A switching power supply
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MORNSUN GUANGZHOU SCI & TECH
- Filing Date
- 2023-01-31
- Publication Date
- 2026-06-02
Smart Images
Figure CN116207971B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of switching power supplies, and particularly to auxiliary power supply for switching power supplies and control methods. Background Technology
[0002] Switching power supplies convert input signals into output signals by switching transistors on and off. Typically, a controller is used to control the switching transistors, and this controller requires a DC voltage supply. In AC-DC switching power supply circuits, low-dropout linear regulators and integrated clamping circuits are commonly used to generate the supply voltage signal. Although using low-dropout linear regulators and integrated clamping circuits to generate the supply voltage signal is structurally simple, it results in significant losses, leading to reduced efficiency of the switching power supply.
[0003] The third winding power supply is a circuit scheme that can generate a power supply voltage signal very well. Figure 1 The diagram shows a common switching power supply circuit powered by a third winding. This method has low power loss and high switching power supply efficiency. However, in this scheme, the power supply voltage signal of the third winding can only be established after the output is established. During the initial startup of the switching power supply circuit, a power supply capacitor is required for a period of time. In general applications, a sufficiently large power supply capacitor or starting current is required, and an auxiliary winding of a transformer is also needed. This increases the cost and size of the switching power supply. Summary of the Invention
[0004] Therefore, the technical problem to be solved by the present invention is to provide a switching power supply that can at least partially solve the shortcomings of the above-mentioned prior art.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:
[0006] A switching power supply includes a transformer, a primary side circuit, a secondary side circuit, and a primary side power supply circuit. The primary side circuit includes a switching transistor Q1, the drain of which is coupled to the positive input terminal of the switching power supply, and the source of which is connected to the input ground terminal of the switching power supply. The primary side power supply circuit includes a capacitor C1, a diode D1, a capacitor C2, and a switching transistor Q2. One end of the capacitor C1 serves as the input terminal of the primary side power supply circuit and is connected to the drain of the switching transistor Q1. The other end of the capacitor C1 is connected to both the anode of the diode D1 and one end of the switching transistor Q2. The cathode of the diode D1 and one end of the capacitor C2 are connected together as the output terminal of the primary side power supply circuit. The other end of the switching transistor Q2 and the other end of the capacitor C2 are connected together as the ground terminal of the primary side power supply circuit and are connected to the source of the switching transistor Q1.
[0007] The primary-side power supply circuit operates as follows during each cycle of the switching power supply:
[0008] When the voltage across capacitor C2 is less than a preset threshold voltage, switch Q2 is turned off. When switch Q1 is turned off, capacitors C1 and C2 are charged through the positive input terminal of the primary side of the switching power supply, and a power supply voltage is provided to the output terminal of the primary side power supply circuit. When switch Q1 is turned on, the energy stored in capacitor C2 provides a power supply voltage to the output terminal of the primary side power supply circuit, and capacitor C1 discharges through switch Q2, thus restoring the charging function of capacitor C1.
[0009] When the voltage across capacitor C2 is greater than or equal to the preset threshold voltage, switch Q2 is turned on, and capacitor C2 is bypassed.
[0010] Preferably, the switching transistor Q2 is a diode, with the cathode of the diode being one end of the switching transistor Q2 and the anode of the diode being the other end of the switching transistor Q2.
[0011] Preferably, the switching transistor Q2 is a MOSFET, with the drain of the MOSFET at one end and the source of the MOSFET at the other end. The primary-side power supply circuit further includes a first charging control circuit, which is used to acquire a first voltage characterizing the voltage between the output terminal of the primary-side power supply circuit and its ground terminal, and to control the switching transistor Q2 to turn off when the first voltage is less than or equal to the preset threshold voltage, and to control the switching transistor Q2 to turn on when the first voltage is greater than the preset threshold voltage.
[0012] Furthermore, the first charging control circuit includes a voltage comparator, the non-inverting input of which is connected to one end of the capacitor C2, the inverting input of which is used to input the preset threshold voltage, and the output of which is connected to the gate of the switching transistor Q2.
[0013] Furthermore, the first charging control circuit has a hysteresis comparison function. When the first voltage is less than or equal to the first preset threshold voltage Vth1, the switch Q2 is controlled to turn off. When the first voltage is greater than or equal to the second preset threshold voltage Vth2, the switch Q2 is controlled to turn on. The first preset threshold voltage Vth1 is less than the second preset threshold voltage Vth2.
[0014] Furthermore, the first charging control circuit includes a hysteresis voltage comparator. The non-inverting input of the hysteresis voltage comparator is connected to one end of the capacitor C2, and the inverting input of the hysteresis voltage comparator is used to input the first preset threshold voltage Vth1 and the second preset threshold voltage Vth2. The output of the hysteresis voltage comparator is connected to the gate of the switching transistor Q2.
[0015] Furthermore, the switching power supply also includes a third winding and a diode D3. The anode of the diode D3 is connected to one end of the third winding, the cathode of the diode D3 is connected to the output terminal of the primary-side power supply circuit, and the other end of the third winding is connected to the input ground terminal of the switching power supply. The supply voltage of the third winding is greater than the second preset value V. th2 .
[0016] Furthermore, the switching power supply also includes a third winding and a MOSFET Q4. The source of the MOSFET Q4 is connected to one end of the third winding, the drain of the MOSFET Q4 is connected to the output terminal of the primary side power supply circuit, and the other end of the third winding is connected to the input ground terminal of the switching power supply. The third winding, the MOSFET Q4, and the capacitor C2 form a clamping structure.
[0017] Preferably, the MOS transistor Q4 is configured to be turned on before the switch transistor Q1 is turned on and to remain on for a period of time, so that the capacitor C2 is discharged and a negative magnetizing current is generated.
[0018] Furthermore, the secondary-side rectifier circuit includes a synchronous rectifier MOSFET Q5 and a capacitor C5. One end of the transformer secondary winding is connected to the positive output terminal of the switching power supply, and the other end of the transformer secondary winding is connected to the drain of the MOSFET Q5. The source of the MOSFET Q5 is connected to the output ground terminal of the switching power supply. The capacitor C5 is connected between the positive output terminal and the output ground terminal of the switching power supply. The transformer secondary winding, the MOSFET Q5, and the capacitor C5 form a clamping structure.
[0019] Preferably, the MOS transistor Q5 is configured to be turned on before the switch transistor Q1 is turned on and to remain on for a period of time, so that the capacitor C5 is discharged and a negative magnetizing current is generated.
[0020] Furthermore, the switching power supply also includes a secondary-side power supply circuit, which includes: capacitor C4, diode D3, capacitor C3, MOSFET Q3, and a second charging control circuit. One end of capacitor C4, the source of MOSFET Q3, and the other end of capacitor C3 are connected together to serve as the input and ground of the secondary-side power supply circuit, and are connected to the drain of MOSFET Q5. The other end of capacitor C4 is connected to the anode of diode D3 and the drain of MOSFET Q3. The cathode of diode D3 and one end of capacitor C4 are connected together to serve as the output of the secondary-side power supply circuit. The second charging control circuit is used to acquire a second voltage characterizing the voltage between the output of the secondary-side power supply circuit and its ground. When the second voltage is less than or equal to a preset threshold voltage, the circuit controls MOSFET Q3 to turn off; when the second voltage is greater than the preset threshold voltage, the circuit controls MOSFET Q3 to turn on.
[0021] Compared with the prior art, the present invention has the following technical effects:
[0022] (1) The primary side power supply circuit in the switching power supply provided by the present invention forms a power supply path through the DC blocking capacitor C1 and the diode D1. When the power energy at the positive input terminal of the switching power supply is turned off, it can charge the power supply capacitor C2. Therefore, the primary side power supply circuit provided by the present invention can meet the power supply requirements of the controller before the voltage VCC of the power supply capacitor of the third winding is established, compared with the power supply of the third winding. This allows the capacitance value of the power supply capacitor C2 and the starting current required by the switching power supply circuit to be reduced, thereby reducing the size of the product and improving the reliability of the product.
[0023] (2) When the switching transistor Q2 of the primary side power supply circuit of the switching power supply provided by the present invention is a MOS transistor, the first voltage characterizing the voltage between the output terminal of the primary side power supply circuit and its ground terminal is obtained by the first charging control circuit, and compared with the preset threshold voltage to control the switching state of the switching transistor Q2. The first voltage can be precisely controlled to be the required power supply voltage, and the overvoltage protection function can be realized at the same time. Moreover, the control signal output by the first charging control circuit is completely independent of the drive signal of the main circuit switching transistor Q1, and the control implementation is simple, thereby expanding the application scenarios of the switching power supply circuit provided by the present invention. Attached Figure Description
[0024] Figure 1 A schematic diagram of a switching power supply using a third winding power supply method based on existing technology;
[0025] Figure 2 This is a schematic diagram of a switching power supply according to the first embodiment of the present invention;
[0026] Figure 3 This is a schematic diagram of another switching power supply according to the first embodiment of the present invention;
[0027] Figure 4 for Figure 3 Waveform diagram of the key working process of a switching power supply;
[0028] Figure 5 This is a schematic diagram of a switching power supply according to a second embodiment of the present invention;
[0029] Figure 6 for Figure 5 Waveform diagrams of the key operating processes of a switching power supply;
[0030] Figure 7 This is a schematic diagram of a switching power supply according to a third embodiment of the present invention;
[0031] Figure 8 This is a schematic diagram of a switching power supply according to the fourth embodiment of the present invention. Detailed Implementation
[0032] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention and its beneficial effects will be further described in detail below with reference to specific embodiments and accompanying drawings. However, the specific embodiments of the present invention are not limited thereto. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.
[0033] It should be noted that the terms "comprising" and "having," and any variations thereof, described in the specification and claims of this application, are intended to cover a non-exclusive inclusion. For example, including a series of components, unit circuits, or control timings is not necessarily limited to those explicitly listed, but may include components, unit circuits, or control timings not explicitly listed or inherent to these circuits. Without conflict, the embodiments and features described in this application can be combined with each other.
[0034] Furthermore, the accompanying drawings are merely illustrative of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions thereof will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.
[0035] First Embodiment
[0036] Figure 2 This is a schematic diagram of a switching power supply according to the first embodiment of the present invention; Figure 3This is a schematic diagram of another switching power supply according to the first embodiment of the present invention. Please refer to [link / reference]. Figure 2 and Figure 3 The switching power supply provided in this embodiment includes a transformer T1, a primary side circuit, a secondary side circuit, and a primary side power supply circuit. The primary side circuit includes a switching transistor Q1, the drain of which is coupled to the positive input terminal of the switching power supply, and the source of which is connected to the input ground terminal of the switching power supply. The primary side power supply circuit includes a capacitor C1, a diode D1, a capacitor C2, and a switching transistor Q2. One end of the capacitor C1 serves as the input terminal of the primary side power supply circuit and is connected to the drain of the switching transistor Q1. The other end of the capacitor C1 is simultaneously connected to the diode D1. The anode of the diode D2 and one end of the switching transistor Q2 are connected together, and the cathode of the diode D2 and one end of the capacitor C2 are connected together as the output terminal of the primary side power supply circuit. The other end of the switching transistor Q2 and the other end of the capacitor C2 are connected together as the ground terminal of the primary side power supply circuit, which is connected to the source of the switching transistor Q1. In each cycle of the switching power supply, the primary side power supply circuit operates as follows: When the voltage across the capacitor C2 is less than the preset threshold voltage, the switching transistor Q2 is turned off. When the switching transistor Q1 is turned off, the capacitors C1 and C2 are charged through the positive input terminal of the primary side of the switching power supply, and the power supply voltage is provided to the output terminal of the primary side power supply circuit. When the switching transistor Q1 is turned on, the energy stored in the capacitor C2 provides the power supply voltage to the output terminal of the primary side power supply circuit, and the capacitor C1 is discharged through the switching transistor Q2, so that the capacitor C1 resumes its charging function. When the voltage across the capacitor C2 is greater than or equal to the preset threshold voltage, the switching transistor Q2 is turned on, and the capacitor C2 is bypassed.
[0037] Among them, the drain of the switching transistor Q1 is coupled to the positive input terminal of the switching power supply. The coupling means that it is not a direct connection, but an indirect connection through the primary winding of the transformer T1.
[0038] In this embodiment, the primary-side power supply circuit of the switching power supply forms a power supply path through a DC blocking capacitor C1 and a diode D1. The electrical energy at the positive input terminal of the switching power supply can charge the power supply capacitor C2 when the switching transistor Q1 is turned off. Therefore, the primary-side power supply circuit, compared to the third winding power supply, can meet the power supply requirements of the controller before the voltage VCC of the third winding's power supply capacitor is established. This allows for a reduction in the capacitance of the power supply capacitor and the starting current required by the switching power supply circuit, resulting in a smaller product size and improved product reliability.
[0039] Further, please see Figure 2 In this circuit, the switching transistor Q2 is a diode D2, with the cathode of diode D2 being one end of the switching transistor Q2 and the anode of diode D2 being the other end of the switching transistor Q2.
[0040] Further, please see Figure 3The switching transistor Q2 is a MOSFET, with the drain of the MOSFET being one end of the switching transistor Q2 and the source of the MOSFET being the other end of the switching transistor Q2. The primary-side power supply circuit also includes a first charging control circuit, which is used to obtain a first voltage that characterizes the voltage between the output terminal of the primary-side power supply circuit and its ground terminal. When the first voltage is less than or equal to a preset threshold voltage, the switching transistor Q2 is turned off, and when the first voltage is greater than the preset threshold voltage, the switching transistor Q2 is turned on.
[0041] Figure 3 It also includes diode D2, which can be an independent diode or the body diode of switching transistor Q2.
[0042] Figure 3 When the switching transistor Q2 is off, the electrical energy at the positive input terminal of the switching power supply charges the DC blocking capacitor C1 when the switching transistor Q1 is off, and further charges the power supply capacitor C2 through the first diode D1. When the second switching transistor Q2 is on, the electrical energy at the positive input terminal of the switching power supply charges the DC blocking capacitor C1 only through the switching transistor Q2 when the switching transistor Q1 is off. The diode D1 and the power supply capacitor C2 are bypassed by the switching transistor Q2, and the charging process is stopped.
[0043] Figure 3 The switching transistor Q2 in the primary-side power supply circuit of the switching power supply is a MOSFET. The first charging control circuit obtains a first voltage characterizing the voltage between the output terminal of the primary-side power supply circuit and its ground terminal, and compares it with a preset threshold voltage to control the switching state of the switching transistor Q2. On the one hand, this can meet the power supply requirements of existing controllers before the voltage VCC of the power supply capacitor in the third winding is established, thereby allowing a reduction in the capacitance of the power supply capacitor and the starting current required by the switching power supply circuit, reducing the product size and improving product reliability. On the other hand, it can precisely control the voltage on the power supply capacitor to the required supply voltage, and can also realize overvoltage protection function. In addition, the control signal of the switching transistor Q2 is completely independent of the drive signal of the main circuit switching transistor Q1, and the control implementation is simple, thereby expanding the application scenarios of the switching power supply circuit provided by this invention.
[0044] Preferably, the first charging control circuit includes a voltage comparator, the non-inverting input of the voltage comparator is connected to one end of the capacitor C2, the inverting input of the voltage comparator is used to input a preset threshold voltage, and the output of the voltage comparator is connected to the gate of the switching transistor Q2.
[0045] Furthermore, the first charging control circuit has a hysteresis comparison function. When the first voltage is less than or equal to the first preset threshold voltage Vth1, the control switch Q2 is turned off; when the first voltage is greater than or equal to the second preset threshold voltage Vth2, the control switch Q2 is turned on, and the first preset threshold voltage Vth1 is less than the second preset threshold voltage Vth2. The purpose of the hysteresis comparison function in the first charging control circuit is to maintain the stability of the first voltage, ensuring that the voltage VCC at the output terminal of the primary side power supply circuit will not fall below the controller's undervoltage threshold to trigger undervoltage protection, nor will it exceed the overvoltage threshold to damage the controller.
[0046] Preferably, see continue to see Figure 3 The first charging control circuit includes a hysteresis voltage comparator. The non-inverting input of the hysteresis voltage comparator is connected to one end of capacitor C2. The inverting input of the hysteresis voltage comparator is used to input the first preset threshold voltage Vth1 and the second preset threshold voltage Vth2. The output of the hysteresis voltage comparator is connected to the gate of the switching transistor Q2.
[0047] Figure 4 for Figure 3 Waveform diagrams of the key operating processes of a switching power supply. Figure 4 The meanings of each waveform are as follows:
[0048] Vcc: The power supply voltage of the controller;
[0049] SW1: The driving waveform of the switching transistor Q1, which is turned on when high and turned off when low;
[0050] SW2: The driving waveform of the switching transistor Q2, which is turned on when high and turned off when low;
[0051] W6: The driving waveform of the switching transistor Q6, which is turned on when high and turned off when low;
[0052] Vds: Drain-source voltage of switching transistor Q1.
[0053] The following combination Figure 4 right Figure 3 The operating timing sequence of the switching power supply is explained in detail:
[0054] Based on the operating state of the switching power supply, each charging cycle can be divided into three subdivided time periods.
[0055] During the first time period (t0~t1), the non-inverting input of the hysteresis voltage comparator of the first charging control circuit acquires a first voltage representing the magnitude of the voltage VCC across the power supply capacitor C2 and a first preset threshold voltage V. th1 The circuit compares and outputs a low level, controlling the switch Q2 to turn off. During this period, switch Q1 is in the conducting state, and the entire primary-side power supply circuit is bypassed; therefore, this period is also called the charging preparation state.
[0056] During the second time period (t1~t2), the controller controls the switch Q1 to turn off, and the electrical energy at the positive terminal of the switching power supply input charges the DC blocking capacitor C1, and further charges the power supply capacitor C2 through the diode D1. The voltage VCC across the power supply capacitor C2 begins to rise. This time period is also called the charging state.
[0057] During the third time period (t2~t3), the non-inverting input of the hysteresis voltage comparator of the first charging control circuit acquires a first voltage and a second preset threshold voltage V, which characterize the magnitude of the voltage VCC across the power supply capacitor C2. th2 The circuit compares and outputs a high level, controlling the switch Q2 to turn on. During this period, diode D1 and power supply capacitor C2 are bypassed by the switch Q2, and the power supply energy at the positive terminal of the switching power supply no longer charges the power supply capacitor C2 until the switch Q2 turns on again in the next charging cycle. This period is also known as the charging stop state.
[0058] Please continue reading Figure 2 and Figure 3 In this embodiment, the switching power supply also includes a clamping circuit. The first end of the clamping circuit is coupled to the connection point between one end of the primary winding of transformer T1 and the input terminal of the switching power supply, and the second end of the clamping circuit is coupled to the connection point between the other end of the primary winding of transformer T1 and the drain of switching transistor Q1.
[0059] This embodiment does not limit the specific implementation circuit and control method of the clamping circuit; those skilled in the art can configure it according to actual conditions. For example, see [link to relevant documentation]. Figure 3 The specific circuits and Figure 4 A superior control method is proposed:
[0060] The clamping circuit consists of a clamping capacitor C6 and a clamping MOSFET Q6 connected in series. For the control method of the clamping MOSFET Q6 in the clamping circuit, please refer to [link to relevant documentation]. Figure 4 The waveform diagram SW6 shows that SW6 is on when it is high and off when it is low. For each operating cycle of the switching power supply, the clamping MOSFET is turned on and maintained for a period of time before the switching transistor Q1 is turned on, so that the clamping capacitor is discharged. The clamping circuit will generate a negative magnetizing current. The purpose is to release the energy on the parasitic capacitance of the switching transistor Q1 and the DC blocking capacitor C1, so as to prepare the switching transistor Q1 to achieve zero voltage conduction, thereby enabling the switching power supply circuit to obtain better efficiency.
[0061] Second Embodiment
[0062] This embodiment provides a switching power supply including a third winding. Please refer to [link / reference]. Figure 5 ,and Figure 3The difference lies in that the switching power supply also includes a third winding and a diode D3. The anode of the diode D3 is connected to one end of the third winding, the cathode of the diode D3 is connected to the output terminal of the primary side power supply circuit, and the other end of the third winding is connected to the input ground terminal of the switching power supply.
[0063] See Figure 6 ,for Figure 5 The waveform diagram of the switching power supply circuit. The switching power supply circuit of the second embodiment can decouple the supply voltage output from the primary-side power supply circuit during startup and steady-state operation. Before the supply voltage of the third winding is established, the switching state of the switching transistor Q2 is controlled to supply power to the controller's power supply port. After the supply voltage of the third winding is established, the third winding supplies power to the controller's power supply port. The supply voltage of the third winding should be set to be greater than the second preset value V. th2 In other words, during steady-state operation, the controller keeps the switching transistor Q2 on. This embodiment can further reduce the starting current requirement and the capacitance of the power supply capacitor while taking into account the power supply effect of the controller during both startup and steady-state operation, thereby improving the reliability of the switching power supply and achieving better efficiency.
[0064] Third Embodiment
[0065] The schematic diagram of the switching power supply in this embodiment can be found here. Figure 7 Unlike the first embodiment, in this embodiment, the clamping circuit is combined with the third winding of transformer T1 to form a third winding clamping structure. The auxiliary switch Q4 serves as the clamping transistor, and the power supply capacitor C2 serves as the clamping capacitor. The preferred control method for switch Q4 is as follows: for each operating cycle of the switching power supply, switch Q4 is turned on and maintained for a period of time before switch Q1 is turned on, allowing the power supply capacitor C2 to discharge. After switch Q4 is turned off, the clamping circuit generates a negative magnetizing current in the primary winding of the transformer. The purpose of this is to release the energy on the parasitic capacitance of switch Q1 and the DC blocking capacitor C1, providing the necessary conditions for switch Q1 to achieve zero-voltage conduction, thereby enabling the switching power supply circuit to achieve better efficiency.
[0066] The working principle of this embodiment is the same as that of the first embodiment, and will not be repeated here. The switching power supply circuit of the third embodiment combines the advantages of the switching power supply of the first embodiment and the switching power supply of the second embodiment, and can reduce the number of components, thereby further reducing the size of the product and reducing the product cost.
[0067] Fourth embodiment
[0068] The schematic diagram of the switching power supply in this embodiment can be found here. Figure 8Unlike the first embodiment, in this embodiment, the clamping circuit is combined with the secondary side circuit to form a secondary clamping structure. The synchronous rectifier MOSFET Q5 is used as the clamping transistor, and the output capacitor C5 is used as the clamping capacitor. The preferred control method for the synchronous rectifier Q5 is as follows: for each working cycle of the switching power supply, the synchronous rectifier Q5 is turned on and maintained for a period of time before the switching transistor Q1 is turned on, so that the output capacitor C5 is discharged. After the synchronous rectifier Q5 is turned off, the clamping circuit will generate a negative magnetizing current in the primary winding of the transformer.
[0069] The working principle of this embodiment is the same as that of the first embodiment, and will not be repeated here.
[0070] Furthermore, this embodiment also applies the primary-side power supply circuit scheme to the secondary-side circuit, meaning the switching power supply also includes a secondary-side power supply circuit, thereby providing the required supply voltage Vcc_s for various secondary-side controllers. In situations where the secondary-side circuit of the switching power supply requires power, such as powering a synchronous rectifier controller, those skilled in the art typically use a method of directly drawing power from the output voltage or supplying power to the synchronous rectifier controller via a voltage divider resistor. This increases the losses in the switching power supply circuit and is not conducive to achieving better system efficiency.
[0071] The secondary power supply circuit in this embodiment includes: capacitor C4, diode D3, capacitor C3, MOSFET Q3, and a second charging control circuit. One end of capacitor C4 serves as the input terminal of the secondary power supply circuit and is connected to the drain of MOSFET Q5. The other end of capacitor C4 is connected to both the anode of diode D3 and the drain of MOSFET Q3. The cathode of diode D3 and one end of capacitor C3 are connected together as the output terminal of the secondary power supply circuit. The source of MOSFET Q3 and the other end of capacitor C3 are connected together as the ground terminal of the secondary power supply circuit and connected to the source of MOSFET Q5. The second charging control circuit is used to obtain a second voltage that characterizes the voltage between the output terminal of the secondary power supply circuit and its ground terminal. When the second voltage is less than or equal to a preset threshold voltage, the circuit controls MOSFET Q3 to turn off. When the second voltage is greater than the preset threshold voltage, the circuit controls MOSFET Q3 to turn on.
[0072] It should be understood that although specific embodiments of the invention have been described to aid in a better understanding of the invention, other equivalent embodiments exist. Unless otherwise specified, the embodiments and features described in this application can be combined with each other. The above embodiments are given by way of illustration rather than limitation; therefore, any modifications or substitutions to all or part of the technical features of the technical solutions described in the embodiments without departing from the spirit or essence of the invention should be considered as covered within the scope of the claims.
Claims
1. A switching power supply, characterized in that: The system includes a transformer, a primary side circuit, a secondary side circuit, and a primary side power supply circuit. The primary side circuit includes a switching transistor Q1, the drain of which is coupled to the positive input terminal of the switching power supply, and the source of which is connected to the input ground terminal of the switching power supply. The primary side power supply circuit includes a capacitor C1, a diode D1, a capacitor C2, and a switching transistor Q2. One end of the capacitor C1 serves as the input terminal of the primary side power supply circuit and is connected to the drain of the switching transistor Q1. The other end of the capacitor C1 is connected to both the anode of the diode D1 and one end of the switching transistor Q2. The cathode of the diode D1 and one end of the capacitor C2 are connected together as the output terminal of the primary side power supply circuit. The other end of the switching transistor Q2 and the other end of the capacitor C2 are connected together as the ground terminal of the primary side power supply circuit and are connected to the source of the switching transistor Q1. The primary-side power supply circuit operates as follows during each cycle of the switching power supply: When the voltage across capacitor C2 is less than a preset threshold voltage, switch Q2 is turned off. When switch Q1 is turned off, capacitors C1 and C2 are charged through the positive input terminal of the primary side of the switching power supply, and a power supply voltage is provided to the output terminal of the primary side power supply circuit. When switch Q1 is turned on, the energy stored in capacitor C2 provides a power supply voltage to the output terminal of the primary side power supply circuit, and capacitor C1 discharges through switch Q2, thus restoring the charging function of capacitor C1. When the voltage across capacitor C2 is greater than or equal to the preset threshold voltage, switch Q2 is turned on, and capacitor C2 is bypassed. The switching transistor Q2 is a MOSFET, with the drain of the MOSFET at one end and the source of the MOSFET at the other end. The primary-side power supply circuit further includes a first charging control circuit, which is used to acquire a first voltage characterizing the voltage between the output terminal of the primary-side power supply circuit and its ground terminal. When the first voltage is less than or equal to the preset threshold voltage, the circuit controls the switching transistor Q2 to turn off, and when the first voltage is greater than the preset threshold voltage, the circuit controls the switching transistor Q2 to turn on.
2. The switching power supply according to claim 1, characterized in that: The first charging control circuit includes a voltage comparator. The non-inverting input of the voltage comparator is connected to one end of the capacitor C2, the inverting input of the voltage comparator is used to input the preset threshold voltage, and the output of the voltage comparator is connected to the gate of the switching transistor Q2.
3. The switching power supply according to claim 1, characterized in that: The first charging control circuit has a hysteresis comparison function. When the first voltage is less than or equal to the first preset threshold voltage Vth1, the switch Q2 is controlled to turn off. When the first voltage is greater than or equal to the second preset threshold voltage Vth2, the switch Q2 is controlled to turn on. The first preset threshold voltage Vth1 is less than the second preset threshold voltage Vth2.
4. The switching power supply according to claim 3, characterized in that: The first charging control circuit includes a hysteresis voltage comparator. The non-inverting input of the hysteresis voltage comparator is connected to one end of the capacitor C2. The inverting input of the hysteresis voltage comparator is used to input the first preset threshold voltage Vth1 and the second preset threshold voltage Vth2. The output of the hysteresis voltage comparator is connected to the gate of the switching transistor Q2.
5. The switching power supply according to claim 3, characterized in that: The switching power supply also includes a third winding and a diode D3. The anode of the diode D3 is connected to one end of the third winding, and the cathode of the diode D3 is connected to the output terminal of the primary-side power supply circuit. The other end of the third winding is connected to the input ground terminal of the switching power supply. The supply voltage of the third winding is greater than the second preset value V. th2 .
6. The switching power supply according to claim 3, characterized in that: The switching power supply also includes a third winding and a MOSFET Q4. The source of the MOSFET Q4 is connected to one end of the third winding, and the drain of the MOSFET Q4 is connected to the output terminal of the primary side power supply circuit. The other end of the third winding is connected to the input ground terminal of the switching power supply. The third winding, the MOSFET Q4, and the capacitor C2 form a clamping structure.
7. The switching power supply according to claim 6, characterized in that: The MOS transistor Q4 is configured to be turned on before the switch transistor Q1 is turned on and to remain on for a period of time, so that the capacitor C2 is discharged and a negative magnetizing current is generated.
8. The switching power supply according to any one of claims 1 to 7, characterized in that: The secondary-side rectifier circuit includes a synchronous rectifier MOSFET Q5 and a capacitor C5. One end of the transformer secondary winding is connected to the positive output terminal of the switching power supply, and the other end of the transformer secondary winding is connected to the drain of the MOSFET Q5. The source of the MOSFET Q5 is connected to the output ground terminal of the switching power supply. The capacitor C5 is connected between the positive output terminal and the output ground terminal of the switching power supply. The transformer secondary winding, the MOSFET Q5, and the capacitor C5 form a clamping structure.
9. The switching power supply according to claim 8, characterized in that: The MOS transistor Q5 is configured to be turned on before the switch transistor Q1 is turned on and to remain on for a period of time, so that the capacitor C5 is discharged and a negative magnetizing current is generated.
10. The switching power supply according to claim 9, characterized in that, The switching power supply further includes a secondary-side power supply circuit, which includes: capacitor C4, diode D3, capacitor C3, MOSFET Q3, and a second charging control circuit. One end of capacitor C4, the source of MOSFET Q3, and the other end of capacitor C3 are connected together to serve as the input and ground of the secondary-side power supply circuit, and are connected to the drain of MOSFET Q5. The other end of capacitor C4 is connected to the anode of diode D3 and the drain of MOSFET Q3. The cathode of diode D3 and one end of capacitor C4 are connected together to serve as the output of the secondary-side power supply circuit. The second charging control circuit is used to acquire a second voltage characterizing the voltage between the output of the secondary-side power supply circuit and its ground. When the second voltage is less than or equal to a preset threshold voltage, the circuit controls MOSFET Q3 to turn off; when the second voltage is greater than the preset threshold voltage, the circuit controls MOSFET Q3 to turn on.