High-voltage starting circuit, control chip and switching power supply

Abstract

The invention discloses a high-voltage starting circuit, a control chip and a switching power supply. The high-voltage starting circuit comprises a starting circuit, a charging circuit and a control circuit, the starting circuit is electrically connected with the charging circuit, the charging circuit is further electrically connected with the power supply end of a control chip and an external capacitor of the control chip at a first node, and the control circuit is electrically connected with the first node and the control end of the charging circuit. When the switching power supply is powered on, the starting circuit generates a starting voltage signal, the charging circuit responds to input of the starting voltage signal and generates charging current, the charging current charges the external capacitor, and power supply voltage is generated at the first node and used for supplying power to the control chip, so that the control chip is started. When the power supply voltage is greater than the preset voltage threshold, the control circuit outputs a stop signal, controls the charging circuit to stop working, timely turns off the charging circuit, reduces the power consumption of the switching power supply, and improves the energy conversion efficiency of the switching power supply.

Description

Technical Field

[0001] This application relates to the technical field of high-voltage startup, and particularly relates to a high-voltage startup circuit, a control chip, and a switching power supply. Background Art

[0002] A switching power supply is a power supply that uses a control chip to control the on and off time ratio of a switching transistor to maintain a stable output voltage. The control chip in the switching power supply needs to be powered to work properly. When the switching power supply is just powered on, generally, a high-voltage startup circuit charges the external capacitor of the control chip to supply power to the control chip.

[0003] In the related art, the high-voltage startup circuit generally uses a startup resistor to supply power to the control chip. Since this startup resistor is connected between the power bus and the external capacitor, even after the control chip works normally, there is still current on the startup resistor, still consuming power, and reducing the energy conversion efficiency of the switching power supply. Summary of the Invention

[0004] Embodiments of this application provide a high-voltage startup circuit, a control chip, and a switching power supply, which can start the control chip when the switching power supply is powered on and reduce power consumption.

[0005] To solve the above technical problems, the embodiments of this application provide the following technical solutions:

[0006] In a first aspect, embodiments of this application provide a high-voltage startup circuit applied to a control chip of a switching power supply. The high-voltage startup circuit includes: a startup circuit, a charging circuit, and a control circuit;

[0007] The startup circuit is electrically connected to the charging circuit, and the startup circuit is used to generate a startup voltage signal when the switching power supply is powered on;

[0008] The charging circuit is electrically connected to the power supply terminal of the control chip and the external capacitor of the control chip at a first node. The charging circuit is used to generate a charging current in response to the input of the startup voltage signal. The charging current is used to charge the external capacitor to generate a supply voltage, and the supply voltage is used to supply power to the control chip;

[0009] The control circuit is respectively electrically connected to the first node and the control terminal of the charging circuit. The control circuit is used to output a stop signal in response to the result that the supply voltage is greater than a preset voltage threshold, so as to control the charging circuit to stop working.

[0010] In some embodiments, the charging circuit includes a first current generation unit and a mirror unit;

[0011] The first current generating unit is electrically connected to the starting circuit, the mirror unit, and the first node respectively. The control terminal of the first current generating unit is also electrically connected to the control terminal of the mirror unit and the control circuit at a second node;

[0012] The first current generating unit is configured to generate a first current in response to the input of the starting voltage signal, and is also configured to stop working in response to the input of the stop signal;

[0013] The mirror unit is also electrically connected to the first node. The mirror unit is configured to generate a second current in response to the input of the first current, and is also configured to stop working in response to the input of the stop signal;

[0014] Wherein, the second current is M times the first current, and the first current and the second current together constitute the charging current, and M is a positive integer.

[0015] In some embodiments, the first current generating unit is further configured to prevent the power supply voltage from flowing back in response to the input of the stop signal;

[0016] The mirror unit is also configured to prevent the power supply voltage from flowing back in response to the input of the stop signal.

[0017] In some embodiments, the first current generating unit includes a first MOS transistor, a second MOS transistor, and a first resistor;

[0018] One end of the first resistor is electrically connected to the starting circuit, and the other end of the first resistor is commonly electrically connected to the drain of the first MOS transistor, the gate of the first MOS transistor, and the gate of the second MOS transistor at the second node. The source of the first MOS transistor is connected to the source of the second MOS transistor, and the drain of the second MOS transistor is electrically connected to the first node.

[0019] In some embodiments, the mirror unit includes a third MOS transistor and a fourth MOS transistor;

[0020] The drain of the third MOS transistor is electrically connected to the starting circuit, the gate of the third MOS transistor is electrically connected to the gate of the fourth MOS transistor at the second node, the source of the third MOS transistor is connected to the source of the fourth MOS transistor, and the drain of the fourth MOS transistor is electrically connected to the first node.

[0021] In some embodiments, the high-voltage starting circuit further includes a current limiting unit, and the current limiting unit is electrically connected between the first node and the charging circuit. The current limiting unit is configured to limit the static electricity current.

[0022] In some embodiments, the current limiting unit includes a second resistor, one end of the second resistor is electrically connected to the first node, and the other end of the second resistor is electrically connected to the charging circuit.

[0023] In some embodiments, the control circuit includes a comparison unit and a second current generation unit;

[0024] The first input terminal of the comparison unit is electrically connected to the first node, the second input terminal of the comparison unit is used to access a reference voltage, the output terminal of the comparison unit is electrically connected to the second current generation unit, and the comparison unit is configured to output a first control signal in response to the result that the supply voltage is greater than or equal to the preset voltage threshold, wherein the voltage value of the reference voltage is the preset voltage threshold;

[0025] The second current generation unit is also electrically connected to the control terminal of the charging circuit, and the second current generation unit is configured to generate the stop signal in response to the input of the first control signal to control the charging circuit to stop working.

[0026] In some embodiments, the comparison unit includes a comparator, and the second current generation unit includes a fifth MOS transistor;

[0027] The positive-phase input terminal of the comparator is electrically connected to the first node, the inverting input terminal of the comparator is used to access the reference voltage, the output terminal of the comparator is connected to the gate of the fifth MOS transistor, the source of the fifth MOS transistor is grounded, and the drain of the fifth MOS transistor is electrically connected to the control terminal of the charging circuit.

[0028] In some embodiments, the control circuit further includes a voltage dividing unit;

[0029] The voltage dividing unit is respectively electrically connected to the first node and the first input terminal of the comparison unit, and the voltage dividing unit is configured to divide the supply voltage to generate and output a voltage dividing signal to the comparison unit.

[0030] In some embodiments, the voltage dividing unit includes a third resistor and a fourth resistor;

[0031] One end of the third resistor is electrically connected to the first node, the other end of the third resistor is respectively electrically connected to one end of the fourth resistor and the first input terminal of the comparison unit, and the other end of the fourth resistor is grounded.

[0032] In some embodiments, the startup circuit includes a JFET transistor, the gate of the JFET transistor is grounded, the source of the JFET transistor is electrically connected to the charging circuit, and the drain of the JFET transistor is used to access a high-voltage power supply.

[0033] In a second aspect, an embodiment of the present application provides a control chip for a switching power supply, and the control chip includes the high-voltage startup circuit as described above.

[0034] In a third aspect, an embodiment of the present application provides a switching power supply, and the switching power supply includes the control chip as described above.

[0035] Compared with the traditional technology, in the high-voltage startup circuit provided by each embodiment of the present application, it includes a startup circuit, a charging circuit, and a control circuit. Among them, the startup circuit is electrically connected to the charging circuit, and the charging circuit is also electrically connected to the power supply terminal of the control chip and the external capacitor of the control chip at a first node. The control circuit is respectively electrically connected to the first node and the control terminal of the charging circuit. When the switching power supply is powered on, the startup circuit generates a startup voltage signal, and the charging circuit responds to the input of the startup voltage signal to generate a charging current. The charging current charges the external capacitor, and a power supply voltage is generated at the first node. The power supply voltage is used to supply power to the control chip, enabling the control chip to complete startup. After the control chip completes startup, that is, when the power supply voltage is greater than a preset voltage threshold, the control circuit outputs a stop signal to control the charging circuit to stop working, promptly turn off the charging circuit, reduce the power consumption of the switching power supply, and thereby improve the energy conversion efficiency of the switching power supply. Description of the Drawings

[0036] One or more embodiments are exemplarily illustrated by pictures in the corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements. Unless otherwise stated, the drawings in the figures do not constitute a scale limitation.

[0037] Figure 1 It is a schematic structural diagram of a charging device provided by an embodiment of the present application;

[0038] Figure 2 It is a schematic structural diagram of a switching power supply circuit provided by an embodiment of the present application;

[0039] Figure 3 It is a schematic structural diagram of a high-voltage startup circuit provided by an embodiment of the present application;

[0040] Figure 4 It is a schematic structural diagram of a high-voltage startup circuit provided by another embodiment of the present application;

[0041] Figure 5 It is a schematic circuit diagram of a high-voltage startup circuit provided by an embodiment of the present application. Detailed Embodiments

[0042] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0043] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not used to limit this application. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items.

[0044] Please refer to Figure 1 , Figure 1 which is a schematic structural diagram of a power supply device provided by an embodiment of the present invention. As Figure 1 shown, the power supply device includes a switching power supply circuit 100, a power supply 200, and a load 300.

[0045] The power supply 200 is connected to the switching power supply circuit 100 through a power bus to supply power to the switching power supply circuit 100. The power supply 200 can be a DC power supply or an AC power supply. When the power supply 200 is an AC power supply, after rectification and filtering, it supplies a DC power supply to the switching power supply circuit 100 through the power bus. Moreover, the power supply 200 can be a power supply circuit composed of any suitable discrete components. For example, in some embodiments, the power supply 200 is a power supply circuit composed of a filtering circuit, a rectifying circuit, and a voltage stabilizing circuit. For another example, in some embodiments, the power supply 200 is an integrated power chip.

[0046] The switching power supply circuit 100 processes the power supplied by the power supply 200 to obtain a secondary high-voltage signal. The voltage of the secondary high-voltage signal is the output voltage. The secondary high-voltage signal can be a high-voltage pulse wave or a high-voltage wave of other shapes.

[0047] The switching power supply circuit 100 is connected to the load 300 to provide an output voltage to the load 300. The load 300 implements corresponding load control logic according to the drive of the secondary high-voltage signal.

[0048] The switching power supply circuit 100 can be a forward switching power supply circuit or a flyback switching power supply circuit, which is not limited herein.

[0049] As Figure 2As shown in the figure, the switching power supply circuit 100 includes a front-end energy storage circuit 1, a switching circuit 2, a control chip 3, and a transformer 4. Among them, the transformer 4 includes a coupled primary coil NP and secondary coil NS. The primary coil NP is electrically connected between the front-end energy storage circuit 1 and the switching circuit 2. The switching circuit 2 is also electrically connected to the ground GND, and the control terminal of the switching circuit 2 is also electrically connected to the control chip 3.

[0050] The front-end energy storage circuit 1 stores energy, specifically the electrical energy of the power supply 200. The control chip 3 controls the switching circuit 2 to enter the conduction state or the off state. The working state of the switching circuit 2 controls the current coupling between the primary coil NP and the secondary coil NS. The energy on the front-end energy storage circuit 1 is coupled through the primary coil NP and the secondary coil NS and converted into a secondary high-voltage signal, which acts on the load 300.

[0051] In some embodiments, the control chip 3 includes a micro control unit (MCU), a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), a single-chip microcomputer, an ARM (Acorn RISC Machine), or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination of these components.

[0052] Please continue to refer to Figure 2 , the switching power supply circuit further includes a high-voltage startup circuit 5 and an auxiliary power supply circuit 6. The high-voltage startup circuit 5 is connected to the power bus and can be integrated into the control chip. An external capacitor C is connected at the power supply terminal of the control chip. The control chip 3 needs to be powered to work properly. When the switching power supply circuit is just powered on, generally, the high-voltage startup circuit 5 charges the external capacitor C to supply power to the control chip 3 so that the control chip 3 works properly. When the control chip 3 completes startup and works normally, the auxiliary power supply circuit 6 couples the energy of the primary coil to charge the external capacitor C of the control chip 3 to continue to supply power to the control chip 3.

[0053] In the related art, the high-voltage startup circuit 5 generally uses a startup resistor to supply power to the control chip 3. The startup resistor is connected between the power bus and the external capacitor C. When the power is turned on, there is current on the startup resistor to charge the external capacitor C, and then supply power to the control chip 3.

[0054] When the control chip 3 works normally and the auxiliary power supply supplies power to the control chip 3, power consumption still exists on the startup resistor, and the startup resistor generally has a large resistance value and large power consumption, which reduces the energy conversion efficiency of the switching power supply circuit.

[0055] Based on the above problems, as Figure 3As shown in the figure, an embodiment of the present application provides a high-voltage startup circuit. The high-voltage startup circuit 5 includes a startup circuit 51, a charging circuit 52, and a control circuit 53. Among them, the startup circuit 51 is electrically connected to the charging circuit 52. The charging circuit 52 is also electrically connected to the power supply terminal of the control chip 3 and the external capacitor C of the control chip 3 at the first node a. The control circuit 53 is respectively electrically connected to the first node a and the control terminal of the charging circuit 52.

[0056] The startup circuit 51 is connected to the high-voltage power supply. Specifically, one end of the startup circuit 51 is electrically connected to the power supply bus. The bus voltage of the power supply bus is Vbus. When the switching power supply circuit is powered on, there is a bus voltage Vbus on the power supply bus. Then, the startup circuit 51 generates a startup voltage signal.

[0057] The charging circuit 52 responds to the input of the startup voltage signal and generates a charging current. The charging current charges the external capacitor C, and a supply voltage VCC is generated at the first node a. The supply voltage VCC is used to supply power to the control chip 3, enabling the control chip 3 to complete startup.

[0058] The voltage at the first node a becomes higher and higher. After the control chip 3 completes startup, when the supply voltage VCC is greater than the preset voltage threshold, the control circuit 53 outputs a stop signal to control the charging circuit 52 to stop working and timely turn off the charging circuit 52.

[0059] Therefore, when the switching power supply circuit is powered on, the charging circuit 52 of the high-voltage startup circuit 515 charges the external capacitor C to generate a supply voltage VCC for supplying power to the control chip 3, quickly completing the startup of the control chip 3. After the control chip 3 completes startup, the auxiliary power supply circuit 6 continues to supply power to the control chip 3, and the control circuit 53 timely turns off the charging circuit 52, reducing the power consumption of the switching power supply circuit, thereby improving the energy conversion efficiency of the switching power supply circuit.

[0060] Please refer to Figure 4 , Figure 4 which is a schematic structural diagram of a high-voltage startup circuit provided by an embodiment of the present application. As Figure 4 shown, the charging circuit 52 includes a first current generation unit 521 and a mirror unit 522. Among them, the first current generation unit 521 is respectively electrically connected to the startup circuit 51, the mirror unit 522, and the first node a. The mirror unit 522 is also electrically connected to the first node a.

[0061] When the switching power supply circuit is powered on, the startup circuit 51 generates a startup voltage signal. The first current generation unit 521 responds to the input of the startup voltage signal and generates a first current. The mirror unit 522 mirrors the first current to generate a second current, where the second current is M times the first current, and M is a positive integer.

[0062] The current value of the first current is small. If the first current is directly used to charge the external capacitor C, the charging time is long, resulting in a long startup time of the control chip 3. Therefore, in the embodiment of the present application, the mirror unit 522 is used to perform proportional mirroring on the first current, magnifying the first current by M times to obtain a second current. The first current and the second current together form a charging current to charge the external capacitor C. Charging the external capacitor C with the larger second current shortens the charging time, enabling the control chip 3 to start quickly.

[0063] The control terminal of the first current generation unit 521 is also electrically connected to the control terminal of the mirror unit 522 and the control circuit 53 at the second node. When the control chip 3 is operating normally, the control circuit 53 outputs a stop signal, and the stop signal acts on the control terminal of the first current generation unit 521 and the control terminal of the mirror unit 522 to control the first current generation unit 521 to stop working and control the mirror unit 522 to stop working.

[0064] When the control chip 3 has completed startup and is operating normally, the control circuit 53 is used to turn off the first current generation unit 521 and the mirror unit 522 in a timely manner to reduce the power consumption of the switching power supply circuit.

[0065] In some embodiments, the first current generation unit 521 responds to the input of the stop signal to prevent the reverse flow of the supply voltage VCC, and the mirror unit 522 responds to the input of the stop signal to prevent the reverse flow of the supply voltage VCC.

[0066] When the control chip 3 has completed startup and is operating normally, the auxiliary power supply circuit 6 continues to supply power to the control chip 3, and the supply voltage VCC at point a of the first node becomes higher and higher. When the supply voltage VCC at point a of the first node is greater than the preset voltage threshold, the control circuit 53 transmits a stop signal to the first current generation unit 521 and the mirror unit 522 to control both to stop working.

[0067] When the first current generation unit 521 and the mirror unit 522 stop working, if the supply voltage VCC reversely flows into the first current generation unit 521 and the mirror unit 522, it will further reversely flow into the power bus, affecting the normal operation of the switching power supply circuit. Therefore, in the embodiment of the present application, when the first current generation unit 521 and the mirror unit 522 stop working, they can prevent the supply voltage VCC at point a of the first node from reversely flowing, enabling the switching power supply circuit to operate normally.

[0068] In some embodiments, please continue to refer to Figure 4, the high-voltage startup circuit 515 further includes a current-limiting unit 523, and the current-limiting unit 523 is electrically connected between the a point of the first node and the charging circuit 52. If an electrostatic discharge (ESD) event occurs at the a point of the first node, a very high electrostatic current will be generated instantaneously. The current-limiting unit 523 is used to limit the electrostatic current, so that the electrostatic current is reduced, thereby preventing the devices inside the high-voltage startup circuit 515 from being damaged due to overcurrent and protecting the devices inside the high-voltage startup circuit 515.

[0069] In some embodiments, please continue to refer to Figure 4 , the control circuit 53 includes a comparison unit 531 and a second current generation unit 532. Among them, the first input terminal of the comparison unit 531 is electrically connected to the a point of the first node, the second input terminal of the comparison unit 531 is used to access a reference voltage Vref, the output terminal of the comparison unit 531 is electrically connected to the second current generation unit 532, and the second current generation unit 532 is also electrically connected to the control terminal of the charging circuit 52.

[0070] The charging current charges the external capacitor C, and the supply voltage VCC at the a point of the first node becomes higher and higher. When the supply voltage VCC is greater than or equal to the reference voltage Vref, the comparison unit 531 outputs a first control signal, so that the second current generation unit 532 generates a stop signal. After receiving the stop signal, the charging circuit 52 stops working and turns off the charging current in time.

[0071] Among them, the voltage value of the reference voltage Vref is a preset voltage threshold. The preset voltage threshold can be set as needed, and it is the voltage value of the rated supply voltage VCC of the control chip 3.

[0072] If the supply voltage VCC does not reach the reference voltage Vref, the comparison unit 531 outputs a second control signal, so that the second current generation unit 532 generates a conduction signal. After receiving the conduction signal, the charging circuit 52 maintains its working state and continues to generate a charging current to charge the external capacitor C.

[0073] In some embodiments, please continue to refer to Figure 4 , the control circuit 53 further includes a voltage-dividing unit 533, and the voltage-dividing unit 533 is respectively electrically connected to the a point of the first node and the first input terminal of the comparison unit 531. The voltage-dividing unit 533 divides the supply voltage VCC at the a point of the first node to generate a voltage-divided signal. The voltage-divided signal acts on the first input terminal of the comparison unit 531. When the voltage of the voltage-divided signal is greater than the reference voltage Vref, the comparison unit 531 outputs a first control signal, so that the second current generation unit 532 generates a stop signal. When the voltage of the voltage-divided signal is less than or equal to the reference voltage Vref, the comparison unit 531 outputs a second control signal, so that the second current generation unit 532 outputs a conduction signal.

[0074] When the supply voltage VCC exceeds the preset voltage threshold, the voltage of the divided voltage signal is greater than the reference voltage Vref. When the supply voltage VCC does not exceed the preset voltage threshold, the voltage of the divided voltage signal is less than or equal to the reference voltage Vref.

[0075] If the comparison unit 531 directly compares the supply voltage VCC and the reference voltage Vref, the comparison unit 531 needs to be a high-voltage-resistant device. If the voltage-dividing unit 533 is used to divide the supply voltage VCC, and the comparison unit 531 then outputs the first control signal or the second control signal based on the voltage of the divided voltage signal and the reference voltage Vref, a smaller reference voltage Vref can be set, and the comparison unit 531 does not need to only select high-voltage-resistant devices and can select more types.

[0076] Please refer to Figure 5 , Figure 5 which is a schematic circuit diagram of a high-voltage startup circuit provided by an embodiment of the present application. As Figure 5 shown, the startup circuit 51 includes a JFET transistor M1. The gate of the JFET transistor M1 is grounded. The source of the JFET transistor M1 is electrically connected to the charging circuit 52, and the drain of the JFET transistor M1 is used to connect to a high-voltage power supply. Specifically, the drain of the JFET transistor M1 is connected to the power bus. When the switching power supply circuit is powered on, the drain of the JFET transistor M1 is connected to the bus voltage VBUS.

[0077] The first current generation unit 521 includes a first MOS transistor Q1, a second MOS transistor Q2, and a first resistor R1. One end of the first resistor R1 is electrically connected to the startup circuit 51. Specifically, one end of the first resistor R1 is connected to the source of the JFET transistor M1. The other end of the first resistor R1 is commonly electrically connected to the drain of the first MOS transistor Q1, the gate of the first MOS transistor Q1, and the gate of the second MOS transistor Q2 at the second node. The source of the first MOS transistor Q1 is connected to the source of the second MOS transistor Q2, and the drain of the second MOS transistor Q2 is electrically connected to the a point of the first node.

[0078] The mirror unit 522 includes a third MOS transistor Q3 and a fourth MOS transistor Q4. The drain of the third MOS transistor Q3 is electrically connected to the startup circuit 51. Specifically, the drain of the third MOS transistor Q3 is connected to the source of the JFET transistor M1. The gate of the third MOS transistor Q3 is electrically connected to the gate of the fourth MOS transistor Q4 at the second node. The source of the third MOS transistor Q3 is connected to the source of the fourth MOS transistor Q4, and the drain of the fourth MOS transistor Q4 is electrically connected to the a point of the first node.

[0079] The current limiting unit 523 includes a second resistor R2. One end of the second resistor R2 is electrically connected to the first node at point a, and the other end of the second resistor R2 is electrically connected to the charging circuit 52. Specifically, the other end of the second resistor R2 is respectively connected to the drain of the second MOS transistor Q2 and the drain of the fourth MOS transistor Q4.

[0080] The second resistor R2 is a large resistor. When an electrostatic discharge event occurs at the first node at point a, it limits the electrostatic current to prevent damage to other devices caused by the electrostatic current.

[0081] The comparison unit 531 includes a comparator Cmp, and the second current generation unit 532 includes a fifth MOS transistor Q5. The non-inverting input terminal of the comparator Cmp is electrically connected to the first node at point a. The inverting input terminal of the comparator Cmp is used to connect to a reference voltage Vref. The output terminal of the comparator Cmp is connected to the gate of the fifth MOS transistor Q5. The source of the fifth MOS transistor Q5 is grounded, and the drain of the fifth MOS transistor Q5 is electrically connected to the control terminal of the charging circuit 52. Specifically, the drain of the fifth MOS transistor Q5 is connected to the second node.

[0082] The voltage dividing unit 533 includes a third resistor R3 and a fourth resistor R4. One end of the third resistor R3 is electrically connected to the first node at point a. The other end of the third resistor R3 is respectively connected to one end of the fourth resistor R4 and the first input terminal of the comparison unit 531. Specifically, the other end of the third resistor R3 is respectively connected to one end of the fourth resistor R4 and the non-inverting input terminal of the comparator Cmp. The other end of the fourth resistor R4 is grounded.

[0083] Combined Figure 5 with

[0084] When the switching power supply circuit is powered on, there is current on the power supply bus. The bus voltage VBUS is connected to the drain of the JFET transistor M1. The JFET transistor M1 conducts, connecting the power supply bus to the first resistor R1. The JFET transistor M1 outputs a startup voltage signal to the first current generation unit 521, and the voltage of the startup voltage signal is the bus voltage VBUS.

[0085] The startup voltage signal generates a first current I1 through the first resistor R1, the first MOS transistor Q1, and the second MOS transistor Q2. The third MOS transistor Q3 and the fourth MOS transistor Q4 mirror and amplify the first current by M times to obtain a second current I2. The first current I1 and the second current I2 together constitute a charging current I. The charging current I charges an external capacitor C through the second resistor R2, and a supply voltage VCC is generated at the first node at point a. The supply voltage VCC powers the control chip 3, enabling the control chip 3 to complete startup and operate normally.

[0086] The third resistor R3 and the fourth resistor R4 divide the supply voltage VCC to generate a divided voltage signal. The comparator Cmp compares the voltage of the divided voltage signal with the reference voltage Vref and outputs a first control signal or a second control signal. As the charging current charges the external capacitor C, the supply voltage VCC at the first node a becomes higher and higher. When the voltage of the divided voltage signal is greater than the reference voltage Vref, the comparator Cmp outputs a high-level first control signal. The first control signal controls the fifth MOS transistor Q5 to conduct. The fifth MOS transistor Q5 outputs a low-level stop signal to the second node, thereby causing the first MOS transistor Q1 to the fourth MOS transistor Q4 to turn off and stop working, so as to timely turn off the charging circuit 52, and the auxiliary power supply circuit 6 supplies power to the control chip 3.

[0087] The source of the first MOS transistor Q1 is connected to the source of the second MOS transistor Q2, so that the connection of the first MOS transistor Q1 and the second MOS transistor Q2 is a back-to-back connection. The body diodes of the first MOS transistor Q1 and the second MOS transistor Q2 are in opposite directions. As Figure 5 shown, the anode of the body diode of the second MOS transistor Q2 is connected to the anode of the body diode of the first MOS transistor Q1. The cathode of the body diode of the second MOS transistor Q2 is connected to the first node a through the second resistor R2. Then when the first MOS transistor Q1 and the second MOS transistor Q2 are turned off, the supply voltage VCC at the first node a cannot be back-fed to the first MOS transistor Q1 through the second MOS transistor Q2, and thus cannot be back-fed to the power bus.

[0088] Similarly, the source of the third MOS transistor Q3 is connected to the source of the fourth MOS transistor Q4, so that the connection of the third MOS transistor Q3 and the fourth MOS transistor Q4 is a back-to-back connection. The body diodes of the third MOS transistor Q3 and the fourth MOS transistor Q4 are in opposite directions. The anode of the body diode of the fourth MOS transistor Q4 is connected to the anode of the third MOS transistor Q3. The cathode of the body diode of the fourth MOS transistor Q4 is connected to the first node a through the second resistor R2. Then when the third MOS transistor Q3 and the fourth MOS transistor Q4 are turned off, the supply voltage VCC at the first node a cannot be back-fed to the third MOS transistor Q3 through the fourth MOS transistor Q4, and thus cannot be back-fed to the power bus.

[0089] In summary, the high-voltage startup circuit can supply power to the control chip when the switching power supply is powered on, so that the control chip works normally. After the control chip completes startup, the charging circuit is timely turned off, the power consumption of the switching power supply is reduced, and thus the energy conversion efficiency of the switching power supply is improved.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting them; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other changes in different aspects of the present application as described above. For the sake of brevity, they are not provided in detail; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high voltage starting circuit, characterized in that: A control chip applied to a switching power supply, wherein the high-voltage startup circuit comprises: a startup circuit, a charging circuit and a control circuit; The startup circuit is electrically connected to the charging circuit, and the startup circuit is used to generate a startup voltage signal when the switching power supply is powered on; The charging circuit is electrically connected to a power supply terminal of the control chip and an external capacitor of the control chip at a first node, and the charging circuit is used to generate a charging current in response to an input of the start voltage signal, and the charging current is used to charge the external capacitor to generate a supply voltage, and the supply voltage is used to power the control chip; The control circuit is electrically connected to the first node and the control end of the charging circuit respectively. The control circuit is used to output a stop signal in response to the result that the supply voltage is greater than a preset voltage threshold, so as to control the charging circuit to stop working.

2. The high voltage starting circuit according to claim 1, characterized in that: The charging circuit includes a first current generating unit and a mirror unit; The first current generating unit is electrically connected to the startup circuit, the mirror unit and the first node respectively, and the control end of the first current generating unit is also electrically connected to the control end of the mirror unit and the control circuit at a second node respectively; The first current generating unit is used to generate a first current in response to the input of the start voltage signal, and is also used to stop working in response to the input of the stop signal; The mirror unit is also electrically connected to the first node, and is used to generate a second current in response to the input of the first current, and is also used to stop working in response to the input of the stop signal; The second current is M times the first current, the first current and the second current together constitute the charging current, and M is a positive integer.

3. The high voltage starting circuit according to claim 2, characterized in that: The first current generating unit is further used to respond to the input of the stop signal to prevent the supply voltage from flowing back; The mirror unit is further used to respond to the input of the stop signal to prevent the supply voltage from flowing back.

4. The high voltage starting circuit according to claim 2 or 3, characterized in that: The first current generating unit includes a first MOS tube, a second MOS tube and a first resistor; One end of the first resistor is electrically connected to the startup circuit, the other end of the first resistor and the drain of the first MOS tube, the gate of the first MOS tube and the gate of the second MOS tube are electrically connected to the second node, the source of the first MOS tube is connected to the source of the second MOS tube, and the drain of the second MOS tube is electrically connected to the first node.

5. The high voltage starting circuit according to claim 2 or 3, characterized in that: The mirror unit includes a third MOS tube and a fourth MOS tube; The drain of the third MOS tube is electrically connected to the startup circuit, the gate of the third MOS tube and the gate of the fourth MOS tube are electrically connected to the second node, the source of the third MOS tube is connected to the source of the fourth MOS tube, and the drain of the fourth MOS tube is electrically connected to the first node.

6. The high voltage starting circuit according to claim 1, characterized in that: The high-voltage startup circuit further includes a current limiting unit, which is electrically connected between the first node and the charging circuit and is used to limit the electrostatic current.

7. The high voltage starting circuit according to claim 6, characterized in that: The current limiting unit includes a second resistor, one end of the second resistor is electrically connected to the first node, and the other end of the second resistor is electrically connected to the charging circuit.

8. The high voltage starting circuit according to claim 1, characterized in that: The control circuit includes a comparison unit and a second current generating unit; The first input terminal of the comparison unit is electrically connected to the first node, the second input terminal of the comparison unit is used to access the reference voltage, the output terminal of the comparison unit is electrically connected to the second current generating unit, and the comparison unit is used to output a first control signal in response to the result that the supply voltage is greater than or equal to the preset voltage threshold, wherein the voltage value of the reference voltage is the preset voltage threshold; The second current generating unit is also electrically connected to the control end of the charging circuit. The second current generating unit is used to generate the stop signal in response to the input of the first control signal to control the charging circuit to stop working.

9. The high voltage starting circuit according to claim 8, characterized in that: The comparison unit includes a comparator, and the second current generating unit includes a fifth MOS tube; The non-inverting input terminal of the comparator is electrically connected to the first node, the inverting input terminal of the comparator is used to access the reference voltage, the output terminal of the comparator is connected to the gate of the fifth MOS tube, the source of the fifth MOS tube is grounded, and the drain of the fifth MOS tube is electrically connected to the control terminal of the charging circuit.

10. The high voltage starting circuit according to claim 8, characterized in that: The control circuit also includes a voltage dividing unit; The voltage dividing unit is electrically connected to the first node and the first input terminal of the comparison unit respectively, and is used to divide the supply voltage to generate and output a voltage dividing signal to the comparison unit.

11. The high voltage starting circuit according to claim 10, characterized in that: The voltage dividing unit includes a third resistor and a fourth resistor; One end of the third resistor is electrically connected to the first node, the other end of the third resistor is electrically connected to one end of the fourth resistor and the first input end of the comparison unit respectively, and the other end of the fourth resistor is grounded.

12. The high voltage starting circuit according to any one of claims 1 to 11, characterized in that: The startup circuit includes a JFET tube, the gate of the JFET tube is grounded, the source of the JFET tube is electrically connected to the charging circuit, and the drain of the JFET tube is used to access a high-voltage power supply.

13. A control chip for a switching power supply, characterized in that: The control chip includes the high-voltage starting circuit as described in any one of claims 1-12.

14. A switching power supply, characterized in that: The switching power supply comprises the control chip as claimed in claim 13.

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