X capacitor discharging circuit and switching power supply
By using a single point fault discharge module and an IC controlled discharge module in the X capacitor discharge circuit, and using a resistor with a larger resistance value for discharge, the problem of difficulty in meeting the low power consumption and discharge time requirements in the prior art is solved, and the lower standby power consumption and discharge effect that meets the discharge time specifications is achieved.
Patent Information
- Application Number
- CN202510029265.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-08
- Publication Date
- 2025-04-22
AI Technical Summary
The existing X-capacitor discharge circuits are difficult to meet the requirements of low power consumption and discharge time at the same time.
The single-point fault discharge module and the IC control discharge module are adopted to discharge the X capacitor through the combination of the control chip and diode, and a resistor with a larger resistance value is used to discharge the voltage quickly during the single-point fault test.
It realizes that while meeting the discharge time specification requirements, it reduces the standby power consumption of switching power supplies, meets increasingly stringent standby power consumption requirements, and saves PCB space, which is conducive to product miniaturization.
Smart Images
Figure CN119865046A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of switching power supplies, and in particular to an X-capacitor discharge circuit and a switching power supply. Background Art
[0002] In order to suppress noise, the input circuit of the switching power supply needs to add an EMC circuit. The EMC circuit is composed of an inductor and a capacitor, where the capacitor is called an X capacitor. In order to effectively filter out noise, the capacity of the X capacitor must be increased. However, when the AC connection of a large-capacity capacitor is unplugged, the residual voltage between the L line and the N line of the AC port of the power supply will be higher. If a person touches it, there is a risk of electric shock. Therefore, the safety certification regulations of various countries have made corresponding provisions for the discharge time of this residual voltage, that is, the voltage on the X capacitor must be reduced to below a certain value within a period of power failure to ensure the safety of personnel. In order to meet this discharge time requirement, the commonly used discharge method is to use a resistor to discharge the X capacitor or to discharge the X capacitor through the HV pin of the PWM controller.
[0003] Please refer to Figure 1 , Figure 1 The schematic diagram of a circuit of a switching power supply using a resistor to discharge an X capacitor is shown in FIG. Figure 1 As shown, the switching power supply includes an EMC circuit, a rectifier circuit and a switching circuit, wherein the EMC circuit includes an X capacitor and an X capacitor discharge circuit, capacitors CX1 and CX2 are X capacitors, and the X capacitor discharge circuit includes resistors R1, R2, R1A and R1B, which are connected in series and parallel at both ends of the X capacitor for discharge. This X capacitor discharge circuit is simple, but has the disadvantage that when the circuit is working normally, there will be power loss in these resistors, which affects the standby power consumption index of the switching power supply.
[0004] Please refer to Figure 2 , Figure 2 The schematic diagram of a circuit of a switching power supply for discharging an X capacitor through the HV pin of a PWM controller is shown in FIG. Figure 2As shown, the switching power supply includes an EMC circuit, a rectifier circuit and a switch circuit, wherein the EMC circuit includes an X capacitor and an X capacitor discharge circuit, capacitors CX1 and CX2 are X capacitors, the X capacitor discharge circuit includes a diode D1, a diode D2, a resistor R15 and a PWM control chip U1, and the diodes D1 and D2 connected at both ends of the X capacitor are connected to the HV pin of the PWM control chip U1 through the resistor R15, the discharge path of the X capacitor is from the diode D1, through the diode D2, the resistor R15, and the PWM control chip U1 to discharge to the ground in sequence, during normal operation, the discharge path of the X capacitor is not turned on, and the loss is very low, when the AC input is unplugged, when the PWM control chip U1 detects that there is no AC input, its internal circuit is turned on, and the X capacitor is discharged, because the resistor R15 is relatively small, the discharge is fast, and this discharge method can well meet the discharge time requirements and no-load power consumption requirements. However, the safety certification regulations of various countries also have single-point fault test requirements for the X capacitor discharge circuit, that is, when a certain device is disconnected in sequence on the X capacitor discharge path, the discharge time is tested to see whether it meets the discharge time requirements. In order to deal with single-point fault testing, resistors R1 and R2 need to be connected in parallel at both ends of the X capacitor so that when diode D1 or diode D2 is disconnected, it can discharge through resistor R1 or resistor R2. In order to meet the discharge time standard requirements, the resistance values of resistors R1 and R2 cannot be too large. Therefore, resistors R1 and R2 will also produce certain losses, which will also affect the standby power consumption index of the switching power supply, making it impossible to meet the increasingly stringent standby power consumption requirements.
[0005] In summary, the existing X-capacitor discharge circuit has the problem of being unable to simultaneously meet the standby low power consumption requirement and the discharge time requirement. Summary of the invention
[0006] The technical problem to be solved by the present invention is to provide an X-capacitor discharge circuit and a switching power supply which can simultaneously meet the requirements of low standby power consumption and discharge time.
[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:
[0008] An X capacitor discharge circuit is applied to a switching power supply. The switching power supply includes an X capacitor, a rectifier circuit and a switching circuit. The AC input voltage is passed through the X capacitor and the rectifier circuit to obtain the input voltage of the switching circuit. The X capacitor discharge circuit includes: a single point fault discharge module, including a first resistor and a second resistor. The first resistor and the second resistor are connected in series and connected in parallel with the X capacitor. The common end of the first resistor and the second resistor is configured as a first node; an IC control discharge module, including a first diode, a second diode, a third diode and a control chip. The anode of the first diode and the anode of the second diode are respectively connected to the two ends of the X capacitor. The common end of the cathode of the first diode and the cathode of the second diode is configured as a second node and connected to the control chip. The anode of the third diode is connected to the first node, and the cathode of the third diode is connected to the second node. When a single point fault occurs in the IC control discharge module and it is detected that the AC input voltage is disconnected, the control chip is coupled to one end of the X capacitor through the third diode and one of the first resistor and the second resistor of the single point fault discharge module to discharge the X capacitor until the voltage on the X capacitor is lower than a predetermined value.
[0009] Preferably, the first diode and the second diode are two diodes in the rectifier circuit whose two anodes are respectively connected to two ends of the X capacitor, and the second node is a non-grounded output end of the rectifier circuit.
[0010] Preferably, the first resistor includes a resistor R1, and the second resistor includes a resistor R2.
[0011] Preferably, the first resistor includes at least two resistors connected in parallel with each other; and the second resistor includes at least two resistors connected in parallel with each other.
[0012] Preferably, a protection resistor is connected between the second node and the control chip.
[0013] Preferably, the X capacitor includes a capacitor CX1 and a capacitor CX2, and the capacitor CX1 is connected in parallel with the capacitor CX2.
[0014] Preferably, the control chip is a PWM control chip, and an HV pin of the PWM control chip is connected to the second node.
[0015] Preferably, when the IC control discharge module detects that the voltage of the second node is continuously lower than a preset threshold value for more than a preset time, it is determined that the AC input voltage is disconnected.
[0016] Preferably, when the branch where the first diode or the second diode is located is disconnected, it is determined that a single point failure occurs in the IC control discharge module.
[0017] A switching power supply comprises an X capacitor, a rectifier circuit and a switching circuit. An AC input voltage is converted into an input voltage of the switching circuit via the X capacitor and the rectifier circuit. The switching power supply further comprises the X capacitor discharge circuit.
[0018] The beneficial technical effect of the present invention is that: in the above-mentioned X-capacitor discharge circuit, when a single-point fault occurs in the IC control discharge module and the AC input voltage is detected to be disconnected, the control chip is coupled to one end of the X-capacitor through the third diode and one of the first resistor and the second resistor of the single-point fault discharge module, so that the residual voltage of the X-capacitor can be quickly released to a voltage lower than a predetermined value. Compared with the X-capacitor discharge circuit in the prior art, which needs to discharge through the first resistor and the second resistor in the single-point fault discharge module in sequence when performing a single-point fault test, the X-capacitor discharge circuit of the present invention only uses one of the first resistor and the second resistor of the single-point fault discharge module to discharge, so that there can be more margin to balance the EMC design, so that the single-point fault discharge module can use a resistor with a larger resistance value, so that the standby power consumption of the switching power supply is lower when the X-capacitor discharge time specification requirements are met, so as to meet the energy efficiency requirements of standby low power consumption. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 The circuit schematic diagram of an existing switching power supply that uses a resistor to discharge an X capacitor;
[0020] Figure 2 A circuit schematic diagram of an existing switching power supply for discharging an X capacitor through an HV pin of a PWM controller;
[0021] Figure 3 A circuit structure block diagram of a switching power supply provided by the present invention;
[0022] Figure 4 A circuit schematic diagram of a switching power supply provided by one embodiment of the present invention;
[0023] Figure 5 A circuit schematic diagram of a switching power supply provided in another embodiment of the present invention;
[0024] Figure 6 To use Figure 2 The voltage-time curve diagram of the X-capacitor discharge circuit shown in FIG.
[0025] Figure 7 The figure is a voltage-time curve diagram of the X-capacitor discharge circuit provided by the present invention when performing X-capacitor discharge. DETAILED DESCRIPTION
[0026] In order to enable those skilled in the art to more clearly understand the objectives, technical solutions and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments.
[0027] The present invention provides an X-capacitor discharge circuit and a switching power supply. The X-capacitor discharge circuit is applied to the switching power supply to discharge the X-capacitor of the switching power supply so that the voltage on the X-capacitor is lower than a predetermined value within a specified time.
[0028] like Figure 3 , 4 As shown, in one embodiment of the present invention, the switching power supply includes an EMC circuit 10, a rectifier circuit 11 and a switching circuit, wherein the EMC circuit 10 includes an X capacitor and an X capacitor discharge circuit, and the AC input voltage is obtained through the X capacitor and the rectifier circuit 11 to obtain the input voltage of the switching circuit. The switching circuit includes a first filter circuit 12, a transformer 13, an output rectifier circuit 14, a second filter circuit 15, a feedback circuit 16, an optocoupler device 17, a PWM control module 18 and a switch tube 19. The circuit schematic diagram of each circuit module of the switching power supply is shown in FIG. Figure 4 As shown, the optocoupler device 17 includes a light emitting diode U4A and a photosensitive tube U4B. The circuit functions of each circuit module of the switching power supply can refer to the existing technology and will not be repeated here.
[0029] In this embodiment, the X capacitor includes a capacitor CX1 and a capacitor CX2, and the capacitor CX1 is connected in parallel with the capacitor CX2. In other embodiments, the X capacitor may include one capacitor or more capacitors connected in parallel.
[0030] The X capacitor discharge circuit includes a single point fault discharge module and an IC control discharge module, the single point fault discharge module includes a first resistor and a second resistor, the first resistor and the second resistor are connected in series and connected in parallel with the X capacitor, and the common end of the first resistor and the second resistor is configured as a first node; the IC control discharge module includes a first diode, a second diode, a third diode and a control chip, the anode of the first diode and the anode of the second diode are respectively connected to the two ends of the X capacitor, the common end of the cathode of the first diode and the cathode of the second diode is configured as a second node (HV) connected to the control chip, the anode of the third diode is connected to the first node, and the cathode of the third diode is connected to the second node. When a single point fault occurs in the IC control discharge module and the AC input voltage is detected to be disconnected, the control chip is coupled to one end of the X capacitor through the third diode and one of the first resistor and the second resistor of the single point fault discharge module, and discharges the X capacitor until the voltage on the X capacitor is lower than a predetermined value.
[0031] The X capacitor (CX1, CX2) is connected across the L line and the N line of the AC input terminal, the anode of the first diode and the anode of the second diode are connected to the two ends of the X capacitor respectively, and the common end of the cathode of the first diode and the cathode of the second diode is configured as a second node connected to the control chip, that is, the second node is the input end of the control chip. When the branch where the first diode or the second diode is located is disconnected, it is determined that a single point failure occurs in the IC control discharge module. The IC control discharge module detects the voltage of the second node through the control chip to determine whether the AC input voltage is disconnected. Specifically, when it is detected that the voltage of the second node is continuously lower than the preset threshold for more than the preset time, it is determined that the AC input voltage is disconnected, and the X capacitor needs to be discharged at this time; when it is detected that the voltage of the second node is continuously higher than the preset threshold for more than the second preset time, it is determined that the AC input voltage exists, and the X capacitor is not discharged at this time.
[0032] In this embodiment, the first resistor includes a resistor R1, and the second resistor includes a resistor R2. In other embodiments, the first resistor includes at least two resistors connected in parallel, and the second resistor includes at least two resistors connected in parallel.
[0033] In this embodiment, the diode D1 is a first diode, the diode D2 is a second diode, and the diode D3 is a third diode. The control chip adopts a PWM control chip U1. The IC control discharge module and the PWM control module 18 of the switch circuit share a PWM control chip, and the HV pin of the PWM control chip U1 is connected to the second node (HV). In other embodiments, the control chip is not limited to the PWM control chip, and the control chip can also adopt other types of control chips.
[0034] A protective resistor is connected between the second node (HV) and the control chip. In this embodiment, the protective resistor is a resistor R15; in other embodiments, the protective resistor may include multiple resistors, which are connected together in parallel or in series-parallel and then connected between the second node (HV) and the control chip.
[0035] The working principle of the X capacitor discharge circuit in this embodiment is as follows:
[0036] In normal operation, diode D3 does not work. When a single-point fault occurs in the IC control discharge module or a single-point fault test is being performed, for example, the branch where diode D2 is located is disconnected. If the AC input is unplugged during the half cycle when the L line is high, the discharge path of the X capacitor starts from diode D1, and discharges to ground through resistor R15 and PWM control chip U1 in sequence. The discharge time of the X capacitor is not affected. If the AC input is unplugged during the half cycle when the N line is high, the discharge path of the X capacitor starts from resistor R2, and discharges to ground through diode D3, resistor R15, and PWM control chip U1 in sequence. After reaching ground, the discharge is completed from bridge stack BD1 to the other end of the X capacitor. For another example, disconnect the branch where the diode D1 is located. If the AC input is unplugged during the half cycle when the N line is high, the discharge path of the X capacitor starts from the diode D2, passes through the resistor R15 and the PWM control chip U1 in sequence to discharge to the ground, and the discharge time of the X capacitor is not affected; if the AC input is unplugged during the half cycle when the L line is high, the discharge path of the X capacitor starts from the resistor R1, passes through the diode D3, the resistor R15, and the PWM control chip U1 in sequence to discharge to the ground, and then discharges from the bridge stack BD1 to the other end of the X capacitor to complete the discharge.
[0037] According to the working principle of the X-capacitor discharge circuit in this embodiment, when a single-point fault occurs in the IC control discharge module or a single-point fault test is being performed, the PWM control chip U1 can be connected to the first node through the diode D3, and then coupled to one end of the X-capacitor through the resistor R1 or the resistor R2. When a single-point fault occurs in the IC control discharge module or a single-point fault test is being performed, the discharge resistor in the discharge path of the X-capacitor is only the resistor R1 or the resistor R2, that is, only one of the resistors R1 and R2 is used in combination with the PWM control chip U1 for discharge. Since the PWM control chip U1 discharges very quickly, compared with the current technology of discharging through the resistors R1 and R2, the discharge time of the X-capacitor discharge circuit in this embodiment will still be significantly reduced. Figure 6 is a voltage-time curve diagram of an X-capacitor discharge circuit in the prior art, Figure 7 The voltage-time curve diagram of the X-capacitor discharge circuit provided in the embodiment of the present invention for X-capacitor discharge. Figure 6 , 7 As shown, under the same circuit parameters and in accordance with the standby power consumption condition, that is, when the resistor R1 and the resistor R2 have the same value and meet the standby power consumption condition, the discharge time of the X capacitor discharge circuit in the prior art is 2.9s, which does not meet the safety discharge time requirement (such as the IEC / EN62368-1 standard requires that the voltage should be discharged to less than 120V within 2s); and the discharge time of the X capacitor discharge circuit provided by the embodiment of the present invention is 1.85s, which meets the safety discharge time requirement.
[0038] In the X capacitor discharge circuit of this embodiment, when a single point fault occurs in the IC control discharge module and the AC input voltage is detected to be disconnected, the control chip is coupled to one end of the X capacitor through the third diode and one of the first resistor and the second resistor of the single point fault discharge module, so that the residual voltage of the X capacitor can be quickly released to a voltage lower than a predetermined value. Compared with the X capacitor discharge circuit in the prior art, which needs to discharge through the first resistor and the second resistor in the single point fault discharge module in sequence when performing a single point fault test, the X capacitor discharge circuit in this embodiment only uses one of the first resistor and the second resistor of the single point fault discharge module to discharge. Therefore, there is more margin to balance the EMC design, so that the single point fault discharge module can use a resistor with a larger resistance value, so that the standby power consumption of the switching power supply is lower when the X capacitor discharge time specification requirement is met, so as to meet the energy efficiency requirement of low standby power consumption. In addition, when a single-point fault occurs in the IC control discharge module and the AC input voltage is detected to be disconnected, the control chip can be coupled to one end of the X capacitor by reusing the resistor of the single-point fault discharge module, without adding an additional resistor, which can save PCB space and facilitate product miniaturization.
[0039] Figure 5 FIG. 1 is a circuit diagram of a switching power supply provided in another embodiment of the present invention. Figure 4 The difference between the switching power supplies in the illustrated embodiments is only that the X-capacitor discharge circuit is different. In the X-capacitor discharge circuit of this embodiment, the first diode and the second diode in the IC control discharge module are not separately provided, but the two diodes whose two anodes in the rectifier circuit 11 are respectively connected to the two ends of the X-capacitor are reused to replace Figure 4 The diode D1 and the diode D2 in the illustrated embodiment serve as the first diode and the second diode, and the second node is a non-grounded output terminal of the rectifier circuit 11. By reusing two diodes whose two anodes in the rectifier circuit 11 are respectively connected to the two ends of the X capacitor as the first diode and the second diode, the number of components of the circuit is reduced, PCB space can be saved, and product miniaturization is facilitated.
[0040] The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Those skilled in the art can make various equivalent changes and improvements based on the above embodiments, and all equivalent changes or modifications made within the scope of the claims should fall within the protection scope of the present invention.
Claims
1. An X-capacitor discharge circuit, which is applied to a switching power supply, wherein the switching power supply comprises an X-capacitor, a rectifier circuit and a switching circuit, wherein an AC input voltage is obtained through the X-capacitor and the rectifier circuit to obtain an input voltage of the switching circuit, wherein: The X-capacitor discharge circuit comprises: A single-point fault discharge module comprises a first resistor and a second resistor, wherein the first resistor and the second resistor are connected in series and then connected in parallel with the X capacitor, and a common end of the first resistor and the second resistor is configured as a first node; An IC controlled discharge module includes a first diode, a second diode, a third diode and a control chip, wherein the anode of the first diode and the anode of the second diode are respectively connected to two ends of the X capacitor, the cathode of the first diode and the cathode of the second diode are configured as a second node connected to the control chip, the anode of the third diode is connected to the first node, and the cathode of the third diode is connected to the second node; When a single-point fault occurs in the IC control discharge module and it is detected that the AC input voltage is disconnected, the control chip is coupled to one end of the X capacitor through the third diode and one of the first resistor and the second resistor of the single-point fault discharge module to discharge the X capacitor until the voltage on the X capacitor is lower than a predetermined value.
2. The X-capacitor discharge circuit according to claim 1, characterized in that: The first diode and the second diode are two diodes in the rectifier circuit whose two anodes are respectively connected to two ends of the X capacitor, and the second node is a non-grounded output end of the rectifier circuit.
3. The X-capacitor discharge circuit according to claim 1, characterized in that: The first resistor includes a resistor R1 , and the second resistor includes a resistor R2 .
4. The X-capacitor discharge circuit according to claim 1, wherein: The first resistor includes at least two resistors connected in parallel with each other; and the second resistor includes at least two resistors connected in parallel with each other.
5. The X-capacitor discharge circuit according to claim 1, wherein: A protection resistor is connected between the second node and the control chip.
6. The X-capacitor discharge circuit according to claim 1, wherein: The X capacitor includes a capacitor CX1 and a capacitor CX2, and the capacitor CX1 is connected in parallel with the capacitor CX2.
7. The X-capacitor discharge circuit according to claim 1, wherein: The control chip is a PWM control chip, and the HV pin of the PWM control chip is connected to the second node.
8. The X-capacitor discharge circuit according to any one of claims 1 to 7, characterized in that: When the IC control discharge module detects that the voltage of the second node is continuously lower than the preset threshold value for more than a preset time, it is determined that the AC input voltage is disconnected.
9. The X-capacitor discharge circuit according to any one of claims 1 to 7, characterized in that: When the branch where the first diode or the second diode is located is disconnected, it is determined that a single point failure occurs in the IC control discharge module.
10. A switching power supply, comprising an X capacitor, a rectifier circuit and a switch circuit, wherein an AC input voltage is obtained through the X capacitor and the rectifier circuit to obtain an input voltage of the switch circuit, characterized in that: The switching power supply further comprises an X-capacitor discharge circuit according to any one of claims 1 to 9.