

[0132] The above embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For those skilled in the art, several equivalent substitutions, improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope 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 switch circuit, a transformer and a secondary synchronous rectifier circuit; characterized in that: The control method comprises: 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 the first threshold value, comparing the peak value of the inductor current with the second threshold value and the third threshold value respectively, and comparing the total excitation and demagnetization time of the inductor current with the fourth threshold value and the fifth threshold value respectively; Determining 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 the drive of the secondary synchronous rectification circuit is turned off 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 drive 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.

2. The method for controlling synchronous rectifiers in a cascade circuit according to claim 1, characterized in that: The step of determining when to turn on and off the driving of the secondary synchronous rectification circuit according to the comparison result includes: When the inductor current valley value is less than or equal to a first threshold value, immediately shutting down the drive 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 the third threshold and the total time of the inductor current excitation and demagnetization is greater than the fifth threshold, the secondary synchronous rectification circuit is driven in the next cycle.

3. The method for controlling synchronous rectifiers in a cascade circuit according to claim 2, characterized in that: Under different working conditions, the threshold value that determines when the driver of the secondary synchronous rectification circuit is turned on and off is configured as one of the following four combinations: ① The first threshold is used to turn off the drive of the secondary synchronous rectification circuit cycle by cycle, the second threshold is used as the threshold at which the drive of the secondary synchronous rectification circuit is not issued, and the third threshold is used as the threshold at which the drive of the secondary synchronous rectification circuit is issued; ② The first threshold is used to turn off the drive of the secondary synchronous rectification circuit cycle by cycle, the second 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; ③ The first threshold is used to turn off 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 third threshold is used as the threshold at which the drive of the secondary synchronous rectification 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.

4. The method for controlling synchronous rectifiers in a cascade circuit according to claim 1, characterized in that: Under the condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-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: The load is light, when the total excitation and demagnetization time of the inductor current is less than the fourth threshold value, the drive of the secondary synchronous rectification circuit is not issued, and the converter works in the 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 driving of the secondary synchronous rectification circuit is normally issued 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 inductor current valley 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.

5. The method for controlling synchronous rectifiers in a cascade circuit according to claim 1, characterized in that: Under the condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-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 value and the valley value of the inductor current is greater than the first threshold value, 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 switch circuit is issued; As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the secondary 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 synchronous rectification circuit is not driven and enters the diode rectification mode.

6. The method for controlling synchronous rectifiers in a cascade circuit according to claim 1, characterized in that: Under the condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-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: The load is light, when the inductor current peak value is less than the second threshold value, the secondary synchronous rectification circuit is not driven, and the converter works 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 driving of the secondary synchronous rectification circuit is normally issued 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 drive of the secondary synchronous rectification circuit is normally issued in each cycle and is turned off before the drive of the corresponding primary switch circuit is issued.

7. The method for controlling synchronous rectifiers in a cascade circuit according to claim 1, characterized in that: Under the condition that the difference between the input voltage of the cascade circuit and the output voltage of the preceding step-up / step-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: 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 drive of the secondary synchronous rectification circuit is normally issued in each cycle and is turned off before the drive of the corresponding primary switch circuit is issued; As the load decreases, when the inductor current valley value is less than or equal to the first threshold value, the secondary 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.

8. A cascade circuit synchronous rectifier control device, the cascade circuit comprising a front-stage buck-boost circuit and a rear-stage isolation switch power supply circuit; the front-stage buck-boost circuit comprises an inductor; the rear-stage isolation switch power supply circuit comprises a primary switch circuit, a transformer and a secondary synchronous rectifier circuit; characterized in that: The control device comprises: The acquisition module is used to acquire 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, used for comparing the valley value of the inductor current with the first threshold value, comparing the peak value of the inductor current with the second threshold value and the third threshold value respectively, and comparing the total excitation and demagnetization time of the inductor current with the fourth threshold value and the fifth threshold value respectively; An execution module, used for determining 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 the drive of the secondary synchronous rectification circuit is turned off 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 drive 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.

9. 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 switch circuit, a transformer and a secondary synchronous rectification circuit; it is characterized in that: the switch power supply also includes the cascade circuit synchronous rectifier tube control device as claimed in claim 8.

10. The switching power supply according to claim 9, characterized in that: 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.

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