Capacitor discharge method, control chip and switching power supply

Abstract

This application provides a method for discharging an X-capacitor, a control chip, and a switching power supply. In the initial state, a first current is used to pull down the high-voltage start-up pin of the control chip connected to the X-capacitor, and the voltage change on the high-voltage start-up pin is periodically detected. If no positive slope is detected on the pin voltage within a first time period, the first current is switched to a slightly larger second current. If the voltage drop slope is detected to be greater than a preset slope threshold within a second time period, the second current is switched to an even larger third current. Thus, regardless of whether the switching power supply has an AC or DC input, the third current can be used to quickly discharge the X-capacitor when the input power is cut off. During normal operation, the third current is not switched to, allowing the same control chip to simultaneously meet both AC and DC input application scenarios, avoiding the continuous power consumption problem caused by the discharge resistor, and saving area and cost.

Description

Technical Field

[0001] This application relates to the field of switching power supply technology, specifically to an X-capacitor discharge method, a control chip, and a switching power supply. Background Technology

[0002] Industrial power supplies typically require compatibility with both AC and DC inputs. AC inputs generally use single-phase AC mains power, ranging from 88 to 264 VAC; DC inputs can be powered by DC rectifier cabinets or backup batteries, ranging from 88 to 264 VDC.

[0003] In switching power supplies, to address electromagnetic interference (EMI) issues, an EMI filter circuit is typically installed at the input. This filter circuit usually includes an X-type filter capacitor (also known as a safety X-type capacitor or X-type safety capacitor, hereinafter referred to as the X-type capacitor) connected in parallel between the live and neutral wires at the AC power input. This capacitor absorbs EMI differential-mode noise and its capacitance is typically in the μF range. When the input power of the switching power supply is disconnected, a certain amount of charge remains on the X-type capacitor, potentially posing a high-voltage risk. If a person accidentally touches the power plug, a discharge circuit is formed, which could lead to an electric shock. Therefore, according to relevant safety certification standards, the voltage must be reduced to within a specified range within a specified time after unplugging the power cord. This necessitates a fast discharge circuit for the X-type capacitor.

[0004] There are currently two methods for controlling the discharge of capacitor X: passive discharge and active discharge. Passive discharge involves connecting a discharge resistor Rx in parallel across capacitor X (Cx) to achieve discharge. In this method, the control chip of the switching power supply does not have a built-in discharge function for capacitor X. Figure 2 and Figure 3 As shown, in this scheme, because the discharge resistor Rx is always connected in parallel across the X capacitor Cx, the discharge speed and static power consumption are contradictory. If the resistance value is increased to reduce the static current, the discharge speed will decrease accordingly, and the X capacitor Cx cannot be discharged in a sufficiently short time, increasing the safety risk. Conversely, if the resistance value is decreased to shorten the discharge time, the static power consumption of the circuit will increase. Active discharge does not require the discharge resistor Rx to be connected in parallel across the X capacitor Cx. In this case, the control chip of the switching power supply has an X capacitor discharge function, such as... Figure 1 As shown, two rectifier diodes (diode D1 and diode D2) are needed to connect the two ends of capacitor X Cx to the high-voltage start pin HV of the control chip. When the control chip detects that the input power is cut off, it controls the start of the discharge of capacitor X. However, this method is currently not compatible with DC input scenarios.

[0005] For switching power supply design, different power supply designs are currently required depending on the type of input power (AC input or DC input). Specifically, for AC input, a control chip with X capacitor discharge function is used, while for DC input, a control chip without X capacitor discharge function is used and a discharge resistor is used to meet safety requirements, which limits the use of control chips. Summary of the Invention

[0006] In view of the above-mentioned technical problems, the purpose of this application is to provide an X capacitor discharge method, a control chip, and a switching power supply. The X capacitor is subjected to graded discharge control based on the multi-segment detection results of the pin voltage of the high-voltage start-up pin of the control chip. This allows the same control chip to simultaneously meet the application scenarios of both AC input and DC input, avoids the continuous power consumption problem caused by the discharge resistor, and saves area and cost.

[0007] According to a first aspect of this application, a method for discharging an X-capacitor is provided for a switching power supply. The switching power supply includes a control chip, and the two ends of the X-capacitor are respectively connected to the high-voltage start-up pin of the control chip through a first diode and a second diode.

[0008] The X capacitor discharge method includes:

[0009] The high-voltage start-up pin is pulled down using a first current;

[0010] When the pull-down current of the high-voltage start-up pin is the first current, the pin voltage change on the high-voltage start-up pin is detected at a preset first time period.

[0011] If no positive slope is detected in the pin voltage within the first time period, the second current is switched to pull down the high-voltage start pin at a preset second time period, and the second current is greater than the first current.

[0012] If the slope of the drop in the pin voltage is detected to be greater than a preset slope threshold during the second time period, a third current is switched to pull down the high-voltage start pin, and the third current is greater than the second current.

[0013] Optionally, if the drop slope of the pin voltage is not detected to be greater than a preset slope threshold within the second time period, the first current is switched to pull down the high-voltage start-up pin, and the pin voltage change on the high-voltage start-up pin is detected periodically at the first time period.

[0014] Optionally, if the drop slope of the pin voltage is not detected to be greater than a preset slope threshold during the second time period, the second current is maintained, and the drop slope of the pin voltage is determined to be greater than the preset slope threshold during the next second time period.

[0015] Optionally, if the slope of the drop in the pin voltage is not detected to be greater than a preset slope threshold for N consecutive second time periods, the first current is switched to pull down the high-voltage start pin, and the pin voltage change on the high-voltage start pin is detected again with the first time period as the cycle, where N is a positive integer greater than 1.

[0016] Optionally, after switching the third current to pull down the high-voltage start pin, the current is maintained for a third time before switching back to the first current.

[0017] Optionally, after switching the third current to pull down the high-voltage start pin, the current is switched to the first current or zero current after the pin voltage is less than a preset voltage threshold.

[0018] Optionally, the first time is greater than or equal to one-quarter of a power frequency cycle.

[0019] According to a second aspect of this application, a control chip is provided for a switching power supply, the switching power supply including an X capacitor, the two ends of the X capacitor being connected to the high-voltage start-up pin of the control chip through a first diode and a second diode, respectively.

[0020] The control chip includes:

[0021] A pull-down control unit is used to provide pull-down current to pull down the high-voltage start-up pin;

[0022] A voltage detection unit is used to detect the change in the pin voltage on the high-voltage start-up pin, and to provide a first enable signal if no positive change slope of the pin voltage is detected within a preset first time period, and to provide a second enable signal if the decrease slope of the pin voltage is detected to be greater than a preset slope threshold within a second time period, wherein the second time period is after the first time period.

[0023] The pull-down control unit provides a first current in the initial state, a second current when it receives the first enable signal, and a third current when it receives the second enable signal. The second current is greater than the first current, and the third current is greater than the second current.

[0024] Optionally, when the pull-down control unit provides the first current, the voltage detection unit detects the pin voltage change on the high-voltage start-up pin at a time interval of the first time.

[0025] Optionally, the voltage detection unit is further configured to provide a reset signal when either of the following conditions is met, and the pull-down control unit provides the first current upon receiving the reset signal:

[0026] No drop slope of the pin voltage greater than a preset slope threshold is detected during at least one consecutive second time period;

[0027] The duration for which the third current pulls down the high-voltage start-up pin reaches the third time;

[0028] After switching the third current to pull down the high-voltage start pin, the pin voltage is less than a preset voltage threshold.

[0029] According to a third aspect of this application, a switching power supply is provided, comprising: a control chip as disclosed in any embodiment of this application.

[0030] The beneficial effects of this application include at least the following:

[0031] The X-capacitor discharge method, control chip, and switching power supply provided in this application are configured to use a first current to pull down the high-voltage start-up pin of the control chip connected to the X-capacitor in the initial state. When the pull-down current of the high-voltage start-up pin is the first current, the method detects the pin voltage change on the high-voltage start-up pin at a preset first time interval. If no positive slope is detected in the pin voltage within the first time interval, a second current slightly larger than the first current is switched to pull down the high-voltage start-up pin at a preset second time interval. Furthermore, if the drop slope of the pin voltage is detected to be greater than a preset slope threshold within the second time interval, a third current larger than the second current is switched to pull down the high-voltage start-up pin to achieve rapid discharge of the X-capacitor. Compared to existing solutions, this application's solution can trigger the switching of different pull-down currents based on different detection results of the voltage slope of the high-voltage start-up pin to achieve segmented pull-down control of the high-voltage start-up pin. Furthermore, when the switch-up pin is turned on... When the power supply is switched off and the input power is cut off, regardless of whether the input signal is AC or DC, the slope of the pin voltage drop in the second time period will always exceed the preset slope threshold, thus enabling the rapid discharge of capacitor X using the third current. However, during normal operation of the power supply, when the input is DC, the slope of the pin voltage drop in the second time period will not exceed the preset slope threshold. Therefore, only a small first current and / or second current can be used to weakly pull down the high-voltage start-up pin. Similarly, when the input is AC, the pin voltage always has a positive slope in the first time period, so only the minimum first current can be used to weakly pull down the high-voltage start-up pin. Neither of these scenarios will switch to the maximum third current. The static power consumption is very low, effectively avoiding the continuous power consumption problem caused by the discharge resistor. This allows the same control chip to simultaneously meet both AC and DC input application scenarios, saving area and cost.

[0032] It should be noted that the above general description and the following detailed description are merely exemplary and explanatory, and do not limit this application. Attached Figure Description

[0033] Figure 1 A schematic diagram of a switching power supply suitable for AC input is shown in the relevant art;

[0034] Figure 2 A schematic diagram of a switching power supply suitable for DC input is shown in the relevant art;

[0035] Figure 3 A schematic diagram of a switching power supply that can simultaneously accommodate AC and DC inputs is shown in the relevant technology.

[0036] Figure 4 Show Figure 1 A schematic diagram of the discharge logic of the X capacitor in a switching power supply.

[0037] Figure 5 This diagram illustrates the structure of a switching power supply according to an embodiment of this application.

[0038] Figure 6 Show Figure 5 A schematic diagram of the timing waveforms of some signals of the switching power supply under AC input.

[0039] Figure 7 Show Figure 5 A schematic diagram of the timing waveforms of some signals of the switching power supply under DC input.

[0040] Figure 8 Show Figure 5 A schematic diagram of the discharge logic of the X capacitor in a switching power supply.

[0041] Figure 9 A schematic flowchart of the X-capacitor discharge method provided according to an embodiment of this application is shown. Detailed Implementation

[0042] The preferred embodiments of this disclosure are described in detail below with reference to the accompanying drawings, but this disclosure is not limited to these embodiments. This disclosure covers any alternatives, modifications, equivalent methods, and solutions made within the spirit and scope of this disclosure.

[0043] In order to provide the public with a thorough understanding of this disclosure, specific details are described in detail in the following preferred embodiments of this disclosure, but those skilled in the art can fully understand this disclosure without these details.

[0044] The present disclosure is described in more detail below by way of example with reference to the accompanying drawings. It should be noted that the drawings are in a simplified form and use non-precise scales, and are only used to facilitate and clarify the illustration of the embodiments of the present disclosure.

[0045] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application may be implemented in various forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0046] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0047] In the description of this application, words such as "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments. The term "and / or" in this document describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. "Multiple" refers to two or more. Furthermore, to facilitate a clear description of the technical solutions of the embodiments of this application, the terms "first," "second," etc., are used to distinguish identical or similar items with substantially the same function and effect. Those skilled in the art will understand that the terms "first," "second," etc., do not limit the quantity or execution order, and that "first," "second," etc., do not necessarily imply differences.

[0048] In addition, the same reference numerals in the figures indicate the same or similar structures, so repeated descriptions of them will be omitted. That is, the various parts in this specification are described in a combination of parallel and progressive manner. Each part focuses on the differences from other parts, and the same or similar parts between the various parts can be referred to each other.

[0049] Figure 1 This diagram illustrates a switching power supply suitable for AC input in the relevant art. Figure 2 This diagram illustrates a switching power supply suitable for DC input in the relevant art. Figure 3 This diagram illustrates a switching power supply that can simultaneously accommodate both AC and DC inputs, as described in the relevant technology.

[0050] like Figure 1 , Figure 2 and Figure 3As shown, the switching power supply includes an input port 110, an X capacitor Cx, a rectifier bridge 120, a power unit 130, and a control chip 140. The input port 110 is used to connect to an external power supply and is connected to the input terminal of the rectifier bridge 120. The X capacitor Cx is positioned between the two input terminals of the rectifier bridge 120, and the output terminal of the rectifier bridge 120 is connected to the power unit 130. The first terminal of the X capacitor Cx is connected to the high-voltage start-up pin HV of the control chip 140 through a diode D1, and the second terminal of the X capacitor Cx is connected to the high-voltage start-up pin HV of the control chip 140 through a diode D2. The control chip 140 provides a drive signal to the power unit 130 to control the power unit 130 to convert the rectified bus voltage Vbus.

[0051] exist Figure 1 In the illustrated embodiment, input port 110 receives an AC signal. The voltage across capacitor X Cx is rectified by diodes D1 and D2 to the high-voltage start-up pin HV of control chip 140. Control chip 140 integrates a capacitor X discharge circuit, which determines whether capacitor X Cx needs to be discharged by detecting the voltage at the high-voltage start-up pin HV. The discharge logic is as follows: Figure 4 As shown, the following steps are involved:

[0052] 410. Pin voltage detection. For example, detecting the magnitude and / or slope of the voltage value of the high-voltage start-up pin HV.

[0053] 420. Pull down the high-voltage start-up pin using a first current. In this step, the first current is a weak current less than a specific current threshold.

[0054] 430. Determine whether a positive slope was not detected within the predetermined time.

[0055] During normal operation, the voltage at the high-voltage start-up pin HV changes periodically with the input AC signal, ensuring a positive slope is always detected within a predetermined time. When the connection between input port 410 and the external power supply is disconnected, the voltage at the high-voltage start-up pin HV will decrease, and a positive slope will not appear. Further, if a positive slope is detected within the predetermined time, step 420 is repeated; if no positive slope is detected within the predetermined time, step 440 is further executed.

[0056] 440. Switch to the third current to pull down the high-voltage start pin. In this step, the third current is greater than the first current. When the third current is used to pull down the high-voltage start pin HV, it can achieve rapid discharge of capacitor Cx.

[0057] However, in DC input switching power supply scenarios, the pin voltage at the high-voltage start-up pin HV does not have a positive slope during normal operation. That is, in DC input applications, the following applies: Figure 1 and Figure 4 The X-capacitor discharge scheme shown also switches to the third current to perform discharge during normal operation of the switching power supply, which clearly does not conform to the original design intent. Therefore, Figure 1 and Figure 4 The X-capacitor discharge scheme shown is only applicable to the AC input application scenario.

[0058] exist Figure 2 In the illustrated embodiment, input port 110 receives a DC signal. The switching power supply also includes a discharge resistor Rx connected in parallel with capacitor Cx (X). The switching power supply primarily discharges capacitor Cx through the discharge resistor Rx, and does not integrate an X capacitor discharge circuit in the control chip 140.

[0059] exist Figure 3 In the illustrated embodiment, the switching power supply compatible with both AC and DC inputs uses a method similar to... Figure 2 With the same structure, regardless of whether its input port 110 receives a DC or AC signal, the discharge resistor Rx can be used to discharge the X capacitor Cx. However, since the discharge resistor Rx also discharges the X capacitor Cx during the normal operation of the switching power supply, the loss is relatively high.

[0060] Figure 5 The diagram shows a schematic of a switching power supply disclosed in an embodiment of this application. This application optimizes the discharge scheme of the X capacitor by the control chip in the switching power supply. This includes performing graded pull-down control on the high-voltage start-up pin based on the multi-level detection results of the pin voltage of the high-voltage start-up pin of the control chip, avoiding the use of a discharge resistor. This ensures that the switching power supply will not cause high losses during normal operation, whether it is AC or DC input, but will only discharge with a large current after the input power is cut off. This allows the same control chip to meet both AC and DC input application scenarios simultaneously, effectively avoiding the continuous power consumption problem caused by the discharge resistor, and saving area and cost.

[0061] like Figure 5As shown in this embodiment, the switching power supply 500 includes: an input port 510, an X capacitor Cx, diodes D1 and D2, a rectifier bridge 520, a power unit 530, and a control chip 540. The input port 510 is used to connect to an external power supply and is connected to the input terminal of the rectifier bridge 520. The X capacitor Cx is disposed between the two input terminals of the rectifier bridge 520. The output terminal of the rectifier bridge 520 is connected to the power unit 530. The first terminal of the X capacitor Cx is connected to the high-voltage start-up pin HV of the control chip 540 through diode D1, and the second terminal of the X capacitor Cx is connected to the high-voltage start-up pin HV of the control chip 540 through diode D2. The control chip 540 provides a drive signal to the power unit 530 to control the power unit 530 to perform power conversion on the rectified bus voltage Vbus.

[0062] In some embodiments, a capacitor C1 is also connected between the two output terminals of the rectifier bridge 520 to filter the bus voltage Vbus output by the rectifier bridge 520.

[0063] In this embodiment, the input port 510 can receive either a DC signal or an AC signal.

[0064] Alternatively, the power unit 530 can be configured to adopt any of the following topologies: buck topology, boost topology, boost-buck topology, and any flyback topology.

[0065] The control chip 540 further includes a voltage detection unit 541 and a pull-down control unit 542. The voltage detection unit 541 is used to detect the pin voltage V on the high-voltage start-up pin HV. HV The system detects changes in the voltage and provides a corresponding enable signal to the pull-down control unit 542 based on the detection results, thereby controlling the pull-down control unit 542 to provide a corresponding pull-down current to pull down the high-voltage start pin HV of the control chip 540.

[0066] In this embodiment, when the voltage detection unit 541 does not detect the pin voltage V within a preset first time (denoted as T0), HV A first enable signal (denoted as EN1) is provided when there is a positive slope, and the pin voltage V is detected at a second time (denoted as T1). HV If the descent slope is greater than a preset slope threshold, a second enable signal (denoted as EN2) is provided. Furthermore, the pull-down control unit 542 provides a first current (denoted as I0) in the initial state, a second current (denoted as I1) upon receiving the first enable signal EN1, and a third current (denoted as Idis) upon receiving the second enable signal EN2. The second current I1 is greater than the first current I0, and the third current Idis is greater than the second current I1.

[0067] Preferably, the initial time T1 is greater than or equal to one-quarter of the AC signal's power frequency cycle. This ensures that the switching power supply 500 has sufficient time to detect the pin voltage V regardless of whether it is under AC or DC input. HV The presence of a positive slope in the change rate is beneficial for improving the accuracy of the detection results. Furthermore, considering static power consumption and human perception, the first time interval is generally designed to be around 200ms, for example, any value between 190ms and 210ms. Additionally, the second and third time intervals can be set according to the actual application.

[0068] In specific implementation, the second time T1 is located after the first time T0. That is, when the pull-down control unit 542 provides the first current I0, the voltage detection unit 541 will periodically detect the pin voltage V on the high-voltage start-up pin HV with the first time T0 as the period. HV The changes in voltage V. And within a certain first time interval T0, no pin voltage V was detected. HV When a positive slope exists, a first switching signal is provided to control the pull-down control unit 542 to switch from providing a first current I0 to providing a second current I1, and further triggers the voltage detection unit 541 to detect the pin voltage V within a second time T1. HV Whether the descent slope is greater than a preset slope threshold. When the voltage detection unit 541 detects the pin voltage V within the second time T1. HV When the downward slope is greater than a preset slope threshold, a second switching signal is provided to control the pull-down control unit 542 to switch from providing a second current I1 to providing a third current Idis.

[0069] Furthermore, when the voltage detection unit 541 does not detect the pin voltage V within the second time T1 HV The descent slope is greater than the preset slope threshold, that is, within the second time T1, the pin voltage V HV If the downward slope is always less than or equal to a preset slope threshold, the voltage detection unit 541 is also configured to provide a reset signal, and the pull-down control unit 542 switches from providing a second current I1 to providing a first current I0 when it receives the reset signal.

[0070] With the pull-down control unit 542 providing a third current Idis to pull down the high-voltage start-up pin HV, the voltage detection unit 541 is also configured to detect the pin voltage V. HV When the voltage value is less than the preset voltage threshold, a reset signal is provided. When the pull-down control unit 542 receives the reset signal, it switches from providing the third current Idis to providing the first current I0 or zero current.

[0071] In some embodiments, the control chip 540 may also be provided with a time detection unit (not shown, such as a timer, etc.). When the pull-down control unit 542 provides a third current Idis to pull down the high-voltage start pin HV, the time detection unit is configured to provide a reset signal when it detects that the duration of pulling down the high-voltage start pin HV using the third current Idis reaches a third time (denoted as Tdis). When the pull-down control unit 542 receives the reset signal, it switches from providing the third current Idis to providing the first current I0 or zero current.

[0072] In this embodiment, the first current I0 is a weak pull-down current, and the third current Idis is a larger discharge current. This ensures that the control chip 540 does not generate a large power consumption when using the first current I0 to pull down its high-voltage start-up pin HV, while using the third current Idis to pull down its high-voltage start-up pin HV enables rapid discharge of the X capacitor Cx.

[0073] Compared to the third current Idis, the second current I1 is also a smaller pull-down current. When the switching power supply 500 uses the second current I1 to pull down the high-voltage start pin HV of the control chip 540, it can also have lower power consumption, which is beneficial to reduce the average power consumption of the switching power supply 500 under DC input.

[0074] Figure 6 Show Figure 5 A schematic diagram of the timing waveforms of some signals of the switching power supply under AC input. Figure 7 Show Figure 5 A schematic diagram of the timing waveforms of some signals of the switching power supply under DC input. Figure 8 Show Figure 5 A schematic diagram of the discharge logic for capacitor X in the switching power supply. During operation, the switching power supply 500 controls the discharge of capacitor X Cx according to the following process:

[0075] 810. Pin Voltage Detection. In this embodiment, the high-voltage start-up pin HV of the control chip 540 is used as the detection node for the voltage on capacitor Cx X. The voltage detection unit 541 in the control chip 540 is used to detect the pin voltage V of the high-voltage start-up pin HV. HV Perform testing, including but not limited to detecting the pin voltage V. HV The slope of change and / or voltage value.

[0076] 820. A first current is used to pull down the high-voltage start-up pin. In this embodiment, the pull-down control unit 542 in the control chip 540 provides the pull-down current, and the discharge control of the voltage on capacitor Cx is achieved by controlling the pull-down of the high-voltage start-up pin HV through the pull-down current. Specifically, in the initial state after the switching power supply 500 is powered on, or after the pull-down control unit 542 receives a reset signal, the pull-down control unit 542 provides a first current I0 to weakly pull down the high-voltage start-up pin HV, so that the pin voltage V at the high-voltage start-up pin HV is... HV The rectified waveform of the input signal changes accordingly. Then, logic 830 is executed.

[0077] 830. Determine whether a positive slope was not detected within the first time period. In this embodiment, when the pull-down control unit 542 provides the first current I0, the voltage detection unit 541 first periodically detects the pin voltage V on the high-voltage start-up pin HV with a first time period T0 as the period. HV The slope changes.

[0078] It is understandable that when an AC input is connected to input port 510 and the pull-down control unit 542 provides a first current I0, the voltage V of the high-voltage start pin HV will be pulled down by the first current I0. HV Under normal conditions, the rectified waveform following the input signal resembles a steamed bun waveform, with its slope alternating between positive and negative, such as... Figure 6 V during time T0_0 HV The waveform is shown. Therefore, when an AC input is connected to input port 510, the voltage detection unit 541 can always detect the pin voltage V at each first moment during the normal operation of the switching power supply 500. HV The positive slope triggers execution logic 820, which continues to use the first current to pull down the high-voltage start pin.

[0079] When the AC input of input port 510 is cut off and the pull-down control unit 542 provides the first current I0, reference Figure 6 During the T0 time interval, the voltage V of the high-voltage start pin HV is pulled down by the first current I0 provided by the pull-down control unit 542. HV The voltage will show a downward trend. At this time, the voltage detection unit 541 will not be able to detect the pin voltage V for a short period of time after the AC input of the input port 510 is cut off. HV The positive slope means that after the first time period ends, the voltage detection unit 541 will output the first enable signal EN1 and trigger the execution logic 840.

[0080] When input port 510 is connected to a DC input and pull-down control unit 542 provides a first current I0, the high-voltage start pin HV is pulled down by the first current I0, and its pin voltage V HV Under normal conditions, the slope of the rectified waveform following the input signal is essentially 0, such as... Figure 7 V during time T0_0 HV The waveform is shown. Therefore, when a DC input is connected to input port 510, voltage detection unit 541 can always detect pin voltage V at each first moment (corresponding) during the normal operation of switching power supply 500. HV Since it does not have a positive slope, the voltage detection unit 541 will output the first enable signal EN1 after the first time ends, and trigger the execution logic 840.

[0081] When the DC input of input port 510 is cut off and the pull-down control unit 542 provides the first current I0, reference Figure 7 During the T0 time interval, the voltage V of the high-voltage start pin HV is pulled down by the first current I0 provided by the pull-down control unit 542. HV The voltage will show a downward trend. At this time, the voltage detection unit 541 will also fail to detect the pin voltage V for a short period of time after the DC input of the input port 510 is cut off. HV The positive slope means that after the first time ends, the voltage detection unit 541 will also output the first enable signal EN1 and trigger the execution logic 840.

[0082] 840. Switch to the second current to pull down the high-voltage start-up pin. In this embodiment, after receiving the first enable signal EN1, the pull-down control unit 542 switches from providing the first current I0 to providing a larger second current I1 to further pull down the high-voltage start-up pin HV. Then, logic 850 is executed.

[0083] 850. Determine whether the drop slope of the pin voltage is greater than a preset slope threshold during the second time period. In this embodiment, when the pull-down control unit 542 provides the second current I1, the voltage detection unit 541 will detect the pin voltage V on the high-voltage start-up pin HV during the second time period T1. HV The slope changes.

[0084] It is understandable that when the AC or DC input of input port 510 is cut off, refer to the corresponding... Figure 6 and Figure 7 The signal waveforms within time T1 are shown. Since there is no signal input at input port 510, the high-voltage start pin HV is pulled down by the second current I1 provided by the pull-down control unit 542, and its pin voltage V... HVDuring the second time period T1, a downward trend with a larger negative slope is observed. Therefore, when the AC or DC input of input port 510 is cut off, the voltage detection unit 541 will be able to detect the pin voltage V during this second time period T1. HV If the downward slope is greater than the preset slope threshold (which can be set by the magnitude of the second current I1 and the size of the X capacitor, etc.), it indicates that the input power supply of the switching power supply 500 has been cut off. Therefore, after the second time T1 ends, the voltage detection unit 541 will output the second enable signal EN2 and trigger the execution logic 860.

[0085] When a DC input is connected to input port 510, since there is still a DC signal input at input port 510, although the high-voltage start pin HV is affected by the pull-down effect of the second current I1 provided by the pull-down control unit 542, its pin voltage V HV The voltage remains constant during the corresponding second time period; that is, when a DC input is connected to the input port 510, the voltage detection unit 541 detects the pin voltage V during this second time period. HV The descent slope will be less than the preset slope threshold. Therefore, after the second time period ends, the voltage detection unit 541 will output a reset signal and trigger the execution logic 820.

[0086] 860. Switching to the third current to pull down the high-voltage start-up pin. In this embodiment, after receiving the second enable signal EN2, the pull-down control unit 542 switches from providing the second current I1 to providing the maximum third current Idis to strongly pull down the high-voltage start-up pin HV. (Reference) Figure 6 and Figure 7 The waveforms of each signal within the Tdis time period, and the pin voltage V at the high-voltage start-up pin HV. HV The voltage will drop rapidly within the Tdis time, thus achieving rapid discharge of the voltage on capacitor Cx.

[0087] Furthermore, in some embodiments, when the pull-down control unit 542 provides a third current Idis, the voltage detection unit 541 will also detect the pin voltage V. HV The voltage value, and the pin voltage V HV After the voltage value drops below a preset voltage threshold, a reset signal is output, controlling the pull-down control unit 542 to switch from providing the third current Idis to providing the initial first current I0; or, the voltage detection unit 541 detects the voltage V at the pin. HV After the voltage value drops below the preset voltage threshold, a third enable signal is output to control the pull-down control unit 542 to switch from providing the third current Idis to providing zero current, so as to completely shut down the switching power supply 500.

[0088] In some embodiments, when the pull-down control unit 542 provides a third current Idis, the time detection unit in the control chip 540 will provide a reset signal or a third enable signal when it detects that the duration of the pull-down control unit 542 providing the third current Idis reaches a third time Tdis. When the pull-down control unit 542 receives the reset signal or the third enable signal, it switches from providing the third current Idis to providing the first current I0 or zero current.

[0089] Based on the above description, assuming the first current I0 is 10uA, the second current I1 is 1mA, the first time T0 is 200ms, and the second time T1 is 5-10ms, then when the input port 510 is connected to an AC input (such as 220VAC), the average power consumption of the switching power supply 500 during normal operation is calculated to be approximately 220VAC·10uA = 2.2mW; and when the input port 510 is connected to a DC input (such as 220VDC), the average current of the switching power supply 500 during normal operation is calculated to be approximately (T0·I0+T1·I1) / (T0+T1) = 57.14uA, and its average power consumption is approximately 220VDC·57.14uA = 12.57mW, which is much smaller than the static power consumption generated when using a discharge resistor in the existing scheme.

[0090] In summary, the solution proposed in this application can determine the pin voltage V of the high-voltage start-up pin HV of the control chip 540. HV Different detection results of the slope trigger the switching of different pull-down currents to achieve segmented pull-down control of the high-voltage start-up pin HV. Furthermore, when the input power supply to the switching power supply 500 is cut off, regardless of whether the input to the switching power supply 500 is an AC signal or a DC signal, the pin voltage V will remain constant within the preset second time T1. HV The descent slope of each capacitor will be greater than a preset slope threshold, thus enabling rapid discharge of capacitor Cx using the third current Idis. During normal operation of the switching power supply 500, when the switching power supply 500 is receiving DC input, the pin voltage V... HV The descent slope will not meet the preset slope threshold, therefore it can only trigger a weak pull-down of the high-voltage start-up pin HV using a smaller first current I0 and a second current I1 alternately, and the pin voltage V of the switching power supply 500 when AC input is applied. HVThere is always a positive slope within the first time T0, so it can only trigger a weak pull-down of the high-voltage start pin HV using the minimum first current I0, and will not switch to the maximum third current Idis. Therefore, the static power consumption of the switching power supply 500 is very low, effectively avoiding the continuous power consumption problem caused by setting the discharge resistor. This allows for simultaneous X capacitor discharge control for both AC and DC input application scenarios within a single control chip, while also saving area and cost.

[0091] Furthermore, this application also discloses an X-capacitor discharge method, which can be applied to the switching power supply 500 shown in any of the foregoing embodiments. Specifically, as... Figure 9 As shown, the X capacitor discharge method includes performing the following steps:

[0092] 910. Use the first current to pull down the high-voltage start pin.

[0093] 920. When the pull-down current of the high-voltage start-up pin is the first current, detect the change of the pin voltage on the high-voltage start-up pin at a preset first time period.

[0094] 930. If no positive slope is detected in the pin voltage within the first time period, the second current is switched to pull down the high-voltage start pin at a preset second time period. The second current is greater than the first current.

[0095] 940. If the slope of the pin voltage drop is detected to be greater than the preset slope threshold in the second time period, switch the third current to pull down the high voltage start pin. The third current is greater than the second current.

[0096] Furthermore, if no slope of the pin voltage drop is detected to be greater than a preset slope threshold within the second time period, in some embodiments, the first current can be switched to pull down the high-voltage startup pin, and the pin voltage change on the high-voltage startup pin can continue to be detected periodically with the first time period as the cycle. In other embodiments, the second current can be maintained, and the slope of the pin voltage drop can continue to be determined in the next second time period to see if it is greater than the preset slope threshold. Furthermore, when maintaining the second current, the number of detection cycles can be set, i.e., the number of detection cycles when detecting periodically with the second time period as the cycle. For example, if no slope of the pin voltage drop is detected to be greater than the preset slope threshold within N consecutive second time periods, the first current is switched to pull down the high-voltage startup pin, and the pin voltage change on the high-voltage startup pin continues to be detected periodically with the first time period as the cycle. N is a positive integer greater than 1, to further reduce overall power consumption. The value of N can be set according to the actual application.

[0097] Furthermore, after switching the third current to pull down the high-voltage start pin, in some embodiments, it is possible to maintain the third time and then switch to the first current or zero current; in other embodiments, it is also possible to switch to the first current or zero current after the pin voltage is less than a preset voltage threshold.

[0098] Preferably, the first time is greater than or equal to one-quarter of the power frequency cycle. For example, the first time is 200ms.

[0099] It should be noted that the specific implementation of each step in the X capacitor discharge method described above and the technical effects that can be obtained can be found in the relevant description of the switching power supply 500 in any of the foregoing embodiments, and will not be repeated here.

[0100] In summary, the switching power supply and its control chip provided in this application embodiment can integrate X-capacitor discharge schemes for both DC and AC inputs within a single control chip, effectively solving the normalization problem of the control chip in the switching power supply. Furthermore, compared to the X-capacitor discharge scheme using a discharge resistor, the solution provided in this application not only reduces the continuous power consumption of the system but also saves PCB board area and system cost.

[0101] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating this application and are not intended to limit the implementation. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for discharging an X-capacitor, used in a switching power supply, the switching power supply including a control chip, wherein the two ends of the X-capacitor are respectively connected to a high-voltage start-up pin of the control chip through a first diode and a second diode. The X capacitor discharge method includes: The high-voltage start-up pin is pulled down using a first current; When the pull-down current of the high-voltage start-up pin is the first current, the pin voltage change on the high-voltage start-up pin is detected at a preset first time period. If no positive slope is detected in the pin voltage within the first time period, the second current is switched to pull down the high-voltage start pin at a preset second time period, and the second current is greater than the first current. If the slope of the drop in the pin voltage is detected to be greater than a preset slope threshold during the second time period, a third current is switched to pull down the high-voltage start pin, and the third current is greater than the second current.

2. The X-capacitor discharge method according to claim 1, wherein, If the drop slope of the pin voltage is not detected to be greater than a preset slope threshold within the second time period, the first current is switched to pull down the high-voltage start pin, and the pin voltage change on the high-voltage start pin is detected again at the first time period.

3. The X-capacitor discharge method according to claim 1, wherein, If the rate of decrease of the pin voltage is not greater than the preset slope threshold during the second time period, the second current is maintained, and the rate of decrease of the pin voltage is determined to be greater than the preset slope threshold during the next second time period.

4. The X-capacitor discharge method according to claim 3, wherein, If no slope of the voltage drop of the pin is detected to be greater than a preset slope threshold for N consecutive second time periods, the first current is switched to pull down the high-voltage start-up pin, and the change of the pin voltage on the high-voltage start-up pin is detected again with the first time period as the cycle, where N is a positive integer greater than 1.

5. The X-capacitor discharge method according to claim 1, wherein, After switching to the third current to pull down the high-voltage start pin, maintain the third current for a third time and then switch back to the first current.

6. The X-capacitor discharge method according to claim 1, wherein, When the third current is switched to pull down the high-voltage start pin, the current is switched back to the first current or zero current after the pin voltage is less than a preset voltage threshold.

7. The X-capacitor discharge method according to any one of claims 1-6, wherein, The first time is greater than or equal to one-quarter of a power frequency cycle.

8. A control chip for a switching power supply, the switching power supply including an X capacitor, the two ends of the X capacitor being connected to a high-voltage start-up pin of the control chip via a first diode and a second diode, respectively. The control chip includes: A pull-down control unit is used to provide pull-down current to pull down the high-voltage start-up pin; A voltage detection unit is used to detect the change in the pin voltage on the high-voltage start-up pin, and to provide a first enable signal if no positive change slope of the pin voltage is detected within a preset first time period, and to provide a second enable signal if the decrease slope of the pin voltage is detected to be greater than a preset slope threshold within a second time period, wherein the second time period is after the first time period. The pull-down control unit provides a first current in the initial state, a second current when it receives the first enable signal, and a third current when it receives the second enable signal. The second current is greater than the first current, and the third current is greater than the second current.

9. The control chip according to claim 8, wherein, When the pull-down control unit provides the first current, the voltage detection unit detects the pin voltage change on the high-voltage start-up pin at the first time interval.

10. The control chip according to claim 8 or 9, wherein, The voltage detection unit is further configured to provide a reset signal when the pull-down control unit receives the first current if either of the following conditions is met: No drop slope of the pin voltage greater than a preset slope threshold is detected during at least one consecutive second time period; The duration for which the third current pulls down the high-voltage start-up pin reaches the third time; After switching the third current to pull down the high-voltage start pin, the pin voltage is less than a preset voltage threshold.

11. A switching power supply, comprising: The control chip as described in any one of claims 8-10.

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