CN117526738A - X capacitor discharging method, discharging circuit and switching power supply - Google Patents

X capacitor discharging method, discharging circuit and switching power supply Download PDF

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Publication number
CN117526738A
CN117526738A CN202311211760.2A CN202311211760A CN117526738A CN 117526738 A CN117526738 A CN 117526738A CN 202311211760 A CN202311211760 A CN 202311211760A CN 117526738 A CN117526738 A CN 117526738A
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CN
China
Prior art keywords
capacitor
voltage
circuit
node
power supply
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CN202311211760.2A
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Chinese (zh)
Inventor
陈湛
张少斌
白永江
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Hangzhou Silergy Semiconductor Technology Ltd
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Hangzhou Silergy Semiconductor Technology Ltd
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Priority to CN202311211760.2A priority Critical patent/CN117526738A/en
Publication of CN117526738A publication Critical patent/CN117526738A/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0032—Control circuits allowing low power mode operation, e.g. in standby mode
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses an X capacitor discharging circuit and an X capacitor discharging method for a switching power supply, wherein the switching power supply comprises an X capacitor, a rectifying circuit and a switching circuit, an alternating current input voltage is obtained through the X capacitor and the rectifying circuit to obtain the input voltage of the switching circuit, a second end of a first capacitor is configured as a first node, and the first end of the first capacitor is at least coupled to one end of the X capacitor; when the time that the voltage of the first node continuously lower than the first threshold value exceeds the first time is detected, the alternating current input voltage is judged to be disconnected, and the X capacitor is discharged until the voltage on the X capacitor is lower than a preset value, so that the purpose of lower power consumption of the whole machine is achieved.

Description

X capacitor discharging method, discharging circuit and switching power supply
Technical Field
The invention relates to the technical field of power electronics, in particular to an X capacitor discharging method, a discharging circuit and a switching power supply.
Background
In an AC/DC power supply, 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 to an AC input terminal. After the ac input is powered down, the voltage on the X capacitor remains. The residual voltage may be harmful to humans, so regulations dictate that the voltage across the X capacitor must be reduced below a certain value during a period of power outage.
Therefore, in the design of the switching power supply, the residual voltage is discharged by adopting the X-capacitor discharging circuit, so as to ensure the safety of human bodies. The current common tapping method is to discharge with a resistor or through the HV pin of a PWM controller. Referring to fig. 1 and 2, there are a schematic diagram and an operating waveform of an X capacitor discharging circuit for discharging through an HV pin of a PWM controller. U1 is PWM controller chip, and HVpin foot is inside to have two modules, AC detection module and high voltage discharge control module.
As shown in right figure 2, at time t1, the voltage of the HV node is always high because of the residual voltage on the X capacitor C1 when the AC input voltage AC is powered off; at time t2, the AC detection module of the PWM controller chip U1 detects that the input is pulled out, i.e. the AC input voltage is disconnected, at this time, the AC detection module instructs the high voltage discharge control module to start discharging and generate a pull-down current, and the current flows from the cathodes of the two diodes D1 and D2 from the inside of the chip U1 to the Vcc pin or GND pin of the chip U1, and as the voltage of the HV node is reduced, the voltage on the X capacitor C1 is also released. However, this method has a disadvantage in that since the peak value of the voltage of the HV node is close to 400V, in the AC detection module, a voltage dividing resistor is generally used to change the high voltage of the HV node into a low voltage signal of 5V or less, and then internal operations such as comparison and judgment are performed, and the voltage dividing resistor is generally several tens of megaohms, and the power consumption consumed at the AC input voltage of 240V is several milliwatts, which is too large for the low power consumption requirement of 5 milliwatts of the whole machine.
Disclosure of Invention
In view of this, the present invention provides a new discharging method for an X capacitor, which uses a capacitor to sample an ac input voltage, isolate dc, and make the loss approach zero watt, so that the whole machine can meet the requirement of low power consumption.
In a first aspect, the present invention provides an X-capacitor discharging method for a switching power supply, the switching power supply including an X-capacitor, a rectifying circuit, and a switching circuit, an ac input voltage being obtained by the X-capacitor and the rectifying circuit as an input voltage of the switching circuit, characterized in that,
configuring a second end of a first capacitor as a first node, wherein the first end of the first capacitor is coupled to at least one end of the X capacitor;
and judging whether the alternating current input voltage is disconnected or not according to the voltage of the first node, and discharging the X capacitor until the voltage on the X capacitor is lower than a preset value when the alternating current input voltage is judged to be disconnected.
Preferably, the ac input voltage is determined to be off when the time when the voltage of the first node is detected to be continuously lower than the first threshold exceeds the first time.
Preferably, when the time when the voltage of the first node is detected to be continuously higher than the first threshold exceeds the second time, the existence of the alternating input voltage is judged, and the X capacitor is not discharged, wherein the second time is smaller than the first time.
Preferably, the first threshold is greater than zero.
Preferably, the voltage of the first node is clamped and then detected.
Preferably, the first end of the first capacitor is coupled to the first end or the second end of the X capacitor.
Preferably, the voltage of the first node is detected once in each power frequency period to determine whether the ac input voltage is disconnected.
In a second aspect, the present invention provides an X capacitor discharging circuit for a switching power supply, where the switching power supply includes an X capacitor, a rectifying circuit, and a switching circuit, and an ac input voltage is obtained by the X capacitor and the rectifying circuit, and the X capacitor discharging circuit is characterized by comprising:
a first capacitor having a first end coupled to one end of the X capacitor and a second end configured as a first node;
the AC detection module judges whether the alternating current input voltage is disconnected or not according to the voltage of the first node;
and the high-voltage discharging module is used for discharging the X capacitor until the voltage on the X capacitor is lower than a preset value in response to the disconnection of the alternating current input voltage.
Preferably, the AC input voltage is determined to be off when the AC detection module detects that the voltage of the first node is continuously lower than the first threshold for more than a first time.
Preferably, when the AC detection module detects that the time when the voltage of the first node is continuously higher than the first threshold exceeds a second time, the AC input voltage is judged to exist, and the high-voltage discharge module does not discharge the X capacitor, wherein the second time is smaller than the first time.
Preferably, the first threshold is greater than zero.
Preferably, the first end of the first capacitor is coupled to the first end or the second end of the X capacitor, and the second end of the first capacitor is coupled to the AC detection module.
Preferably, the AC detection module includes a clamping circuit for clamping the voltage of the first node and then detecting the voltage.
Preferably, the clamping circuit includes a zener diode, and the clamping circuit clamps the voltage of the first node between a regulated voltage of the zener diode and a forward conduction voltage drop.
Preferably, the high voltage discharge module includes a first diode and a second diode, anodes of the first diode and the second diode are respectively connected to two ends of the X capacitor, a common terminal of a cathode thereof is configured as a second node, and a first terminal of the first capacitor is coupled to the second node.
Preferably, the first capacitor is integrated inside a chip, and the second node is coupled to a first end of the first capacitor and a high voltage discharge control circuit in the high voltage discharge module through pins of the same chip, respectively.
Preferably, the high voltage discharging module is responsive to the ac input voltage to disconnect the second node from ground or a power supply terminal to discharge the X capacitance.
Preferably, the first diode and the second diode are two diodes of which two anodes are respectively connected to two ends of the X capacitor in the rectifying circuit, the second node is an output end of the rectifying circuit which is not grounded, and the second node is connected to the ground potential through an element in the switching circuit.
Preferably, the high voltage discharge module further includes a transistor connected in series between the second node and a ground potential, the high voltage discharge module controlling the transistor to be turned on in response to the ac input voltage being turned off.
In a third aspect, the present invention provides a switching power supply, including an X capacitor, a rectifying circuit, and a switching circuit, where an ac input voltage is obtained by the X capacitor and the rectifying circuit, and the switching power supply is characterized by comprising:
the X capacitor discharging circuit.
The invention aims to provide an X capacitor discharging method, which adopts a first capacitor coupled to at least one end of an X capacitor to sample an alternating current input voltage, and the characteristic that the capacitor isolates direct current and passes alternating current is adopted to enable the sampling loss of the alternating current input voltage to approach zero watt, and further clamp the sampling voltage of the alternating current input voltage without dividing voltage by a divider resistor, so that the loss caused by the divider resistor is avoided, and the power consumption of the whole machine is greatly reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a conventional X-capacitor discharge circuit;
FIG. 2 is a diagram showing the operation waveforms of a conventional X capacitor discharge circuit;
FIG. 3 is a schematic diagram of an X capacitor discharging circuit according to a first embodiment of the present invention;
FIG. 4 is a schematic diagram of an X capacitor discharging circuit according to a second embodiment of the present invention;
FIG. 5 is a diagram showing an operational waveform of an X capacitor discharging circuit according to a second embodiment of the present invention;
FIG. 6 is a schematic diagram of an X capacitor discharging circuit according to a third embodiment of the present invention;
FIG. 7 is a schematic diagram of an X capacitor discharging circuit according to a fourth embodiment of the present invention;
FIG. 8 is a waveform of the X capacitor discharging circuit according to the fifth embodiment of the present invention;
fig. 9 is a schematic diagram of an X capacitor discharging circuit according to a sixth embodiment of the present invention.
Detailed Description
The present invention is described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth in detail. The present invention will be fully understood by those skilled in the art without the details described herein. Well-known methods, procedures, flows, components and circuits have not been described in detail so as not to obscure the nature of the invention.
Moreover, those of ordinary skill in the art will appreciate that the drawings are provided herein for illustrative purposes and that the drawings are not necessarily drawn to scale.
Meanwhile, it should be understood that in the following description, "circuit" refers to a conductive loop constituted by at least one element or sub-circuit through electrical connection or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or being "connected between" two nodes, it can be directly coupled or connected to the other element or intervening elements may be present and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled to" or "directly connected to" another element, it means that there are no intervening elements present between the two.
Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, it is the meaning of "including but not limited to".
In the description of the present invention, it should be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Furthermore, in the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more.
Fig. 3 is a schematic diagram of an X-capacitor discharging circuit for a switching power supply according to a first embodiment of the present invention. As shown in fig. 3, the switching power supply of the present embodiment includes an X capacitor C1, a rectifying circuit 31, a switching circuit 32, an AC detection module 33, and a high-voltage discharge module 34. The ac input voltage Vac obtains the input voltage Vbus of the switching circuit 33 via the X capacitor C1 and the rectifying circuit 31. Here, the switching circuit 32 includes all power converters including switching devices, and the specific configuration thereof is not limited.
The AC detection module 33 receives information of the AC input voltage Vac through the first capacitor C2, the first end of the first capacitor C2 is at least coupled to one end of the X capacitor C1, the X capacitor C1 is connected across the AC input terminal L and the N point, and the second end of the first capacitor C2 is configured as a first node. The first end of the first capacitor C2 is coupled to the first end or the second end of the X capacitor C1, and the second end of the first capacitor C2 is coupled to the input end of the AC detection module 33.
The AC detection module 33 is configured to detect the voltage of the first node, so as to determine whether the AC input voltage Vac is disconnected. Specifically, when the AC input voltage Vac exists, the voltage at the N point or the L point has a rising edge, and the first capacitor C2 couples this rising edge to the AC detection module 33; when the AC input voltage Vac is off, the AC detection module 33 receives no signal of the transition, and determines that the AC input voltage Vac is off.
Preferably, when the AC detection module 33 detects that the time when the voltage Vn of the first node continues to be lower than the first threshold Vth1 exceeds the first time T1, it determines that the AC input voltage Vac is turned off, and at this time, the X capacitor C1 is discharged; when the time when the voltage of the first node is detected to be continuously higher than the first threshold Vth exceeds the second time T2, it is judged that the alternating input voltage Vac exists, and the X capacitor is not discharged at this time, wherein the second time T2 is smaller than the first time T1.
Further, the AC detection module 33 detects the voltage of the first node once every power frequency period to determine whether the AC input voltage Vac is disconnected. And preferably, the AC detection module 33 determines that the AC input voltage Vac is turned off after performing the detection determination multiple times, that is, when the AC detection module 33 detects that the voltage of the first node is continuously lower than the first threshold Vth1 for more than the first time T1 in a plurality of continuous power frequency periods, the AC detection module 33 determines that the AC input voltage Vac is turned off to enhance the reliability of the detection.
The high-voltage discharging module 34, in response to the AC detecting module 33 detecting that the AC input voltage Vac is off, discharges the X capacitor C1 until the voltage across the X capacitor C1 is lower than a predetermined value. The predetermined value is adapted to the specific requirements of the safety standard.
According to the X capacitor discharging method, the alternating current input voltage Vac is sampled by adopting the first capacitor C2 at least coupled to one end of the X capacitor C1, and the sampling loss of the alternating current input voltage Vac is close to zero watt due to the characteristic that the capacitor isolates direct current and passes through alternating current, so that the whole machine can meet the requirement of low power consumption.
Fig. 4 is a schematic diagram of an X-capacitor discharging circuit for a switching power supply according to a second embodiment of the present invention. The switching power supply of the present embodiment includes an X capacitor C1, a rectifying circuit 31, a switching circuit 32, an AC detection module 43, and a high-voltage discharge module 34. The difference from the first embodiment is only that the schematic structure of the AC detection module 43 is shown, and the connection and functions of other circuit modules are the same as those of the first embodiment, and are not described herein.
The AC detection module 43 includes a clamp circuit 431, a comparison circuit 432, and a timing circuit 433. The clamp circuit 431 is used for clamping the voltage Vn of the first node and then detecting the voltage Vn. The clamping circuit 431 includes a zener diode D7, and the clamping circuit 431 clamps the voltage Vn of the first node between the regulated voltage of the zener diode D7 and the forward conduction voltage drop. The voltage Vn of the first node does not exceed the regulated voltage (clamp voltage) of the zener diode D7 due to the presence of the zener diode D7, and preferably the regulated voltage of the zener diode D7 is configured to several V to ten or more V, which is not particularly limited here, and may be configured according to the needs of the circuit. Therefore, in the AC detection module 43, the voltage dividing resistor is no longer required to detect the low voltage signal in which the voltage Vn of the first node is 5V or less. Therefore, the capacitor discharge circuit of the embodiment also has no power consumption of the voltage dividing resistor, so that the power consumption of the whole machine can be reduced.
Here, it should be noted that, the resistor R2 connected between the first node and the input terminal of the AC detection module 43 is a protection resistor, which may be configured to have a smaller resistance value, or may be zero ohm, that is, the resistor is not provided, and since the influence on the voltage Vn of the first node is smaller, the voltage of the common node between the resistor R2 and the input terminal of the AC detection module 43 is also equivalent to the voltage Vn of the first node in this embodiment.
The comparison circuit 432 compares the voltage Vn of the first node with the first threshold Vth1, and outputs the comparison result Vc. The timing circuit 433 receives the comparison result Vc, counts a level interval in which the comparison result Vc indicates that the voltage Vn of the first node is lower than the first threshold Vth1, and generates a detection result Vdet in a state of indicating that the input voltage Vac is turned off when the count result exceeds the first time T1, and the AC detection module 43 generates an enable signal according to at least the detection result Vdet of one detection period, where the enable signal is used to instruct the high voltage discharge module 34 to discharge the X capacitor C1.
The high voltage discharge module 34 includes a first diode D1, a second diode D2, and a high voltage discharge control circuit 341. Anodes of the first diode D1 and the second diode D2 are respectively connected to both ends of the X capacitor C1, a common end of cathodes of the first diode D1 and the second diode D2 is configured as a second node, and the second node is coupled to the high voltage discharge control circuit 341 in the high voltage discharge module 34. It should be noted that, the resistor R1 between the common terminal of the cathodes of the first diode D1 and the second diode D2 and the input terminal of the high voltage discharge control circuit 341 is a protection resistor, which prevents the voltage or current input to the HV node from being too large, and in some embodiments, may be zero ohm.
The first diode D1, the second diode D2, and the first capacitor C2 are configured to be externally connected to the outside of the control chip U1, and the high-voltage discharge control circuit 341 and the AC detection module 43 are configured to be integrally sealed inside the control chip U1. The high voltage discharging control circuit 341, in response to the enable signal, characterizes the ac input voltage Vac to be disconnected, couples the second node to the ground potential GND or the power supply terminal Vcc to discharge the X capacitor C1. Specifically, the high voltage discharge control circuit 341 generates a pull-down current in response to the enable signal, the pull-down current flows from the cathode of the first diode D1 and the second diode D2 from the inside of the control chip U1 to the Vcc pin or the GND pin of the control chip U1 via the HVpin pin, and the voltage on the X capacitor C1 is also discharged as the HV node voltage decreases.
Fig. 5 is an operation waveform of the X capacitor discharging circuit according to the second embodiment of the present invention. Wherein Vac is the waveform of the alternating current input voltage, is the voltage value from the L point to the N point, has positive negative (-390V-390V) and is a standard sine voltage waveform; VN is the voltage at N point, that is, the N point waveform seen with the ground potential GND of the control chip U1 as the reference point; since only the N-point waveform is of interest, the L-point waveform is absent, so that the waveform is approximately a sinusoidal half wave, has only positive pressure (0V-390V), and has no negative pressure.
The voltage Vn of the first node is coupled by the first capacitor C2 with one end connected to the N point, when the voltage at the N point has a rising edge, the voltage Vn of the first node also rises until being clamped at its voltage stabilizing value (typically several V to ten and several V) by the zener diode D7; when the voltage rising slope of the N point decreases and gradually approaches 0, the voltage Vn of the first node also starts to decrease and gradually decreases to 0V; when the voltage at the N point has a falling edge, the voltage Vn of the first node is clamped at its forward conduction voltage drop value (about-0.6V) by the zener diode and is kept unchanged, so that it is known that the voltage Vn of the first node can reflect the rate of change of the voltage at the N point and also can reflect the rate of change of the AC input voltage Vac, and therefore, the AC detection module 43 can detect the power-down information of the AC input voltage Vac according to the voltage Vn of the first node, and thus determine whether to perform the discharging of the X capacitor C1.
At time t1, when the AC input voltage AC is powered off, the AC input voltage Vac will remain unchanged, as shown in fig. 5, and the voltage at the N point is maintained at 390V under the action of the X capacitor C1, because the voltage Vn of the first node is characterized by the change rate of the voltage at the N point, the voltage Vn of the first node will be maintained near 0V, based on which, in the embodiment of the present invention, the value of the first threshold Vth1 is selected to be slightly greater than zero, for example, 0.5V, but the present invention is not limited to specific values. Accordingly, the AC detection module 43 can determine whether the AC input voltage AC power-off occurs according to whether the time for which the voltage Vn of the first node continuously falls below the first threshold Vth1 exceeds the first time T1.
According to the X capacitor discharging method, the alternating current input voltage Vac is sampled by the first capacitor C2 at least coupled to one end of the X capacitor C1, and the sampling loss of the alternating current input voltage Vac is close to zero watt due to the characteristic that direct current is isolated by the capacitor, and the sampling voltage of the alternating current input voltage Vac is further clamped without voltage dividing resistance to divide, so that the loss caused by the voltage dividing resistance is avoided, and the power consumption of the whole machine is greatly reduced.
Fig. 6 is a schematic diagram of an X-capacitor discharging circuit for a switching power supply according to a third embodiment of the present invention. The difference between the first capacitor C2 and the second embodiment is that the first end of the first capacitor C2 is not connected to the N point but connected to the L point, and the connection and the function of other circuit modules are the same as those of the first embodiment, which is not described herein.
Fig. 7 is a schematic diagram of an X-capacitor discharging circuit for a switching power supply according to a fourth embodiment of the present invention. The only difference from the second embodiment is that the first capacitor C2 is integrated inside the control chip U1. Anodes of the first diode D1 and the second diode D2 are respectively connected to two ends of the X capacitor C1, a common end of cathodes of the first diode D1 and the second diode D2 is configured as a second node, the second node is respectively coupled to the first end of the first capacitor C2 and the high voltage discharge control circuit 341 through the pin HV of the same control chip U1 via the protection resistor R2, and a second end of the first capacitor C2 is connected to the AC detection module 73. In this embodiment, the first diode D1 and the second diode D2 form a rectifying circuit, and the output voltage of the rectifying circuit may reflect the change of the AC power supply, and the change of the AC input voltage Vac may be reflected by detecting the output voltage of the rectifying circuit, so the AC detection module 43 may detect the power failure information of the AC input voltage Vac according to the voltage Vn of the first node, and thereby determine whether to perform the discharging of the X capacitor C1. The connection and function of other circuit modules are the same as those in the first embodiment, and will not be described here again. The first capacitor C2 inside the control chip U1 may be a capacitor on a silicon chip, or may be a sealed capacitor.
Fig. 8 is a schematic diagram of an X-capacitor discharging circuit for a switching power supply according to a fifth embodiment of the present invention. The only difference from the second embodiment is that the high voltage discharge module 84 further comprises a transistor M1 connected in series between the second node and ground potential, in this embodiment the control terminal of the transistor M1 is connected to the COMP pin for generating the voltage or current compensation signal. The high voltage discharge control circuit 841 controls the transistor M1 to be turned on to discharge the voltage on the X capacitor C1 in response to the ac input voltage Vac being turned off. When the AC detection module 33 detects that the AC input voltage Vac is disconnected, the high voltage discharge control circuit 841 shorts the COMP pin with the power supply terminal Vcc, and at this time, the transistor M1 (depletion MOSFET) is turned on, and the discharge current flows to the power supply terminal Vcc through the resistor R1, the transistor M1, and the diode D7, so as to achieve the purpose of discharging the X capacitor C1.
It should be noted that, the control terminal of the transistor M1 is connected to the COMP pin, and only the function of multiplexing the COMP pin is selected manually, and if the control terminal of the transistor M1 is separately connected to a dedicated pin or connected to another pin, the same function can be achieved, so the present invention is not limited thereto.
Fig. 9 is a schematic diagram of an X-capacitor discharging circuit for a switching power supply according to a sixth embodiment of the present invention. The difference from the second embodiment is that the first diode and the second diode in the high voltage discharging module 94 are not separately provided, but two anodes in the multiplexing rectifier circuit 31 are respectively connected to two diodes D5 and D3 at two ends of the X capacitor C1, as the first diode D1 and the second diode D2, the second node is one output end of the rectifier circuit 31 which is not grounded, that is, a common node of the diodes D5 and D3, the second node is connected to the high voltage discharging control circuit 941 through the inductance element L1 in the switch circuit 92, the high voltage discharging control circuit 941 is turned on with the ground potential or the power supply end Vcc in response to the ac input voltage Vac, and it is to be noted that the PFC circuit is also schematically illustrated in fig. 9, including but not limited to M2 in this example and the PFC controller which controls the PFC circuit, and when included, the node needs to be connected to the input end of the PFC.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, and various modifications and variations may be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (20)

1. An X capacitor discharging method for a switch power supply, the switch power supply comprises an X capacitor, a rectifying circuit and a switch circuit, an alternating current input voltage is obtained by the X capacitor and the rectifying circuit to obtain the input voltage of the switch circuit, the X capacitor discharging method is characterized in that,
configuring a second end of a first capacitor as a first node, wherein the first end of the first capacitor is coupled to at least one end of the X capacitor;
and judging whether the alternating current input voltage is disconnected or not according to the voltage of the first node, and discharging the X capacitor until the voltage on the X capacitor is lower than a preset value when the alternating current input voltage is judged to be disconnected.
2. The X-capacitor discharging method for a switching power supply according to claim 1, wherein the ac input voltage is judged to be off when a time when the voltage of the first node is detected to be continuously lower than a first threshold value exceeds a first time.
3. The X-capacitor discharging method for a switching power supply according to claim 2, wherein the presence of the ac input voltage is judged when a time in which the voltage of the first node is detected to be higher than a first threshold value exceeds a second time, which is smaller than the first time, without discharging the X-capacitor.
4. The X-capacitor discharging method for a switching power supply according to claim 2, wherein the first threshold is greater than zero.
5. The X-capacitor discharging method for a switching power supply according to claim 1, wherein the voltage of the first node is clamped and then detected.
6. The X-capacitor discharging method for a switching power supply according to claim 1, wherein a first end of the first capacitor is coupled to a first end or a second end of the X-capacitor.
7. The X-capacitor discharging method for a switching power supply according to claim 1, wherein the voltage of the first node is detected once every power frequency period to determine whether the ac input voltage is off.
8. An X capacitor discharging circuit for a switching power supply, the switching power supply including an X capacitor, a rectifying circuit, and a switching circuit, an ac input voltage being obtained by the X capacitor and the rectifying circuit as an input voltage of the switching circuit, the switching power supply comprising:
a first capacitor having a first end coupled to one end of the X capacitor and a second end configured as a first node;
the AC detection module judges whether the alternating current input voltage is disconnected or not according to the voltage of the first node;
and the high-voltage discharging module is used for discharging the X capacitor until the voltage on the X capacitor is lower than a preset value in response to the disconnection of the alternating current input voltage.
9. The X-capacitor discharge circuit for a switching power supply of claim 8, wherein the AC input voltage is determined to be off when the AC detection module detects that the voltage at the first node is below a first threshold for more than a first time.
10. The X-capacitor discharge circuit for a switching power supply of claim 9, wherein the AC detection module determines that the AC input voltage is present when it detects that the voltage at the first node is above a first threshold for more than a second time, wherein the high voltage discharge module does not discharge the X-capacitor, wherein the second time is less than the first time.
11. The X-capacitor discharge circuit for a switching power supply of claim 9, wherein the first threshold is greater than zero.
12. The X-capacitor discharge circuit for a switching power supply of claim 8, wherein a first end of the first capacitor is coupled to either a first end or a second end of the X-capacitor, and a second end of the first capacitor is coupled to the AC detection module.
13. The X-capacitor discharge circuit of claim 8, wherein the AC detection module includes a clamping circuit for clamping the voltage of the first node and then detecting the voltage.
14. The X-capacitor discharge circuit for a switching power supply of claim 13, wherein the clamping circuit comprises a zener diode, the clamping circuit clamping the voltage of the first node between a regulated voltage of the zener diode and a forward conduction voltage drop.
15. The X-capacitor discharge circuit for a switching power supply of claim 8, wherein the high voltage discharge module comprises a first diode and a second diode, anodes of the first diode and the second diode being connected to two ends of the X-capacitor, respectively, a common terminal of a cathode thereof being configured as a second node, a first terminal of the first capacitor being coupled to the second node.
16. The X-capacitor discharge circuit for a switching power supply of claim 15, wherein the first capacitor is integrated inside a chip, and the second node is coupled to a first terminal of the first capacitor and a high voltage discharge control circuit in the high voltage discharge module, respectively, through pins of the same chip.
17. The X-capacitor discharge circuit for a switching power supply of claim 15, wherein the high voltage discharge module is responsive to the ac input voltage being disconnected to couple the second node to ground or a supply terminal to discharge the X-capacitor.
18. The X-capacitor discharge circuit for a switching power supply according to claim 17, wherein the first diode and the second diode are two diodes of the rectifying circuit having two anodes respectively connected to both ends of the X-capacitor, the second node is an ungrounded output terminal of the rectifying circuit, and the second node is connected to the ground potential through an element in the switching circuit.
19. The X-capacitor discharge circuit for a switching power supply of claim 15 wherein the high voltage discharge module further comprises a transistor connected in series between the second node and ground potential, the high voltage discharge module controlling the transistor to turn on in response to the ac input voltage being off.
20. The utility model provides a switching power supply, includes X electric capacity, rectifier circuit and switching circuit, and the input voltage of switching circuit is obtained to alternating current input voltage through X electric capacity and rectifier circuit, its characterized in that still includes:
the X-capacitor discharge circuit of any one of claims 8-19.
CN202311211760.2A 2023-09-19 2023-09-19 X capacitor discharging method, discharging circuit and switching power supply Pending CN117526738A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202311211760.2A CN117526738A (en) 2023-09-19 2023-09-19 X capacitor discharging method, discharging circuit and switching power supply

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202311211760.2A CN117526738A (en) 2023-09-19 2023-09-19 X capacitor discharging method, discharging circuit and switching power supply

Publications (1)

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CN117526738A true CN117526738A (en) 2024-02-06

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Application Number Title Priority Date Filing Date
CN202311211760.2A Pending CN117526738A (en) 2023-09-19 2023-09-19 X capacitor discharging method, discharging circuit and switching power supply

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