A switching power supply, a high-voltage starting circuit and a control chip thereof

Abstract

The application discloses a switching power supply, a high-voltage starting circuit thereof and a control chip. The high-voltage starting circuit is used for supplying power to a to-be-powered circuit of the switching power supply in a starting stage of the switching power supply. A high-voltage end of the high-voltage starting circuit receives an input voltage, and a power supply end of the high-voltage starting circuit is connected with a power supply capacitor to output a power supply voltage. The high-voltage starting circuit comprises a starting transistor, a first end of the starting transistor being connected with the high-voltage end; a voltage pull-up element, the voltage pull-up element being connected between a second end and a control end of the starting transistor; and a starting control circuit, the starting control circuit being connected between the second end, the control end and the power supply end of the starting transistor. The starting control circuit controls a charging current flowing from the high-voltage end to the power supply capacitor according to a size of the power supply voltage and a turn-on threshold voltage of the to-be-powered circuit or according to the size of the turn-on threshold voltage of the to-be-powered circuit. The turn-on threshold voltage of the to-be-powered circuit is a power supply voltage capable of enabling the to-be-powered circuit to work normally. The high-voltage starting circuit has extremely low static loss and is especially suitable for high-voltage application fields such as photovoltaic power generation and electric vehicles.

Description

Technical Field

[0001] This invention relates to the field of power electronics, and more particularly to a switching power supply and its high-voltage starting circuit and control chip. Background Technology

[0002] The control chip of a switching power supply requires a high-voltage startup circuit for power before the power supply can operate normally. One existing high-voltage startup scheme uses a high-voltage startup resistor, such as... Figure 1 As shown, in this high-voltage start-up scheme, the high-voltage start-up resistor Rbus is connected between the DC bus and the capacitor Ccc. During the startup phase of the switching power supply, the DC bus voltage Vbus forms a charging current through the start-up resistor Rbus to charge the capacitor Ccc. The voltage Vcc on the capacitor Ccc powers the control chip. When the switching power supply is operating normally, the power is supplied by the auxiliary winding N. AUX It supplies power to the control chip. However, this high-voltage startup scheme has a large static power consumption during normal operation, especially in situations with high DC bus voltage, because the high-voltage startup resistor Rbus cannot be disconnected. When the DC bus voltage is high, multiple resistors need to be connected in series to divide the voltage, and the charging current is not constant.

[0003] The second high-voltage startup scheme in the prior art is through a depletion-type MOSFET Q. D To start, such as Figure 2 As shown, the depletion-type MOSFET Q D Connected between the DC bus and capacitor Ccc, resistor R SG Connected to depletion-type MOSFET Q D During the startup phase of the switching power supply, a resistor R connects the gate and source terminals. SG Self-current limiting is implemented, and the depletion-mode MOSFET Q is achieved through normal operation of the auxiliary winding during normal operation of the switching power supply. D Reliable shutdown, but resistor R SG There are many design limitations during use, and the resistor R is normally... SG The losses are still significant in the path where the auxiliary winding supplies power to the control chip. Furthermore, in high-voltage fields such as photovoltaic energy storage and electric vehicles, the maximum voltage of batteries can generally reach 1100V or 1500V. Currently, the more common high-voltage startup scheme is to use multiple MOSFETs in series, which results in a relatively complex external circuit. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a switching power supply and its high-voltage startup circuit and control chip, so as to solve the technical problems of high static power consumption and complex peripheral circuit of the switching power supply at high DC bus voltage in the prior art.

[0005] The technical solution of the present invention is to provide a high-voltage startup circuit for a switching power supply, used to supply power to the circuit to be powered by the switching power supply during the startup phase of the switching power supply. Its high-voltage terminal receives the input voltage, and its power supply terminal is connected to a power supply capacitor to output the power supply voltage. The high-voltage startup circuit includes:

[0006] The transistor is activated, with its first terminal connected to the high-voltage terminal.

[0007] A voltage pull-up element is connected between the second terminal of the start-up transistor and the control terminal;

[0008] A start-up control circuit is connected between the second terminal, the control terminal, and the power supply terminal of the start-up transistor. It controls the charging current flowing from the high-voltage terminal to the power supply capacitor according to the magnitude of the power supply voltage and the turn-on threshold voltage of the circuit to be powered, or according to the magnitude of the turn-on threshold voltage of the circuit to be powered.

[0009] The turn-on threshold voltage of the circuit to be powered is the power supply voltage that enables the circuit to operate normally.

[0010] Optionally, the voltage pull-up element includes a first resistor.

[0011] Optionally, the startup control circuit controls the impedance between the control terminal of the startup transistor and ground based on the magnitude of the power supply voltage and the turn-on threshold voltage of the circuit to be powered, or based on the magnitude of the turn-on threshold voltage of the circuit to be powered, so as to regulate the charging current flowing from the high-voltage terminal to the power supply capacitor.

[0012] Optionally, when the startup control circuit adjusts the charging current flowing from the high-voltage terminal to the power supply capacitor based on the magnitude of the supply voltage and the turn-on threshold voltage of the circuit to be powered, the startup control circuit includes a first startup control unit. The first startup control unit controls whether to provide charging current from the high-voltage terminal to the power supply capacitor based on the comparison result of the supply voltage and the first reference voltage.

[0013] When the supply voltage is lower than the first reference voltage, the system controls the supply of charging current from the high-voltage terminal to the supply capacitor.

[0014] When the supply voltage is greater than the first reference voltage, the charging current supplied from the high voltage terminal to the supply capacitor is stopped.

[0015] Wherein, the first reference voltage is greater than or equal to the turn-on threshold voltage of the circuit to be powered.

[0016] Optionally, the first startup control unit controls the impedance between the control terminal of the startup transistor and ground based on the comparison result of the supply voltage and the first reference voltage, so as to control whether to provide charging current from the high-voltage terminal to the supply capacitor.

[0017] When the supply voltage is less than the first reference voltage, the impedance between the control terminal of the start-up transistor and ground is set to high impedance.

[0018] When the supply voltage is greater than the first reference voltage, the impedance between the control terminal of the start-up transistor and ground is controlled to be low.

[0019] Optionally, the first start control unit includes:

[0020] The first switching transistor has its first terminal connected to the control terminal of the start-up transistor and its second terminal grounded.

[0021] The first comparator circuit has a first input terminal that receives the power supply voltage, a second input terminal that receives the first reference voltage, and an output terminal that is connected to the control terminal of the first switching transistor.

[0022] Optionally, when the startup control circuit regulates the charging current flowing from the high-voltage terminal to the power supply capacitor according to the magnitude of the turn-on threshold voltage of the circuit to be powered, the startup control circuit includes a second startup control unit. The second startup control unit controls whether to provide charging current from the high-voltage terminal to the power supply capacitor according to the magnitude of the second voltage.

[0023] When the control terminal voltage of the start-up transistor is less than the second voltage, the charging current is supplied from the high-voltage terminal to the power supply capacitor.

[0024] When the control terminal voltage of the start-up transistor reaches the second voltage, the charging current supplied from the high-voltage terminal to the power supply capacitor is stopped.

[0025] Wherein, the second voltage is greater than the turn-on threshold voltage of the circuit to be powered.

[0026] Optionally, the second startup control unit controls the impedance between the control terminal of the startup transistor and ground based on the magnitude of the second voltage, thereby controlling whether charging current is supplied from the high-voltage terminal to the power supply capacitor.

[0027] When the control terminal voltage of the start-up transistor is less than the second voltage, the impedance between the control terminal of the start-up transistor and ground is set to high impedance.

[0028] When the voltage at the control terminal of the start-up transistor reaches the second voltage, the impedance between the control terminal of the start-up transistor and ground is controlled to be low.

[0029] Optionally, the second start control unit includes:

[0030] The first Zener diode has its anode grounded and its cathode connected to the control terminal of the start-up transistor.

[0031] The stabilizing voltage of the first Zener diode is the second voltage.

[0032] Optionally, the start-up control circuit further includes a current limiting unit, which adjusts the magnitude of the charging current when a charging current is supplied from the high-voltage terminal to the power supply capacitor.

[0033] Optionally, the current limiting unit further includes:

[0034] The second resistor has its first end connected to the second end of the start-up transistor and its second end connected to the power supply terminal.

[0035] The second switching transistor has its first end connected to the control terminal of the start-up transistor, its second end connected to the second terminal of the second resistor, and its control terminal connected to the first terminal of the second resistor.

[0036] Optionally, the start-up control circuit further includes:

[0037] The first unidirectional conducting device has its anode connected to the second terminal of the second resistor and its cathode connected to the power supply terminal.

[0038] Optionally, the high-voltage starting circuit further includes:

[0039] A protection circuit is connected between the second terminal of the startup transistor and ground to reduce interference to the second terminal of the startup transistor when the input voltage changes at a high rate.

[0040] Optionally, the protection circuit includes:

[0041] The third resistor has its first end connected to the second end of the start-up transistor, and its second end connected to the first end of the second resistor.

[0042] The third switching transistor has its first terminal connected to the second terminal of the third resistor, and its second terminal is grounded.

[0043] The fourth resistor is connected between the control terminal of the third switch and ground;

[0044] The first capacitor is connected between the second terminal of the start-up transistor and the control terminal of the third switch.

[0045] Optionally, the startup transistor is a depletion-type transistor.

[0046] Optionally, the startup transistor is any one of a metal-oxide-semiconductor field-effect transistor, a silicon carbide transistor, or a gallium nitride transistor.

[0047] Optionally, the input voltage is the DC bus voltage of the switching power supply, or the switching node voltage of the power switching transistor of the switching power supply.

[0048] In a second aspect, a control chip for a switching power supply is provided. The control chip includes a control circuit and a high-voltage startup circuit, wherein the high-voltage startup circuit is used to supply power to the control circuit during the startup phase of the switching power supply.

[0049] Thirdly, a switching power supply is provided, the switching power supply including the high-voltage starting circuit.

[0050] Compared with the prior art, the high-voltage starting circuit of the present invention has the following advantages:

[0051] (1) Low static power consumption;

[0052] (2) It has good constant current charging accuracy;

[0053] (3) The start-up transistor can be any one of metal oxide semiconductor field effect transistor, silicon carbide transistor or gallium nitride transistor. When high voltage wide bandgap devices such as silicon carbide transistor and gallium nitride transistor are used, the upper limit of DC bus voltage of the switching power supply can be increased.

[0054] (4) The high-voltage start-up circuit can be integrated into the control chip of the switching power supply, which can simplify the peripheral circuit of the switching power supply used in high-voltage fields such as electric vehicles and photovoltaics. Furthermore, the high-voltage terminal of the high-voltage start-up circuit can be connected to the switching node of the power switching transistor, which can reduce the number of pins of the control chip used to connect to the DC bus, thereby further simplifying the peripheral system.

[0055] (5) The robustness of the high voltage starting circuit under high input voltage change rate can be improved by adding a protection circuit.

[0056] (6) The start-up control circuit can be compatible with both enhancement-type and depletion-type start-up transistors, which facilitates device selection. When a depletion-type start-up transistor is used, it can have lower static power consumption and a lower limit of DC bus voltage. Attached Figure Description

[0057] Figure 1 A schematic diagram of the circuit structure of a switching power supply for the first high-voltage starting scheme in the prior art;

[0058] Figure 2 A schematic diagram of the circuit structure of a switching power supply for a second high-voltage starting scheme in the prior art;

[0059] Figure 3 This is a schematic diagram of the circuit structure of a switching power supply according to an embodiment of the present invention;

[0060] Figure 4 This is a schematic diagram of the circuit structure of the high-voltage starting circuit according to the first embodiment of the present invention;

[0061] Figure 5 This is a schematic diagram of the circuit structure of the high-voltage starting circuit according to the second embodiment of the present invention;

[0062] Figure 6 This is a schematic diagram of the circuit structure of the high-voltage starting circuit according to the third embodiment of the present invention. Detailed Implementation

[0063] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0064] To provide the public with a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the invention, but those skilled in the art can fully understand the invention without these details.

[0065] The invention is described in more detail below by way of example with reference to the accompanying drawings. It should be noted that the drawings are in a simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0066] like Figure 3 As shown, a switching power supply according to an embodiment of the present invention includes a high-voltage startup circuit 110 and a power supply circuit such as a control circuit 120, as well as a power switching transistor Qp. The control circuit 120 controls the on / off state of the power switching transistor Qp. The high-voltage startup circuit 110 supplies power to the control circuit 120 during the startup phase of the switching power supply. The high-voltage terminal of the high-voltage startup circuit 110 receives the input voltage, and the power supply terminal is connected to a power supply capacitor Ccc to output a power supply voltage Vcc. In some embodiments, the high-voltage startup circuit includes a startup transistor Q. D The voltage pull-up element 111 and the start-up control circuit 112 start-up transistor Q D The first terminal is connected to the high-voltage terminal; the voltage pull-up element 111 is connected to the start-up transistor Q. D Between the second terminal and the control terminal; the start-up control circuit 112 is connected to the start-up transistor Q. DBetween the second terminal, the control terminal, and the power supply terminal, the charging current flowing from the high-voltage terminal to the power supply capacitor Ccc is adjusted according to the magnitude of the power supply voltage Vcc and the turn-on threshold voltage of the control circuit 120, or according to the magnitude of the turn-on threshold voltage of the control circuit 120; wherein, the turn-on threshold voltage of the control circuit 120 is the power supply voltage that enables the control circuit 120 to operate normally. For example, the start-up control circuit 112 can control the start-up transistor Q according to the magnitude of the power supply voltage Vcc and the turn-on threshold voltage of the control circuit 120, or according to the magnitude of the turn-on threshold voltage of the control circuit 120. D The impedance between the control terminal and ground is adjusted to regulate the charging current flowing from the high-voltage terminal to the power supply capacitor Vcc. In one embodiment, transistor Q is activated. D For a depletion-type transistor, the start-up transistor Q is... D It can be any one of a metal-oxide-semiconductor field-effect transistor, a silicon carbide transistor, or a gallium nitride transistor. Figure 3 Using a depletion-type N-channel metal-oxide-semiconductor field-effect transistor as the startup transistor Q D Example: The transistor Q is activated. D With the drain as the first terminal, the source as the second terminal, and the gate as the control terminal, transistor Q is activated. D The control terminal voltage (gate voltage) is pulled up by a voltage pull-up element 111, which, for example, includes a first resistor R1. In other embodiments, the high-voltage startup circuit 110 further includes a protection circuit 113 connected to the startup transistor Q. D Between the second terminal and ground, it is used to mitigate the impact of the input voltage received by the high-voltage startup circuit 110 on the startup transistor Q when the voltage changes at a high rate. D Interference at the second end. In one embodiment, the high-voltage terminal of the high-voltage starting circuit 110 can be connected to the DC bus of the switching power supply, that is, the input voltage can be the DC bus voltage Vbus of the switching power supply. In another embodiment, the high-voltage terminal of the high-voltage starting circuit can also be connected to the switching node SW of the power switch Qp of the switching power supply, that is, the input voltage can also be the switching node voltage Vsw of the power switch Qp of the switching power supply. The switching power supply in this embodiment also includes an auxiliary winding N. AUX When the switching power supply is operating normally, the auxiliary winding N AUX Power is supplied to control circuit 120.

[0067] Continue to refer to Figure 3In this embodiment, the high-voltage startup circuit 110 and the control circuit 120 are integrated within the control chip 100, which simplifies the peripheral circuitry of switching power supplies used in electric vehicles, photovoltaics, and other fields. Furthermore, the high-voltage terminal of the high-voltage startup circuit 110 can be connected to the switching node SW of the power switching transistor Qp, reducing the number of pins on the control chip 100 used to connect to the DC bus, further simplifying the peripheral system. It is understood that in other embodiments, the high-voltage startup circuit 110 and the control circuit 120 may not be integrated into the same chip. It should be noted that this application uses an isolated switching power supply as an example to describe the switching power supply and its high-voltage startup circuit and control chip, but it is not limited to isolated switching power supplies; it is equally applicable to non-isolated switching power supplies.

[0068] Figure 4 A schematic diagram of the high-voltage startup circuit according to a first embodiment of the present invention is shown. The high-voltage startup circuit 110 includes a startup transistor Q. D A voltage pull-up element 111 and a start-up control circuit 112, wherein the start-up transistor Q D The voltage pull-up element 111 has been described above and will not be repeated here. In this embodiment, the start-up control circuit 112 regulates the charging current flowing from the high-voltage end to the power supply capacitor Ccc according to the magnitude of the power supply voltage Vcc and the turn-on threshold voltage of the circuit to be powered. The startup control circuit 112 of this embodiment includes a first startup control unit 1121 and a current limiting unit 1122. The first startup control unit 1121 controls whether to provide charging current from the high-voltage terminal to the power supply capacitor Ccc based on the comparison result of the supply voltage Vcc and the first reference voltage V1. When the supply voltage Vcc is less than the first reference voltage V1, it controls the supply of charging current from the high-voltage terminal to the power supply capacitor Ccc. When the supply voltage Vcc is greater than the first reference voltage V1, it stops providing charging current from the high-voltage terminal to the power supply capacitor Ccc. The first reference voltage V1 can be set to be greater than or equal to the turn-on threshold voltage of the circuit to be powered. The turn-on threshold voltage of the circuit to be powered is the supply voltage that enables the circuit to operate normally. Preferably, the first reference voltage V1 can be set to be equal to the turn-on threshold voltage of the circuit to be powered to further reduce the power consumption of the circuit. For example, the first startup control unit 1121 can control the startup transistor Q based on the comparison result of the supply voltage Vcc and the first reference voltage V1. D The impedance between the control terminal and ground is used to control whether charging current is supplied from the high-voltage terminal to the power supply capacitor Ccc. When the power supply voltage Vcc is less than the first reference voltage V1, the start-up transistor Q is controlled. D The impedance between the control terminal and ground is high. When the supply voltage Vcc is greater than the first reference voltage V1, the start-up transistor Q is controlled.D The impedance between the control terminal and ground is low. Specifically, the first start control unit 1121 includes a first switching transistor Q1 and a first comparator circuit 11211, with the first terminal of the first switching transistor Q1 connected to the start transistor Q. D The control terminal of the first comparison circuit 11211 is connected to the control terminal of the first switching transistor Q1, and the second terminal is grounded. The first input terminal of the first comparison circuit 11211 receives the supply voltage Vcc, the second input terminal receives the first reference voltage V1, and the output terminal is connected to the control terminal of the first switching transistor Q1. In one embodiment, the first comparison circuit 11211 is configured to output a low level when the supply voltage Vcc is less than the first reference voltage V1 to control the first switching transistor Q1 to be in a turned-off state, and to output a high level when the supply voltage Vcc is greater than the first reference voltage V1 to control the first switching transistor Q1 to be in a turned-on state. When the first start-up control unit 1121 controls the supply of charging current from the high-voltage terminal to the supply capacitor, the current-limiting circuit 1122 adjusts the magnitude of the charging current. Specifically, the current-limiting unit 1122 includes a second resistor R2 and a second switching transistor Q2, with the first terminal of the second resistor R2 connected to the start-up transistor Q1. D The second terminal is connected to the power supply terminal of the high-voltage starting circuit 110; the first terminal of the second switching transistor Q2 is connected to the starting transistor Q. D The control terminal is connected to the second terminal of the second resistor R2, and the control terminal is connected to the first terminal of the second resistor R2. In one embodiment, the start-up control circuit further includes a first unidirectional conducting device, which is exemplified here by a first diode D1. The anode of the first diode D1 is connected to the second terminal of the second resistor, and the cathode is connected to the power supply terminal.

[0069] In the high-voltage startup circuit of Embodiment 1 of the present invention, when the switching power supply is operating normally and the supply voltage Vcc is greater than the first reference voltage V1, the first switching transistor Q1 is turned on, the first diode D1 is reverse-biased and cut off, and the second switching transistor Q2 is turned off. The high-voltage startup circuit stops charging the supply capacitor Ccc, and only the startup transistor Q1 is active. D A very small leakage current flows through the second resistor R2, and the static power consumption of the high-voltage startup circuit in this embodiment is lower than that of... Figure 1 and Figure 2 The static power consumption of the high-voltage startup circuit in the prior art is shown. During the startup phase of the switching power supply, when the supply voltage Vcc is less than the first reference voltage V1, the first switch Q1 is turned off, and the second switch Q2 regulates the startup transistor Q through closed-loop control by sampling the voltage across the second resistor R2. D The control terminal (gate) voltage achieves the effect of constant current charging of the power supply capacitor Ccc. In this embodiment, the constant current charging accuracy depends only on the threshold voltage of the second switch Q2, which can be integrated into the chip, and the accuracy of the second resistor R2, and is related to the start-up transistor Q. D The threshold voltage accuracy is independent, which can avoid situations such as Figure 2 The high-voltage start-up circuit shown in the prior art suffers from poor constant current charging accuracy when using an external start-up transistor with a large threshold voltage variation.

[0070] In summary, the high-voltage starting circuit of Embodiment 1 of the present invention has at least the following advantages: low static power consumption; good constant current charging accuracy, and the constant current charging accuracy is not affected by the type and / or accuracy of the selected starting transistor; the starting transistor can be any one of metal oxide semiconductor field-effect transistors, silicon carbide transistors, or gallium nitride transistors. When high-voltage wide bandgap devices such as silicon carbide transistors and gallium nitride transistors are used, the upper limit of the DC bus voltage of the switching power supply can be increased, and it can be applied to high-voltage fields such as electric vehicles and photovoltaics.

[0071] Figure 5 A schematic diagram of the high-voltage start-up circuit according to a second embodiment of the present invention is shown. The high-voltage start-up circuit 110 provided in this embodiment is basically the same as that in the first embodiment, and will not be described again here. The difference is that the start-up control circuit in the first embodiment includes a first start-up control unit 1121, while the start-up control circuit 112 in this embodiment includes a second start-up control unit 1121'. The start-up control circuit 112 in this embodiment regulates the charging current flowing from the high-voltage end to the power supply capacitor Ccc according to the magnitude of the turn-on threshold voltage of the circuit to be powered. The second start-up control unit 1121' controls whether to provide charging current from the high-voltage end to the power supply capacitor Ccc according to the magnitude of the second voltage. When the start-up transistor Q D When the control terminal voltage is less than the second voltage, the control provides charging current from the high-voltage terminal to the power supply capacitor. When the start-up transistor Q... D When the control terminal voltage reaches the second voltage, the charging current supplied from the high-voltage terminal to the power supply capacitor Ccc is stopped; wherein, the second voltage is greater than the turn-on threshold voltage of the circuit to be powered. For example, the second start control unit 1121' can control the start transistor Q according to the magnitude of the second voltage. D The impedance between the control terminal and ground is used to control whether charging current is supplied from the high-voltage terminal to the power supply capacitor Ccc, when the start-up transistor Q... D When the control terminal voltage is less than the second voltage, the impedance between the control terminal of the start-up transistor and ground is high. When the start-up transistor Q... D When the control terminal voltage reaches the second voltage, the start-up transistor Q is controlled. D The impedance between the control terminal and ground is low. Specifically, the second start control unit 1121' includes a first Zener diode Dz, the anode of the first Zener diode Dz is grounded, and the cathode is connected to the start transistor Q. DThe control terminal; the stable voltage of the first Zener diode Dz is the second voltage.

[0072] The high-voltage startup circuit 110 of Embodiment 2 of the present invention ensures that the transistor Q is started when the supply voltage Vcc is less than the turn-on threshold voltage of the circuit to be powered by setting the stable voltage of the first Zener diode Dz to be greater than the turn-on threshold voltage of the circuit to be powered. D The control terminal voltage is less than the stable voltage of the first Zener diode Dz, so the first Zener diode Dz is in the off state. That is, the impedance between the control terminal of the startup transistor and ground is high, which allows charging current to be provided from the high voltage terminal to the power supply capacitor. When the supply voltage Vcc rises to a level that makes the startup transistor Q... D When the control terminal voltage reaches the stable voltage of the first Zener diode Dz, transistor Q is activated. D The control terminal voltage is greater than the stable voltage of the first Zener diode Dz, and the first Zener diode Dz is in a regulated state (reverse breakdown state). That is, the impedance between the control terminal of the startup transistor and ground is low, which can stop the supply of charging current from the high-voltage terminal to the power supply capacitor. The second startup control unit 1121' of Embodiment 2 of the present invention only requires one first Zener diode Dz. By designing the stable voltage of the first Zener diode Dz according to the magnitude of the turn-on threshold voltage of the circuit to be powered, the control of whether to supply charging current from the high-voltage terminal to the power supply capacitor Ccc can be realized, which can greatly simplify the circuit structure.

[0073] Figure 6 This diagram illustrates the circuit structure of a high-voltage starting circuit according to a third embodiment of the present invention. The high-voltage starting circuit provided in this embodiment is essentially the same as that in Embodiment 1, and will not be described again here. The difference lies in that the high-voltage starting circuit 110 in this embodiment further includes a protection circuit 113, which is connected to the starting transistor Q. D The second terminal, between the current limiting unit 1122 and ground, is used to mitigate the impact of the input voltage received by the high-voltage startup circuit 110 on the startup transistor Q when the input voltage changes at a high rate. D Interference at the second end. Specifically, the protection circuit includes a third resistor R3, a third switch Q3, a fourth resistor R4, and a first capacitor C1. The first end of the third resistor R3 is connected to the startup transistor Q. D The second terminal of the third switch Q3 is connected to the first terminal of the second resistor R2; the first terminal of the third switch Q3 is connected to the second terminal of the third resistor R3, and the second terminal is grounded; the fourth resistor R4 is connected between the control terminal of the third switch Q3 and ground; the first capacitor C1 is connected to the start-up transistor Q. D Between the second terminal and the control terminal of the third switch Q3.

[0074] The working principle of the protection circuit 113 in Embodiment 3 of the present invention is as follows: When the input high voltage received by the high voltage starting circuit 110 has a high voltage change rate, the transistor Q is activated. D The voltage at the second terminal will also exhibit a rapid change, causing current to flow through the first capacitor C1. This current, flowing through the fourth resistor R4, generates a voltage drop. This voltage drop turns on the third switch Q3, and the third resistor R3 will activate the transistor Q. D The voltage at the second terminal is pulled down, thereby reducing the impact of the input voltage received by the high-voltage startup circuit 110 on the startup transistor Q when the input voltage changes at a high rate of change. D Interference at the second end. The third embodiment of the present invention, by setting up a protection circuit 113, can improve the robustness of the high-voltage starting circuit under high input voltage change rates, making the high-voltage starting circuit more suitable for high-voltage fields such as photovoltaics and electric vehicles.

[0075] Furthermore, the startup transistor Q in the high-voltage startup circuit of this embodiment of the invention D As a depletion-type transistor, the startup control circuit 112 and protection circuit 113 in the high-voltage startup circuit of this embodiment can also be compatible with enhancement-type transistors, facilitating device selection. When an enhancement-type startup transistor is selected, the connection method of the voltage pull-up element 111 needs to be changed. Specifically, in one embodiment, please refer to... Figure 4 , can Figure 4 Based on this, transistor Q will be activated. D Replace with enhanced startup transistor Q E The voltage pull-up element 111 is replaced by the fifth resistor R5 (not shown in the figure). The fifth resistor R5 is connected to the high-voltage terminal and the enhancement-mode transistor Q. E Between the gates. When the power-on transistor is an enhancement transistor Q. E At that time, the static power consumption will be greater than that of the depletion-type transistor used in this invention. The specific analysis is as follows: the startup transistor uses the enhancement-type transistor Q. E When the switching power supply is operating normally, the first switching transistor Q1 is turned on, and the enhancement-mode startup transistor Q1 is activated. E With both the second switch Q2 and the second switch off, and assuming the high-voltage terminal of the high-voltage starting circuit is connected to the high-voltage bus voltage Vbus is 1000V, and the fifth resistor R5 = 36MΩ, then the static power consumption of the high-voltage starting circuit is: When a depletion-type transistor is selected as the startup transistor, during normal operation of the switching power supply, the first switch Q1 is turned on, the second switch Q2 is turned off, and the startup transistor Q... D The gate-source voltage is close to its threshold voltage. Assuming the first resistor R5 = 1MΩ, the transistor Q is started. D With a threshold voltage Vth = 3V, the static power consumption of the high-voltage startup circuit is only: The smaller startup transistor uses an enhancement-type startup crystal Q. EThe static power consumption at that time. On the other hand, in order to enable the enhanced startup transistor Q... E The DC bus voltage Vbus must be at least higher than that of the enhancement-mode startup transistor Q to enable it to conduct and charge the power supply capacitor Ccc. E The source voltage is higher than that of the enhancement-mode start-up transistor Q. E The threshold voltage of the DC bus voltage Vbus is higher than that of the depletion-mode start-up transistor, which is a normally-on device and does not have this problem. Therefore, when using a depletion-mode start-up transistor as the start-up transistor, the lower limit of the DC bus voltage Vbus can be lower. This shows that compared to using an enhancement-mode start-up transistor Q... E When a depletion-type transistor is used as the startup transistor, the high-voltage startup circuit has lower static power consumption and a lower lower limit for the DC bus voltage.

[0076] In summary, the high-voltage starting circuit of the present invention has the following advantages: low static power consumption; good constant current charging accuracy, which is not affected by the type and / or accuracy of the selected starting transistor; the starting transistor can be any one of metal-oxide-semiconductor field-effect transistors, silicon carbide transistors, or gallium nitride transistors without affecting the constant current charging accuracy; when using high-voltage wide-bandgap devices such as silicon carbide transistors and gallium nitride transistors, the upper limit of the DC bus voltage of the switching power supply can be increased, enabling its application in high-voltage fields such as electric vehicles and photovoltaics; the high-voltage starting circuit can be integrated into the control chip of the switching power supply, simplifying its application in electric vehicles. The peripheral circuits of switching power supplies in high-voltage fields such as automobiles or photovoltaics can be used to start high-voltage circuits. The high-voltage terminal of the high-voltage starting circuit can be connected to the switching node of the power switching transistor, which can reduce the number of pins of the control chip used to connect to the DC bus, thus further simplifying the peripheral system. Through protection circuits, the robustness of the high-voltage starting circuit under high input voltage change rates can be improved, making the high-voltage starting circuit more suitable for high-voltage fields such as photovoltaics and electric vehicles. The starting regulation circuit and / or protection circuit can be compatible with both enhancement-mode and depletion-mode starting transistors, which facilitates device selection. When using depletion-mode starting transistors, lower static power consumption and a lower lower limit of DC bus voltage can be achieved.

[0077] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.

Claims

1. A high-voltage startup circuit for a switching power supply, used to supply power to the circuit to be powered by the switching power supply during the startup phase of the switching power supply, wherein its high-voltage terminal receives an input voltage, and its power supply terminal is connected to a power supply capacitor to output a power supply voltage, characterized in that, The high-voltage starting circuit includes: The transistor is activated, with its drain connected to the high-voltage terminal; A voltage pull-up element is connected between the source and the control terminal of the start-up transistor; A start-up control circuit is connected between the source, control terminal, and power supply terminal of the start-up transistor. Based on the power supply voltage and the turn-on threshold voltage of the circuit to be powered, or based on the control terminal voltage of the start-up transistor and the turn-on threshold voltage of the circuit to be powered, the charging current flowing from the high-voltage terminal to the power supply capacitor is controlled. The turn-on threshold voltage of the circuit to be powered is the power supply voltage that enables the circuit to operate normally.

2. The high-voltage starting circuit according to claim 1, characterized in that, The voltage pull-up element includes a first resistor.

3. The high-voltage starting circuit according to claim 1, characterized in that, The startup control circuit controls the impedance between the control terminal of the startup transistor and ground based on the magnitude of the power supply voltage and the turn-on threshold voltage of the circuit to be powered, or based on the magnitude of the control terminal voltage of the startup transistor and the turn-on threshold voltage of the circuit to be powered, so as to regulate the charging current flowing from the high voltage terminal to the power supply capacitor.

4. The high-voltage starting circuit according to claim 1, characterized in that, When the startup control circuit adjusts the charging current flowing from the high-voltage terminal to the power supply capacitor based on the magnitude of the supply voltage and the turn-on threshold voltage of the circuit to be powered, the startup control circuit includes a first startup control unit. The first startup control unit controls whether to provide charging current from the high-voltage terminal to the power supply capacitor based on the comparison result of the supply voltage and the first reference voltage. When the supply voltage is lower than the first reference voltage, the system controls the supply of charging current from the high-voltage terminal to the supply capacitor. When the supply voltage is greater than the first reference voltage, the charging current supplied from the high voltage terminal to the supply capacitor is stopped. Wherein, the first reference voltage is greater than or equal to the turn-on threshold voltage of the circuit to be powered.

5. The high-voltage starting circuit according to claim 4, characterized in that, The first startup control unit controls the impedance between the control terminal of the startup transistor and ground based on the comparison result of the supply voltage and the first reference voltage, so as to control whether to provide charging current from the high voltage terminal to the supply capacitor. When the supply voltage is less than the first reference voltage, the impedance between the control terminal of the start-up transistor and ground is set to high impedance. When the supply voltage is greater than the first reference voltage, the impedance between the control terminal of the start-up transistor and ground is controlled to be low.

6. The high-voltage starting circuit according to claim 4, characterized in that, The first start-up control unit includes: The first switching transistor has its first terminal connected to the control terminal of the start-up transistor and its second terminal grounded. The first comparator circuit has a first input terminal that receives the power supply voltage, a second input terminal that receives the first reference voltage, and an output terminal that is connected to the control terminal of the first switching transistor.

7. The high-voltage starting circuit according to claim 1, characterized in that, When the startup control circuit regulates the charging current flowing from the high-voltage terminal to the power supply capacitor based on the control terminal voltage of the startup transistor and the turn-on threshold voltage of the circuit to be powered, the startup control circuit includes a second startup control unit. The second startup control unit controls whether to provide charging current from the high-voltage terminal to the power supply capacitor based on the magnitude of the second voltage. When the control terminal voltage of the start-up transistor is less than the second voltage, the charging current is supplied from the high-voltage terminal to the power supply capacitor. When the control terminal voltage of the start-up transistor reaches the second voltage, the charging current supplied from the high-voltage terminal to the power supply capacitor is stopped. Wherein, the second voltage is greater than the turn-on threshold voltage of the circuit to be powered.

8. The high-voltage starting circuit according to claim 7, characterized in that, The second startup control unit controls the impedance between the control terminal of the startup transistor and ground based on the magnitude of the second voltage, thereby controlling whether charging current is supplied from the high-voltage terminal to the power supply capacitor. When the control terminal voltage of the start-up transistor is less than the second voltage, the impedance between the control terminal of the start-up transistor and ground is set to high impedance. When the voltage at the control terminal of the start-up transistor reaches the second voltage, the impedance between the control terminal of the start-up transistor and ground is controlled to be low.

9. The high-voltage starting circuit according to claim 7, characterized in that, The second start control unit includes: The first Zener diode has its anode grounded and its cathode connected to the control terminal of the start-up transistor. The stabilizing voltage of the first Zener diode is the second voltage.

10. The high-voltage starting circuit according to claim 4 or 7, characterized in that, The startup control circuit also includes a current limiting unit, which adjusts the magnitude of the charging current when a charging current is supplied from the high voltage terminal to the power supply capacitor.

11. The high-voltage starting circuit according to claim 10, characterized in that, The current limiting unit further includes: The second resistor has its first end connected to the source of the startup transistor and its second end connected to the power supply terminal. The second switching transistor has its first end connected to the control terminal of the start-up transistor, its second end connected to the second terminal of the second resistor, and its control terminal connected to the first terminal of the second resistor.

12. The high-voltage starting circuit according to claim 11, characterized in that, The start-up control circuit also includes: The first unidirectional conducting device has its anode connected to the second terminal of the second resistor and its cathode connected to the power supply terminal.

13. The high-voltage starting circuit according to claim 11, characterized in that, The high-voltage starting circuit also includes: A protection circuit is connected between the source of the startup transistor and ground to reduce interference to the source of the startup transistor when the input voltage changes at a high rate.

14. The high-voltage starting circuit according to claim 13, characterized in that, The protection circuit includes: The third resistor has its first end connected to the source of the start-up transistor and its second end connected to the first end of the second resistor. The third switching transistor has its first terminal connected to the second terminal of the third resistor, and its second terminal is grounded. The fourth resistor is connected between the control terminal of the third switch and ground; The first capacitor is connected between the source of the start-up transistor and the control terminal of the third switch.

15. The high-voltage starting circuit according to claim 1, characterized in that, The startup transistor is a depletion-type transistor.

16. The high-voltage starting circuit according to claim 1, characterized in that, The startup transistor is any one of a metal-oxide-semiconductor field-effect transistor, a silicon carbide transistor, or a gallium nitride transistor.

17. The high-voltage starting circuit according to claim 1, characterized in that, The input voltage is the DC bus voltage of the switching power supply, or the switching node voltage of the power switching transistor of the switching power supply.

18. A control chip for a switching power supply, characterized in that, The control chip includes a control circuit and a high-voltage start-up circuit as described in any one of claims 1-17, wherein the high-voltage start-up circuit is used to supply power to the control circuit during the startup phase of the switching power supply.

19. A switching power supply, characterized in that, The switching power supply includes a high-voltage starting circuit as described in any one of claims 1-17.

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