An ac power-down detection circuit with low power consumption and adjustable response time
By combining an AC-to-DC converter module and a trigger module, a low-power AC power-down detection circuit with adjustable response time is realized, solving the problems of high power consumption and fixed response time in traditional circuits. It is suitable for scenarios such as switching power supplies.
Patent Information
- Application Number
- CN202521933553.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-09
- Publication Date
- 2026-08-25
- Estimated Expiration
- 2035-09-09
AI Technical Summary
Traditional AC power failure detection circuits have high power consumption and fixed response time, making it difficult to meet the requirements of low power consumption and adjustable response time.
An AC-to-DC module is used to convert AC signals into μA or nA level DC signals. Combined with a trigger module and an optocoupler module, the optocoupler module is controlled to conduct by the trigger module with a preset response time, thereby achieving low power consumption and adjustable response time.
It greatly reduces power consumption. The optocoupler module only turns on when the power is off, and the response time can be adjusted according to the needs, solving the problems of high power consumption and fixed response time in traditional circuits.
Smart Images
Figure CN224684099U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of detection circuit technology, and in particular to a low-power AC power failure detection circuit with adjustable response time. Background Technology
[0002] Traditional AC (alternating current) power failure detection circuits, such as Figure 1 As shown, AC power is connected to optocoupler U3 via a voltage divider circuit composed of resistors R50 and R51. When AC power is lost, optocoupler U3 switches from conducting to disconnecting, which is detected by the controller (such as an MCU) connected to optocoupler U3. However, traditional AC power loss detection circuits have the following problems: (1) Because it is necessary to maintain the minimum operating current of optocoupler U3 and ensure that optocoupler U3 is saturated and conducting (otherwise the output waveform will be severely distorted), the impedance of the voltage divider circuit cannot be too small. Therefore, the resistor in series in the voltage divider circuit must at least make the current on the light source side of optocoupler U3 in the milliampere level. Assuming that the current on the light source side of optocoupler U3 is 2mA, when the effective value of the AC input voltage is 240V, the loss of the voltage divider circuit is at least 0.48W (240×0.002=0.48W), which is too large.
[0003] Especially when traditional AC power failure detection circuits are used in switching power supplies, most switching power supply products require standby / no-load power consumption of <0.5W (or even <0.3W), which is clearly difficult for traditional AC power failure detection circuits to achieve. More importantly, in traditional AC power failure detection circuits, the optocoupler U3 is always conducting when AC power is on, which will continuously generate losses.
[0004] (2) Because when the AC power failure detection circuit fails, the current on the light source side of the optocoupler U3 disappears, so the control signal sent from the light receiver side of the optocoupler U3 to the controller will disappear immediately, and the response time is fixed. When some products need to set a longer AC power failure time to trigger the subsequent circuit to work (mainly to avoid temporary fluctuations in the power grid and avoid false triggering), the traditional AC power failure detection circuit obviously cannot meet the requirements. Utility Model Content
[0005] To address the aforementioned shortcomings, the purpose of this invention is to propose a low-power AC power failure detection circuit with adjustable response time, thereby solving the problems of high power consumption and fixed response time in traditional detection circuits.
[0006] To achieve this objective, the present invention adopts the following technical solution: A low-power AC power failure detection circuit with adjustable response time includes an AC-to-DC module, a trigger module, and an optocoupler module; after the AC-to-DC module is connected to an external AC power supply, it is electrically connected to the optocoupler module via the trigger module, and the optocoupler module outputs a detection signal to the outside. When the AC power supply is not interrupted, the AC to DC module converts the AC signal into a μA or nA DC signal and transmits it to the trigger module, thereby limiting the trigger module from driving the optocoupler module to conduct. When the AC power supply fails, the AC to DC module does not transmit a signal to the trigger module, and the trigger module drives the optocoupler module to conduct according to its preset response time.
[0007] Furthermore, the trigger module includes a reference source, an operational amplifier U1, a resistor R23, and a capacitor C21; the positive input terminal of the operational amplifier U1 is electrically connected to the reference source, the negative input terminal of the operational amplifier U1 is electrically connected to the AC to DC module via the resistor R23, the capacitor C21 is connected in parallel between the negative input terminal and the output terminal of the operational amplifier U1, and the output terminal of the operational amplifier U1 is electrically connected to the optocoupler module.
[0008] Furthermore, both resistor R23 and capacitor C21 are detachably electrically connected to the circuit board.
[0009] Furthermore, the optocoupler module includes an optocoupler U2, a resistor R31, a resistor R33, an input switch circuit, and an output switch circuit; the anode of the light source of the optocoupler U2 is connected to the power supply voltage via the resistor R31, and the cathode of the light source of the optocoupler U2 is electrically connected to the trigger module via the input switch circuit 31. The collector of the photodetector of the optocoupler U2 is connected to the power supply voltage through the resistor R33, and the emitter of the photodetector of the optocoupler U2 outputs the detection signal to the outside through the output switch circuit. The optocoupler module is turned on only when the input switch circuit, the optocoupler U2, and the output switch circuit are all turned on.
[0010] Furthermore, the input switch circuit includes a resistor R32, a capacitor C16, and a MOSFET Q3; the gate of the MOSFET Q3 is electrically connected to the trigger module, the drain of the MOSFET Q3 is electrically connected to the cathode of the light source of the optocoupler U2, the source of the MOSFET Q3 is connected to the PGND ground terminal, and both the resistor R32 and the capacitor C16 are connected in parallel between the gate and the source of the MOSFET Q3.
[0011] Furthermore, the trigger module also includes a diode D21; the output terminal of the operational amplifier U1 is electrically connected to the cathode of the diode D21, and the anode of the diode D21 is electrically connected to the optocoupler module.
[0012] Furthermore, the AC to DC module includes capacitor C11, capacitor C12, diode D11, diode D12, resistor R11, resistor R12, and capacitor C13; one end of capacitor C11 and one end of capacitor C12 are both used to connect to the external AC power supply. The other end of capacitor C11 is electrically connected to the anode of diode D11, the other end of capacitor C12 is electrically connected to the anode of diode D12, the cathodes of diode D11 and D12 are both electrically connected to one end of resistor R11, the other end of resistor R11 and one end of resistor R12 are both electrically connected to one end of capacitor C13, and the other end of resistor R12 and capacitor C13 are both connected to the PGND ground terminal. The other end of the resistor R11 is electrically connected to the trigger module.
[0013] Furthermore, the output switching circuit includes resistor R34, resistor R35, capacitor C17, and MOSFET Q31; the emitter of the photodetector of the optocoupler U2 and the gate of the MOSFET Q31 are electrically connected. The drain of the MOS transistor Q31 is connected to the power supply voltage via the resistor R35, and the source of the MOS transistor Q3 is connected to the ground terminal SGND. The resistor R34 and the capacitor C17 are both connected in parallel between the gate and the source of the MOS transistor Q3. The detection signal is output from the drain of the MOS transistor Q31.
[0014] Furthermore, the reference source includes capacitor C14, resistor R21, and resistor R22; one end of resistor R21 is connected to the power supply voltage, the other end of resistor R21 and one end of resistor R22 are both electrically connected to one end of capacitor C14, the other end of resistor R22 and the other end of capacitor C14 are both connected to the PGND ground terminal, and the other end of resistor R21 is electrically connected to the positive input terminal of operational amplifier U1.
[0015] The technical solution provided by this utility model can include the following beneficial effects: First, by adding an AC-to-DC module to convert AC signals into μA or nA-level DC signals (such as 45nA) to drive subsequent circuits, the subsequent circuits (i.e., the trigger module) can recognize μA or nA-level DC signals, resulting in extremely low power consumption. Furthermore, the optocoupler module only conducts when power is off, eliminating power consumption during normal operation. This significantly reduces power consumption compared to the mA level of traditional circuits (in extreme cases, it can be reduced by tens of thousands of times, as can be easily verified using the power formula P=UI). Second, by adding a trigger module with a preset response time (or delay time) to control the conduction of the optocoupler module as needed, the problem of a fixed response time for the optocoupler module (i.e., the optocoupler) is solved. Attached Figure Description
[0016] Figure 1 This is a circuit diagram of a traditional AC power failure detection circuit.
[0017] Figure 2 This is a circuit diagram of a low-power AC power failure detection circuit with adjustable response time, which is one embodiment of this utility model.
[0018] The components include: AC to DC module 1, trigger module 2, optocoupler module 3, reference source 21, operational amplifier U1, resistor R23, capacitor C21, optocoupler U2, resistor R31, resistor R33, input switch circuit 31, output switch circuit 32, resistor R32, capacitor C16, MOSFET Q3, diode D21, capacitor C11, capacitor C12, diode D11, diode D12, resistor R11, resistor R12, capacitor C13, resistor R34, resistor R35, capacitor C17, MOSFET Q31, capacitor C14, resistor R21, and resistor R22. Detailed Implementation
[0019] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.
[0020] In the description of embodiments of this utility model, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of embodiments of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.
[0021] In the description of the embodiments of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this utility model according to the specific circumstances.
[0022] The following is combined Figure 2 This invention describes a low-power AC power failure detection circuit with adjustable response time according to an embodiment of the present invention.
[0023] A low-power AC power failure detection circuit with adjustable response time includes an AC-to-DC module 1, a trigger module 2, and an optocoupler module 3. After the AC-to-DC module 1 is connected to an external AC power supply, it is electrically connected to the optocoupler module 3 via the trigger module 2, and the optocoupler module 3 outputs a detection signal to the outside. When the AC power supply is not interrupted, the AC to DC module 1 converts the AC signal into a μA or nA DC signal and transmits it to the trigger module 2. This limits the trigger module 2 from driving the optocoupler module 3 to conduct. At this time, the optocoupler module 3 is disconnected and outputs a detection signal indicating that the power is not interrupted, which is then recognized by the receiving end (such as MCU, load device, etc.). When the AC power supply fails, the AC to DC module 1 does not transmit a signal to the trigger module 2. The trigger module 2 drives the optocoupler module 3 to conduct and outputs a detection signal representing the power failure, which is recognized by the receiving end (e.g., MCU).
[0024] This utility model proposes a low-power AC power failure detection circuit with adjustable response time. In a preferred embodiment, as shown below... Figure 2 As shown. First, an AC-to-DC module 1 is added to convert AC signals into μA or nA-level DC signals (such as 45nA) to drive subsequent circuits. The subsequent circuit (i.e., trigger module 2) can recognize μA or nA-level DC signals, resulting in extremely low power consumption. Furthermore, the optocoupler module 3 only operates when power is off, eliminating power consumption during normal operation. This significantly reduces power consumption compared to the mA-level of traditional circuits (in extreme cases, it can be reduced by tens of thousands of times, as can be easily verified using the power formula P=UI). Then, a trigger module 2 with a preset response time (or delay time) is added to control the conduction of the optocoupler module 3 as needed, thus solving the problem of a fixed response time for the optocoupler module 3 (i.e., the optocoupler).
[0025] Furthermore, the trigger module 2 includes a reference source 21, an operational amplifier U1, a resistor R23, and a capacitor C21; the positive input terminal of the operational amplifier U1 is electrically connected to the reference source 21, the negative input terminal of the operational amplifier U1 is electrically connected to the AC to DC module 1 via the resistor R23, the capacitor C21 is connected in parallel between the negative input terminal and the output terminal of the operational amplifier U1, and the output terminal of the operational amplifier U1 is electrically connected to the optocoupler module 3.
[0026] In this embodiment, the trigger module 2 is preferably composed of an integrating circuit consisting of a reference source 21, an operational amplifier U1, a resistor R23, and a capacitor C21. The typical bias current of the operational amplifier U1 (e.g., LM321 model) is in the nA range (e.g., 45nA), which can identify the μA or nA DC signal transmitted from the AC to DC module 1. Furthermore, the operational amplifier U1 can compare the reference voltage (Ref) obtained from the reference source 21 with the voltage (ACT) of the DC signal to determine whether there is a power failure. That is, there is no power failure when ACT > Ref, and power failure when ACT < Ref. Thus, it matches the μA or nA DC signal and realizes the power failure judgment.
[0027] More importantly, the response time of the integrating circuit is determined by resistor R23 and capacitor C21. Different response times can be preset by adjusting the values of resistor R23 and capacitor C21, thus achieving a preset response time. Furthermore, the advantages of using an integrating circuit include: (1) Energy is accumulated by integration to trigger; when the load (the receiving object of the detection signal output by the optocoupler module 3) consumes more energy, the delay trigger time (i.e. response time) is shorter, which better protects the internal power devices of the application circuit; when the load consumes less energy, the delay trigger time (i.e. response time) is longer, allowing for a longer overload and avoiding false triggering caused by overload; thus, while the response time can be preset, it has adaptive adaptability to the receiving object of the detection signal.
[0028] (2) Among the resistor R23 and capacitor C21 used to implement the operational amplifier integration operation, capacitor C21 does not need to have a large capacity. Usually, a small capacitor is sufficient, which can greatly reduce the size of the capacitor C21 device.
[0029] Furthermore, both resistor R23 and capacitor C21 are detachably electrically connected to the circuit board.
[0030] In this embodiment, in order to facilitate the adjustment of the preset response time of the trigger module 2, the mounting method of resistor R23 and capacitor C21 on the circuit board is preferably changed to a detachable electrical connection. For example, corresponding plug-in interfaces are set at the pins of resistor R23 and capacitor C21, and resistor R23 and capacitor C21 are inserted into the plug-in interfaces to achieve electrical connection with the circuit board.
[0031] Furthermore, the optocoupler module 3 includes an optocoupler U2, a resistor R31, a resistor R33, an input switch circuit 31, and an output switch circuit 32; the anode of the light source of the optocoupler U2 is connected to the power supply voltage through the resistor R31, and the cathode of the light source of the optocoupler U2 is electrically connected to the trigger module 2 through the input switch circuit 31. The collector of the photodetector of optocoupler U2 is connected to the power supply voltage through resistor R33, and the emitter of the photodetector of optocoupler U2 outputs the detection signal to the outside through output switch circuit 32. The optocoupler module 3 is turned on only when the input switch circuit 31, the optocoupler U2, and the output switch circuit 32 are all turned on.
[0032] In this embodiment, based on the consideration of setting clear breakpoints at the input and output ends, the optocoupler module 3 preferably has an input switch circuit 31 and an output switch circuit 32 respectively provided on the light source side and the light source side of the optocoupler U2.
[0033] It should be noted that the power supply voltage in the circuit can be the same or different, and the voltage level is not fixed. It needs to be set according to the actual needs, such as VCC, 5V or 3.3V.
[0034] Furthermore, the input switch circuit 31 includes a resistor R32, a capacitor C16, and a MOSFET Q3; the gate of the MOSFET Q3 is electrically connected to the trigger module 3, the drain of the MOSFET Q3 is electrically connected to the cathode of the light source of the optocoupler U2, the source of the MOSFET Q3 is connected to the PGND ground terminal, and the resistor R32 and the capacitor C16 are both connected in parallel between the gate and the source of the MOSFET Q3.
[0035] In this embodiment, the input switch circuit 31 is preferably composed of a MOS transistor Q31 with low loss and fast response speed and its peripheral circuit, wherein the resistor R32 and capacitor C16 are mainly used for shaping and filtering.
[0036] Furthermore, the trigger module 2 also includes a diode D21; the output terminal of the operational amplifier U1 is electrically connected to the cathode of the diode D21, and the anode of the diode D21 is electrically connected to the optocoupler module 3.
[0037] In this embodiment, considering that the optocoupler module 3 is equipped with an input switch circuit 31, the input switch circuit 31 will use a shaping filter structure, for example, composed of a resistor R32 and a capacitor C16, which will consume the charge of capacitor C21 in the integrator circuit, resulting in an inaccurate preset response time. Therefore, the diode D21 is added for isolation to prevent the charge of capacitor C21 from flowing to the input switch circuit 31 and being consumed.
[0038] It should be noted that at this time, the pull-up resistor R24 of the operational amplifier U1 should be connected to the anode of the diode D21 to achieve the pull-up function normally.
[0039] Furthermore, the AC to DC module 1 includes capacitor C11, capacitor C12, diode D11, diode D12, resistor R11, resistor R12 and capacitor C13; one end of capacitor C11 and one end of capacitor C12 are both used to connect to an external AC power supply. The other end of capacitor C11 is electrically connected to the anode of diode D11, the other end of capacitor C12 is electrically connected to the anode of diode D12, the cathodes of diode D11 and D12 are both electrically connected to one end of resistor R11, the other end of resistor R11 and one end of resistor R12 are both electrically connected to one end of capacitor C13, and the other end of resistor R12 and the other end of capacitor C13 are both connected to the PGND ground terminal. The other end of resistor R11 is electrically connected to trigger module 2.
[0040] In this embodiment, the AC to DC conversion of the AC to DC module 1 is mainly achieved by using diodes D11 and D12 for rectification, and then by a voltage divider circuit composed of resistors R11, R12 and C13 to obtain a stable detection voltage for comparison between the operational amplifier U1 and the reference voltage.
[0041] More importantly, the AC power supply first passes through capacitors C11 and C12, and then through diodes D11 and D12. When L / N is struck by lightning, capacitors C11 and C12 can absorb some of the lightning energy, reducing the voltage stress on diodes D11 and D12 and ensuring the reliability of the detection circuit.
[0042] Furthermore, the output switching circuit 32 includes resistors R34 and R35, capacitor C17, and MOSFET Q31; the emitter of the photodetector of optocoupler U2 and the gate of MOSFET Q31 are electrically connected. The drain of MOSFET Q31 is connected to the power supply voltage via resistor R35, and the source of MOSFET Q3 is connected to ground SGND. Resistor R34 and capacitor C17 are both connected in parallel between the gate and source of MOSFET Q3. The drain of MOSFET Q31 outputs a detection signal.
[0043] In this embodiment, similar to the input switch circuit 31, the output switch circuit 32 is also preferably composed of a MOS transistor Q31 with low loss and fast response speed and its peripheral circuit.
[0044] Furthermore, the reference source 21 includes capacitor C14, resistor R21 and resistor R22; one end of resistor R21 is connected to the power supply voltage, the other end of resistor R21 and one end of resistor R22 are both electrically connected to one end of capacitor C14, the other end of resistor R22 and the other end of capacitor C14 are both connected to the PGND ground terminal, and the other end of resistor R21 is electrically connected to the positive input terminal of operational amplifier U1.
[0045] In this embodiment, the reference source 21 is preferably composed of a voltage divider circuit consisting of resistors R21 and R22 connected to the power supply voltage to generate a reference voltage (i.e., Ref) which is provided to the operational amplifier U1 to determine whether there is a power failure. The capacitor C14 is mainly used for filtering to ensure the stability of the reference voltage.
[0046] Other configurations and operations of the low-power AC power failure detection circuit with adjustable response time according to the embodiments of this utility model are known to those skilled in the art and will not be described in detail here.
[0047] In this specification, the terms "embodiment," "example," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0048] Although embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the claims and their equivalents.
Claims
1. A low-power AC power failure detection circuit with adjustable response time, characterized in that: It includes an AC to DC converter module, a trigger module, and an optocoupler module; after the AC to DC converter module is connected to an external AC power supply, it is electrically connected to the optocoupler module via the trigger module, and the optocoupler module outputs a detection signal to the outside; When the AC power supply is not interrupted, the AC to DC module converts the AC signal into a μA or nA DC signal and transmits it to the trigger module, thereby limiting the trigger module from driving the optocoupler module to conduct. When the AC power supply fails, the AC to DC module does not transmit a signal to the trigger module, and the trigger module drives the optocoupler module to conduct according to its preset response time.
2. The low-power AC power failure detection circuit with adjustable response time according to claim 1, characterized in that: The trigger module includes a reference source, an operational amplifier U1, a resistor R23, and a capacitor C21. The positive input terminal of the operational amplifier U1 is electrically connected to the reference source, the negative input terminal of the operational amplifier U1 is electrically connected to the AC to DC module via the resistor R23, the capacitor C21 is connected in parallel between the negative input terminal and the output terminal of the operational amplifier U1, and the output terminal of the operational amplifier U1 is electrically connected to the optocoupler module.
3. The low-power AC power failure detection circuit with adjustable response time according to claim 2, characterized in that: Both resistor R23 and capacitor C21 are detachably electrically connected to the circuit board.
4. The low-power AC power failure detection circuit with adjustable response time according to claim 2, characterized in that: The optocoupler module includes an optocoupler U2, resistors R31 and R33, an input switch circuit, and an output switch circuit; the anode of the light source of the optocoupler U2 is connected to the power supply voltage through the resistor R31, and the cathode of the light source of the optocoupler U2 is electrically connected to the trigger module through the input switch circuit. The collector of the photodetector of the optocoupler U2 is connected to the power supply voltage through the resistor R33, and the emitter of the photodetector of the optocoupler U2 outputs the detection signal to the outside through the output switch circuit. The optocoupler module is turned on only when the input switch circuit, the optocoupler U2, and the output switch circuit are all turned on.
5. The low-power AC power failure detection circuit with adjustable response time according to claim 4, characterized in that: The input switch circuit includes a resistor R32, a capacitor C16, and a MOSFET Q3; the gate of the MOSFET Q3 is electrically connected to the trigger module, the drain of the MOSFET Q3 is electrically connected to the cathode of the light source of the optocoupler U2, the source of the MOSFET Q3 is connected to the PGND ground terminal, and the resistor R32 and the capacitor C16 are both connected in parallel between the gate and the source of the MOSFET Q3.
6. The low-power AC power failure detection circuit with adjustable response time according to claim 2, characterized in that: The trigger module also includes a diode D21; the output terminal of the operational amplifier U1 is electrically connected to the cathode of the diode D21, and the anode of the diode D21 is electrically connected to the optocoupler module.
7. The low-power AC power failure detection circuit with adjustable response time according to claim 1, characterized in that: The AC to DC converter module includes capacitor C11, capacitor C12, diode D11, diode D12, resistor R11, resistor R12, and capacitor C13; one end of capacitor C11 and one end of capacitor C12 are both used to connect to the external AC power supply. The other end of capacitor C11 is electrically connected to the anode of diode D11, the other end of capacitor C12 is electrically connected to the anode of diode D12, the cathodes of diode D11 and D12 are both electrically connected to one end of resistor R11, the other end of resistor R11 and one end of resistor R12 are both electrically connected to one end of capacitor C13, and the other end of resistor R12 and capacitor C13 are both connected to the PGND ground terminal. The other end of the resistor R11 is electrically connected to the trigger module.
8. The low-power AC power failure detection circuit with adjustable response time according to claim 4, characterized in that: The output switching circuit includes resistor R34, resistor R35, capacitor C17, and MOSFET Q31; the emitter of the photodetector of the optocoupler U2 is electrically connected to the gate of the MOSFET Q31. The drain of the MOS transistor Q31 is connected to the power supply voltage via the resistor R35, and the source of the MOS transistor Q3 is connected to the SGND ground terminal. The resistor R34 and the capacitor C17 are both connected in parallel between the gate and the source of the MOS transistor Q3. The detection signal is output from the drain of the MOS transistor Q31.
9. The low-power AC power failure detection circuit with adjustable response time according to claim 2, characterized in that: The reference source includes capacitor C14, resistor R21, and resistor R22; one end of resistor R21 is connected to the power supply voltage, the other end of resistor R21 and one end of resistor R22 are both electrically connected to one end of capacitor C14, the other end of resistor R22 and the other end of capacitor C14 are both connected to the PGND ground terminal, and the other end of resistor R21 is electrically connected to the positive input terminal of operational amplifier U1.