A switching power supply

Abstract

The application discloses a switching power supply, comprising a transformer, a primary side loop, a secondary side loop and a primary side power supply circuit, wherein the primary side loop is a half-bridge resonant circuit, the primary side power supply circuit comprises a first capacitor, a first diode, a second capacitor and a third switch tube, one end of the second capacitor is an input end of the power supply circuit, the other end of the transformer primary winding is connected to the other end of the second capacitor, the other end of the second capacitor is connected to the anode of the first diode and one end of the third switch tube, the cathode of the first diode and one end of the first capacitor are connected together to serve as an output end of the power supply circuit, the other end of the third switch tube and the other end of the first capacitor are connected together to serve as a grounding end of the power supply circuit, and the source of a second switch tube is connected; the third switch tube is configured to be turned off when the voltage across the first capacitor is less than or equal to a preset threshold voltage and to be turned on when the voltage across the first capacitor is greater than the preset threshold voltage. The switching power supply has the advantages of lower cost, smaller size, simpler control and higher integration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a switching power supply. BACKGROUND

[0002] The switching power supply circuit converts input signal into output signal by switching on and off of the switching tube. Generally, the switching power supply circuit uses a control device to control the switching on and off of the switching tube, and the control device needs DC voltage for power supply. In the switching power supply circuit, low dropout linear regulator, integrated clamping circuit and other ways are often used to generate the power supply voltage signal. Although the structure of generating the power supply voltage signal by using low dropout linear regulator and integrated clamping circuit is simple, the loss is large, which leads to the reduction of switching power supply efficiency.

[0003] The third winding power supply is a circuit scheme which can well generate the power supply voltage signal. Taking the asymmetric half-bridge flyback transformer circuit as an example, as shown in the figure Figure 1 The figure is a common circuit using the third winding power supply scheme, including a transformer, a switching tube Q1, a switching tube Q2, a diode D1, a capacitor C1, a capacitor C2, a control device and a secondary side loop, wherein the voltage across the capacitor C2 is the power supply voltage Vcc of the control device. This power supply method has small power loss and high switching power supply efficiency. However, the power supply voltage signal of the third winding needs to be established after the output voltage is established, so an additional starting circuit is needed to charge the power supply capacitor C2 when the switching power supply circuit is just started, and the power supply capacitor C2 needs to maintain power supply for a period of time, so the starting current is generally required to be large enough or the capacitance value of the power supply capacitor C2 is required to be large enough. Moreover, the third winding power supply scheme needs to increase an auxiliary winding of the transformer, which will increase the cost and the volume of the switching power supply.

[0004] In addition, in the product with constant current function, if the constant current voltage is low, the third winding power supply cannot provide sufficient power supply voltage during the constant current process. In this case, the forward and flyback power supply is usually needed, and the power supply circuit is more complex and has high cost, so it is necessary to optimize and improve the power supply circuit of the switching power supply. SUMMARY

[0005] Therefore, the present application aims to solve the technical problem of providing a switching power supply which can at least solve the above technical problems to some extent.

[0006] The technical scheme adopted by the embodiments of the present application is as follows:

[0007] A switching power supply comprises a transformer, a primary side circuit, a secondary side circuit and a primary side power supply circuit, the primary side circuit is a half-bridge resonant circuit, the half-bridge resonant circuit comprises a first switch tube Q1 and a second switch tube Q2 in a bridge arm, the drain of the first switch tube Q1 is connected to the input positive terminal of the switching power supply, the connection point of the source of the first switch tube Q1 and the drain of the second switch tube Q2 is coupled to one end of the primary winding of the transformer, and the source of the second switch tube Q2 is coupled to the other end of the primary winding of the transformer and the primary input ground terminal of the switching power supply; the primary side power supply circuit comprises a first capacitor, a first diode, a second capacitor and a third switch tube, one end of the second capacitor is connected to the other end of the primary winding of the transformer as the input terminal of the power supply circuit, the other end of the second capacitor is connected to the anode of the first diode and one end of the third switch tube, the cathode of the first diode and one end of the first capacitor are connected together as the output terminal of the power supply circuit, the other end of the third switch tube and the other end of the first capacitor are connected together as the ground terminal of the power supply circuit and are connected to the source of the second switch tube Q2; the third switch tube is configured to be turned off when the voltage across the first capacitor is less than or equal to a preset threshold voltage, and to be turned on when the voltage across the first capacitor is greater than the preset threshold voltage.

[0008] Further, the third switch tube is configured to have a hysteresis between the on and off states, i.e., to be turned off when the voltage across the first capacitor is less than or equal to a first preset threshold voltage Vth1, and to be turned on when the voltage across the first capacitor is greater than or equal to a second preset threshold voltage Vth2, the first preset threshold voltage Vth1 being less than the second preset threshold voltage Vth2.

[0009] Further, the switching power supply further comprises a third winding and a diode D4, the anode of the diode D4 is connected to one end of the third winding, the cathode of the diode D4 is connected to the output terminal of the power supply circuit, the other end of the third winding is connected to the primary input ground terminal of the switching power supply, and the power supply voltage of the third winding is greater than the second preset value Vth2. th2 .

[0010] Further, the first capacitor is a resonant capacitor in the half-bridge resonant circuit.

[0011] Further, the primary side circuit is a half-bridge LLC resonant circuit.

[0012] Further, the first capacitor is a resonant capacitor in the half-bridge LLC resonant circuit.

[0013] Preferably, the third switch tube is a MOS tube.

[0014] Compared with the prior art, the present application has the following technical effects:

[0015] The third switch tube is controlled in the embodiment of the present application, which can establish sufficient power supply voltage signal 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, reduce the capacitance value of the power supply capacitor and the starting current required by the switching power supply circuit, so that the switching power supply has lower cost and smaller size; on the other hand, the working timing of the third switch tube is independent of the first switch tube and the second switch tube in the half-bridge resonant circuit, the control is simpler and the integration is higher, so that the application scenarios can be expanded. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A switching power supply principle diagram of a third winding power supply mode of the prior art;

[0017] Figure 2 A switching power supply principle diagram of the first embodiment of the present application;

[0018] Figure 3 A key working process waveform diagram of the switching power supply provided by the first embodiment;

[0019] Figure 4 A switching power supply principle diagram of the second embodiment of the present application;

[0020] Figure 5 A key working process waveform diagram of the switching power supply provided by the second embodiment;

[0021] Figure 6 A switching power supply principle diagram of the third embodiment of the present application;

[0022] Figure 7 A switching power supply principle diagram of the fourth embodiment of the present application;

[0023] Figure 8 A switching power supply principle diagram of the fourth embodiment of the present application;

[0024] Figure 9 A switching power supply principle diagram of the fifth embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application and its beneficial effects will be further described in detail in combination with specific embodiments and the drawings of the specification. However, the specific embodiments of the present application are not limited to this. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the present application.

[0026] It should be noted that the terms "comprising" and "having" and any variations thereof used in the specification and claims of the present application are intended to cover both non-exclusive inclusion, such as a series of elements, unit circuits or control timing not necessarily limited to those clearly listed, but can include elements, unit circuits or control timing not clearly listed or inherent to these circuits. The embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0027] In addition, the drawings of the present disclosure are only schematic and not necessarily to scale. The same reference signs in the drawings represent the same or similar parts, and thus repeated description thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities, which do not necessarily have to correspond to physically or logically independent entities. These functional entities can be implemented by software, or in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0028] First embodiment

[0029] Figure 2 For the schematic diagram of the switching power supply of the first embodiment of the present application, please refer to Figure 2 The switching power supply includes a transformer T1, a primary side loop, a secondary side loop and a primary side power supply circuit. The primary side loop is a half-bridge resonant circuit, which includes a first switch tube Q1 and a second switch tube Q2 in the bridge arm of the half-bridge resonant circuit. The drain of the first switch tube Q1 is connected to the input positive terminal Vin of the switching power supply. The connection point of the source of the first switch tube Q1 and the drain of the second switch tube Q2 is coupled to one end of the primary winding of the transformer T1. The source of the second switch tube Q2 is coupled to the other end of the primary winding of the transformer and the primary input ground terminal of the switching power supply at the same time. The primary side power supply circuit includes a first capacitor C2, a first diode D1, a second capacitor C3 and a third switch tube Q3. One end of the second capacitor C3 is connected to the other end of the primary winding of the transformer T1 as the input terminal of the power supply circuit. The other end of the second capacitor C3 is connected to the anode of the first diode D1 and one end of the third switch tube Q3 at the same time. The cathode of the first diode D1 and one end of the first capacitor C2 are connected together as the output terminal VCC of the power supply circuit. The other end of the third switch tube Q3 and the other end of the first capacitor C2 are connected together as the ground terminal of the power supply circuit, which is connected to the source of the second switch tube Q2. The third switch tube Q3 is configured to be turned off when the voltage across the first capacitor C2 is less than or equal to a preset threshold voltage, and turned on when the voltage across the first capacitor C2 is greater than the preset threshold voltage.

[0030] The source of the second switch tube Q2 is coupled to the other end of the primary winding of the transformer, which means that the source of the second switch tube Q2 is not directly connected to the other end of the primary winding of the transformer, but is indirectly connected through the resonance capacitor C1. The source of the second switch tube Q2 is coupled to the primary input ground of the switching power supply, which means that the source of the second switch tube Q2 is not directly connected to the primary input ground of the switching power supply, but is indirectly connected through the resistor R1.

[0031] Further, the third switch tube Q3 is configured to have a hysteresis when turned on and turned off, that is, when the voltage across the first capacitor C2 is less than or equal to the first preset threshold voltage Vth1, the third switch tube Q3 is turned off, and when the voltage across the first capacitor C2 is greater than or equal to the second preset threshold voltage Vth2, the third switch tube Q3 is turned on. The first preset threshold voltage Vth1 is less than the second preset threshold voltage Vth2.

[0032] When the voltage across the first capacitor C2 is less than or equal to the first preset threshold voltage Vth1, the third switch tube Q3 is configured to be turned off, so that the forward resonant current ILr flowing into the one end of the primary winding of the transformer T1 charges the second capacitor C3, and continues to charge the first capacitor C2 through the first diode D1.

[0033] When the voltage across the first capacitor C2 is greater than or equal to the second preset threshold voltage Vth2, the third switch tube Q3 is configured to be turned on, and the first capacitor C2 is bypassed by the third switch tube Q3, stopping charging the first capacitor C2, and the forward resonant current ILr flowing into the one end of the primary winding of the transformer T1 only charges the second capacitor C3.

[0034] Figure 3 The key working process waveform diagram of the switching power supply provided for the first embodiment, wherein Vcc is the power supply voltage of the control device; SW1 is the driving waveform of the first switch tube Q1, which is turned on when the high level and turned off when the low level; SW2 is the driving waveform of the second switch tube Q2, which is turned on when the high level and turned off when the low level; SW3 is the driving waveform of the third switch tube Q3, which is turned on when the high level and turned off when the low level; ILr is the resonant current flowing through the primary winding of the transformer. Please refer to Figure 3 In the state that the first switch tube Q1 is turned on and the second switch tube Q2 is turned off in each working cycle of the switching power supply, the charging of the power supply voltage Vcc can be divided into three subdivided time periods:

[0035] In the time period (t0~t1), the voltage Vcc across the first capacitor C2 is less than or equal to the first preset threshold voltage Vth1, the third switch Q3 is in the off state, the first switch Q1 is in the on state, the energy of the input positive terminal Vin of the switching power supply is used to excite the primary winding of the transformer T1, the positive forward resonant current ILr flowing into the primary winding of the transformer T1 charges the second capacitor C3 and continues to charge the first capacitor C2 through the first diode D1, and the charging current gradually increases; after the first switch Q1 is turned off, the energy stored in the primary winding of the transformer T1 is transmitted to the secondary side circuit, in this process, the positive forward resonant current ILr demagnetizes the primary winding of the transformer T1, and the charging current gradually decreases. In this time period, the switching power supply works in the charging state.

[0036] In the time period (t1~t2), the voltage Vcc across the first capacitor C2 is greater than or equal to the second preset value Vth2, the third switch Q3 is in the on state, the first diode D1 and the first capacitor C2 are bypassed by the third switch Q3, and the first capacitor C2 will not be charged at any moment when the resonant current ILr is positive or negative, and this time period is also called the charging stop state. th2

[0037] In the third time period (t2~t3), the voltage Vcc across the first capacitor C2 is less than the first preset threshold voltage Vth1, and the third switch Q3 is turned off to prepare for the charging process in the next switching period. In this time period, the negative resonant current ILr cannot charge the first capacitor C2, and the switching power supply is in the standby charging state until the resonant current ILr direction reverses to positive.

[0038] In this embodiment, by controlling the switching state of the third switch Q3, on the one hand, the sufficient power supply voltage signal can be established when the switching power supply circuit is just started, the starting time of the switching power supply is reduced, the power supply circuit structure is simplified, the capacitance of the power supply capacitor C1 and the starting current required by the switching power supply circuit are reduced, the cost of the switching power supply is lower, and the volume is smaller; on the other hand, the working time sequence of the third switch Q3 is independent of the first switch Q1 and the second switch Q2 in the half-bridge resonant circuit, the control is simpler, the integration is higher, and the application scenarios can be expanded.

[0039] Second embodiment

[0040] Figure 4 For the principle diagram of the switching power supply of the second embodiment of the present application, please refer to Figure 4 ​The difference between the embodiment and the first embodiment is that the switching power supply further comprises a third winding and a diode D4, an anode of the diode D4 is connected to one end of the third winding, a cathode of the diode D4 is connected to an output end of the power supply circuit, the other end of the third winding is connected to a primary side input ground end of the switching power supply, and a power supply voltage of the third winding is greater than the second preset value V th2 .

[0041] Figure 5 The key working process waveform diagram of the switching power supply provided for the second embodiment can realize decoupling of the primary side power supply circuit in the starting process and the steady state working process, supply power for the control device by controlling the switching state of the third switch Q3 before the power supply voltage of the third winding is established, and supply power for the control device by the third winding after the power supply voltage of the third winding is established, so that the power supply voltage of the third winding is required to be greater than the second preset value V th2 , that is, the control device of the switching power supply keeps the third switch Q3 conducting in the steady state working process.

[0042] The embodiment can reduce the starting current demand and the capacitance value of the power supply capacitor while taking into account the primary side power supply circuit in the starting process and the steady state working process, improve the reliability of the switching power supply, and make the switching power supply obtain better efficiency.

[0043] Third embodiment

[0044] Figure 6 For the principle diagram of the switching power supply of the third embodiment of the present application, please refer to Figure 6 The difference between the embodiment and the first embodiment is that the switching power supply further comprises a third winding and a diode D4, an anode of the diode D4 is connected to one end of the third winding, a cathode of the diode D4 is connected to an output end of the power supply circuit, the other end of the third winding is connected to a primary side input ground end of the switching power supply, and a power supply voltage of the third winding is greater than the second preset value V Figure 2 Figure 2 The secondary side loop of the switching power supply of the first embodiment is half-wave rectification, and the switching power supply of the embodiment is full-wave rectification.

[0045] For the principle diagram of the switching power supply of the third embodiment of the present application, please refer to Figure 7 The working principle of the switching power supply of the embodiment is consistent with that of the first embodiment, which will not be described here.

[0046] Fourth embodiment

[0047] Figure 8 For the principle diagram of the switching power supply of the fourth embodiment of the present application, please refer to Figure 8 The difference between the embodiment and the first embodiment is that the switching power supply further comprises a third winding and a diode D4, an anode of the diode D4 is connected to one end of the third winding, a cathode of the diode D4 is connected to an output end of the power supply circuit, the other end of the third winding is connected to a primary side input ground end of the switching power supply, and a power supply voltage of the third winding is greater than the second preset value V Figure 2 Figure 2 The secondary side loop of the first embodiment is half-wave rectification, and the second capacitor C3 and the first diode D1 are located in the primary side loop, so that the first capacitor can also be charged, and the same technical effects as the switching power supply are realized.

[0048] ​​The switch power supply of the embodiment can further simplify the structure of the primary side power supply circuit while considering the power supply voltage power supply effect, so that the switch power supply has lower cost and higher integration.

[0049] Fifth embodiment

[0050] Figure 9 For the schematic diagram of the switch power supply of the fifth embodiment of the present application, please refer to Figure 9 The difference between the third embodiment and the fifth embodiment is that in the fifth embodiment, the half-bridge resonant circuit is a half-bridge LLC transformer circuit, that is, the primary side loop of the switch power supply further comprises a resonant inductor L1; in addition, the first capacitor is a resonant capacitor in the half-bridge LLC resonant circuit, that is, the first capacitor is a resonant capacitor C1 in the half-bridge LLC resonant circuit, at this time, the second capacitor C3 and the first diode D1 are located in the primary side loop, so as to also charge the first capacitor. The working principle of the switch power supply of the fifth embodiment is consistent with that of the first embodiment, which will not be described here.

[0051] It should be understood that, although the specific embodiments of the present application are described in order to better understand and understand the present application, there are other embodiments equivalent to the embodiments. The embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The above embodiments are given as examples in an illustrative rather than limiting manner, so any modification or replacement of all or part of the technical features of the technical solutions recorded in the embodiments without departing from the spirit or essence of the present application should be considered as covered within the scope of the claims.

Claims

1. A switching power supply, characterized by: The switching power supply comprises a transformer, a primary side circuit, a secondary side circuit and a primary side power supply circuit, the primary side circuit is a half-bridge resonant circuit, the bridge arm of the half-bridge resonant circuit comprises a first switch tube Q1 and a second switch tube Q2, the drain of the first switch tube Q1 is connected to the input positive terminal of the switching power supply, the connection point of the source of the first switch tube Q1 and the drain of the second switch tube Q2 is coupled to one end of the primary winding of the transformer, and the source of the second switch tube Q2 is coupled to the other end of the primary winding of the transformer and the primary input ground terminal of the switching power supply at the same time. The primary side power supply circuit comprises a first capacitor, a first diode, a second capacitor and a third switch tube, one end of the second capacitor is connected to the other end of the primary winding of the transformer as the input terminal of the power supply circuit, the other end of the second capacitor is connected to the anode of the first diode and one end of the third switch tube at the same time, the cathode of the first diode and one end of the first capacitor are connected together as the output terminal of the power supply circuit, the other end of the third switch tube and the other end of the first capacitor are connected together as the ground terminal of the power supply circuit and are connected to the source of the second switch tube Q2, and the third switch tube is configured to be turned off when the voltage across the first capacitor is less than or equal to a preset threshold voltage and to be turned on when the voltage across the first capacitor is greater than the preset threshold voltage.

2. The switching power supply of claim 1, wherein The third switch tube is configured to have a hysteresis between the on and off states, that is, the third switch tube is turned off when the voltage across the first capacitor is less than or equal to a first preset threshold voltage Vth1 and is turned on when the voltage across the first capacitor is greater than or equal to a second preset threshold voltage Vth2, and the first preset threshold voltage Vth1 is less than the second preset threshold voltage Vth2.

3. The switching power supply of claim 2, wherein: The switching power supply further comprises a third winding and a diode D4, the anode of the diode D4 is connected to one end of the third winding, the cathode of the diode D4 is connected to the output terminal of the power supply circuit, the other end of the third winding is connected to the primary input ground terminal of the switching power supply, and the power supply voltage of the third winding is greater than the second preset threshold voltage Vth2.

4. The switching power supply according to any one of claims 1 to 3, characterized in that: The primary side circuit is a half-bridge LLC resonant circuit.

5. The switching power supply according to any one of claims 1 to 3, characterized in that: The third switch tube is a MOS tube.

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