A clamping module and switching power supply

Abstract

The present invention discloses a clamping module and a switching power supply. The clamping module includes: a clamping switch, a power supply control switch, a first diode, a second diode, a clamping control circuit, and a power supply capacitor. The clamping control circuit is used to obtain a first voltage representing the voltage magnitude across the power supply capacitor, and to obtain a shutdown signal representing the first switch being at a shutdown moment, and to perform a control action according to the following logic: when the first voltage is less than or equal to a first threshold, the power supply control switch is controlled to be turned off; when the first voltage is greater than or equal to a second threshold, the power supply control switch is controlled to be turned on; the first threshold is less than the second threshold; according to the shutdown signal, the clamping switch is controlled to be turned on, thereby suppressing the peak voltage generated when the first switch tube is turned off, absorbing leakage inductance energy, and recovering the absorbed energy. The clamping module of the present invention is applied to a switching power supply. When connected in series with a clamping capacitor, it can clamp the voltage spike of the switch tube and recover leakage inductance energy. No bootstrap power supply is required, thereby expanding the application scenarios.

Description

Technical Field

[0001] The present invention relates to the field of switching power supplies, and more particularly to a clamping module and a switching power supply. Background Art

[0002] In the field of low-power power supply, flyback converter is widely used due to its simple circuit structure, mature control technology and low cost. However, traditional flyback converters such as Figure 1 As shown in Figure 1, an RCD-like clamping circuit is required to suppress the leakage inductance voltage spike and absorb the leakage inductance energy. To effectively suppress the voltage spike, RCD losses account for a large proportion, especially in situations with large leakage inductance, which greatly affects the efficiency of the power converter.

[0003] The active clamp flyback converter is a circuit solution that can effectively solve the leakage inductance voltage spike and recover the leakage inductance energy. Figure 2 The active-clamp flyback converter shown in Figure 1 has become a research hotspot in recent years. It utilizes the clamping capacitor Cr and the clamping switch QA to recover leakage inductance energy and convert some of this energy into a negative current in the transformer's primary winding, thereby achieving zero-voltage switching (ZVS). However, this solution requires a floating driver for the clamping switch, which typically requires a bootstrap power supply. This makes it unsuitable for half-bridge circuits, limiting its application flexibility.

[0004] The limited flexibility of the above-mentioned switch floating drive application is common in the field of switching power supplies. It is not limited to flyback converters, but also exists in forward converters. Summary of the Invention

[0005] In view of this, the technical problem solved by the present invention is to provide a clamping module and a switching power supply. The clamping module is used to be connected in series with the clamping capacitor in the switching power supply to clamp the voltage spike when the switch tube is turned off and recover the leakage inductance energy. The clamping module does not require self-bootstrapping power supply, which can expand its application scenarios and reduce product costs.

[0006] As a first aspect of the present invention, an embodiment of the clamping module is provided as follows:

[0007] A clamping module is applied to a switching power supply, wherein the switching power supply includes a first switch and a clamping capacitor. The clamping module includes: a clamping switch, a power supply control switch, a first diode, a second diode, a clamping control circuit, and a power supply capacitor;

[0008] The cathode of the first diode, the anode of the second diode, the drain of the power supply control switch, and the first detection end of the clamp control circuit are connected together as one end of the clamp module, the cathode of the second diode is simultaneously connected to the positive power supply voltage connection end of the clamp control circuit and one end of the power supply capacitor, the other end of the power supply capacitor is simultaneously connected to the negative power supply voltage connection end of the clamp control circuit, the source of the power supply control switch, the anode of the first diode, and the source of the clamp switch, the drain of the clamp switch serves as the other end of the clamp module, the first drive voltage output end of the clamp control circuit is connected to the gate of the power supply control switch, and the second drive voltage output end of the clamp control circuit is connected to the gate of the clamp switch;

[0009] The clamp control circuit is used to obtain a first voltage representing the voltage across the power supply capacitor, and obtain a shutdown signal representing the first switch is at a shutdown moment, and perform a control action according to the following logic:

[0010] When the first voltage is less than or equal to a first threshold, the power supply control switch is controlled to be turned off; when the first voltage is greater than a second threshold, the power supply control switch is controlled to be turned on; and the first threshold is less than the second threshold;

[0011] According to the shutdown signal, the conduction of the clamp switch is controlled to suppress the peak voltage generated when the first switch tube is turned off, absorb the leakage inductance energy, and recover the absorbed energy.

[0012] Furthermore, the first diode is a body diode of the power supply control switch.

[0013] Preferably, the clamp control circuit acquires a first voltage representing the voltage magnitude across the power supply capacitor by detecting the voltage at the positive power supply voltage connection terminal.

[0014] Preferably, the clamp control circuit obtains the shutdown signal by detecting the voltage of the first detection terminal during the conduction period of the power supply control switch; and obtains the shutdown signal by detecting the voltage of the positive power supply voltage connection terminal during the off period of the power supply control switch.

[0015] Furthermore, acquiring the shutdown signal by detecting the voltage of the first detection terminal, and controlling the clamp switch to be turned on according to the shutdown signal, includes:

[0016] The clamp switch is turned on when the shutdown signal is obtained for the first time or after a first delay time, and the clamp switch is turned off when the shutdown signal is obtained for the second time.

[0017] Furthermore, acquiring the shutdown signal by detecting the voltage of the first detection terminal, and controlling the clamp switch to be turned on according to the shutdown signal, includes:

[0018] The clamp switch is turned on when the shutdown signal is acquired for the first time or after a second delay time, and is turned off when the shutdown signal is acquired for the second time or after a third delay time.

[0019] Furthermore, the clamp control circuit is provided with a delayed conduction adjustment terminal for setting the second delay time through an external resistor.

[0020] Furthermore, based on the set second delay time, the second delay time is adaptively adjusted according to the magnitude of the excitation current. The greater the excitation current, the longer the corresponding second delay time.

[0021] Preferably, the clamp switch is turned off after being turned on for a first time.

[0022] Furthermore, the leakage inductance of the flyback converter and the clamping capacitor are configured to resonate and operate according to a certain resonant period, and the second time is 0.75 to 1 times of the resonant period.

[0023] Furthermore, the clamping control circuit is provided with a resonance period adjustment terminal for setting the resonance period through an external resistor.

[0024] As a second aspect of the present invention, an embodiment of a switching power supply is provided as follows:

[0025] A switching power supply, comprising:

[0026] a transformer, including a primary winding and a secondary winding;

[0027] A primary-side circuit includes a main switch, a first clamping capacitor, and a first clamping module. The first clamping module is an embodiment of any of the above clamping modules. The main switch is coupled to the input side of the switching power supply via the primary winding. The first clamping module is connected in series with the first clamping capacitor and then in parallel across the primary winding.

[0028] The secondary side circuit includes a rectifier switch tube, and the secondary winding is coupled to the output side of the switching power supply through the rectifier switch tube.

[0029] A switching power supply, comprising:

[0030] a transformer, including a primary winding and a secondary winding;

[0031] The primary side circuit includes a main switch tube, wherein the main switch tube is coupled to the input side of the switching power supply through the primary winding;

[0032] The secondary side circuit includes a rectifier switch tube, a second clamping capacitor and a second clamping module. The second clamping module is an embodiment of any of the clamping modules described above. The secondary winding is coupled to the output side of the switching power supply through the rectifier switch tube. The clamping module is connected in series with the clamping capacitor and then in parallel at both ends of the rectifier switch tube.

[0033] A switching power supply, comprising:

[0034] a transformer, including a primary winding and a secondary winding;

[0035] A primary-side circuit includes a main switch, a first clamping capacitor, and a first clamping module. The first clamping module is an embodiment of any of the above clamping modules. The main switch is coupled to the input side of the switching power supply via the primary winding. The first clamping module is connected in series with the first clamping capacitor and then in parallel across the primary winding.

[0036] The secondary side circuit includes a rectifier switch tube, a second clamping capacitor and a second clamping module. The second clamping module is an embodiment of any of the clamping modules described above. The secondary winding is coupled to the output side of the switching power supply through the rectifier switch tube. The clamping module is connected in series with the clamping capacitor and then in parallel at both ends of the rectifier switch tube.

[0037] Preferably, the switching power supply is a flyback switching power supply.

[0038] The embodiments of the present invention have at least the following beneficial effects:

[0039] (1) The clamping module is used to replace the clamping switch tube of the existing technology. The clamping structure formed by the clamping module and the clamping capacitor can also greatly suppress the voltage spike of the main switch and recover the leakage inductance energy of the transformer. Compared with the RCD clamping circuit solution, it can improve the efficiency of the power converter and can directly replace the RCD clamp. There is no need for active clamping chips and high-voltage bootstrap drivers. Ordinary flyback chips can be used. Compared with the existing active clamping technology, it can reduce product cost and volume. It is especially suitable for low-power, small-volume and low-cost flyback converters.

[0040] (2) The clamping module adopts self-power supply and detection control, and can be combined with ordinary flyback converters, resonant flyback converters, and forward converters to suppress the voltage spike when the primary side main switch is turned off and recover the leakage inductance energy, thereby improving the efficiency of the switching power supply and having strong practicality;

[0041] (3) The clamping module can be combined with a switching power supply with secondary side clamping to solve the main switch voltage spike and energy loss problems caused by transformer leakage inductance;

[0042] (4) When the clamping module is connected in series with the capacitor and then in parallel at both ends of the rectifier switch tube in the secondary circuit, it can also suppress the voltage spike caused by the reverse recovery of the secondary side rectifier switch tube and recover the reverse recovery energy of the rectifier switch tube.

[0043] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained through the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the schematic diagram of the existing RCD clamped flyback converter;

[0045] Figure 2 The schematic diagram of the existing active clamp flyback converter is shown in FIG.

[0046] Figure 3 A schematic diagram of a clamping module provided in the first embodiment of the present invention;

[0047] Figure 3a for Figure 3 The first waveform diagram of the control of the shutdown of the clamping module by detecting the voltage of the first detection terminal to obtain a shutdown signal;

[0048] Figure 3b for Figure 3 The second waveform diagram in which the shutdown of the clamping module is controlled by detecting the voltage of the first detection terminal to obtain a shutdown signal;

[0049] Figure 4 for Figure 3 Schematic diagram of the logic processing of the clamp control circuit in the clamp module;

[0050] Figure 5 A schematic diagram of another clamping module provided in the first embodiment;

[0051] Figure 6 A schematic diagram of a switching power supply provided in accordance with a second embodiment of the present invention;

[0052] Figure 7a 、 Figure 7b for Figure 6 The key working process waveforms of the switching power supply shown;

[0053] Figure 8 A schematic diagram of a switching power supply provided in a third embodiment of the present invention;

[0054] Figure 9 This is a schematic diagram of a switching power supply provided in accordance with a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0055] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0056] 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.

[0057] 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 described 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.

[0058] 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.

[0059] 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.

[0060] First embodiment

[0061] Figure 3 For a schematic diagram of a clamping module provided by the first embodiment of the present invention, see Figure 3The clamping module is applied to a switching power supply, which includes a first switch and a clamping capacitor.

[0062] The clamping module includes: a clamping switch QA2, a power supply control switch QA1, a first diode D1, a second diode D2, a clamping control circuit and a power supply capacitor C1;

[0063] The cathode of the first diode D1, the anode of the second diode D2, the drain of the power supply control switch QA1 and the first detection terminal VD1 of the clamp control circuit are connected together as one end of the clamp module (ie Figure 3 The cathode of the second diode D2 is connected to the positive power supply voltage connection terminal Vcc of the clamp control circuit and one end of the power supply capacitor C1. The other end of the power supply capacitor C1 is connected to the negative power supply voltage connection terminal Vee of the clamp control circuit, the source of the power supply control switch QA1, the anode of the first diode D1 and the source of the clamp switch QA2. The drain of the clamp switch QA2 serves as the other end of the clamp module (i.e. Figure 3 The first driving voltage output terminal Vg1 of the clamping control circuit is connected to the gate of the power supply control switch QA1, and the second driving voltage output terminal Vg2 of the clamping control circuit is connected to the gate of the clamping switch QA2;

[0064] The clamp control circuit is used to obtain a first voltage representing the voltage across the power supply capacitor C1 and a shutdown signal representing the first switch being turned off, and perform a control action according to the following logic:

[0065] When the first voltage is less than or equal to the first threshold, the power supply control switch QA1 is controlled to be turned off, so that the current can flow through the second diode D2, the power supply capacitor C1, and the clamp switch QA2 in sequence, thereby achieving clamping and charging the power supply capacitor C1. When the first voltage is greater than the second threshold, the power supply control switch QA1 is controlled to be turned on, so that the current can flow through the power supply control switch QA1, thereby bypassing the power supply capacitor C1. The clamp control circuit is powered by the charge stored in the power supply capacitor C1. The first threshold is less than the second threshold.

[0066] According to the obtained shutdown signal, that is, the signal of the first zero-crossing increase of the clamping loop current (such as Figure 3a As shown), the clamp switch QA2 is controlled to be turned on, so as to suppress the peak voltage generated when the first switch tube is turned off, absorb the leakage inductance energy, and recover the absorbed energy.

[0067] The function of the first diode D1 is to provide a path for the negative current of the clamping capacitor when the power supply control switch QA1 is turned off, thereby achieving ampere-second balance of the clamping capacitor voltage.

[0068] The second diode D2 is used to provide a charging path for the power supply capacitor C1 so that charge can be stored in the power supply capacitor while preventing voltage backflow of the power supply capacitor C1 .

[0069] The power supply capacitor C1 is used to supply power to the clamping control circuit via the charge stored therein when the power supply control switch QA1 is turned on.

[0070] The two ends of the first switch refer to ports where current flows into and out of the switch, for example, for a MOS transistor, they refer to a drain and a source, and for a diode, they refer to an anode and a cathode.

[0071] The clamping module of this embodiment is provided with a clamping switch QA2. By configuring the timing, the clamping module of this embodiment can replace the clamping switch tube of the prior art (for example, replacing Figure 2 The clamping switch tube QA in the circuit), the clamping structure formed by the clamping module and the clamping capacitor can also greatly suppress the voltage spike of the main switch and recover the leakage inductance energy of the transformer.

[0072] At the same time, the clamping module of this embodiment is also provided with a power supply control switch QA1, a first diode D1, a second diode D2, a clamping control circuit and a power supply capacitor C1. Through self-power supply and detection control, it can be combined with a conventional flyback converter, a resonant flyback converter, and a forward converter to suppress the voltage spike when the primary-side main switch tube is turned off and recover leakage inductance energy, thereby improving the efficiency of the switching power supply and having strong practicality.

[0073] It should be noted that the clamping module of this embodiment can be combined with a switching power supply with secondary side clamping to solve the main switch voltage spike caused by transformer leakage inductance and RCD clamping energy loss problems.

[0074] In addition, when the rectifier switch tube of the secondary circuit is a diode, there will be a large reverse recovery energy when the diode is turned off, resulting in a large reverse recovery current. This causes the two ends of the diode to withstand a large voltage spike stress, which in turn affects the reliability of the switching power supply. When the rectifier switch tube of the secondary circuit is a MOS tube synchronous rectifier, there will also be problems caused by the large reverse recovery energy after the synchronous rectifier tube in the MOS tube is turned off. The clamping module of this embodiment is connected in series with the capacitor and then in parallel at both ends of the rectifier switch tube of the secondary circuit. This can suppress the voltage spike caused by the reverse recovery of the secondary-side rectifier switch tube and recover the reverse recovery energy of the rectifier switch tube.

[0075] Furthermore, the first diode D1 is the body diode of the power supply control switch QA1, thereby simplifying the circuit of the clamping module.

[0076] Preferably, the clamp control circuit acquires the first voltage representing the voltage across the power supply capacitor C1 by detecting the voltage of the positive power supply voltage connection terminal Vcc.

[0077] Preferably, the clamp control circuit obtains a shutdown signal by detecting the voltage of the first detection terminal VD1 during the on-state of the power supply control switch QA1; and obtains the shutdown signal by detecting the voltage of the positive power supply voltage connection terminal Vcc during the off-state of the power supply control switch QA1.

[0078] Among them, the implementation of the clamping control circuit includes but is not limited to using discrete devices to build the functional circuit, designing an independent chip, or integrating it with the main control chip of the switching power supply. The specific implementation method is not limited in this embodiment, and technicians in this field can choose according to actual conditions. Figure 4 for Figure 3 For the schematic diagram of the logic processing of the clamp control circuit in the clamp module, see Figure 4 Comparator X2 is a hysteresis comparator, and the detection result obtained is used to control the power supply control switch QA1; comparator X3 is used to detect the voltage of the positive power supply voltage connection terminal VCC, and comparator X1 is used to detect the voltage of the first detection terminal VD1. The two detection results are combined to obtain a detection result to control the clamp switch QA2.

[0079] The purpose of setting the above control logic is to control the voltage of the power supply capacitor C1 within a certain range, so that the power supply capacitor can provide sufficient operating voltage for the control circuit, realize self-powering of the clamping module, and replace the bootstrap power supply usually required by the floating drive circuit, so that the application scenario of the clamping module of this embodiment is expanded.

[0080] The on and off of the clamp module is controlled by detecting the voltage of the first detection terminal VD1 to obtain a shutdown signal, including the following two control schemes:

[0081] Solution 1: The clamp switch QA2 is turned on when the shutdown signal is obtained for the first time or after a first delay time, and the clamp switch QA2 is turned off when the shutdown signal is obtained for the second time. Figure 3a for Figure 3 The first waveform diagram of the control of the shutdown of the clamp module is achieved by detecting the voltage of the first detection terminal to obtain the shutdown signal. Please refer to Figure 3a , where the secondary current may cross zero prematurely, causing the detection-type synchronous rectification to be turned off prematurely. Therefore, the following solution 2 is proposed.

[0082] Solution 2: The clamp switch QA2 is turned on when the shutdown signal is obtained for the first time or after the second delay time, and the clamp switch QA2 is turned off when the shutdown signal is obtained for the second time or after the third delay time. Figure 3bfor Figure 3 The second waveform diagram of the control is implemented by detecting the voltage of the first detection terminal to obtain a shutdown signal for shutting down the clamping module.

[0083] The second control scheme described above can accurately control the on-time of the clamp switch QA2 and optimize the output current waveform of the switching power supply, thereby reducing the effective value of the output current and avoiding premature shutdown of the synchronous rectifier.

[0084] Furthermore, for the second control solution described above, the clamp control circuit is provided with a delayed conduction adjustment terminal for setting the second delay time through an external resistor.

[0085] Furthermore, for the above-mentioned second control scheme, based on the set second delay time, the second delay time is adaptively adjusted according to the size of the excitation current, and the size of the excitation current can be detected by the first detection end; the larger the excitation current, the longer the corresponding second delay time.

[0086] Figure 5 For a schematic diagram of another clamping module provided in the first embodiment, see Figure 5 The clamp module is provided with a delayed turn-on adjustment terminal, and a second delay time is set by an external resistor RI. The external resistor RI is connected between the delayed turn-on adjustment terminal and the negative power supply voltage connection terminal Vee. When the clamp switch QA1 is turned on, reverse current is transmitted to the rectifier output. This current is superimposed on the normal rectifier current to form a voltage spike. Preferably, the clamp switch is turned on when the excitation current decreases to less than approximately 1 / 2 of the peak value. Therefore, the larger the excitation current peak, the longer the required delay time. The delay time is preferably between Lm*Ipk / 2nVo and 2Lm*Ipk / 3nVo (n is the transformer primary-to-secondary turns ratio, and Ipk is the primary peak current). This reduces the current peak and the effective current value while not affecting the synchronous rectification operation. Therefore, the value of the resistor RI should follow this rule: as the peak current increases, the second delay time adaptively increases based on the set minimum value. The lower the frequency and the greater the peak current, the longer the required second delay time, and vice versa.

[0087] In addition, the clamp switch QA2 of this embodiment can be turned off by setting the clamp switch QA2 to be turned on for a fixed time, that is, the clamp switch is turned on for a first time and then turned off.

[0088] Furthermore, for the above-mentioned turn-off control scheme in which the clamp switch QA2 is set to be turned on for a fixed time, the leakage inductance and the clamp capacitor of the flyback converter are configured to resonate according to a certain resonant period, and the second time is 0.75 to 1 times the resonant period, thereby ensuring that the clamp switch is turned off at zero voltage without affecting the entire clamping process.

[0089] Furthermore, the clamping control circuit is provided with a resonance period adjustment terminal for setting the above-mentioned resonance period through an external resistor.

[0090] Second embodiment

[0091] Figure 6 For the schematic diagram of the switching power supply provided by the second embodiment of the present invention, please refer to Figure 6 , the switching power supply of this embodiment includes:

[0092] A transformer TX including a primary winding P1 and a secondary winding S1;

[0093] The primary-side circuit includes a main switch Q1, a first clamping capacitor Cr, and a first clamping module. The first clamping module is the clamping module of the first embodiment. The main switch Q1 is coupled to the input side of the switching power supply via the primary winding P1. The first clamping module is connected in series with the first clamping capacitor Cr and then in parallel across the primary winding P1.

[0094] The secondary side circuit includes a rectifier switch tube D3 , and the secondary winding S1 is coupled to the output side of the switching power supply through the rectifier switch tube D3 .

[0095] The main switch tube Q1 in this embodiment is the first switch in the first embodiment, and the first clamping capacitor Cr is the clamping capacitor in the first embodiment.

[0096] The first switch and the clamping capacitor are connected in series, and their positions can be interchanged.

[0097] Figure 7a 、 Figure 7b for Figure 6 The key working process waveforms of the switching power supply are shown, and the specific timing is described as follows:

[0098] The main switch Q1 is turned on, and the input voltage excites the primary excitation inductor Lm of the transformer;

[0099] After the main switch Q1 is turned off, the excitation current ILm charges the junction capacitance of the main switch Q1 to Vin + nVo (n is the primary-to-secondary turns ratio of the transformer). The excitation current ILm is then transmitted through the transformer to the secondary winding S1 and supplied to the output via the rectifier switch D3. At the same time, the leakage inductance current is clamped by a branch connected in series with the first clamping module and the first clamping capacitor Cr.

[0100] When the first voltage representing the voltage across the power supply capacitor is less than or equal to the first threshold, the power supply control switch QA1 is turned off by the clamp control circuit, and the leakage inductor current charges the power supply capacitor C1 through the second diode D2, the power supply capacitor C1, and the clamp switch QA2;

[0101] When the power supply capacitor C1 is charged to a first voltage representing the voltage across the power supply capacitor greater than a second threshold, and the first threshold is less than the second threshold, the clamp control circuit in the first clamp module controls the voltage control switch QA1 therein to turn on, thereby bypassing the charging circuit of the power supply capacitor C1. The clamp control circuit is powered by the charge stored on the power supply capacitor C1.

[0102] Figure 7a 、 Figure 7b The waveform is designed to obtain a shutdown signal indicating that the main switch Q1 is at the off-state during the on-state period of the power supply control switch QA1. During this period, when the leakage inductor current flows from the first clamping capacitor Cr, a voltage rise signal is generated on the on-resistance of the power supply control switch QA1. This voltage can be detected by detecting the voltage VD1 at the first detection terminal. This voltage can represent the operating state of the main switch Q1, and thus a shutdown signal indicating that the main switch Q1 is at the off-state can be obtained. When the shutdown signal is obtained, the clamping control circuit controls the clamping switch QA2 according to the shutdown signal, as shown in FIG. Figure 7b As shown in the S1 area, when the main switch tube Q1 is turned off, the first clamping capacitor Cr absorbs the peak voltage generated when the main switch tube Q1 is turned off through the clamping switch QA2 and the first diode D1 in the first clamping module, and recovers the absorbed energy. The first embodiment of the present invention cites three control schemes for turning off the clamping switch QA2. Those skilled in the art can select a specific control scheme for turning off the clamping switch tube according to actual conditions, and can use the control scheme of the first embodiment or other control schemes.

[0103] Since the drain-source voltage of the power supply control switch QA1 is low, typically within 15V, and thus operates at low voltage, the voltage change state of the power supply capacitor C1 can be quickly and effectively detected, including peaks, valleys, and zero crossings. Therefore, it is easy to obtain a first voltage representing the voltage across the power supply capacitor C1 by detecting the voltage of the positive power supply voltage connection terminal VCC.

[0104] When the power supply capacitor C1 is discharged so that the first voltage representing the voltage across the power supply capacitor C1 is less than or equal to the first threshold, the power supply control switch QA1 is turned off, allowing the leakage inductance current to flow through the second diode D2 in the first clamping module, the power supply capacitor C1, and the clamping switch QA2 in sequence, thereby achieving clamping and charging the power supply capacitor C1. During the period when the power supply control switch QA1 is turned off, please refer to Figure 7b As shown in the S2 interval.

[0105] It should be noted that due to the unidirectional conductivity of the second diode D2, the charge on the first clamping capacitor Cr can only be discharged through the first diode D1 or the body diode of the power supply control switch QA1, thereby maintaining the charge and discharge balance of the first clamping capacitor Cr.

[0106] Furthermore, if a shutdown signal indicating that the main switch Q1 is being turned off is required during the off-state period of the power control switch QA1, the parasitic capacitance between the drain and source of the power control switch QA1 is very small. When leakage inductor current flows from the first clamping capacitor, the voltage of the power control switch QA1 rapidly rises to the second threshold voltage, causing two distinct oscillations in the drain-source voltage of the main switch Q1: high-frequency oscillations caused by the leakage inductance and the parasitic capacitance between the drain and source of the power control switch QA1, and high-frequency oscillations caused by the magnetizing inductance and the parasitic capacitance between the drain and source of the power control switch QA1. This can easily affect the detection of the clamping control circuit and cause abnormal drive control of the clamping switch QA2. Therefore, during the off-state period of the power control switch QA1, when leakage inductor current flows from the first clamping capacitor Cr, the rise in the voltage of the power supply capacitor C1 can be easily detected. During this period, the shutdown signal indicating that the main switch Q1 is being turned off can be obtained by detecting the voltage at the positive power supply voltage connection terminal VCC, thereby reliably controlling the on and off of the clamping switch QA2.

[0107] Third embodiment

[0108] Figure 8 For the schematic diagram of the switching power supply provided by the third embodiment of the present invention, please refer to Figure 8 The switching power supply of this embodiment includes:

[0109] A transformer TX including a primary winding P1 and a secondary winding S1;

[0110] The primary side circuit includes a main switch tube Q1, which is coupled to the input side of the switching power supply through a primary winding S1;

[0111] The secondary-side circuit includes a rectifier switch tube Q2, a second clamping capacitor Cr2, and a second clamping module. The second clamping module is the clamping module of the first embodiment. The secondary winding S1 is coupled to the output side of the switching power supply through the rectifier switch tube Q2. The second clamping module is connected in series with the second clamping capacitor Cr2 and then in parallel with both ends of the rectifier switch tube Q2.

[0112] The rectifier switch tube Q2 in this embodiment is the first switch in the first embodiment, and the second clamping capacitor Cr is the clamping capacitor in the first embodiment.

[0113] This embodiment can effectively suppress the voltage spike of the rectifier switch tube Q2 and recover the reverse recovery leakage energy of the rectifier switch tube Q2, thereby using a rectifier MOS with lower stress, thereby improving efficiency and integration.

[0114] Fourth embodiment

[0115] Figure 9 For the schematic diagram of the switching power supply provided by the fourth embodiment of the present invention, please refer to Figure 9 The switching power supply of this embodiment includes:

[0116] A transformer TX including a primary winding P1 and a secondary winding S1;

[0117] The primary-side circuit includes a main switch Q1, a first clamping capacitor Cr, and a first clamping module. The first clamping module is the clamping module of the first embodiment. The main switch Q1 is coupled to the input side of the switching power supply via the primary winding P1. The first clamping module is connected in series with the first clamping capacitor Cr and then in parallel across the primary winding P1.

[0118] The secondary-side circuit includes a rectifier switch tube Q2, a second clamping capacitor Cr2, and a second clamping module. The second clamping module is the clamping module of the first embodiment. The secondary winding S1 is coupled to the output side of the switching power supply through the rectifier switch tube Q2. The second clamping module is connected in series with the second clamping capacitor Cr2 and then in parallel with both ends of the rectifier switch tube Q2.

[0119] This embodiment includes two sets of the first switches and clamping capacitors of the first embodiment. In one set, the main switch Q1 serves as the first switch in the first embodiment, and the first clamping capacitor Cr serves as the clamping capacitor in the first embodiment. In the other set, the rectifier switch Q2 serves as the first switch in the first embodiment, and the second clamping capacitor Cr serves as the clamping capacitor in the first embodiment.

[0120] This embodiment is an integration of the second embodiment and the third embodiment, thereby making the performance of the switching power supply more superior.

[0121] Preferably, the switching power supplies of the above-mentioned second embodiment, third embodiment and fourth embodiment are flyback switching power supplies, thereby achieving lossless absorption of leakage inductance energy and voltage clamping of the main switch tube and / or rectifier switch tube, avoiding the use of semiconductor devices with higher voltage specifications, and achieving better performance when using the flyback converter topology in the field of low-power power supplies.

[0122] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention. Persons skilled in the art will appreciate that equivalent power supplies, improvements, and modifications may be made without departing from the spirit and scope of the present invention. These equivalent power supplies, improvements, and modifications should also be considered within the scope of protection of the present invention. Examples will not be used here for further elaboration. The scope of protection of the present invention shall be determined by the scope defined in the claims.

Claims

1. A clamping module, applied to a switching power supply, wherein the switching power supply comprises a first switch and a clamping capacitor, characterized in that: The clamping module includes: a clamping switch, a power supply control switch, a first diode, a second diode, a clamping control circuit and a power supply capacitor; The cathode of the first diode, the anode of the second diode, the drain of the power supply control switch, and the first detection end of the clamp control circuit are connected together as one end of the clamp module, the cathode of the second diode is simultaneously connected to the positive power supply voltage connection end of the clamp control circuit and one end of the power supply capacitor, the other end of the power supply capacitor is simultaneously connected to the negative power supply voltage connection end of the clamp control circuit, the source of the power supply control switch, the anode of the first diode, and the source of the clamp switch, the drain of the clamp switch serves as the other end of the clamp module, the first drive voltage output end of the clamp control circuit is connected to the gate of the power supply control switch, and the second drive voltage output end of the clamp control circuit is connected to the gate of the clamp switch; The clamp control circuit is used to obtain a first voltage representing the voltage across the power supply capacitor, and obtain a shutdown signal representing the first switch is at a shutdown moment, and perform a control action according to the following logic: When the first voltage is less than or equal to a first threshold, the power supply control switch is controlled to be turned off; when the first voltage is greater than a second threshold, the power supply control switch is controlled to be turned on; and the first threshold is less than the second threshold; According to the shutdown signal, the clamp switch is controlled to be turned on, so as to suppress the peak voltage generated when the first switch tube is turned off, absorb the leakage inductance energy, and recover the absorbed energy.

2. The clamping module according to claim 1, characterized in that: The first diode is a body diode of the power supply control switch.

3. The clamping module according to claim 1, characterized in that: The clamp control circuit acquires a first voltage representing the voltage magnitude across the power supply capacitor by detecting the voltage at the positive power supply voltage connection terminal.

4. The clamping module according to claim 1, characterized in that: The clamp control circuit obtains the shutdown signal by detecting the voltage of the first detection terminal when the power supply control switch is turned on; and obtains the shutdown signal by detecting the voltage of the positive power supply voltage connection terminal when the power supply control switch is turned off.

5. The clamping module according to claim 4, characterized in that: The acquiring the shutdown signal by detecting the voltage of the first detection terminal, and controlling the clamp switch to be turned on according to the shutdown signal, comprises: The clamp switch is turned on when the shutdown signal is obtained for the first time or after a first delay time, and the clamp switch is turned off when the shutdown signal is obtained for the second time.

6. The clamping module according to claim 4, characterized in that: The acquiring the shutdown signal by detecting the voltage of the first detection terminal, and controlling the clamp switch to be turned on according to the shutdown signal, comprises: The clamp switch is turned on when the shutdown signal is acquired for the first time or after a second delay time, and is turned off when the shutdown signal is acquired for the second time or after a third delay time.

7. The clamping module according to claim 6, characterized in that: The clamp control circuit is provided with a delayed conduction adjustment terminal for setting the second delay time through an external resistor.

8. The clamping module according to claim 7, characterized in that: Based on the set second delay time, the second delay time is adaptively adjusted according to the magnitude of the excitation current. The greater the excitation current, the longer the corresponding second delay time.

9. The clamping module according to claim 1, characterized in that: The clamp switch is turned off after being turned on for a first time.

10. The clamping module according to claim 9, characterized in that: The leakage inductance of the switching power supply and the clamping capacitor are configured to operate in resonance according to a certain resonance period, and the first time is 0.75 to 1 times of the resonance period.

11. The clamping module according to claim 10, characterized in that: The clamping control circuit is provided with a resonance period adjustment terminal for setting the resonance period through an external resistor.

12. A switching power supply, characterized in that: include: a transformer, including a primary winding and a secondary winding; A primary-side circuit, comprising a main switch, a first clamping capacitor, and a first clamping module, wherein the first clamping module is the clamping module according to any one of claims 1 to 11, wherein the main switch is coupled to an input side of a switching power supply via the primary winding, and the first clamping module is connected in series with the first clamping capacitor and then in parallel across the primary winding. The secondary side circuit includes a rectifier switch tube, and the secondary winding is coupled to the output side of the switching power supply through the rectifier switch tube.

13. A switching power supply, characterized in that: include: a transformer, including a primary winding and a secondary winding; The primary side circuit includes a main switch tube, wherein the main switch tube is coupled to the input side of the switching power supply through the primary winding; The secondary side circuit includes a rectifier switch tube, a second clamping capacitor and a second clamping module, the second clamping module is the clamping module described in any one of claims 1 to 11, the secondary winding is coupled to the output side of the switching power supply through the rectifier switch tube, and the clamping module is connected in series with the clamping capacitor and then in parallel at both ends of the rectifier switch tube.

14. A switching power supply, characterized in that: include: a transformer, including a primary winding and a secondary winding; A primary-side circuit, comprising a main switch, a first clamping capacitor, and a first clamping module, wherein the first clamping module is the clamping module according to any one of claims 1 to 11, wherein the main switch is coupled to an input side of a switching power supply via the primary winding, and the first clamping module is connected in series with the first clamping capacitor and then in parallel across the primary winding. The secondary side circuit includes a rectifier switch tube, a second clamping capacitor and a second clamping module, the second clamping module is the clamping module described in any one of claims 1 to 11, the secondary winding is coupled to the output side of the switching power supply through the rectifier switch tube, and the clamping module is connected in series with the clamping capacitor and then in parallel at both ends of the rectifier switch tube.

15. The switching power supply according to any one of claims 12 to 14, characterized in that: The switching power supply is a flyback switching power supply.

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