Switching power supply and control method thereof

Abstract

The application discloses a switching power supply and a control method thereof, and one embodiment comprises a transformer, a first switch tube, a second switch tube, a first resistor, a first diode, a first capacitor, a control device and a secondary side loop. The control device controls the switching state of the second switch tube by comparing the supply voltage Vcc with a preset value, which can ensure that enough supply voltage signal is established when the switching power supply circuit is just started, reduce the starting time of the switching power supply, simplify the structure of the power supply circuit, allow the capacitance value and starting current of the power supply capacitor to be reduced, and be beneficial to reducing the loss of the starting circuit; on the other hand, the working time sequence of the second switch tube is independent of the first switch tube, the control is simpler, the cost of the switching power supply is lower, and the integrability is higher.

Description

Technical Field

[0001] This invention relates to the field of switching power supplies, and in particular to a switching power supply and its control method. Background Technology

[0002] Switching power supply circuits convert input signals into output signals by turning on and off transistors. Typically, a control device is used to control the switching on and off of the transistors, and this control device requires a DC power supply. In switching power supply circuits, low-dropout linear regulators, integrated clamping circuits, and third windings are commonly used to generate the supply voltage signal. While using low-dropout linear regulators and integrated clamping circuits to generate the supply voltage signal is structurally simple, it suffers from significant losses, leading to reduced efficiency. While generating the supply voltage signal through a third winding has lower losses, the supply voltage signal from the third winding requires a period of time to establish during initial startup, placing higher demands on the power supply circuit.

[0003] like Figure 1 The diagram shows a prior art switching power supply circuit that utilizes a third winding to generate a supply voltage signal. The circuit includes a transformer, a first switching transistor, a first diode, a first capacitor, a control device, and a secondary circuit. The voltage across the first capacitor is the supply voltage Vcc of the control device. When the switching power supply circuit starts up, the input voltage charges the first capacitor through an additional startup circuit. Once Vcc increases sufficiently to enable the control device to operate, the third winding of the transformer supplies power to the control device through the first diode. To ensure the control device can maintain normal operation before the supply voltage signal from the third winding is established, a sufficiently large starting current or a sufficiently large capacitance of the first capacitor is typically required. However, increasing the starting current increases the power consumed by the startup circuit, leading to a decrease in the efficiency of the switching power supply. Increasing the capacitance of the first capacitor results in a longer startup time for the switching power supply, while also increasing the cost and size of the power supply. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a switching power supply and its control method, which generates the power supply voltage required by the control device and establishes a sufficient power supply voltage signal when the switching power supply is started, thereby reducing the startup time of the switching power supply, and also reducing the startup current and power supply capacitor value of the switching power supply, thereby reducing product cost and product size.

[0005] The technical solution adopted in this invention is as follows:

[0006] In a first aspect, a switching power supply is provided, comprising: a transformer, a first switching transistor, a first resistor, a control device, a power supply circuit, and a secondary side circuit; the power supply circuit includes a second switching transistor and a power supply branch.

[0007] The first end of the primary winding of the transformer serves as the positive input terminal of the switching power supply, and the secondary winding is connected to the secondary side circuit.

[0008] The output terminal of the secondary side circuit serves as the output terminal of the switching power supply for connection to the load.

[0009] The first end of the first switching transistor is electrically connected to the second end of the primary winding of the transformer, the second end of the first switching transistor is electrically connected to the first control end of the control device, and the third end of the first switching transistor is electrically connected to the first end of the second switching transistor and the first end of the power supply branch.

[0010] The second terminal of the second switching transistor is electrically connected to the second control terminal of the control device, and the third terminal of the second switching transistor is electrically connected to the first terminal of the first resistor and the third terminal of the power supply branch.

[0011] The second terminal of the first resistor is grounded;

[0012] The second end of the power supply circuit and the power supply branch is electrically connected to the power supply voltage terminal of the control device.

[0013] When the control device determines that the supply voltage VCC at the supply voltage terminal is less than the first preset value V th1 At that time, the second switch is turned off;

[0014] When the control device determines that the supply voltage VCC at the supply voltage terminal is greater than or equal to the first preset value V th2 When the second switch is turned on, it controls the second switch to conduct.

[0015] Preferably, the third end of the power supply branch is also connected to the ground terminal of the control device; the power supply branch includes a first capacitor and a first diode; the anode of the first diode serves as the first end of the power supply branch; the cathode of the first diode is connected to the first end of the first capacitor and serves as the second end of the power supply branch; the second end of the first capacitor serves as the third end of the power supply branch.

[0016] Preferably, the switching power supply further includes a second diode, and the transformer has a third winding; the third winding is located on the primary side of the transformer, the first end of the third winding is grounded, and the second end is connected to the anode of the second diode; the cathode of the second diode is connected to the cathode of the first diode and the first end of the first capacitor.

[0017] Preferably, the power supply branch further includes a fourth terminal, which is connected to the ground terminal of the control device; the power supply branch includes a first capacitor, a first diode, a second resistor, and a second capacitor; the anode of the first diode serves as the first terminal of the power supply branch; the cathode of the first diode is connected to the first terminal of the first capacitor and the first terminal of the second resistor; the second terminal of the second resistor is connected to the first terminal of the second capacitor, serving as the second terminal of the power supply branch; the second terminal of the second capacitor serves as the fourth terminal of the power supply branch; and the second terminal of the first capacitor serves as the third terminal of the power supply branch.

[0018] Preferably, the resistance value of the second resistor is a predetermined multiple of the resistance value of the first resistor, wherein the predetermined multiple is greater than 10.

[0019] Preferably, it further includes a clamping circuit, wherein a first end of the clamping circuit is connected to a first end of the primary winding, and a second end is connected to a second end of the primary winding and a first end of the first switching transistor.

[0020] Preferably, the clamping circuit is a passive clamping circuit or an active clamping circuit.

[0021] Preferably, the first switching transistor and / or the second switching transistor are MOS transistors, with the first terminal of the first switching transistor and the second switching transistor being the drain, the second terminal being the gate, and the third terminal being the source.

[0022] Secondly, a control method for a switching power supply is provided, including:

[0023] In the second switch turn-off step, when the control device determines that the supply voltage VCC at the supply voltage terminal is less than the first preset value V... th1 When the first switch is turned on, the second switch is turned off so that the electrical energy at the positive input terminal of the switching power supply is charged and stored in the power supply branch when the first switch is turned on.

[0024] In the second switch-on step, when the control device determines that the supply voltage VCC at the supply voltage terminal is greater than or equal to the first preset value V... th2 When the first switch is turned on, the second switch is controlled to be turned on so that when the first switch is turned on, the switching power supply excites the primary winding of the transformer through the first switch and the second switch, and when the first switch is turned off, the energy stored in the primary winding of the transformer is transferred to the secondary circuit.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] This invention controls the switching state of the second switching transistor by comparing the supply voltage Vcc with a preset value. On one hand, it ensures a sufficient supply voltage signal is established when the switching power supply circuit starts up, reducing the power supply startup time, simplifying the power supply circuit structure, allowing for a reduction in the capacitance of the supply capacitor and the startup current, which helps reduce losses in the startup circuit, resulting in a lower cost and smaller size for the switching power supply. On the other hand, in the power supply circuit of this invention, the charging current supplied to Vcc by the input voltage through the first switching transistor and the first diode flows entirely or mostly through the first resistor, without affecting the sampling of the peak current of the power stage, facilitating precise control of the output constant current and output overcurrent protection. Furthermore, the operating timing of the second switching transistor in the switching power supply circuit using this invention is independent of that of the first switching transistor, making control implementation simpler and allowing for higher integration. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a switching power supply using a third winding power supply method based on existing technology.

[0028] Figure 2 The schematic diagram shows the switching power supply using the first embodiment of the present invention.

[0029] Figure 3 The waveform diagram shows the key operating process of the switching power supply provided in the first embodiment.

[0030] Figure 4 The schematic diagram shows the switching power supply according to the second embodiment of the present invention.

[0031] Figure 5 Another schematic diagram of a switching power supply applying the second embodiment of the present invention.

[0032] Figure 6 The schematic diagram of the switching power supply according to the third embodiment of the present invention.

[0033] Figure 7 Waveform diagram of the key operating process of the switching power supply provided in the third embodiment. Detailed Implementation

[0034] 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.

[0035] 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.

[0036] 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.

[0037] First Embodiment

[0038] Please see Figure 2 This is a schematic diagram of a switching power supply applying a first embodiment of the present invention. In this embodiment, a switching power supply is provided, comprising: a transformer T1, a first switching transistor Q1, a first resistor R1, a control device, a power supply circuit, and a secondary side circuit. The power supply circuit includes a first diode D1, a second switching transistor Q2, a second resistor R2, a first capacitor C1, and a second capacitor C2.

[0039] The first terminal of the first switch Q1 is electrically connected to the second terminal of the primary winding of the transformer T1, the second terminal of the first switch Q1 is electrically connected to the first control terminal of the control device, and the third terminal of the first switch Q1 is electrically connected to the first terminal of the second switch Q2 and the anode of the first diode D1.

[0040] The second terminal of the second switch Q2 is electrically connected to the second control terminal of the control device, and the third terminal of the second switch Q2 is electrically connected to the first terminal of the first resistor R1 and the second terminal of the first capacitor C1.

[0041] The cathode of the first diode D1 is electrically connected to the first terminal of the first capacitor C1 and the first terminal of the second resistor R2;

[0042] The second end of the second resistor R2 is electrically connected to the first end of the second capacitor C1, and the second end of the second resistor R2 is also electrically connected to the power supply voltage terminal Vcc.

[0043] The second end of the first resistor R1 is electrically connected to the second end of the second capacitor C2. The second end of the first resistor R1 is electrically connected to the input ground of the switching power supply and is the reference ground GND of the control device.

[0044] In this embodiment, the switching power supply further includes a clamping circuit. The first end of the clamping circuit is electrically connected to the first end of the primary winding of the transformer T1 and the positive input terminal Vin of the switching power supply. The second end of the clamping circuit is electrically connected to the second end of the primary winding of the transformer T1 and the first end of the first switching transistor Q1.

[0045] In this embodiment, the resistance value of the second resistor R2 is a predetermined multiple of the resistance value of the first resistor R1, and the predetermined multiple is greater than 10.

[0046] Specifically, the first control terminal of the control device outputs a first control signal SW1 to control the first switch Q1 to turn on or off, and the second control terminal of the control device outputs a second control signal SW2 to control the second switch Q2 to turn on or off. The first switch Q1 and the second switch Q2 can both be MOSFETs, or other devices capable of performing the same switching function; in specific implementations, both the first switch Q1 and the second switch Q2 are NMOS enhancement-mode field-effect transistors, with the first terminal being the drain, the second terminal being the gate, and the third terminal being the source.

[0047] Specifically, the secondary side circuit described in this embodiment can be Figure 1 The secondary circuit shown can also be as follows: Figure 2 The secondary side circuit shown is not restricted here.

[0048] In conjunction with the above-described switching power supply, this embodiment provides a control method for a switching power supply, comprising the following steps:

[0049] The second switch Q2 is turned off when the control device obtains that the supply voltage Vcc is less than the first preset value V. th1 When the first switch Q1 is turned on, the second switch Q2 is turned off so that when the first switch Q1 is turned on, the electrical energy at the positive input terminal Vin of the switching power supply charges the first capacitor C1 through the first switch Q1 and the first diode D1, and continues to charge the second capacitor C2 through the second resistor R2.

[0050] In the second switch Q2 conduction step, when the control device obtains that the supply voltage Vcc is greater than the second preset value V... th2When the first switch Q1 is turned on, the second switch Q2 is turned on so that the input voltage Vin of the switching power supply is used to excite the primary winding of the transformer T1 through the first switch Q1 and the second switch Q2 when the first switch Q1 is turned on. When the first switch Q1 is turned off, the energy stored in the primary winding of the transformer T1 is transferred to the secondary circuit.

[0051] This embodiment controls the switching state of the second switching transistor by comparing the supply voltage Vcc with a preset value. On the one hand, this ensures a sufficient supply voltage signal is established when the switching power supply circuit starts up, reducing the power supply startup time, simplifying the power supply circuit structure, allowing for a reduction in the capacitance of the supply capacitor and the startup current, which helps reduce losses in the startup circuit, resulting in a lower cost and smaller size for the switching power supply. On the other hand, since the resistance of the second resistor R2 is much larger than that of the first resistor R1, the charging current supplied to Vcc by the input voltage through the first switching transistor and the first diode in the power supply circuit of this invention will flow entirely or mostly through the first resistor, without affecting the sampling of the peak current of the power stage, facilitating precise control of the output constant current and output overcurrent protection. Furthermore, the operating timing of the second switching transistor in the switching power supply circuit using this invention is independent of that of the first switching transistor, making control implementation simpler and allowing for higher integration.

[0052] refer to Figure 3 The following is a waveform diagram of the switching power supply in this embodiment. Figure 3 The control method of this embodiment will be described in detail below:

[0053] Based on the operating state of the switching power supply, each charging cycle of the supply voltage Vcc can be divided into three subdivided time periods.

[0054] During the first time period (t0~t1), the second switch Q2 is off, and the first switch Q1 is on. The electrical energy at the positive input terminal Vin of the switching power supply excites the primary winding of the transformer T1, while simultaneously charging the first capacitor C1 through the first switch Q1 and the first diode D1 with a first current value, and continuing to charge the second capacitor C2 through the second resistor R2 with a second current value. During this time period, the switching power supply operates in a charging state. Since the resistance of the second resistor R2 is much greater than that of the first resistor R1, the first current value is much greater than the second current value. Therefore, detecting the first current value during this time period will not significantly affect the sampling of the peak current of the power stage.

[0055] During the second time period (t1~t2), the control device obtains that the supply voltage Vcc is greater than or equal to the second preset value V. th2The second switch Q2 is turned on. When the first switch Q1 is turned on, the electrical energy at the positive input terminal Vin of the switching power supply further excites the primary winding of transformer T1 through the first switch Q1 and the second switch Q2; when the first switch Q1 is turned off, the energy stored in the primary winding of transformer T1 is transferred to the secondary circuit. During this period, the operating state of the switching power supply is consistent with that of a normal flyback circuit.

[0056] During the third time period (t2~t3), the control device obtains that the supply voltage Vcc is less than the first preset value V. th1 The second switch Q2 is turned off, preparing for the charging process in the next switching cycle. During this period, the first switch Q1 is not yet turned on, and the electrical energy at the positive input terminal Vin of the switching power supply cannot charge the second capacitor C2. The switching power supply is in a pre-charging state until the first switch Q1 is turned on in the next cycle.

[0057] Wherein, Vcc: the power supply voltage of the control device;

[0058] SW1: The driving waveform of the first switching transistor Q1, which is turned on when high and turned off when low;

[0059] SW2: The driving waveform of the second switch Q2, which is turned on when high and turned off when low.

[0060] Second Embodiment

[0061] Please see Figure 4 This is a schematic diagram of a switching power supply applying a second embodiment of the present invention. Unlike the first embodiment, in this embodiment, the power supply circuit includes a first diode D1 and a first capacitor C1.

[0062] The first terminal of the first switch Q1 is electrically connected to the second terminal of the primary winding of the transformer T1, the second terminal of the first switch Q1 is electrically connected to the first control terminal of the control device, and the third terminal of the first switch Q1 is electrically connected to the first terminal of the second switch Q2 and the anode of the first diode D1.

[0063] The second terminal of the second switch Q2 is electrically connected to the second control terminal of the control device, the third terminal of the second switch Q2 is electrically connected to the first terminal of the first resistor R1 and the second terminal of the first capacitor C1, and the third terminal of the second switch Q2 is also connected to the reference ground GNDA of the control device.

[0064] The cathode of the first diode D1 is electrically connected to the first terminal of the first capacitor C1, and the cathode of the first diode D1 is also electrically connected to the power supply voltage terminal Vcc.

[0065] The second end of the first resistor R1 is electrically connected to the input ground of the switching power supply;

[0066] Figure 4 The circuit shown differs from the first embodiment in that, Figure 4 In the first embodiment, the reference ground of the control device is electrically connected to the first end of the first resistor R1, while in the second embodiment, the reference ground of the control device is electrically connected to the second end of the first resistor R1 and the input ground of the switching power supply. The working principle of both is the same, and will not be described again here.

[0067] The Vcc charging current of the switching power supply using the power supply circuit of the second embodiment of the present invention will all flow through the first resistor R1, thus enabling accurate sampling of the peak current of the power stage; at the same time, it can further simplify the power supply circuit structure, making the switching power supply cheaper and more integrable.

[0068] Third Embodiment

[0069] This embodiment provides a switching power supply including a third winding. Please refer to [link / reference]. Figure 6 The second embodiment includes a first switching transistor Q1, a first resistor R1, a first diode D1, a first capacitor C1, a control device, a power supply circuit, a clamping circuit, and a secondary side circuit, as well as a second diode D2 and a transformer T1 including a third winding. The same-name terminal of the third winding is connected to the reference ground GNDA of the control device, the opposite-name terminal of the third winding is electrically connected to the anode of the second diode D2, and the cathode of the second diode D2 is electrically connected to the cathode of the first diode D1.

[0070] refer to Figure 7 The image shows the operating waveform of the switching power supply circuit using this embodiment. The switching power supply circuit using the third embodiment of this invention can achieve decoupling of the Vcc power supply during startup and steady-state operation. The power supply voltage signal V of the third winding... th3 Prior to this, the control device's power supply voltage Vcc is supplied by controlling the switching state of the second switching transistor, and the power supply voltage signal V of the third winding is... th3 After establishment, the control device is powered by the third winding using the supply voltage Vcc. The supply voltage signal V of the third winding... th3 Greater than the second preset value V th2 The control device controls the second switching transistor to remain on. This embodiment can further reduce the starting current requirement and the capacitance value of the power supply capacitor while taking into account the Vcc power supply effect during both the startup process and steady-state operation, thereby improving the reliability of the switching power supply and achieving better efficiency.

[0071] 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, include: The system includes a transformer, a first switching transistor, a first resistor, a control device, a power supply circuit, and a secondary side circuit; the power supply circuit includes a second switching transistor and a power supply branch. The first end of the primary winding of the transformer serves as the positive input terminal of the switching power supply, and the secondary winding is connected to the secondary side circuit. The output terminal of the secondary side circuit serves as the output terminal of the switching power supply for connection to the load. The first end of the first switching transistor is electrically connected to the second end of the primary winding of the transformer, the second end of the first switching transistor is electrically connected to the first control end of the control device, and the third end of the first switching transistor is electrically connected to the first end of the second switching transistor and the first end of the power supply branch. The second terminal of the second switching transistor is electrically connected to the second control terminal of the control device, and the third terminal of the second switching transistor is electrically connected to the first terminal of the first resistor and the third terminal of the power supply branch. The second terminal of the first resistor is grounded; The power supply circuit and the second terminal of the power supply branch are electrically connected to the power supply voltage terminal of the control device; The power supply branch also includes a fourth terminal, which is connected to the ground terminal of the control device; the power supply branch includes a first capacitor, a first diode, a second resistor, and a second capacitor; the anode of the first diode serves as the first terminal of the power supply branch; the cathode of the first diode is connected to the first terminal of the first capacitor and the first terminal of the second resistor; the second terminal of the second resistor is connected to the first terminal of the second capacitor, thus serving as the second terminal of the power supply branch; the second terminal of the second capacitor serves as the fourth terminal of the power supply branch; and the second terminal of the first capacitor serves as the third terminal of the power supply branch. When the control device determines that the supply voltage VCC at the supply voltage terminal is less than the first preset value Vth1, it controls the second switch to turn off. When the control device determines that the power supply voltage VCC at the power supply voltage terminal is greater than or equal to the first preset value Vth2, it controls the second switch to turn on.

2. A switching power supply, characterized in that, include: The system includes a transformer, a first switching transistor, a first resistor, a control device, a power supply circuit, and a secondary side circuit; the power supply circuit includes a second switching transistor and a power supply branch. The first end of the primary winding of the transformer serves as the positive input terminal of the switching power supply, and the secondary winding is connected to the secondary side circuit. The output terminal of the secondary side circuit serves as the output terminal of the switching power supply for connection to the load. The first end of the first switching transistor is electrically connected to the second end of the primary winding of the transformer, the second end of the first switching transistor is electrically connected to the first control end of the control device, and the third end of the first switching transistor is electrically connected to the first end of the second switching transistor and the first end of the power supply branch. The second terminal of the second switching transistor is electrically connected to the second control terminal of the control device, and the third terminal of the second switching transistor is electrically connected to the first terminal of the first resistor and the third terminal of the power supply branch. The second terminal of the first resistor is grounded; The power supply circuit and the second terminal of the power supply branch are electrically connected to the power supply voltage terminal of the control device; The third end of the power supply branch is also connected to the ground terminal of the control device; the power supply branch includes a first capacitor and a first diode; the anode of the first diode serves as the first end of the power supply branch; the cathode of the first diode is connected to the first end of the first capacitor and serves as the second end of the power supply branch; the second end of the first capacitor serves as the third end of the power supply branch. When the control device determines that the supply voltage VCC at the supply voltage terminal is less than the first preset value Vth1, it controls the second switch to turn off. When the control device determines that the power supply voltage VCC at the power supply voltage terminal is greater than or equal to the first preset value Vth2, it controls the second switch to turn on.

3. The switching power supply according to claim 2, characterized in that, The switching power supply also includes a second diode, and the transformer has a third winding; the third winding is located on the primary side of the transformer, the first end of the third winding is grounded, and the second end is connected to the anode of the second diode; the cathode of the second diode is connected to the cathode of the first diode and the first end of the first capacitor.

4. The switching power supply according to any one of claims 1-2, characterized in that, The resistance value of the second resistor is a predetermined multiple of the resistance value of the first resistor, wherein the predetermined multiple is greater than 10.

5. The switching power supply according to any one of claims 1-4, characterized in that, It also includes a clamping circuit, the first end of which is connected to the first end of the primary winding, and the second end of which is connected to the second end of the primary winding and the first end of the first switching transistor.

6. The switching power supply according to claim 5, characterized in that, The clamping circuit is either a passive clamping circuit or an active clamping circuit.

7. The switching power supply according to any one of claims 1-4, wherein the first switching transistor and / or the second switching transistor is a MOSFET, wherein the first terminal of the first switching transistor and the second switching transistor are both drains, the second terminal of both switching transistors are both gates, and the third terminal of both switching transistors are both sources.

8. A control method for a switching power supply according to any one of claims 1-7, characterized in that, include: In the second switch-off step, when the control device determines that the power supply voltage VCC at the power supply voltage terminal is less than the first preset value Vth1, it controls the second switch-off to ensure that the power supply branch charges and stores energy when the first switch-off is turned on. In the second switch-on step, when the control device determines that the supply voltage VCC at the supply voltage terminal is greater than or equal to the first preset value Vth2, it controls the second switch-on to be turned on, so that when the first switch-on is turned on, the switching power supply excites the primary winding of the transformer through the first switch-on and the second switch-on, and when the first switch-on is turned off, it transfers the energy stored in the primary winding of the transformer to the secondary side circuit.

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