Soft-start circuit, soft-start method and power conversion system using it

Abstract

Embodiments of this invention disclose a soft-start circuit, a soft-start method, and a power conversion system using the same. During the startup phase of the main power circuit, an auxiliary power supply circuit, which powers the control circuit of the main power circuit, is reused, allowing the auxiliary power supply circuit to pre-charge the energy storage capacitor of the main power circuit. By reusing the auxiliary power supply circuit, this invention eliminates the need for complex control or additional auxiliary circuits to achieve soft-start of the main power circuit.

Description

[Technical Field]

[0001] This invention relates to the field of power electronics, and more specifically, to a soft-start circuit, a soft-start method, and a power conversion system using the same. [Previous Technology]

[0002] In a power converter scheme, the main power circuit drives the load. Without a soft-start circuit, the output voltage of the main power circuit at startup is 0V, causing the inductor current to exceed its rated value and potentially damaging the main power unit. Therefore, a soft-start circuit is needed to soft-start the main power switching circuit. Existing technologies use control methods such as high-frequency starting, phase-shifting starting, or variable duty cycle starting to achieve soft starting of the main power circuit. However, soft starting through control methods is overly complex, difficult to control, and has low circuit reliability. [Summary of the Invention]

[0003] In view of this, the present invention proposes a soft-start circuit, a soft-start method, and a power conversion system using the same, to solve the technical problem that the soft-start method through control in the prior art is too complicated.

[0004] In the first embodiment, the present invention provides a soft-start circuit for soft-starting a main power circuit, including an auxiliary power supply circuit. The auxiliary power supply circuit includes a power stage circuit, which is configured to: supply power to the control circuit of the main power circuit; and charge the energy storage capacitor in the main power circuit during the startup phase of the main power circuit.

[0005] Preferably, the output terminal of the power stage circuit generates a first voltage, which is configured to power the control circuit; during the startup phase, the first voltage is configured to charge the energy storage capacitor in the main power circuit.

[0006] Preferably, the soft-start circuit further includes a first switching module, which is coupled between the auxiliary power supply circuit and the energy storage capacitor; wherein, during the startup phase, the first switching module is enabled so that the first voltage charges the energy storage capacitor through the first switching module.

[0007] Preferably, the first switch module includes a first power switch, which is coupled between the auxiliary power supply circuit and the energy storage capacitor; wherein, during the startup phase, the first power switch is turned on so that the first voltage charges the energy storage capacitor through the first power switch.

[0008] Preferably, the first switching module includes a diode coupled between the auxiliary power supply circuit and the energy storage capacitor; wherein, during the startup phase, the diode is turned on so that the first voltage charges the energy storage capacitor through the diode.

[0009] Preferably, the power stage circuit includes a first inductor, and the soft-start circuit further includes a second inductor coupled to the first inductor; the output terminal of the power stage circuit generates a first voltage, which is configured to power the control circuit; during the startup phase, the energy storage capacitor is charged through the second inductor.

[0010] Preferably, the soft-start circuit further includes a rectifier circuit coupled to the second inductor and configured to rectify the voltage on the second inductor to generate a second voltage to charge the energy storage capacitor.

[0011] Preferably, the soft-start circuit further includes a second switching module coupled between the rectifier circuit and the energy storage capacitor.

[0012] Preferably, the power stage circuit includes a first inductor, and the soft-start circuit further includes a second inductor coupled to the first inductor; the output terminal of the power stage circuit generates a first voltage, which is configured to charge the energy storage capacitor during the startup phase; and the control circuit is powered through the second inductor.

[0013] Preferably, the soft-start circuit further includes a rectifier circuit coupled to the second inductor and configured to rectify the voltage on the second inductor to generate a second voltage to power the control circuit.

[0014] Preferably, the soft-start circuit further includes a third switching module coupled between the first inductor and the energy storage capacitor.

[0015] Preferably, the power stage circuit is configured to charge the output capacitor coupled to the output terminal of the main power circuit during the startup phase, so as to increase the output voltage of the output terminal of the main power circuit.

[0016] Preferably, when the main power circuit is configured as a resonant circuit, the power stage circuit is configured to charge the resonant capacitor in the resonant circuit during the startup phase.

[0017] Preferably, during the startup phase, the power stage circuit charges the energy storage capacitor; when the voltage of the energy storage capacitor is not less than a first preset voltage, the power stage circuit stops charging the energy storage capacitor, and / or the main power circuit starts working.

[0018] Preferably, during the startup phase, the output of the main power circuit is disconnected from the load; when the power stage circuit stops charging the energy storage capacitor, and / or the main power circuit starts working, the control circuit generates a first enable signal to control the load to be connected to the output terminal of the main power circuit.

[0019] Preferably, the soft-start circuit further includes a fourth switching module coupled between the output of the main power circuit and the load; wherein, when the power stage circuit stops charging the energy storage capacitor and / or the main power circuit starts working, when the control circuit generates the first enable signal, the fourth switching module is controlled to turn on, so that the load is connected to the output terminal of the main power circuit.

[0020] Preferably, during the startup phase, the load is not enabled; when the voltage on the energy storage capacitor is not less than the first preset voltage, the power stage circuit stops charging the energy storage capacitor, and / or when the main power circuit starts working, the control circuit generates a first enable signal to enable the load.

[0021] In the second embodiment, the present invention also provides a soft-start method for soft-starting the main power circuit. During the startup phase of the main power circuit, the energy storage capacitor of the main power circuit is charged through the power stage circuit in the auxiliary power supply circuit; and the control circuit of the main power circuit is powered through the power stage circuit in the auxiliary power supply circuit.

[0022] Preferably, during the startup phase, the first voltage is configured to charge the energy storage capacitor in the main power circuit, wherein the output terminal of the power stage circuit generates the first voltage, which is configured to supply power to the control circuit.

[0023] Preferably, during the startup phase, the first switching module is enabled so that the first voltage charges the energy storage capacitor through the first switching module; wherein the first switching module is coupled between the auxiliary power supply circuit and the energy storage capacitor.

[0024] Preferably, during the startup phase of the main power circuit, the energy storage capacitor is charged through the second inductor; wherein, the output terminal of the power stage circuit generates a first voltage, which is configured to supply power to the control circuit; the second inductor is coupled to the first inductor in the power stage circuit.

[0025] Preferably, during the startup phase of the main power circuit, the voltage on the second inductor is rectified to generate a second voltage to charge the energy storage capacitor.

[0026] Preferably, during the startup phase, the energy storage capacitor is charged through the first inductor, and the control circuit is powered through the second inductor; wherein the power stage circuit includes the first inductor, and the second inductor is coupled to the first inductor.

[0027] Preferably, during the startup phase of the main power circuit, the voltage on the second inductor is rectified to generate a second voltage to power the control circuit.

[0028] Preferably, during the startup phase, the power stage circuit charges the energy storage capacitor; when the voltage on the energy storage capacitor is not less than the first preset voltage, the power stage circuit stops charging the energy storage capacitor, and / or the main power circuit starts working.

[0029] Preferably, during the startup phase, the load of the main power circuit and the output terminal of the main power circuit are disconnected; when the voltage on the energy storage capacitor is not less than the first preset voltage, the control circuit generates a first enable signal so that the load is connected to the output terminal of the main power circuit.

[0030] Preferably, during the startup phase, the load is controlled to be de-energized; when the voltage on the energy storage capacitor is not less than a first preset voltage, the control circuit generates a first energizing signal to enable the load.

[0031] In the third embodiment, the present invention also provides a power conversion system, including a main power circuit, an auxiliary power supply circuit, a control circuit and the soft-start circuit described above.

[0032] Compared with the prior art, the technical solution of the present invention has the following advantages: The soft-start circuit of the present invention, through the reuse of the auxiliary power supply circuit that supplies power to the control circuit in the main power circuit, charges the energy storage capacitor in the main power circuit during the startup phase, thereby reducing the inductor current of the main power circuit during the startup phase. Specifically, the soft-start circuit of the present invention, through the same power stage circuit in the auxiliary power supply circuit, realizes the supply of power to the control circuit of the main power circuit throughout the power-on process, and realizes the supply of power to the energy storage capacitor during the startup phase, thus achieving the soft start of the main power circuit without the need for an additional soft-start circuit; furthermore, when the resonant converter is used as the main power circuit, complex control is eliminated, thereby reducing costs and avoiding complex soft-start control methods; the present invention charges the energy storage capacitor in the main power circuit during the startup phase of the main power circuit, and when the main power circuit is working normally, by disconnecting the switching device, it ensures that the main power circuit does not affect the auxiliary power supply circuit when working normally. Furthermore, by pre-charging the output capacitor during the startup phase, this invention significantly reduces the current stress of the inductor current in the main power circuit during startup, thereby alleviating or even avoiding the pressure on the main power circuit during startup, reducing control difficulty, and increasing circuit reliability.

Implementation Method

[0034] The present invention will now be described based on embodiments, but the present invention is not limited to these embodiments. In the following detailed description of the present invention, certain specific details are described in detail. Those skilled in the art will fully understand the present invention even without these detailed descriptions. To avoid obscuring the essence of the present invention, well-known methods, processes, flows, elements, and circuits are not described in detail.

[0035] Furthermore, those skilled in the art should understand that the accompanying drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.

[0036] At the same time, it should be understood that in the following description, "circuit" refers to a conductive loop formed by at least one element or sub-circuit through electrical or electromagnetic connections. When an element or circuit is said to be "connected" to another element or "connected" between two nodes, it can be directly coupled or connected to another element, or there may be intermediate elements. The connection between elements can be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled" or "directly connected" to another element, it means that there are no intermediate elements between them.

[0037] As shown in Figure 1, this is a schematic block diagram of a power conversion system including a soft-start circuit according to an embodiment of the present invention. The power conversion system includes a main power circuit 11, a control circuit 13, and a soft-start circuit. The main power circuit 11 is used to receive an input voltage Vin and generate an output voltage Vo to drive the load. The control circuit 13 is used to control and / or drive the main power circuit 11. Optionally, the control circuit 13 can also control the soft-start circuit. Optionally, another control module can also control the soft-start circuit. The soft-start circuit is used to soft-start the main power circuit 11. The soft-start circuit includes an auxiliary power supply circuit 12, which includes a power stage circuit (not shown in Figure 1). The power stage circuit is configured to: supply power to the control circuit 13 throughout the system power-on process; and charge the energy storage capacitor in the main power circuit 11 during the startup phase of the main power circuit 11. The power stage circuit can be a buck circuit, a boost circuit, or a buck-boost circuit, etc., and this embodiment does not limit this.

[0038] As shown in Figure 1, the output terminal of the auxiliary power supply circuit 12 generates a first voltage V1, which is configured to supply power to the control circuit 13; and during the startup phase of the main power circuit 11, the first voltage V1 is configured to charge the energy storage capacitor Cout in the main power circuit 11.

[0039] Furthermore, the soft-start circuit also includes a first switch module 14, which is coupled between the output terminal of the auxiliary power supply circuit 12 and the energy storage capacitor Cout; during the startup phase of the main power circuit 11, the first switch module 14 is turned on, and through the power stage circuit in the multiplexed auxiliary power supply circuit, the first voltage V1 charges the energy storage capacitor Cout of the main power circuit 11 through the first switch module 14.

[0040] It should be noted that the first voltage V1 generated by the auxiliary power supply circuit 12 can also supply power to other circuits of the main power circuit 11, and this is not limited here. In addition, the startup stage in this invention refers to the stage after the main power circuit is powered on and before the main power circuit is working normally.

[0041] During the startup phase, the power stage circuit charges the energy storage capacitor. In one example, when the voltage across the energy storage capacitor is not less than a first preset voltage Vset1, the power stage circuit stops charging the energy storage capacitor, and then the control circuit 13 controls the main power circuit 11 to start operating. In another example, when the voltage across the energy storage capacitor is not less than the first preset voltage Vset1, the control circuit 13 controls the main power circuit 11 to start operating, and then the power stage circuit stops charging the energy storage capacitor. In a third example, when the voltage across the energy storage capacitor is not less than the first preset voltage Vset1, the power stage circuit stops charging the energy storage capacitor, and simultaneously the control circuit 13 controls the main power circuit 11 to start operating.

[0042] Specifically, when the soft-start circuit further includes a first switching module 14 coupled between the auxiliary power supply circuit and the energy storage capacitor, during the startup phase of the main power circuit 11, the first switching module 14 is enabled so that the first voltage V1 charges the energy storage capacitor through the first switching module 14. When the main power circuit 11 starts working, the first switching module 14 is disconnected, or when the first switching module 14 is disconnected and the main power circuit 11 starts working normally, or when the first switching module 14 is disconnected and the main power circuit 11 starts working normally, the charging of the energy storage capacitor of the main power circuit 11 during the startup phase of the main power circuit 11 will not affect the power supply of the auxiliary power supply circuit to the control circuit 13, and when the main power circuit 11 is working normally, it will not affect the auxiliary power supply circuit 12.

[0043] It should be noted that in this embodiment, the input voltage of the power stage circuit in the auxiliary power supply circuit 12 is the input voltage Vin, that is, the same input voltage as the main power circuit. In other examples, the auxiliary power supply circuit 12 may also have a different input voltage than the main power circuit, and the present invention does not limit this.

[0044] Specifically, as an example, the first switch module 14 may include a first power switch, which is coupled between the auxiliary power supply circuit and the energy storage capacitor; wherein, during the startup phase of the main power circuit 11, the first power switch is controlled to be turned on so that the first voltage V1 charges the energy storage capacitor through the first power switch. As a second example, the first switch module 14 may include a diode coupled between the auxiliary power supply circuit and the energy storage capacitor. The anode of the diode is connected to the output terminal of the auxiliary power supply circuit, and the cathode is connected to the energy storage capacitor. During the startup phase of the main power circuit 11, since the output voltage of the auxiliary power supply circuit is greater than the voltage across the energy storage capacitor, the diode conducts, allowing the first voltage V1 to charge the energy storage capacitor through the diode. When the voltage of the energy storage capacitor reaches a first preset value, the main power circuit 11 begins normal operation. At this time, the output voltage of the main power circuit 11 (i.e., the voltage of the energy storage capacitor) is greater than the output voltage of the auxiliary power supply circuit, the diode is cut off, and the output terminal of the auxiliary power supply circuit is disconnected from the energy storage capacitor, thereby stopping the charging of the energy storage capacitor. Due to the unidirectional conduction characteristic of the diode, the control circuit process is eliminated. In another example, the first switch module 12 is a switch circuit and may also include other switching devices; this invention does not limit this.

[0045] When the main power circuit 11 uses a resonant converter, in scenarios where the circuit requires soft start, the existing technology uses relatively complex control methods to achieve soft start, such as high-frequency start, phase-shift start, or variable duty cycle start. If soft start is achieved through control, the main power conversion circuit needs to establish DC output by increasing the switching frequency or adjusting the duty cycle before the main power circuit 11 can operate in a stable state. Furthermore, the soft start solution through control places higher demands on the accuracy of the controller, and inevitably introduces a large current stress during the startup process. Therefore, the solution of the present invention has significant advantages when the main power circuit is a resonant converter.

[0046] Specifically, as shown in Figure 2, the main power circuit 11 is illustrated using an LLC resonant topology as an example. The energy storage capacitor is the output capacitor Cout of the main power circuit 11. When the main power circuit 11 starts, if pre-charging is not performed, the output voltage Vo of the main power circuit 11 is 0V, the transformer voltage VT is k*Vo=0V, and the capacitor voltage VC is 0V. Therefore, the inductor voltage VL is Vin without pre-charging, resulting in a large inductor current. Through the pre-charging process of this invention, the output voltage Vo of the main power circuit 11 is raised to the first preset voltage Vset1, and the inductor voltage is reduced to VL, = Vin - k*Vset1, where k is the transformer ratio of the primary to the secondary side. It can be seen that VL, < VL. If pre-charging is not performed, the inductor current will exceed the rated value, thereby damaging the inductor or the switching transistor. Therefore, by pre-charging the output capacitor Cout, the voltage VL across the resonant inductor is significantly reduced, which helps to reduce the inductor current stress when the main power circuit 11 starts up. It also allows for soft start using a larger initial pulse width. Compared with the control method of the main power circuit 11 using a resonant converter in the prior art, this reduces the control difficulty and the requirements for controller accuracy, and increases the reliability of the circuit.

[0047] As shown in Figure 2, the input voltage Vin of this circuit ranges from Va to Vb, with a fixed k:1 voltage conversion ratio. The output voltage range of the main power circuit 11 during normal operation is Vo = Va / k ~ Vb / k. The output voltage of the auxiliary power supply circuit 12 is V1. In addition to supplying power to the control circuit 13, the auxiliary power supply circuit 12 is also connected to the output capacitor Cout of the main power circuit 11 through the first switching module 14. After the input voltage Vin is connected, the auxiliary power supply circuit 12 starts to work. As the output voltage V1 of the auxiliary power supply circuit is established, the first switching module 14 is turned on, charging the output capacitor Cout through the auxiliary power supply circuit 12. Assuming that the voltage drop of the first switching module 14 is VD, the output voltage Vo at this time satisfies Vo = V1 - VD. Optionally, this voltage can be denoted as the first preset voltage Vset1 = V1 - VD. In this example, when the control circuit 13 detects that the output voltage Vo reaches the first preset voltage Vset1, it controls the main power circuit 11 to start normal operation. During this process, depending on the input voltage, the output voltage Vo will be raised to Va / k~Vb / k. Since Va / k > Vset1 at this time, the first switching module 14 is disconnected, and the output voltage Vo is disconnected from the output terminal of the auxiliary power supply circuit 12, ensuring that the main power circuit 11 will not affect the auxiliary power supply circuit when it is working normally. In another embodiment, when the control circuit 13 detects that the output voltage Vo reaches the first preset voltage Vset1, it controls the first switching module 14 to disconnect, and then or simultaneously controls the main power circuit 11 to start working normally.

[0048] It should be noted that the LLC topology resonant converter is used as an example in Figure 2. In other examples, it can also be an LC resonant circuit. In addition to the resonant converter, it can also be a converter of the switched capacitor, phase-shifted full bridge, dual active bridge, etc., or even a simple converter such as a buck converter or boost converter. There are no limitations here.

[0049] The above examples are all described with the output voltage of the auxiliary power supply circuit 12 matching the voltage of the energy storage capacitor and the operating voltage of the control circuit 13 when the main power circuit 11 is working. In this case, the output of the auxiliary power supply circuit 12 directly charges the energy storage capacitor without voltage or power conversion, and the auxiliary power supply circuit 12 also directly supplies power to the control circuit without voltage or power conversion. When the output voltage of the auxiliary power supply circuit 12 does not match one of the output voltage of the main power circuit 11 during normal operation or the operating voltage of the control circuit 13, based on the power stage circuit including the first inductor, by setting a second inductor coupled to the first inductor, and by changing the turns ratio of the first inductor and the second inductor, the voltage of the second inductor can be adjusted as needed to match the output voltage of the main power circuit 11 during normal operation or the operating voltage of the control circuit 13. At this time, the auxiliary power supply scheme will change from a converter with only one output to a power supply scheme with two outputs, wherein the first output supplies power to the control circuit 13 of the main power circuit 11, and the second output precharges the energy storage capacitor.

[0050] Optionally, the first inductor and the second inductor can be configured as a transformer or a coupled inductor. The soft-start circuit may further include a rectifier circuit coupled to the second inductor to rectify the voltage on the second inductor to generate a second voltage V2, thereby charging or supplying power to the energy storage capacitor connected to the output terminal of the rectifier circuit or to the control circuit 13.

[0051] Figure 3 is a schematic block diagram of a soft-start circuit according to an embodiment of the present invention. As shown in Figure 3, the auxiliary power supply circuit includes a power stage circuit including a switching transistor and a first inductor 161. The auxiliary power supply circuit of the soft-start circuit also includes a second inductor 162 coupled to the first inductor 161. When the output voltage of the auxiliary power supply circuit 12 does not match the output voltage of the main power circuit 11, especially when the output voltage of the power stage circuit is significantly lower than the output voltage of the main power circuit 11, the pre-charging effect of directly charging the output capacitor Cout through the auxiliary power supply circuit 12 is very limited. Therefore, the output voltage of the other path of the power stage circuit can be adjusted by changing the turns ratio of the first inductor 161 and the second inductor 162, so that the voltage generated by the power stage circuit through the second inductor 162 matches the output voltage of the main power circuit 11, and the original output voltage of the power stage circuit matches the operating voltage of the control circuit 13.

[0052] As shown in Figure 3, this is a schematic block diagram of a soft-start circuit of the present invention; the output terminal of the power stage circuit generates a first voltage V1, which is configured to power the control circuit 13; during the startup phase of the main power circuit 11, the output capacitor Cout is charged through the second inductor 162; in this embodiment, the soft-start circuit further includes a rectifier circuit coupled to the second inductor 162, configured to rectify the voltage on the second inductor 162 to generate a second voltage V2 to charge the output capacitor Cout. In this example, the rectifier circuit includes a capacitor C1 and a diode D2, which are connected in series across the two ends of the second inductor 162. The anode of the diode D2 is connected to reference ground. The soft-start circuit further includes a second switch module 24, one end of the capacitor C1 is connected to the anode of the diode D2, and the other end is connected to the second switch module 24, thereby connecting the second switch module 24 between the rectifier circuit and the output capacitor Cout.

[0053] Figure 4 is another schematic block diagram of the soft-start circuit of the present invention; as shown in Figure 4, the power stage circuit includes a switching transistor and a first inductor 161, and the soft-start circuit also includes a second inductor 162 coupled to the first inductor 161. When the output voltage of the auxiliary power supply circuit 12 does not match the operating voltage of the control circuit 13, the output voltage of the other path of the power stage circuit is adjusted by changing the turns ratio of the first inductor 161 and the second inductor 162, so that the original output voltage of the power stage circuit matches the output voltage of the main power circuit 11 when it is working, and the voltage generated by the power stage circuit through the second inductor 162 matches the operating voltage of the control circuit 13. The output of the power stage circuit generates a first voltage V1. During the startup phase of the main power circuit 11, the first voltage V1 is configured to charge the output capacitor Cout. The control circuit 13 is powered through the second inductor 162. The soft-start circuit also includes a rectifier circuit. In this example, the rectifier circuit includes a first capacitor C1 and a diode D2. The capacitor C1 and the diode D2 are connected in series across the two ends of the second inductor. The anode of the diode D2 is connected to reference ground. One end of the capacitor C1 is connected to the anode of the diode D2, and the other end is connected to the control circuit 13. This rectifies the voltage on the second inductor 162 to generate a second voltage V2 to power the control circuit 13. The soft-start circuit also includes a third switching module 34, which is coupled between the first inductor 161 and the output capacitor Cout.

[0054] It should be noted that in the above example, the output voltage of the auxiliary power supply circuit 12 does not match the output voltage of the main power circuit 11 when it is working, which means that the output voltage of the auxiliary power supply circuit 12 is significantly different from the output voltage of the main power circuit 11 when it is working; the output voltage of the auxiliary power supply circuit 12 does not match the operating voltage of the control circuit 13, which means that the output voltage of the auxiliary power supply circuit 12 is significantly different from the operating voltage of the control circuit 13, and the auxiliary power supply circuit 12 cannot directly supply power to the control circuit 13.

[0055] In one example, during the startup phase, the load of the main power circuit is coupled to the output terminal of the main power circuit or the load is enabled. When the voltage on the energy storage capacitor is not less than a first preset voltage, the power stage circuit stops charging the energy storage capacitor, and / or the control circuit controls the main power circuit to start working. In another example, during the startup phase, the load of the main power circuit is disconnected from the output terminal of the main power circuit or the load is not enabled. When the voltage on the energy storage capacitor is not less than a first reference voltage, the power stage circuit stops charging the energy storage capacitor, and / or the control circuit controls the main power circuit to start working. The control circuit generates a first enable signal to control the load to be connected to the output terminal of the main power circuit or the load to be enabled.

[0056] When the energy storage capacitor is the output capacitor Cout of the main power circuit 11, the voltage across the output capacitor Cout is the output voltage of the main power circuit 11. When the load connected to the output terminal of the main power circuit requires a large operating power, during the startup phase, the auxiliary power supply circuit alone may not be able to output a voltage sufficient to meet the normal operation of the load. Therefore, the scheme of using the first enable signal to control the load to operate normally or connect to the main power circuit is more advantageous. Specifically, one implementation is as follows: during the startup phase of the main power circuit 11, the load is not enabled, for example, the load can be made to work in standby mode; when the voltage on the energy storage capacitor is not less than the first preset voltage, the main power circuit 11 starts to work and / or the power stage circuit stops charging the energy storage capacitor, and the control circuit 13 sends the first enable signal to the load, enabling the load to work in normal operating mode. The second implementation is as follows: during the startup phase, the load of the main power circuit 11 and the output of the main power circuit 11 are disconnected; when the voltage on the energy storage capacitor is not less than the first preset voltage, the main power circuit 11 starts to work and / or the power stage circuit stops charging the energy storage capacitor, and the control circuit 13 generates a first enable signal so that the load is connected to the output terminal of the main power circuit 11.

[0057] Specifically, as shown in Figure 5, as an example corresponding to Figure 1, a fourth switching module 15 is coupled between the output of the main power circuit 11 and the load. During the startup phase of the main power circuit 11, the fourth switching module 15 is turned off, thereby disconnecting the load of the main power circuit 11 from its output. When the main power circuit 11 starts working and / or the power stage circuit stops charging the energy storage capacitor, the fourth switching module 15 is turned on, allowing the load to be connected to the output of the main power circuit 11. As an example, the fourth switching module 15 can be a switching device such as a relay.

[0058] It should be noted that the fourth switch module 15 is coupled between the output of the main power circuit 11 and the load. The fourth switch module 15 can be coupled between the output terminal of the main power circuit and the load, or it can be coupled between the first terminal of the output capacitor and the output terminal of the main power circuit. The output terminal of the main power circuit is a port connected to an external load, and the second terminal of the energy storage capacitor is connected to a reference ground potential. In addition, Figure 5 uses the soft-start circuit in Figure 1 as an example for illustration. In the examples corresponding to Figures 3 and 4, the fourth switch module 15 can also be set between the output capacitor of the main power circuit and the load.

[0059] It should be further noted that, in the examples of Figures 1 to 5, the energy storage capacitor is used as the output capacitor Cout of the main power circuit 11 for illustration. In other examples, the energy storage capacitor can also be the bus capacitor, the resonant capacitor of the half-bridge LLC, etc., and is not limited here. When the main power circuit is a resonant circuit, the energy storage capacitor can be the resonant capacitor in the resonant circuit or the output capacitor of the resonant circuit. It can be understood that charging the resonant capacitor in the resonant circuit during the startup phase to perform a soft start on the resonant circuit is also within the scope of protection of this invention.

[0060] The soft-start circuit of the present invention reduces the inductor current of the main power circuit during the startup phase by multiplexing an auxiliary power supply circuit that supplies power to the control circuit in the main power circuit. Specifically, the soft-start circuit of the present invention achieves full power supply to the control circuit of the main power circuit after power-on and power supply to the energy storage capacitor during the startup phase through the same power stage circuit in the auxiliary power supply circuit, thus eliminating the need for an additional power stage circuit for soft-start setup. In the examples of Figures 2 and 3, one of the output voltage of the power stage circuit and the voltage of the second inductor coupled to the first inductor in the power stage circuit supplies power to the control circuit, and the other of the output voltage of the power stage circuit and the voltage of the second inductor coupled to the first inductor in the power stage circuit supplies power to the energy storage capacitor during the startup phase. In the example of Figure 3, since the voltage supplying power to the control circuit and the voltage charging the energy storage capacitor during the startup phase are not the same, it has a greater advantage when the rated values ​​of the output voltage of the auxiliary power supply circuit and the output voltage of the main power circuit differ significantly.

[0061] In summary, the present invention provides a soft-start circuit and a soft-start method. During the startup phase before the main power circuit operates, the energy storage capacitor of the main power circuit is charged through an auxiliary power supply circuit. The auxiliary power supply circuit supplies power to the control circuit of the main power circuit and includes a power stage circuit. By reusing the auxiliary power supply circuit, the present invention eliminates the need for an additional auxiliary circuit for pre-charging of the main power circuit. Furthermore, for resonant converters, it eliminates the need for complex soft-start control, thereby reducing costs and avoiding complex soft-start control methods. The present invention reuses the auxiliary power supply circuit, connecting its output to the energy storage capacitor of the main power circuit through a switching device. Before the main power circuit starts, the internal energy storage capacitor is charged. When the main power circuit is operating normally, the switching device is disconnected, ensuring that the main power circuit's normal operation does not affect the auxiliary power supply circuit.

[0062] In embodiments of the present invention, the switching transistor may be any of the existing electrically controllable switch types, such as metal oxide semiconductor field-effect transistors (MOSFETs), bipolar transistors (BJTs), or insulated-gate bipolar transistors (IGBTs), and the present invention does not limit this.

[0063] Although the embodiments or implementations have been described and explained separately above, some common technologies are involved. Those skilled in the art can replace and integrate them between the embodiments or implementations. If the content is not explicitly described in one embodiment or implementation, another embodiment that is described can be referred to.

[0064] As described above, these embodiments of the present invention do not exhaustively describe all details, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to make good use of the present invention and modifications based on it. The present invention is limited only to the scope of the claims and their full scope and equivalents. [Simplified Explanation of the Diagram]

[0033] The above and other objects, features and advantages of the present invention will become clearer from the following description of embodiments of the present invention with reference to the accompanying drawings, in which: [Figure 1] is a first schematic diagram of a power conversion system according to an embodiment of the present invention; [Figure 2] is a schematic diagram of a main power circuit with an LLC topology according to an embodiment of the present invention; [Figure 3] is a first schematic diagram of a soft-start circuit according to an embodiment of the present invention; [Figure 4] is a second schematic diagram of a soft-start circuit according to an embodiment of the present invention; [Figure 5] is a second schematic diagram of a power conversion system according to an embodiment of the present invention.

Claims

1. A soft-start circuit for soft-starting a main power circuit, characterized in that: it includes an auxiliary power supply circuit, the auxiliary power supply circuit including a power stage circuit, the power stage circuit being configured to: supply power to the control circuit of the main power circuit; and charge the energy storage capacitor in the main power circuit during the startup phase of the main power circuit; wherein, During the startup phase, the power stage circuit charges the energy storage capacitor; when the voltage of the energy storage capacitor is not less than a first preset voltage, the power stage circuit stops charging the energy storage capacitor, and / or the main power circuit starts working.

2. The soft-start circuit according to claim 1, wherein: The output of the power stage circuit generates a first voltage, which is configured to power the control circuit. During the startup phase, the first voltage is configured to charge the energy storage capacitor in the main power circuit.

3. The soft-start circuit according to claim 2, wherein: The soft-start circuit further includes a first switching module coupled between the auxiliary power supply circuit and the energy storage capacitor; wherein, during the startup phase, the first switching module is enabled so that the first voltage charges the energy storage capacitor through the first switching module.

4. The soft-start circuit according to claim 3, wherein: The first switching module includes a first power switch, which is coupled between the auxiliary power supply circuit and the energy storage capacitor; wherein, during the startup phase, the first power switch is turned on so that the first voltage charges the energy storage capacitor through the first power switch.

5. The soft-start circuit according to claim 3, wherein: The first switching module includes a diode coupled between the auxiliary power supply circuit and the energy storage capacitor; wherein, during the startup phase, the diode is turned on so that the first voltage charges the energy storage capacitor through the diode.

6. The soft-start circuit according to claim 1, wherein: The power stage circuit includes a first inductor, and the soft-start circuit further includes a second inductor coupled to the first inductor; the output terminal of the power stage circuit generates a first voltage, which is configured to power the control circuit; during the startup phase, the energy storage capacitor is charged through the second inductor.

7. The soft-start circuit according to claim 6, wherein: The soft-start circuit further includes a rectifier circuit coupled to the second inductor, configured to rectify the voltage on the second inductor to generate a second voltage to charge the energy storage capacitor.

8. The soft-start circuit according to claim 7, wherein: The soft-start circuit also includes a second switching module, which is coupled between the rectifier circuit and the energy storage capacitor.

9. The soft-start circuit according to claim 1, wherein: The power stage circuit includes a first inductor, and the soft-start circuit further includes a second inductor coupled to the first inductor; the output terminal of the power stage circuit generates a first voltage, which is configured to charge the energy storage capacitor during the startup phase; and the control circuit is powered through the second inductor.

10. The soft-start circuit according to claim 9, wherein: The soft-start circuit further includes a rectifier circuit coupled to the second inductor, configured to rectify the voltage on the second inductor to generate a second voltage to power the control circuit.

11. The soft-start circuit according to claim 9, wherein: The soft-start circuit also includes a third switching module, which is coupled between the first inductor and the energy storage capacitor.

12. The soft-start circuit according to any one of claims 1, 2, 6 or 9, wherein: The power stage circuit is configured to charge the output capacitor coupled to the output terminal of the main power circuit during the startup phase, thereby increasing the output voltage of the output terminal of the main power circuit.

13. The soft-start circuit according to any one of claims 1, 2, 6 or 9, wherein: When the main power circuit is configured as a resonant circuit, the power stage circuit is configured to charge the resonant capacitor in the resonant circuit during the startup phase.

14. The soft-start circuit according to claim 1, wherein: During the startup phase, the output of the main power circuit is disconnected from the load; when the power stage circuit stops charging the energy storage capacitor, and / or the main power circuit starts working, the control circuit generates a first enable signal to control the load to connect to the output terminal of the main power circuit.

15. The soft-start circuit according to claim 14, wherein: The soft-start circuit further includes a fourth switching module coupled between the output of the main power circuit and the load; wherein, when the power stage circuit stops charging the energy storage capacitor and / or the main power circuit starts working, when the control circuit generates the first enable signal, the fourth switching module is controlled to turn on, so that the load is connected to the output terminal of the main power circuit.

16. The soft-start circuit according to claim 1, wherein: During the startup phase, the load is not enabled; when the voltage on the energy storage capacitor is not less than the first preset voltage, the power stage circuit stops charging the energy storage capacitor, and / or when the main power circuit starts working, the control circuit generates a first enable signal to enable the load.

17. A soft-start method for soft-starting a main power circuit, characterized in that: during the startup phase of the main power circuit, the energy storage capacitor of the main power circuit is charged through a power stage circuit in an auxiliary power supply circuit; and the control circuit of the main power circuit is powered through the power stage circuit in the auxiliary power supply circuit; wherein, During the startup phase, the power stage circuit charges the energy storage capacitor; when the voltage on the energy storage capacitor is not less than a first preset voltage, the power stage circuit stops charging the energy storage capacitor, and / or the main power circuit starts working.

18. The soft-start method according to claim 17, wherein: During the startup phase, the first voltage is configured to charge the energy storage capacitor in the main power circuit, wherein the output of the power stage circuit generates the first voltage, which is configured to supply power to the control circuit.

19. The soft-start method according to claim 18, wherein: During the startup phase, the first switching module is enabled so that the first voltage charges the energy storage capacitor through the first switching module; wherein the first switching module is coupled between the auxiliary power supply circuit and the energy storage capacitor.

20. The soft-start method according to claim 17, wherein: During the startup phase of the main power circuit, the energy storage capacitor is charged through the second inductor; wherein, the output terminal of the power stage circuit generates a first voltage, which is configured to supply power to the control circuit; wherein, the power stage circuit includes a first inductor, and the second inductor is coupled to the first inductor.

21. The soft-start method according to claim 20, wherein: During the startup phase of the main power circuit, the voltage on the second inductor is rectified to generate a second voltage, which is used to charge the energy storage capacitor.

22. The soft-start method according to claim 17, wherein: During the startup phase, the energy storage capacitor is charged through the first inductor, and the control circuit is powered through the second inductor; wherein, the power stage circuit includes the first inductor, and the second inductor is coupled to the first inductor.

23. The soft-start method according to claim 22, wherein: During the startup phase of the main power circuit, the voltage on the second inductor is rectified to generate a second voltage to power the control circuit.

24. The soft-start method according to claim 17, wherein: During the startup phase, the load of the main power circuit and the output terminal of the main power circuit are disconnected; when the voltage on the energy storage capacitor is not less than the first preset voltage, the control circuit generates a first enable signal so that the load is connected to the output terminal of the main power circuit.

25. The soft-start method according to claim 17, wherein: During the startup phase, the load is kept unenabled; when the voltage on the energy storage capacitor is not less than the first preset voltage, the control circuit generates a first enable signal to enable the load.

26. A power conversion system, characterized in that it comprises: The main power circuit, the control circuit, and the soft-start circuit as described in any one of claims 1 to 16.

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