High-voltage starting and discharging control circuit and switching power supply

Abstract

The embodiment of the invention provides a high-voltage starting and discharging control circuit and a switching power supply with the high-voltage starting and discharging control circuit, and the high-voltage starting and discharging control circuit comprises a high-voltage starting circuit, a power failure detection circuit and an X capacitor discharging circuit. Wherein the high-voltage starting circuit is used for providing a voltage required by working for a system through an input voltage until the system works normally when the system is in a power-on stage or when an external VCC voltage does not reach a starting threshold value of a system control chip; the power failure detection circuit is used for detecting the output voltage of the high-voltage clamping circuit in real time and judging whether the input end of the switching power supply is powered down or not according to the voltage; when judging that the input end of the switching power supply is powered down, outputting a discharge control signal; and the X capacitor discharging circuit responds to the discharging control signal and discharges the X capacitor until the voltage on the X capacitor is lower than a preset threshold value. The starting time of the switching power supply system is saved, and the static power consumption of the system is reduced.

Description

Technical Field

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

[0002] In the context of the information and intelligent era, the demand for power management chips is very strong. An AC-DC (alternating current-direct current) switching power supply can convert the grid AC voltage into the DC voltage required by terminal devices, and is widely used in various consumer products, such as mobile phone chargers, laptop adapters, etc. With the rapid increase in terminal power-consuming devices, environmental and energy issues have attracted more and more widespread attention, and more stringent safety standards and energy efficiency need to be met.

[0003] In current AC-DC switching power supplies, high-voltage startup is usually achieved by connecting a resistor across the rectified high-voltage power grid and the high-voltage input pin of the chip. This method is easy to implement. However, since the resistor is simply connected across the rectified high-voltage power grid and the high-voltage input pin of the chip, this path current always exists, increasing the static power consumption of the system and making it difficult to meet the requirements of the new energy consumption standard. If the power consumption is reduced by increasing the resistance value of the startup resistor to reduce the branch current, the startup of the switching power supply circuit will be slow.

[0004] At the same time, in order to reduce the pollution of the power supply to the power grid and improve the EMI performance of the system, an X capacitor is usually connected in parallel at the AC input end, and its capacitance value is generally at the uF level. When the AC power supply is cut off, the voltage on the X capacitor is very high. In the prior art, one processing method is to connect a resistor in parallel across the X capacitor to provide a charge discharge path. This method brings a large power consumption and a very poor discharge effect, and it is still very easy to cause a safety accident of high-voltage electric shock to the human body, and is only applicable to simple circuits. Another processing method is to add an independent X capacitor discharge chip. This method can well reduce the static power consumption of the system, but undoubtedly increases the cost of the system.

[0005] In view of the above problems, it is necessary to propose a new high-voltage startup circuit and X capacitor discharge circuit to reduce the static power consumption of the system to solve the energy consumption problem of power products, and at the same time achieve fast startup and safe discharge of the X capacitor. Summary of the Invention

[0006] The present application provides a high-voltage startup and discharge control circuit and a switching power supply, which can solve the technical problems of slow high-voltage startup and high static power consumption existing in the existing switching power supply circuit.

[0007] In a first aspect, an embodiment of the present application provides a high-voltage startup and discharge control circuit, which is applied to a switching power supply; the switching power supply at least includes an X capacitor and a high-voltage clamping circuit connected between the input terminals of the switching power supply; the AC input voltage passes through the X capacitor to obtain the input voltage of the high-voltage clamping circuit;

[0008] The high-voltage startup and discharge control circuit includes:

[0009] A high-voltage startup circuit, connected to the high-voltage clamping circuit; the high-voltage startup circuit is used to provide the voltage required for the system to work through the input voltage during the system power-on stage or when the external VCC voltage does not reach the startup threshold of the system control chip; after the system works normally, it stops working;

[0010] A power-down detection circuit, connected to the high-voltage clamping circuit; the power-down detection circuit is used to obtain the output voltage of the high-voltage clamping circuit and judge whether the power supply input end of the switching power supply has a power-down according to the output voltage; when it is judged that the power supply input end of the switching power supply has a power-down, it outputs a discharge control signal;

[0011] An X-capacitor discharge circuit, connected to the high-voltage clamping circuit and the power-down detection circuit; the X-capacitor discharge circuit responds to the discharge control signal and discharges the X-capacitor until the voltage on the X-capacitor is lower than a preset threshold.

[0012] In some embodiments, the high-voltage startup circuit includes a logic enable unit and a charging current control unit;

[0013] After the system is powered on, the logic enable unit responds to an enable signal and charges the VCC capacitor that provides the external VCC voltage through the output voltage obtained from the high-voltage clamping circuit until the external VCC voltage reaches the startup threshold of the system control chip;

[0014] The charging current control unit is used to adjust the charging mode and / or charging current when charging the VCC capacitor according to the startup speed required by the high-voltage startup circuit.

[0015] In some embodiments, the logic enabling unit includes a comparator COMP1, a logic NOT gate, a logic AND gate, a resistor R3, a switching transistor NM4, a zener diode Z1, a switching transistor NM1, and a resistor R4; the non-inverting input terminal of the comparator COMP1 is used to obtain a first reference voltage, the inverting input terminal of the comparator COMP1 is used to obtain a divided voltage signal of the external VCC voltage, and the enabling terminal of the comparator COMP1 is used to obtain an enabling signal indicating a power failure at the input terminal of the switching power supply; the input terminal of the logic NOT gate is connected to the output terminal of the comparator COMP1; the first input terminal of the logic AND gate is connected to the output terminal of the logic NOT gate, and the second input terminal of the logic AND gate is used to obtain an enabling signal indicating that the charging of the VCC capacitor is completed; the first end of the resistor R3 is connected to the output terminal of the high-voltage clamping circuit to obtain the output voltage of the high-voltage clamping circuit; the control terminal of the switching transistor NM4 is connected to the output terminal of the logic AND gate, the first end of the switching transistor NM4 is connected to the second end of the resistor R3, and the second end of the switching transistor NM4 is connected to a preset voltage terminal; the first end of the zener diode Z1 is connected to the second end of the resistor R3, and the second end of the zener diode Z1 is connected to the preset voltage terminal; the control terminal of the switching transistor NM1 is connected to the second end of the resistor R3, the first end of the switching transistor NM1 is connected to the first end of the resistor R3; the first end of the resistor R4 is connected to the second end of the switching transistor NM1, and the second end of the resistor R4 is connected to the preset voltage terminal;

[0016] The charging current control unit includes a switching transistor PM2, a switching transistor PM1, a switching transistor NM2, and a variable resistor Rvar; the first end of the switching transistor PM2 is connected to the input terminal of the charging current control unit to obtain the output voltage of the high-voltage clamping circuit, and the second end of the switching transistor PM2 is connected to the output terminal of the charging current control unit; the control terminal of the switching transistor PM1 is connected to the control terminal of the switching transistor PM2, and the first end of the switching transistor PM1 is connected to the first end of the switching transistor PM2; the substrates of the switching transistor PM1 and the switching transistor PM2 are connected; the control terminal of the switching transistor NM2 is connected to the second end of the switching transistor NM1, and the first end of the switching transistor NM2 is connected to the second end of the switching transistor PM1; the control terminal of the variable resistor Rvar is used to obtain an externally input adjustment control signal, the first end of the variable resistor Rvar is connected to the second end of the switching transistor NM2, and the second end of the variable resistor Rvar is connected to the preset voltage terminal.

[0017] In some embodiments, the high-voltage startup circuit further includes an anti-current backflow unit connected between the output end of the high-voltage clamping circuit and the charging current control unit, and is used to prevent current from flowing from the external VCC voltage output end to the output end of the high-voltage clamping circuit when the output voltage of the high-voltage clamping circuit is less than the external VCC voltage;

[0018] The anti-current backflow unit includes at least one of a high-voltage diode and a high-voltage PMOS device.

[0019] In some embodiments, the high-voltage startup circuit is connected to the power-down detection circuit; the high-voltage startup circuit charges the VCC capacitor with the output voltage obtained from the high-voltage clamping circuit in response to the discharge control signal.

[0020] In some embodiments, the X-capacitor discharge circuit includes a charge discharge enabling unit and a charge discharge unit; the charge discharge enabling unit outputs a discharge enabling signal in response to the discharge control signal; the charge discharge unit discharges the X-capacitor to the ground in response to the discharge enabling signal until the voltage on the X-capacitor is lower than a preset threshold;

[0021] The charge discharge enabling unit includes a switching transistor NM3; the charge discharge unit includes a resistor R5; the control end of the switching transistor NM3 is used to obtain the discharge control signal, and the second end of the switching transistor NM3 is connected to a preset voltage terminal; the first end of the resistor R5 is connected to the input end of the charge discharge unit, and the second end of the resistor R5 is connected to the second end of the switching transistor NM3.

[0022] In some embodiments, the power-down detection circuit includes an AC valley detection unit and a timing unit;

[0023] The AC valley detection unit is used to compare the output voltage of the high-voltage clamping circuit obtained in the current cycle with the output voltage obtained in the previous cycle. When it is not detected that the output AC power obtained in the current cycle has the same valley value as the output voltage obtained in the previous cycle, it is determined that a power-down has occurred at the input end of the switching power supply, and a first timing signal is output; when it is detected that the output AC power obtained in the current cycle has the same valley value as the output AC power obtained in the previous cycle, it is determined that no power-down has occurred at the input end of the switching power supply, and a second timing signal is output;

[0024] The timing unit starts timing in response to the first timing signal; resets the timing in response to the second timing signal; and outputs the discharge control signal when the second timing signal is not obtained within a first preset time period after the start of timing.

[0025] In some embodiments, the AC valley detection unit includes a resistor R1, a resistor R2, and a comparator COMP2; the first end of the resistor R1 is connected to the input end of the AC valley detection unit for obtaining the output voltage of the high-voltage clamping circuit; the first end of the resistor R2 is connected to the second end of the resistor R1, and the second end of the resistor R2 is connected to a preset voltage terminal; the non-inverting input terminal of the comparator COMP2 is connected to the second end of the resistor R1, the inverting input terminal of the comparator COMP2 is used to obtain a second reference voltage, and the output terminal of the comparator COMP2 is connected to the output end of the AC valley detection unit;

[0026] The timing unit includes n cascaded D flip-flops; the reset terminals of the n D flip-flops are all connected to the input end of the timing unit for obtaining the first timing signal or the second timing signal; the output terminal of the last D flip-flop is connected to the output end of the timing unit.

[0027] In some embodiments, the high-voltage clamping circuit includes at least one junction field effect transistor or depletion-mode gallium nitride transistor;

[0028] The high-voltage clamping circuit, the high-voltage startup circuit, the power-down detection circuit, and the capacitor discharge circuit are integrated in an integrated chip;

[0029] Alternatively, the high-voltage startup circuit, the power-down detection circuit, and the capacitor discharge circuit are integrated in an integrated chip, and an input terminal of the integrated chip is connected to the output terminal of the high-voltage clamping circuit.

[0030] In a second aspect, an embodiment of the present application provides a switching power supply, which at least includes an X capacitor connected between the input terminals of the switching power supply, a high-voltage clamping circuit, and the high-voltage startup and discharge control circuit as described in any of the above embodiments;

[0031] The high-voltage startup and discharge control circuit is used to provide the voltage required for the system to work through a power supply circuit when the system is powered on, so as to realize the rapid startup of the switching power supply; after the system works normally, stop supplying power through the external power supply circuit; and, when it is determined that a power-down occurs at the input terminal of the switching power supply, discharge the capacitor until the voltage on the capacitor is lower than a preset threshold.

[0032] The high-voltage startup and discharge control circuit provided by the embodiments of the present application and the switching power supply having the high-voltage startup and discharge control circuit. The high-voltage startup and discharge control circuit includes a high-voltage startup circuit, a power-down detection circuit, and an X-capacitor discharge circuit. The high-voltage startup circuit is used to provide the working voltage required by the system through the input voltage during the power-on stage of the system or when the external VCC voltage does not reach the startup threshold of the system control chip until the system works normally; the power-down detection circuit is used to output voltage detected in real time by the high-voltage clamping circuit and determine whether the input end of the switching power supply has a power-down according to the voltage; when it is determined that the input end of the switching power supply has a power-down, a discharge control signal is output; the X-capacitor discharge circuit responds to the discharge control signal and discharges the X-capacitor until the voltage on the X-capacitor is lower than a preset threshold. Through the high-voltage startup circuit of the present application, the startup time of the switching power supply system is saved, and after the system works normally, the high-voltage startup circuit stops working to reduce the power consumption of the system. And when starting up at high voltage, by dynamically controlling the charging current, it can also well avoid the large-current charging problem caused by the VCC short-circuit fault; through the X-capacitor discharge circuit, when the switching power supply has a power-down, the X-capacitor is discharged. The charge discharge path of the X-capacitor is simple, which can ensure the safety of the system; at the same time, the structure of the high-voltage startup and discharge control circuit is simple, which also reduces the manufacturing cost. Description of the Drawings

[0033] The drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0034] Figure 1 It is a schematic structural diagram of a typical switching power supply provided for an embodiment.

[0035] Figure 2 It is a schematic structural diagram of a switching power supply provided for an embodiment of the present application.

[0036] Figure 3 It is a schematic structural diagram of a high-voltage startup and discharge control circuit provided for an embodiment of the present application.

[0037] Figure 4 It is a schematic structural diagram of a high-voltage startup and discharge control circuit provided for another embodiment of the present application.

[0038] Figure 5 It is a schematic structural diagram of a high-voltage startup and discharge control circuit provided for yet another embodiment of the present application.

[0039] Figure 6 It is a schematic structural diagram of a high-voltage startup and discharge control circuit provided for yet another embodiment of the present application.

[0040] Figure 7The circuit diagram of the high-voltage startup and discharge control circuit provided by an embodiment of the present application.

[0041] Figure 8 The waveform diagram of the output voltage of the high-voltage clamping circuit provided by an embodiment of the present application.

[0042] Figure 9 The waveform diagram of the high-voltage startup process provided by an embodiment of the present application.

[0043] Figure 10 The waveform diagram of the X-capacitor discharge process provided by an embodiment of the present application.

[0044] Figure 11 The circuit diagram of the switching power supply provided by an embodiment of the present application.

[0045] Figure 12 The structural schematic diagram of the primary control chip U1 provided by an embodiment of the present application.

[0046] Through the above-mentioned drawings, the specific embodiments of the present application have been shown, and more detailed descriptions will be given in the following text. These drawings and text descriptions are not intended to limit the scope of the concept of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. Detailed Description of the Embodiment

[0047] The present application will be further described in detail below in conjunction with the drawings through specific embodiments. Similar elements in different embodiments are labeled with related similar element numbers. In the following embodiments, many detailed descriptions are provided to enable a better understanding of the present application. However, those skilled in the art can easily recognize that some of these features can be omitted in different situations, or can be replaced by other elements, materials, or methods. In some cases, some operations related to the present application are not shown or described in the specification to avoid overshadowing the core part of the present application with excessive descriptions. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations based on the descriptions in the specification and general technical knowledge in the field.

[0048] In addition, the features, operations, or characteristics described in the specification can be combined in any appropriate manner to form various embodiments. At the same time, the steps or actions in the method description can also be reordered or adjusted in an obvious manner by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment and do not mean a necessary sequence, unless it is stated that a certain sequence must be followed.

[0049] The terms "first", "second", etc. in the description and claims of this application are used to distinguish similar objects, rather than to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of this application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are usually of the same type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the description and claims means at least one of the connected objects, and the character " / ", generally represents an "or" relationship between the associated objects before and after. And the "connection" and "coupling" mentioned in this application, unless otherwise specified, both include direct and indirect connection (coupling).

[0050] Figure 1 Schematic diagram of the structure of a typical switching power supply provided for an embodiment. As Figure 1 shown, the switching power supply provided in this embodiment at least includes an X-capacitor 110, a rectifier circuit 120, a switching circuit 130, and a voltage conversion circuit 140 connected between the input terminals of the switching power supply.

[0051] The X capacitor 110 is connected between the live wire (L) and the neutral wire (N) at the input end of the switching power supply. It belongs to the safety capacitor (Class X) and is mainly used to filter out high-frequency noise (such as switching noise and power grid transient interference) between the live wire and the neutral wire, improve electromagnetic compatibility (EMI / EMC), and suppress differential-mode interference. At the same time, it can also reduce the interference of high-frequency clutter at the input end to the subsequent rectification and switching circuit 130 to protect the subsequent circuit. The rectification circuit 120 is usually composed of a bridge rectifier (four diodes form a full-bridge or half-bridge structure), which converts the AC input (such as mains 220V AC) into pulsating DC, realizing the conversion of sinusoidal AC into unidirectional pulsating DC. After rectification, it needs to be filtered by a large-capacity electrolytic capacitor to smooth the pulsating voltage and form a stable high-voltage DC bus. The switching circuit 130 is composed of a power switch tube (such as MOSFET, IGBT), a PWM controller, and a drive circuit. It is used to cut the high-voltage DC into high-frequency pulses, control the energy transmission by adjusting the duty cycle, dynamically adjust the duty cycle according to the feedback signal, and achieve regulated voltage or constant current output. The switch tube works in the saturation / cut-off state, reducing the conduction loss and improving the overall efficiency. The voltage conversion circuit 140 can include a high-frequency transformer, an RCD clamping circuit, a feedback circuit, and a power supply circuit. Among them, the high-frequency transformer is used to isolate the input and output sides, ensuring safety and anti-interference ability, and converting the high-frequency pulse voltage into the target voltage (such as step-down or step-up) based on the turns ratio of the primary and secondary windings. The RCD clamping circuit can absorb the reverse peak voltage generated by the leakage inductance of the transformer (such as the voltage spike at the drain of the MOSFET) when the switching circuit 130 is turned off, preventing the switch tube from being broken down by overvoltage. It can also convert the spike energy into heat energy through a resistor or temporarily store it through a capacitor and then feedback it to the input. The feedback circuit usually includes an optocoupler (such as PC817), a voltage reference (such as TL431), or an auxiliary winding feedback. By real-time detecting the output voltage, comparing it with the reference voltage to generate an error signal, and transmitting the error signal to the PWM controller on the primary side through the optocoupler, it dynamically adjusts the duty cycle of the switch tube to achieve voltage regulation. The power supply circuit includes an auxiliary winding (led out from the high-frequency transformer) or an independent power supply module, providing stable low voltage for the controller and drive circuit of the switching circuit 130, and establishing the initial power supply through a starting resistor or an auxiliary winding at the initial stage of power supply startup. The output circuit can include a secondary rectifier and a filtering circuit, converting the high-frequency AC pulse output by the transformer into unidirectional pulsating DC, and then filtering out the ripple through an inductor and a capacitor to output stable DC.

[0052] With the increasing requirements for energy conservation, integrated and low-power high-voltage startup solutions have become the standard in modern switch-mode power supply design. The high-voltage startup circuit is the bridge for the switch-mode power supply to transition from "static" to "dynamic operation", and its design directly affects the startup speed, efficiency, and reliability of the power supply. The control chip of the switch-mode power supply (such as the controller of the switching circuit) requires stable low-voltage power supply (such as 12V or 5V) to operate. However, at the moment of power supply startup, the auxiliary winding (provided by the high-frequency transformer) has not yet generated energy, and the control chip cannot obtain power supply by itself. The high-voltage startup circuit directly obtains energy from the high-voltage DC bus, and after stepping down the voltage through a current-limiting resistor or a high-voltage startup IC, it provides the initial working voltage for the control chip, triggers it to start working, and then drives the switching transistor to generate high-frequency pulses.

[0053] However, as described in the background art, in current AC-DC switch-mode power supplies, high-voltage startup is usually achieved by connecting a resistor across the rectified high-voltage power grid and the high-voltage input pin of the chip. This method is easy to implement. However, since the resistor is simply connected across the rectified high-voltage power grid and the high-voltage input pin of the chip, this path current always exists, increasing the static power consumption of the system and making it difficult to meet the requirements of the new energy consumption standard. If the power consumption is reduced by increasing the resistance value of the startup resistor to decrease the branch current, it will cause the switch-mode power supply circuit to start slowly.

[0054] At the same time, in a switch-mode power supply, a capacitor is directly connected to the AC input terminal (between the live wire L and the neutral wire N). After the power supply is disconnected, the X capacitor may still store residual voltage as high as several hundred volts (such as the peak value of the mains voltage 311V). If the user touches the plug or the metal shell, it may cause an electric shock hazard. Therefore, an X capacitor discharge circuit is also necessary. The currently common discharge circuit is to quickly discharge the electrical energy stored in the X capacitor through a discharge resistor or an active discharge circuit after the power supply is disconnected, ensuring that the voltage is within a safe range, which can guarantee safety. However, the existing discharge circuits have technical problems such as high power consumption, poor discharge effect, and high cost.

[0055] This application intends to propose a high-voltage startup and discharge control circuit for a switch-mode power supply or an AC-DC converter, which can achieve fast startup of the switch-mode power supply with a large charging current when just powered on, and quickly discharge the charge on the X capacitor when the AC source is unplugged or an abnormality occurs, meeting the requirements of the safety standard.

[0056] The following will specifically describe the technical solutions of this application and how the technical solutions of this application solve the above technical problems with specific embodiments. These several specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of this application will be described below with reference to the accompanying drawings.

[0057] Figure 2The structural schematic diagram of a switching power supply provided by an embodiment of the present application. As Figure 2 shown, the switching power supply provided by this embodiment at least includes an X capacitor 210, a rectification circuit 220, a high-voltage clamping circuit 230, a drive control circuit 240, a voltage conversion circuit 250, and a high-voltage start-up and discharge control circuit 260 connected between the input terminals of the switching power supply.

[0058] The input terminal of the switching power supply is connected to an AC power supply, such as an AC source. The AC input terminal is connected to the first end and the second end of the X capacitor 210. The input terminal of the rectification circuit 220 is connected to the AC input terminal. The high-voltage clamping circuit 230 is connected to the AC input terminal through a diode and a resistor. The input terminal of the drive control circuit 240 is connected to the output terminal of the high-voltage start-up and discharge control circuit. The first input terminal of the voltage conversion circuit 250 is connected to the output terminal of the drive control circuit 240. The second input terminal of the voltage conversion circuit 250 is connected to the output terminal of the rectification circuit. The output terminal of the voltage conversion circuit 250 is used to output the required voltage after rectifying and converting the alternating current.

[0059] In some embodiments, the high-voltage clamping circuit 230 at least includes a junction field effect transistor or a depletion-mode gallium nitride transistor, generally a high-voltage switching device.

[0060] As Figure 2 shown, in some embodiments, the high-voltage start-up and discharge control circuit 260 is connected to both ends of the X capacitor 210 through a diode D1, a diode D2, and a resistor R HV The high-voltage start-up and discharge control circuit 260 is used to achieve rapid start-up of the switching power supply with a large charging current when the power is just turned on, and to detect whether the input terminal of the switching power supply has a power failure. After the power failure, it controls the rapid discharge of the charge on the X capacitor.

[0061] Figure 3 The structural schematic diagram of a high-voltage start-up and discharge control circuit provided by an embodiment of the present application. As Figure 3 shown, the high-voltage start-up and discharge control circuit 260 provided by this embodiment includes a high-voltage start-up circuit 310, a power failure detection circuit 320, and an X capacitor discharge circuit 330.

[0062] In some embodiments, in the switching power supply, the high-voltage start-up circuit 310, the power failure detection circuit 320, and the capacitor discharge circuit in the high-voltage start-up and discharge control circuit 260 are integrated in an integrated chip. One input terminal of the integrated chip is connected to the output terminal of the high-voltage clamping circuit 230. In other embodiments, in the switching power supply, the high-voltage clamping circuit 230 and each part in the high-voltage start-up and discharge control circuit 260 can also be integrated in an integrated chip.

[0063] It should be noted that the integrated chip also includes other functional circuits, such as a power supply circuit, an FB / CS detection circuit, a PWM signal generation circuit, and a drive circuit, which are not specifically limited in this embodiment.

[0064] As Figure 3 shown, in this embodiment, the high-voltage startup circuit 310 is connected to the output terminal of the high-voltage clamping circuit 230 and is also connected to an external power supply circuit to provide the VCC voltage. An external power supply circuit includes a VCC capacitor. When the high-voltage startup circuit 310 is in the power-on stage of the system or the external VCC voltage has not reached the startup threshold of the system control chip, it provides the working voltage required by the system through the AC input voltage, that is, the high-voltage startup circuit 310 draws power from the input AC power supply to charge the VCC capacitor and outputs the VCC voltage required for normal operation, which provides the working voltage VCC for the integrated chip. After the system works normally, the high-voltage startup circuit 310 will stop working. At this time, the VCC voltage reaches the startup threshold voltage of the system control chip, and the VCC provides the working voltage of the system; the power-down detection circuit 320 is connected to the output terminal of the high-voltage clamping circuit 230. The power-down detection circuit 320 is used to detect the output voltage of the high-voltage clamping circuit 230 and determine whether the input of the switching power supply is powered down through voltage; when it is determined that the input of the switching power supply is powered down, a discharge control signal is output. The X-capacitor discharge circuit is connected to the high-voltage clamping circuit 230 and the power-down detection circuit 320. The X-capacitor discharge circuit is used to discharge the X-capacitor in response to the discharge control signal until the voltage on the X-capacitor is lower than the preset threshold.

[0065] In some embodiments, the high-voltage startup circuit 310 is connected to the power-down detection circuit 320; the high-voltage startup circuit charges the VCC capacitor through the output voltage obtained from the high-voltage clamping circuit 230 in response to the discharge control signal.

[0066] Specifically, when the switching power supply (AC-DC converter) is just powered on and the VCC voltage provided by the power supply circuit has not reached the startup threshold for the normal operation of the system control chip, the high-voltage startup circuit 310 starts to work at this time, draws current from the AC input power supply to charge the VCC capacitor, and provides the system working voltage; when the VCC voltage reaches the voltage required for the normal operation of the system control chip, the system starts to work normally. At this time, the high-voltage startup circuit 310 will stop working to save power consumption. At this time, the power-down detection circuit 320 will continuously monitor the voltage output by the high-voltage clamping circuit 230, that is, the voltage output after the AC power supply is rectified. The power-down detection circuit 320 determines whether the power supply of the AC power supply is normal through the voltage, that is, it can determine whether the AC power supply has a power-down situation according to whether the voltage changes; at the same time, if it is determined that the AC power supply has a power-down situation, it will trigger the X-capacitor protection, control the high-voltage clamping circuit 230 to conduct, and start to discharge the X-capacitor through the discharge circuit.

[0067] Figure 4 Schematic diagram of the high-voltage startup and discharge control circuit provided by another embodiment of the present application. As Figure 4 shown, the high-voltage startup and discharge control circuit 260 provided in this embodiment includes a high-voltage startup circuit 310, a power-down detection circuit 320, and an X-capacitor discharge circuit 330. Among them, the high-voltage startup circuit 310 includes a logic enable unit 3101 and a charging current control unit 3102.

[0068] In this embodiment, after the system is powered on, the logic enable unit 3101 charges the VCC capacitor in response to an enable signal EN by obtaining the output voltage from the high-voltage clamping circuit 230 until the output voltage of the VCC capacitor reaches the startup threshold voltage of the system control chip. Usually, under the control of the enable signal EN, the logic enable unit 3101 charges the capacitor to provide a working voltage for the system control chip in the initial stage of power-on. The charging current control unit 3102 is used to adjust the charging mode and / or charging current when charging the VCC capacitor according to the startup speed required by the high-voltage startup circuit 310.

[0069] In some embodiments, the high-voltage startup circuit 310 includes a logic enable unit 3101, a charging current control unit 3102, and an anti-current backflow unit 3103.

[0070] The anti-current backflow unit 3103 is connected between the output terminal of the high-voltage clamping circuit 230 and the charging current control unit 3102, and is used to prevent current from flowing from the output terminal of the VCC capacitor to the output terminal of the high-voltage startup circuit 310 when the output voltage of the high-voltage clamping circuit 230 is less than the output voltage of the VCC capacitor.

[0071] In some embodiments, the anti-current backflow unit 3103 includes at least one of a high-voltage diode and a high-voltage PMOS device.

[0072] Figure 5 Schematic diagram of the high-voltage startup and discharge control circuit provided by yet another embodiment of the present application. As Figure 5 shown, the high-voltage startup and discharge control circuit 260 provided in this embodiment includes a high-voltage startup circuit 310, a power-down detection circuit 320, and an X-capacitor discharge circuit 330. Among them, the power-down detection circuit 320 includes an AC valley detection unit 3201 and a timing unit 3202.

[0073] In this embodiment, the AC voltage valley detection unit 3201 is configured to compare the output voltage of the high-voltage clamping circuit 230 obtained in the current cycle with the output voltage obtained in the previous cycle. When it is not detected that the output voltage obtained in the current cycle and the output voltage obtained in the previous cycle have the same voltage valley value, it is determined that a power failure has occurred at the input end of the switching power supply, and a first timing signal is output; when it is detected that the output voltage obtained in the current cycle and the output voltage obtained in the previous cycle have the same voltage valley value, it is determined that no power failure has occurred at the input end of the switching power supply, and a second timing signal is output. Wherein, the first timing signal and the second timing signal can be two signals, or the high and low levels of one signal.

[0074] The timing unit 3202 starts timing in response to the first timing signal; resets the timing in response to the second timing signal; and outputs a discharge control signal when the second timing signal is not obtained within a first preset time period after the start of timing.

[0075] Figure 6 It is a schematic structural diagram of a high-voltage startup and discharge control circuit provided by another embodiment of the present application. As Figure 6 shown, the high-voltage startup and discharge control circuit 260 provided in this embodiment includes a high-voltage startup circuit 310, a power failure detection circuit 320, and an X-capacitor discharge circuit 330. Among them, the X-capacitor discharge circuit 330 includes a charge discharge enabling unit 3301 and a charge discharge unit 3302.

[0076] In this embodiment, the charge discharge enabling unit 3301 outputs a discharge enabling signal in response to the discharge control signal; the charge discharge unit 3302 discharges the X-capacitor to the ground in response to the discharge enabling signal until the voltage on the X-capacitor is lower than a preset threshold.

[0077] Figure 7 It is a circuit diagram of a high-voltage startup and discharge control circuit provided by an embodiment of the present application. As Figure 7 shown, the high-voltage startup and discharge control circuit 260 provided in this embodiment includes a high-voltage startup circuit 310, a power failure detection circuit 320, and an X-capacitor discharge circuit 330. Among them, the high-voltage startup circuit 310 includes a logic enabling unit 3101, a charging current control unit 3102, and an anti-current backflow unit 3103. The power failure detection circuit 320 includes an AC voltage valley detection unit 3201 and a timing unit 3202. The X-capacitor discharge circuit 330 includes a charge discharge enabling unit 3301 and a charge discharge unit 3302.

[0078] As Figure 7As shown, in this embodiment, the logic enabling unit 3101 includes a comparator COMP1, a logic NOT gate, a logic AND gate, a resistor R3, a switching transistor NM4, a zener diode Z1, a switching transistor NM1, and a resistor R4. The non-inverting input terminal of the comparator COMP1 is used to obtain a first reference voltage Vref1. The inverting input terminal of the comparator COMP1 is used to obtain a divided voltage signal VCCdiv of the supply voltage VCC. The enabling terminal of the comparator COMP1 is used to obtain an enabling signal ACunplug indicating a power failure at the input terminal of the switching power supply. The input terminal of the logic NOT gate is connected to the output terminal of the comparator COMP1. The first input terminal of the logic AND gate is connected to the output terminal of the logic NOT gate. The second input terminal of the logic AND gate is used to obtain an enabling signal VCC_OK indicating that the charging of the VCC capacitor is completed. The first end of the resistor R3 is connected to the input terminal of the logic enabling unit 3101 and is used to obtain the output voltage HV_clamp of the high-voltage clamping circuit 230. The control terminal of the switching transistor NM4 is connected to the output terminal of the logic AND gate. The first end of the switching transistor NM4 is connected to the second end of the resistor R3. The second end of the switching transistor NM4 is connected to a preset voltage terminal, that is, connected to the ground voltage terminal. The first end of the zener diode Z1 is connected to the second end of the resistor R3. The second end of the zener diode Z1 is connected to the preset voltage terminal. The control terminal of the switching transistor NM1 is connected to the second end of the resistor R3. The first end of the switching transistor NM1 is connected to the first end of the resistor R3. The first end of the resistor R4 is connected to the second end of the switching transistor NM1. The second end of the resistor R4 is connected to the preset voltage terminal.

[0079] Figure 8 This is a waveform diagram of the output voltage of the high-voltage clamping circuit provided by an embodiment of the present application. As Figure 8 shown, the output voltage HV_clamp of the high-voltage clamping circuit 230 is a voltage signal obtained by shaping the AC voltage input by the AC power source through diodes D1 and D2 into a periodic "bun-shaped wave" voltage signal HV and then clamping it through the high-voltage clamping circuit 230. Due to the operating characteristics of the high-voltage switching device JFET in the high-voltage clamping circuit 230, when the system is operating normally, the signal of HV_clamp is a "bun-shaped wave" with the top cut off, and the maximum value of the HV_clamp voltage will be clamped to the threshold voltage of the JFET.

[0080] The anti-current backflow unit 3103 includes a diode D7. The first end of the diode D7 is connected to the input terminal of the anti-current backflow unit 3103 and is used to obtain the output voltage HV_clamp of the high-voltage clamping circuit 230.

[0081] The charging current control unit 3102 includes a switching transistor PM2, a switching transistor PM1, a switching transistor NM2, and a variable resistor Rvar. The first end of the switching transistor PM2 is connected to the input end of the charging current control unit 3102, that is, connected to the second end of the diode D7. The second end of the switching transistor PM2 is connected to the output end of the charging current control unit 3102 for outputting the VCC voltage. The control end of the switching transistor PM1 is connected to the control end of the switching transistor PM2, and the first end of the switching transistor PM1 is connected to the first end of the switching transistor PM2. The substrates of the switching transistor PM1 and the switching transistor PM2 are connected. The control end of the switching transistor NM2 is connected to the second end of the switching transistor NM1, and the first end of the switching transistor NM2 is connected to the second end of the switching transistor PM1. The control end of the variable resistor Rvar is used to obtain an externally input adjustment control signal. The first end of the variable resistor Rvar is connected to the second end of the switching transistor NM2, and the second end of the variable resistor Rvar is connected to the preset voltage terminal.

[0082] As Figure 7 shown, in this embodiment, the AC valley detection unit 3201 includes a resistor R1, a resistor R2, and a comparator COMP2. The first end of the resistor R1 is connected to the input end of the AC valley detection unit 3201 for obtaining the output voltage HV_clamp of the high-voltage clamping circuit 230. The first end of the resistor R2 is connected to the second end of the resistor R1, and the second end of the resistor R2 is connected to the preset voltage terminal. The non-inverting input terminal of the comparator COMP2 is connected to the second end of the resistor R1. The inverting input terminal of the comparator COMP2 is used to obtain the second reference voltage Vref2. The output terminal of the comparator COMP2 is connected to the output end of the AC valley detection unit 3201 for outputting the first timing signal and the second timing signal Reset to the timing unit 3202.

[0083] The timing unit 3202 includes n serially connected D flip-flops. The reset terminals of the n D flip-flops are all connected to the input end of the timing unit 3202 for obtaining the first timing signal or the second timing signal. The output terminal of the last D flip-flop is connected to the output end of the timing unit 3202.

[0084] As Figure 7 shown, in this embodiment, the charge discharge enabling unit 3301 includes a switching transistor NM3. The charge discharge unit 3302 includes a resistor R5. The control end of the switching transistor NM3 is used to obtain a discharge control signal. The second end of the switching transistor NM3 is connected to the preset voltage terminal. The first end of the resistor R5 is connected to the input end of the charge discharge unit 3302, and the second end of the resistor R5 is connected to the second end of the switching transistor NM3.

[0085] In this embodiment, the high-voltage start-up circuit 310, power-down detection circuit, and capacitor discharge circuit in the high-voltage start-up and discharge control circuit 260 are integrated into an integrated chip, denoted as the primary control chip U1, which has an HV pin for receiving the output voltage of the high-voltage clamping circuit 230.

[0086] The working process of the high-voltage start-up and discharge control circuit 260 provided in this embodiment is as follows:

[0087] The AC voltage output by the AC power supply passes through the rectifier circuit composed of diodes D1 and D2 and resistor R HV and then is input to the HV pin of the primary control chip U1, that is, the HV input port of the high-voltage start-up and X-capacitor discharge circuit 330. After rectification, the HV signal is in the shape of a periodic "mantou wave". After passing through the high-voltage switching device JFET in the high-voltage clamping circuit 230, the HV_clamp voltage signal is generated. Due to the working characteristics of the high-voltage switching device JFET, the maximum voltage value of this signal is clamped to the threshold voltage of the high-voltage switching device JFET, that is, the HV_clamp signal is also in the shape of a "mantou wave" with the top cut off (as Figure 8 shown). When the system is working normally, the "valley bottom" of the HV_clamp signal will appear periodically. The AC power supply valley bottom detection unit will detect the HV_clamp signal in real time. If the corresponding "valley bottom" is detected in the current cycle, the "Reset" signal sent to the timing unit 3202 is at a low level (that is, the above-mentioned second timing signal, and in this embodiment, the low level of this "Reset" signal is used as the second timing signal), and the timing unit 3202 will be reset; if the corresponding "valley bottom" is not detected in the current cycle, the "Reset" signal sent to the timing unit 3202 is at a high level (that is, the above-mentioned first timing signal), and the timing unit 3202 starts timing. If the "valley bottom" of the HV_clamp signal is not detected within the preset time, the timing unit 3202 will output an enable signal ACunplug indicating that the input end of the switching power supply has lost power, that is, it indicates that the AC input power supply has been unplugged. At this time, the X-capacitor charge discharge unit 3302 starts to work. The X-capacitor charge discharge unit 3302 is the main discharge path for the charge. The charge on the X-capacitor is discharged from the HV pin through the X-capacitor charge discharge unit 3302 to GND. At the same time, the ACunplug signal is also output to the high-voltage start-up circuit 310, and the circuit therein is reused to make HV charge VCC to assist in charge discharge.

[0088] In the high-voltage start-up circuit 310, the logic enable unit 3101 receives the enable signal EN from outside the module, enables the high-voltage start-up circuit 310 when the system is powered on, and the current inputs from the HV port, flows through the anti-current backflow unit 3103 and the charging current control unit 3102 and outputs to the VCC port, and charges the VCC capacitor C outside the primary control chip U1VCC ( Figure 7 is not shown) for charging. When the voltage on the VCC capacitor C VCC reaches the corresponding threshold (for example, reaches the UVLO turn-on threshold of the primary control chip U1), the system starts to work normally. At this time, the input enable signal of the logic enable unit 3101 is in an invalid state, and the high-voltage start-up circuit 310 stops working.

[0089] The charging current control unit can adjust and control the charging current of HV to VCC during high-voltage start-up according to the actual circuit conditions, realizing slow / fast, constant current / staged charging. For example, when the system is just powered on, it charges with a smaller current to prevent a large current from charging VCC when the VCC of the primary control chip U1 is short-circuited, causing a safety hazard. When there is no abnormality in the primary control chip U1, the charging current will then be increased to achieve a fast start. In applications where there is no need for power-on VCC short-circuit protection, it can also be set to a constant current charging mode, and the charging current can be adjusted according to the start-up speed required by its actual application to achieve a relatively slow or fast start. The diode D7 in the anti-current backflow unit 3103 is mainly used to prevent current from flowing back from VCC to HV in the reverse direction when the voltage of HV is less than VCC.

[0090] The VCC_OK signal is the system VCC charging completion enable signal, that is, when the voltage on the VCC capacitor reaches the system UVLO turn-on threshold, the VCC_OK signal will become high level, indicating that the system power-on is completed and VCC has reached the normal working threshold. When the system is just powered on, VCC_OK is at a low level. At this time, NM4 is turned off and NM1 is turned on, further enabling NM2, PM1, and PM2 to conduct. HV charges VCC through the diode D7 and PM2. Among them, the diode D7 is used to prevent current from flowing back to HV when the VCC voltage exceeds HV. This diode can also be replaced by the body diode of a high-voltage PMOS. When the VCC voltage reaches the UVLO turn-on threshold, the VCC_OK signal becomes high level, and then NM4 conducts, and NM1, NM2, PM1, and PM2 are turned off, closing the path for HV to charge VCC, and the system completes the high-voltage start-up process. The current mirror composed of PM1 and PM2 can control the magnitude of the VCC charging current.

[0091] The AC signal is shaped into a periodic "bun-shaped wave" HV after passing through the diodes D1 and D2. Due to the working characteristics of the JFET, when the system is working normally, the signal of HV_clamp is a "clipped" "bun-shaped wave", and the maximum value of the HV_clamp voltage is clamped to the threshold voltage of the JFET. Figure 8 In the shown circuit, the "AC power valley detection unit" uses the comparator COMP2 to realize the detection of the "valley" of the AC power signal (in practice, other valley detection methods can also be adopted). Figure 8In it, resistors R1 and R2 divide the voltage of HV_clamp to generate the HVdiv signal, which is used to detect the removal of the AC source. When HVdiv is higher than the internal reference voltage Vref2, the comparator COMP2 outputs a high level to start the counter for timing.

[0092] If the AC source is not removed, the HV_clamp signal remains in the shape of a periodic "chopped-top" "bun wave". Before the counter counts up, HVdiv becomes lower than the reference voltage Vref2 again, and the counter is reset until HVdiv is higher than the reference voltage Vref2 again for a new count.

[0093] If the AC source is removed, the HV_clamp signal will remain at a high voltage, HVdiv will always be higher than the reference voltage Vref2, and the counter will keep counting until it reaches its maximum value, making the ACunplug signal go high, turning on NM3, and starting to discharge the X capacitor. The charge on the X capacitor discharges through the path of JFET - HV - NM3, and the voltage of HV will start to drop until HVdiv is lower than the reference voltage Vref2, at which point the counter is reset and ACunplug is also reset to a low level, completing the X capacitor discharge process. The comparator COMP1 can enable the high-voltage startup circuit 310 to assist in discharging the charge on the X capacitor. When it is detected that the AC source is removed, the comparator COMP1 is enabled. At this time, if VCCdiv (the voltage signal after the VCC voltage is divided by a resistor) is lower than the internal reference voltage Vref1, NM4 will be turned off, turning on NM1, NM2, PM1, and PM2, reusing the circuit of the high-voltage startup part, and allowing HV to charge VCC to assist in discharging the charge on the X capacitor.

[0094] In summary, the high-voltage startup and discharge control circuit provided by any of the above embodiments and the switching power supply having the high-voltage startup and discharge control circuit. The high-voltage startup and discharge control circuit includes a high-voltage startup circuit, a power-down detection circuit, and an X-capacitor discharge circuit. The high-voltage startup circuit is used to provide the working voltage required by the system through the input voltage during the system power-on stage or when the external VCC voltage does not reach the startup threshold of the system control chip until the system works normally; the power-down detection circuit is used to judge whether a power-down occurs at the input end of the switching power supply by detecting the output voltage of the high-voltage clamping circuit in real time and according to this voltage, and output a discharge control signal when judging a power-down at the input end of the switching power supply; the X-capacitor discharge circuit responds to the discharge control signal to discharge the X capacitor until the voltage on the X capacitor is lower than a preset threshold.

[0095] Through the high-voltage startup circuit of this application, the startup time of the switching power supply system is saved. After the system works normally, the high-voltage startup circuit stops working to reduce the power consumption of the system. And when starting up under high voltage, by dynamically controlling the charging current, it can also well avoid the large-current charging problem caused by the VCC short-circuit fault; through the X-capacitor discharge circuit, when the switching power supply loses power, the X capacitor is discharged of its charge. The charge discharge path of the X capacitor is simple, which can ensure the safety of the system; at the same time, the high-voltage startup and discharge control circuit has a simple structure, which also reduces the manufacturing cost.

[0096] Figure 9 It is a waveform diagram of the high-voltage startup process provided by an embodiment of this application. As Figure 9 shown, the voltage HV is in the shape of a periodic "mantou wave", and the HV_clamp signal after being clamped by the high-voltage switching device is in the shape of a "mantou wave" with the top cut off. During the period from the system power-on to the completion of high-voltage startup, the VCC voltage waveform has two different slopes k1 and k2 (here, the VCC voltage waveform when the power-on VCC short-circuit protection function is set is schematically given. In the actual circuit, according to different application scenarios, it can also be a constant-current charge with a fixed slope). When the system is just powered on, the enable signal EN_LI of the charging current control unit is at a low level, and HV charges VCC with a small current, corresponding to the slope k1. If there is no abnormality in the high-voltage startup circuit, as the VCC voltage rises, the supply voltage V5V signal of the high-voltage startup circuit also rises. When it reaches the set threshold, EN_LI becomes high level. At this time, the charging current will be increased, and VCC rises rapidly with a larger slope k2 to achieve rapid startup. When the VCC voltage reaches the set threshold (as shown in the figure, the enable signal VCC_OK = 1), the system completes the high-voltage startup process, and the high-voltage startup circuit stops working.

[0097] Figure 10 It is a waveform diagram of the X-capacitor discharge process provided by an embodiment of this application. As Figure 10 shown, when the AC power source is unplugged, the HV signal presents a continuous high voltage. Since the AC power source valley detection unit can never detect the "valley" of the AC input source, the reset signal Reset of the timing unit will be continuously at a high level, and the timing unit keeps timing. After the set count value is full, the discharge control signal ACunplug becomes high level, and starts to discharge the charge on the X capacitor. After the discharge is completed, the discharge control signal ACunplug becomes low level again, completing the X-capacitor discharge process.

[0098] Figure 11 It is a circuit diagram of the switching power supply provided by an embodiment of this application. As Figure 11 shown, the switching power supply provided by this embodiment includes an X capacitor, a rectifier circuit, a high-voltage clamping circuit, a voltage conversion circuit between the input terminals of the switching power supply, and a primary control chip U1.

[0099] The rectifier circuit in this embodiment includes diode D3, diode D4, diode D5, diode D6 and bus capacitor C bulk . Among them, the first ends of diode D3 and diode D4 are both connected to the primary side of the voltage conversion circuit. The first ends of diode D5 and diode D6 are respectively connected to the second ends of diode D3 and diode D4. The first end of diode D5 is connected to the live wire L of the AC power supply, and the first end of diode D6 is connected to the neutral wire N of the AC power supply. The second ends of diode D5 and diode D6 are both grounded; the first end of bus capacitor C bulk is connected to the first end of diode D4, and the second end of bus capacitor C bulk is grounded. The output of the first end of diode D4 is converted into a DC voltage V bulk after passing through the full-bridge rectifier circuit.

[0100] The voltage conversion circuit includes transformer T1, RCD clamping circuit, feedback circuit, power supply circuit, output circuit. Among them, the RCD clamping circuit includes resistor R clamp , capacitor C clamp , diode D8. The feedback circuit includes an optocoupler device, a three-terminal voltage regulator chip TL431, resistors R1, R2, R3, capacitor C1, auxiliary winding Na, feedback resistors R FBH , R FBL and resistor R CS . The power supply circuit includes auxiliary winding Na and diode D9. The output circuit includes transformer secondary winding Ns, secondary rectifier diode Ds, output capacitor Cout and load resistor R load .

[0101] The primary control chip U1 schematically includes seven pins, namely HV, VCC, FB, GATE, COMP, CS, GND. Among them, the HV pin is used for high-voltage startup and X-capacitor discharge functions; the VCC pin is the power supply pin of the chip; the GATE pin is the drive signal output pin of the power switch tube; the FB pin, CS pin, and COMP pin receive relevant circuit information returned by the feedback circuit to adjust the PWM drive signal output of the chip; the GND pin is the reference ground of the chip.

[0102] The primary control chip U1 includes the above-mentioned high-voltage startup and discharge control circuit. Its specific structure can be the combination of the structure and circuit diagram described in any of the above embodiments. To avoid repetition, it will not be elaborated here.

[0103] Figure 12 is a schematic structural diagram of the primary control chip U1 provided by an embodiment of the present application. As Figure 12As shown in the figure, in addition to the high-voltage start-up and discharge control circuits, the primary control chip U1 provided in this embodiment further includes basic components of a traditional flyback AC-DC converter primary control chip, such as a power supply circuit, an FB / CS detection circuit, a PWM signal generation circuit, and a drive circuit.

[0104] The power supply circuit is used to supply power to the primary control chip U1 during normal operation of the system, and outputs a logic enable signal EN and reference voltage (Vref1 and Vref2) signals; the FB / CS detection circuit receives feedback signals from an external circuit through the FB and CS pins, and generates corresponding control signals to be output to the PWM signal generation circuit; the PWM signal generation circuit receives the control signals output by the FB / CS detection circuit and the feedback information of the COMP pin, and generates a PWM drive signal to the drive circuit; the drive circuit is used to output a drive signal for the power switch tube M1.

[0105] The working process of the switching power supply provided in the above embodiment is as follows:

[0106] Assume that the AC input voltage input by the AC power source is 85V to 265V, and the X capacitor Cx is connected across the live wire L and the neutral wire N of the AC line network. The AC line network voltage is converted into a DC voltage V after passing through the full-bridge rectifier circuit composed of D3, D4, D5, and D6. bulk V bulk is connected to the primary side of the transformer T1.

[0107] The primary control chip U1 is used to output a PWM signal to drive the conduction and turn-off of the primary power tube M1, and an output voltage Vout is generated through the secondary output circuit of the transformer T1, completing the AC-DC voltage conversion of the system.

[0108] When the system is just powered on, the high-voltage start-up circuit inside the primary control chip U1 starts to work and charges the VCC capacitor C VCC connected to the chip. When the voltage on the VCC capacitor C VCC reaches the UVLO turn-on threshold of the control chip U1, the system starts to work normally. The primary control chip U1 drives the primary power switch tube M1 through the GATE pin, and the output voltage V out is gradually established, and the voltage V aux on the auxiliary winding Na is also established accordingly. At this time, the high-voltage start-up circuit in the primary control chip U1 will be turned off. During normal operation of the system, the power supply of the primary control chip U1 is provided by the auxiliary winding, that is, V aux charges the VCC capacitor C VCC through the diode D9.

[0109] It should be noted that the switching power supply and the primary control chip U1 for the switching power supply or voltage converter provided in the above embodiments both have the structures of the high-voltage startup and discharge control circuits described in any of the above embodiments, and can achieve the same technical effects. To avoid repetition, they will not be elaborated here.

[0110] The embodiments of the present application have been described above in conjunction with the accompanying drawings. However, the present application is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present application, those of ordinary skill in the art, without departing from the purpose of the present application and the scope protected by the claims, can make several simple deductions, deformations or substitutions according to the idea of the present application, and all belong to the protection scope of the present application.

Claims

1. A high voltage startup and discharge control circuit, applied to a switching power supply; the switching power supply at least comprises an X capacitor and a high voltage clamping circuit connected between the input terminals of the switching power supply; The AC input voltage is passed through the X capacitor to obtain the input voltage of the high-voltage clamping circuit; the characteristics are: The high voltage starting and discharge control circuit comprises: A high-voltage startup circuit is connected to the high-voltage clamping circuit; the high-voltage startup circuit is used to provide the system with the voltage required for operation through the input voltage when the system is powered on or the external VCC voltage does not reach the startup threshold of the system control chip; and stops working after the system works normally; A power-off detection circuit is connected to the high-voltage clamp circuit; the power-off detection circuit is used to obtain the output voltage of the high-voltage clamp circuit, and judge whether the input end of the switching power supply has a power-off according to the output voltage; when it is judged that the input end of the switching power supply has a power-off, output a discharge control signal; The X-capacitor discharge circuit is connected to the high-voltage clamp circuit and the power-off detection circuit. In response to the discharge control signal, the X-capacitor discharge circuit discharges the X-capacitor until the voltage on the X-capacitor is lower than a preset threshold.

2. The high voltage starting and discharge control circuit according to claim 1, characterized in that: The high-voltage startup circuit includes a logic enabling unit and a charging current control unit; After the system is powered on, the logic enabling unit responds to an enabling signal to charge the VCC capacitor providing the external VCC voltage through the output voltage obtained from the high-voltage clamping circuit until the external VCC voltage reaches the startup threshold of the system control chip; The charging current control unit is used to adjust the charging mode and / or charging current when charging the VCC capacitor according to the startup speed required by the high-voltage startup circuit.

3. The high voltage starting and discharge control circuit according to claim 2, characterized in that: The logic enable unit includes a comparator COMP1, a logic NOT gate, a logic AND gate, a resistor R3, a switch tube NM4, a voltage regulator diode Z1, a switch tube NM1 and a resistor R4; the in-phase input terminal of the comparator COMP1 is used to obtain a first reference voltage, the inverting input terminal of the comparator COMP1 is used to obtain a voltage division signal of the external VCC voltage, and the enable terminal of the comparator COMP1 is used to obtain an enable signal indicating that the input terminal of the switching power supply has lost power; the input terminal of the logic NOT gate is connected to the output terminal of the comparator COMP1; the first input terminal of the logic AND gate is connected to the output terminal of the logic NOT gate, and the second input terminal of the logic AND gate is used to obtain an enable signal indicating that the charging of the VCC capacitor is completed; the resistor R3 The first end is connected to the output end of the high-voltage clamping circuit, and is used to obtain the output voltage of the high-voltage clamping circuit; the control end of the switch tube NM4 is connected to the output end of the logic AND gate, the first end of the switch tube NM4 is connected to the second end of the resistor R3, and the second end of the switch tube NM4 is connected to the preset voltage end; the first end of the voltage regulator diode Z1 is connected to the second end of the resistor R3, and the second end of the voltage regulator diode Z1 is connected to the preset voltage end; the control end of the switch tube NM1 is connected to the second end of the resistor R3, and the first end of the switch tube NM1 is connected to the first end of the resistor R3; the first end of the resistor R4 is connected to the second end of the switch tube NM1, and the second end of the resistor R4 is connected to the preset voltage end; The charging current control unit includes a switch tube PM2, a switch tube PM1, a switch tube NM2 and a variable resistor Rvar; the first end of the switch tube PM2 is connected to the input end of the charging current control unit for obtaining the output voltage of the high-voltage clamping circuit, and the second end of the switch tube PM2 is connected to the output end of the charging current control unit; the control end of the switch tube PM1 is connected to the control end of the switch tube PM2, and the first end of the switch tube PM1 is connected to the first end of the switch tube PM2; the substrates of the switch tube PM1 and the switch tube PM2 are connected; the control end of the switch tube NM2 is connected to the second end of the switch tube NM1, and the first end of the switch tube NM2 is connected to the second end of the switch tube PM1; the control end of the variable resistor Rvar is used to obtain an external input adjustment control signal, the first end of the variable resistor Rvar is connected to the second end of the switch tube NM2, and the second end of the variable resistor Rvar is connected to the preset voltage end.

4. The high voltage starting and discharge control circuit according to claim 2, characterized in that: The high-voltage startup circuit also includes a current backflow prevention unit connected between the output end of the high-voltage clamping circuit and the charging current control unit, and used to prevent the current from flowing from the external VCC voltage output end to the output end of the high-voltage clamping circuit when the output voltage of the high-voltage clamping circuit is less than the external VCC voltage; The current backflow prevention unit includes at least one of a high-voltage diode and a high-voltage PMOS device.

5. The high voltage starting and discharge control circuit according to claim 1, characterized in that: The high-voltage startup circuit is connected to the power-off detection circuit; the high-voltage startup circuit charges the VCC capacitor via the output voltage obtained from the high-voltage clamping circuit in response to the discharge control signal.

6. The high voltage starting and discharge control circuit according to claim 1, characterized in that: The X capacitor discharge circuit comprises a charge discharge enabling unit and a charge discharge unit; the charge discharge enabling unit outputs a discharge enabling signal in response to the discharge control signal; the charge discharge unit discharges the X capacitor to ground in response to the discharge enabling signal until the voltage on the X capacitor is lower than a preset threshold; The charge discharge enabling unit includes a switch tube NM3; the charge discharge unit includes a resistor R5; the control end of the switch tube NM3 is used to obtain the discharge control signal, and the second end of the switch tube NM3 is connected to the preset voltage end; the first end of the resistor R5 is connected to the input end of the charge discharge unit, and the second end of the resistor R5 is connected to the second end of the switch tube NM3.

7. The high voltage starting and discharge control circuit according to claim 1, characterized in that: The power failure detection circuit includes an AC valley detection unit and a timing unit; The AC valley detection unit is used to compare the output voltage of the high-voltage clamp circuit obtained in the current cycle with the output voltage obtained in the previous cycle, and when it is not detected that the output AC power obtained in the current cycle has the same valley value as the output voltage obtained in the previous cycle, determine that the input end of the switching power supply has a power failure, and output a first timing signal; when it is detected that the output AC power obtained in the current cycle has the same valley value as the output AC power obtained in the previous cycle, determine that the input end of the switching power supply has not a power failure, and output a second timing signal; The timing unit starts timing in response to the first timing signal; and resets timing in response to the second timing signal; And, when the second timing signal is not obtained within a first preset time period after the timing starts, the discharge control signal is output.

8. The high voltage starting and discharge control circuit according to claim 7, characterized in that: The AC valley detection unit includes a resistor R1, a resistor R2, and a comparator COMP2; the first end of the resistor R1 is connected to the input end of the AC valley detection unit to obtain the output voltage of the high-voltage clamping circuit; the first end of the resistor R2 is connected to the second end of the resistor R1, and the second end of the resistor R2 is connected to the preset voltage end; the in-phase input end of the comparator COMP2 is connected to the second end of the resistor R1, the inverting input end of the comparator COMP2 is used to obtain a second reference voltage, and the output end of the comparator COMP2 is connected to the output end of the AC valley detection unit; The timing unit includes n stages of D flip-flops connected in series; the reset ends of the n stages of D flip-flops are all connected to the input end of the timing unit for obtaining the first timing signal or the second timing signal; the output end of the last stage of the D flip-flop is connected to the output end of the timing unit.

9. The high voltage starting and discharge control circuit according to claim 1, characterized in that: The high voltage clamping circuit comprises at least a junction field effect transistor or a depletion-type gallium nitride transistor; The high-voltage clamping circuit, the high-voltage startup circuit, the power-off detection circuit and the capacitor discharge circuit are integrated into an integrated chip; Alternatively, the high-voltage startup circuit, the power-off detection circuit and the capacitor discharge circuit are integrated into an integrated chip, and an input end of the integrated chip is connected to the output end of the high-voltage clamping circuit.

10. A switching power supply, characterized in that: At least comprising an X capacitor connected between the input terminals of a switching power supply, a high voltage clamping circuit and a high voltage startup and discharge control circuit as claimed in any one of claims 1 to 9; The high-voltage startup and discharge control circuit is used to provide the voltage required for system operation through a power supply circuit when the system is powered on, so as to achieve rapid startup of the switching power supply; after the system works normally, stop supplying power through the external power supply circuit; and, when it is determined that a power failure occurs at the input end of the switching power supply, discharge the capacitor until the voltage on the capacitor is lower than a preset threshold.

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