Pulse output type control loop access state detection circuit

Abstract

The utility model discloses an access state detection circuit for a pulse output type control loop. The access state detection circuit comprises a current limiting unit, a rectification unit, a driving unit and an isolation signal conversion unit, the current limiting unit is electrically connected with the rectification unit and the relay through wires. The rectifying unit is in electrical input connection with the driving unit through a wire; the driving unit is in electrical input connection with an isolation signal conversion unit through a wire; the current limiting unit is used for limiting the magnitude of the direct current; the rectifying unit is used for rectifying an alternating current power supply connected to the input end into stable direct current; the driving unit is used for amplifying current and driving the isolation signal conversion unit; the isolation signal conversion unit is used for signal isolation and outputting a control loop access state detection signal. According to the utility model, the technical problem that the existing circuit cannot realize reliable work under the condition of tiny leakage current and reliable detection of a wide-range power supply access state is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of relays, in particular to a pulse output control loop access state detection circuit. Background Art

[0002] At present, the control relay contact power access methods include optocoupler direct drive method and auxiliary power supply drive method. The control relay contact access power supply belongs to strong electricity, while the signal detection system belongs to weak electricity. The two parts need to be isolated and usually isolated by optocouplers. Since the optocoupler primary photodiode needs a certain driving current to be turned on, its secondary phototransistor has a certain leakage current, and the leakage current has a positive temperature coefficient, which means that the leakage current of the conventional detection circuit cannot be very small, otherwise there will be misjudgment. In other words, direct drive by optocoupler is easily affected by the optocoupler characteristics, has poor applicability, and cannot achieve wide input range detection. In some applications, an external auxiliary power supply is used to ensure that the leakage current is small to meet the circuit operation, but this method is costly and the circuit structure is relatively complex.

[0003] The patent document with application number 202310936899.7 discloses a method for measuring leakage current of MLCC capacitors. The first optocoupler MOS tube is turned on and the power module is started. The high-low internal resistance switching module is in the low internal resistance input state, and the MLCC capacitor is charged. When the charging time of the MLCC capacitor reaches the preset time, the first optocoupler MOS tube is turned off, and the first resistor of the high-low internal resistance switching module is turned on. The charge of the integral capacitor of the second optocoupler MOS tube is cleared to zero. When the voltage output by the integral operational amplifier module is within the threshold comparison range and the control module is in a high level state, the second optocoupler MOS tube is turned off. The ADC acquisition module sends the target voltage value to the control module. The control module measures the leakage current value of the MLCC capacitor according to the target voltage value and the voltage threshold range of the threshold comparison module. It also cannot solve the precise detection of micro leakage current and the detection of wide-range power access status. Therefore, it is urgent to propose a pulse output control loop access status detection circuit to solve the technical problem that the existing circuit cannot achieve reliable operation under the condition of micro leakage current and reliable detection of wide-range power access status. Utility Model Content

[0004] The main purpose of the utility model is to propose a pulse output control loop access status detection circuit, aiming to solve the technical problem that the existing circuit cannot achieve reliable operation under the condition of small leakage current and reliable detection of wide range power access status.

[0005] To achieve the above object, the utility model provides a pulse output control loop access state detection circuit, wherein the pulse output control loop access state detection circuit comprises:

[0006] Current limiting unit, rectification unit, driving unit and isolation signal conversion unit;

[0007] The current limiting unit is electrically connected to the rectifying unit and the relay through wires; the rectifying unit is electrically connected to the driving unit through wires; the driving unit is electrically connected to the isolation signal conversion unit through wires;

[0008] The current limiting unit is used to limit the magnitude of the direct current;

[0009] The rectifier unit is used to rectify the AC power supply connected to the input end into a stable DC;

[0010] The driving unit is used for current amplification and for driving the isolation signal conversion unit;

[0011] The isolation signal conversion unit is used for signal isolation and outputs a control loop access status detection signal.

[0012] In one of the preferred schemes, the current limiting unit includes resistors R4, R5, R6, R11, R12, and R13; one end of the resistor R4 is connected to the RELAY_NO terminal of the relay, the other end of the resistor R4 is connected to the resistor R6 through the resistor R5, and the other end of the resistor R6 is connected to the rectifier unit; one end of the resistor R11 is connected to the RELAY_COM terminal of the relay, the other end of the resistor R11 is connected to the resistor R13 through the resistor R12, and the other end of the resistor R13 is connected to the rectifier circuit.

[0013] In one preferred embodiment, the rectifier circuit includes a rectifier bridge BR1, a capacitor C3 and a diode VD1;

[0014] Pin 1 of the rectifier bridge BR1 is connected to the resistor R6, pin 2 of the rectifier bridge BR1 is connected to the resistor R13, pin 3 of the rectifier bridge BR1 is respectively connected to the capacitor C3 and the diode VD1, and pin 4 of the rectifier bridge BR1, the capacitor C3 and the other end of the diode VD1 are grounded.

[0015] In one of the preferred embodiments, the rectifier bridge BR1 includes a diode VD2, a diode VD3, a diode VD4 and a diode VD5; the cathode of the diode VD2 is connected to the cathode of the diode VD3, the anode of the diode VD3 is connected to the cathode of the diode VD4, the anode of the diode VD4 is connected to the anode of the diode VD5, and the cathode of the diode VD5 is connected to the anode of the diode VD2.

[0016] In one preferred solution, the driving unit includes a capacitor C4, a voltage divider circuit, an acceleration circuit, a Darlington transistor V, a resistor R8, a resistor R10, a transistor VT1 and an AC positive feedback circuit;

[0017] One end of the Darlington transistor V is connected to the acceleration circuit, and the other end of the acceleration circuit is respectively connected to the AC positive feedback circuit, the voltage divider circuit and the capacitor C4, and the other end of the capacitor C4 and the voltage divider circuit is grounded; one end of the Darlington transistor V is respectively connected to the voltage divider circuit and the isolation signal conversion unit; one end of the Darlington transistor V is connected to the resistor R8, and the other end of the resistor R8 is respectively connected to the resistor R10 and the base of the transistor VT1, the collector of the transistor VT1 is respectively connected to the AC positive feedback circuit and the isolation signal conversion unit, and the emitter of the transistor VT1 and the other end of the resistor R10 are grounded.

[0018] In one preferred embodiment, the Darlington transistor V comprises a transistor V1 and a transistor V2;

[0019] The emitter of the transistor V1 is connected to the voltage divider circuit, the base of the transistor V1 is connected to the emitter of the transistor V2, the collector of the transistor V1 is connected to the collector of the transistor V2 and the resistor R8 respectively, and the base of the transistor V2 is connected to the acceleration circuit.

[0020] In one of the preferred embodiments, the acceleration circuit includes a resistor R7 and a capacitor C2; one end of the resistor R7 is connected to the base of the transistor V2 and the capacitor C2, and the other end of the resistor R7 is connected to the voltage divider circuit, the AC positive feedback circuit and the other end of the capacitor C2.

[0021] In one of the preferred solutions, the voltage divider circuit includes a resistor R3 and a resistor R9; one end of the resistor R3 is connected to the emitter of the transistor V1, and the other end of the resistor R3 is respectively connected to the capacitor C4, the resistor R9 and the acceleration circuit; the other end of the resistor R9 is grounded.

[0022] In one of the preferred solutions, the AC positive feedback circuit includes a capacitor C5 and a resistor R14; one end of the resistor R14 is connected to the acceleration circuit, the other end of the resistor R14 is connected to the capacitor C5, and the other end of the capacitor C5 is connected to the collector of the transistor VT1.

[0023] In one of the preferred schemes, the isolated signal conversion unit includes an optocoupler D1, a resistor R1, a resistor R2 and a capacitor C1; pin 1 of the optocoupler D1 is connected to the resistor R2, and the other end of the resistor R2 is connected to the drive circuit; pin 2 of the optocoupler D1 is connected to the drive circuit; pin 3 of the optocoupler D1 is grounded; pin 4 of the optocoupler D1 is respectively connected to the resistor R1 and the capacitor C1, the other end of the resistor R1 is connected to the power supply end, and the other end of the capacitor C1 is grounded.

[0024] In the above technical solution of the utility model, the pulse output control loop access state detection circuit includes a current limiting unit, a rectifier unit, a drive unit and an isolation signal conversion unit; the current limiting unit is electrically connected to the rectifier unit and the relay through wires respectively; the rectifier unit is electrically input connected to the drive unit through wires; the drive unit is electrically input connected to the isolation signal conversion unit through wires; the current limiting unit is used to limit the magnitude of the DC current; the rectifier unit is used to rectify the AC power supply connected to the input end into a stable DC; the drive unit is used for current amplification and for driving the isolation signal conversion unit; the isolation signal conversion unit is used for signal isolation and outputs a control loop access state detection signal. The utility model solves the technical problem that the existing circuit cannot achieve reliable operation under the condition of small leakage current and reliable detection of a wide range of power access states.

[0025] In the utility model, by designing a driving unit with an AC positive feedback function, power connection state detection is achieved in which the leakage current is less than 100uA regardless of whether the power supply is DC 12V or AC 220V. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0027] Figure 1 This is a schematic diagram of a pulse output control loop access state detection circuit according to an embodiment of the utility model;

[0028] Figure 2 This is a first schematic diagram of a pulse output control loop access state detection circuit according to an embodiment of the utility model;

[0029] Figure 3 The present invention is a field application schematic diagram of a pulse output control loop connected to a state detection circuit according to an embodiment of the present invention.

[0030] Description of Figure Numbers:

[0031] A01, current limiting unit; A02, rectification unit; A03, driving unit; A04, isolation signal conversion unit.

[0032] The realization of the purpose, functional features and advantages of the utility model will be further explained in conjunction with the implementation methods and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0034] In addition, in the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0035] Furthermore, the technical solutions between the various implementation modes of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0036] See also Figure 1-Figure 2 According to one aspect of the utility model, the utility model provides a pulse output control loop access state detection circuit, wherein the pulse output control loop access state detection circuit includes a current limiting unit A01, a rectifying unit A02, a driving unit A03 and an isolation signal conversion unit A04;

[0037] The current limiting unit A01 is electrically connected to the rectifying unit A02 and the relay through wires; the rectifying unit A02 is electrically connected to the driving unit through wires; the driving unit A03 is electrically connected to the isolation signal conversion unit A04 through wires;

[0038] The current limiting unit A01 is used to limit the magnitude of the direct current;

[0039] The rectifier unit A02 is used to rectify the AC power connected to the input end into a stable DC;

[0040] The driving unit A03 is used for current amplification and for driving the isolation signal conversion unit A04;

[0041] The isolation signal conversion unit A04 is used for signal isolation and outputs a control loop access status detection signal.

[0042] Specifically, in this embodiment, the current limiting unit A01 includes a resistor R4, a resistor R5, a resistor R6, a resistor R11, a resistor R12, and a resistor R13; one end of the resistor R4 is connected to the relay RELAY_NO terminal, the other end of the resistor R4 is connected to the resistor R6 through the resistor R5, and the other end of the resistor R6 is connected to the rectifier unit A02; one end of the resistor R11 is connected to the relay RELAY_COM terminal, the other end of the resistor R11 is connected to the resistor R13 through the resistor R12, and the other end of the resistor R13 is connected to the rectifier unit A02. The current limiting unit A01 is used to limit the current in the branch to prevent excessive current from burning out the components in series. The current limiting unit A01 determines the leakage current of the detection circuit. Due to the relay RELAY_NO end and the relay RELAY_COM end, the relay RELAY_NO end is the normally open contact of the relay, and the relay RELAY_COM end is the common contact, that is, in extreme cases, 1KV will appear between the normally open contact of the relay and the common contact. Therefore, the current limiting resistor is connected in series to limit the branch current.

[0043] Specifically, in this embodiment, the rectifier circuit includes a rectifier bridge BR1, a capacitor C3 and a diode VD1; pin 1 of the rectifier bridge BR1 is connected to the resistor R6, pin 2 of the rectifier bridge BR1 is connected to the resistor R13, pin 3 of the rectifier bridge BR1 is respectively connected to the capacitor C3 and the diode VD1, and pin 4 of the rectifier bridge BR1, the capacitor C3 and the other end of the diode VD1 are grounded; the control relay contacts are connected to the AC power supply through the rectifier bridge BR1 to rectify it into a pulsating DC, the capacitor C3 is a filter capacitor, which converts the pulsating DC into a stable DC, and the diode VD1 is a voltage-stabilizing diode, which can limit the DC amplitude and protect the drive unit A03 from overvoltage damage.

[0044] Specifically, in this embodiment, the rectifier bridge BR1 includes a diode VD2, a diode VD3, a diode VD4 and a diode VD5; the cathode of the diode VD2 is connected to the cathode of the diode VD3, the anode of the diode VD3 is connected to the cathode of the diode VD4, the anode of the diode VD4 is connected to the anode of the diode VD5, and the cathode of the diode VD5 is connected to the anode of the diode VD2.

[0045] Specifically, in this embodiment, the driving unit A03 includes a capacitor C4, a voltage divider circuit, an acceleration circuit, a Darlington transistor V, a resistor R8, a resistor R10, a transistor VT1 and an AC positive feedback circuit; one end of the Darlington transistor V is connected to the acceleration circuit, and the other end of the acceleration circuit is respectively connected to the AC positive feedback circuit, the voltage divider circuit and the capacitor C4, and the other ends of the capacitor C4 and the voltage divider circuit are grounded; one end of the Darlington transistor V is respectively connected to the voltage divider circuit and the isolation signal conversion unit A04; One end of the Darlington transistor V is connected to the resistor R8, the other end of the resistor R8 is respectively connected to the resistor R10 and the base of the transistor VT1, the collector of the transistor VT1 is respectively connected to the AC positive feedback circuit and the isolation signal conversion unit A04, the emitter of the transistor VT1 and the other end of the resistor R10 are grounded; the capacitor C4 is a holding capacitor, the resistor R8 is a current limiting resistor, and the resistor R10 is a pull-down resistor; the optocoupler D1 in the isolation signal conversion unit A04 is isolated through the transistor VT1.

[0046] Specifically, in the present embodiment, the Darlington transistor V includes a transistor V1 and a transistor V2; the emitter of the transistor V1 is connected to the voltage divider circuit, the base of the transistor V1 is connected to the emitter of the transistor V2, the collector of the transistor V1 is respectively connected to the collector of the transistor V2 and the resistor R8, and the base of the transistor V2 is connected to the acceleration circuit; the Darlington transistor V is a homopolar Darlington, and the Darlington transistor V has a higher amplification factor than that of an ordinary transistor by compound connecting the two transistors together according to the current flow direction, and the specific amplification factor is equal to the product of the amplification factors of the two transistors, thereby realizing current amplification and improving the driving capability of the circuit.

[0047] Specifically, in this embodiment, the acceleration circuit includes a resistor R7 and a capacitor C2; one end of the resistor R7 is connected to the base of the transistor V2 and the capacitor C2, and the other end of the resistor R7 is connected to the voltage divider circuit, the AC positive feedback circuit and the other end of the capacitor C2; the acceleration circuit can accelerate the voltage change rate at the load end.

[0048] Specifically, in this embodiment, the voltage divider circuit includes a resistor R3 and a resistor R9; one end of the resistor R3 is connected to the emitter of the transistor V1, and the other end of the resistor R3 is respectively connected to the capacitor C4, the resistor R9 and the acceleration circuit; the other end of the resistor R9 is grounded; the resistor R3 and the resistor R9 are voltage divider resistors, and the voltage divider circuit can not only convert a high voltage into a low voltage, but also adjust the input voltage to a desired value, that is, the voltage divider circuit provides a working threshold for the driving unit A03.

[0049] Specifically, in this embodiment, the AC positive feedback circuit includes a capacitor C5 and a resistor R14; one end of the resistor R14 is connected to the acceleration circuit, the other end of the resistor R14 is connected to the capacitor C5, and the other end of the capacitor C5 is connected to the collector of the transistor VT1.

[0050] Specifically, in this embodiment, the isolated signal conversion unit A04 includes an optocoupler D1, a resistor R1, a resistor R2 and a capacitor C1; pin 1 of the optocoupler D1 is connected to the resistor R2, and the other end of the resistor R2 is connected to the drive circuit; pin 2 of the optocoupler D1 is connected to the drive circuit; pin 3 of the optocoupler D1 is grounded; pin 4 of the optocoupler D1 is respectively connected to the resistor R1 and the capacitor C1, the other end of the resistor R1 is connected to the power supply end, and the other end of the capacitor C1 is grounded; the isolated signal conversion unit A04 realizes signal isolation transmission to ensure safety requirements; the DET_MCU signal output by pin 4 of the optocoupler D1 in the isolated signal conversion unit A04 is a control loop access status detection signal. When the trip switch control relay is in an un-attracted state and the control relay contact power supply is connected, the DET_MCU signal is a pulse signal. When the trip switch control relay is not attracted and the control relay contact power supply is not connected, the DET_MCU signal is a high level.

[0051] Specifically, in this embodiment, the current limiting unit A01 determines the magnitude of the leakage current of the detection loop, and the leakage current is:

[0052]

[0053] Among them, I D To detect the loop leakage current, V is the power supply voltage for the control relay contact, V BR is the conduction voltage drop of the rectifier bridge BR1, and R4, R5, R6, R11, R12, and R13 are the resistance values ​​of resistor R4, resistor R5, resistor R6, resistor R11, resistor R12, and resistor R13 respectively.

[0054] Specifically, in this embodiment, see Figure 3The present invention is a schematic diagram of the field application of a pulse output control loop access state detection circuit, that is, the control loop access state detection unit is a pulse output control loop access state detection circuit, K1 is a control relay, K2 is a trip switch control relay, wherein K1 is used to control the power supply of the trip switch control relay coil, when the K1 contact is energized, the K2 coil is energized, and the K2 contact is energized, the corresponding control switch realizes the opening and closing functions, and then realizes the automatic connection or disconnection function of the distribution line. In order to be able to measure the action of the trip switch control relay and ensure that the switch does not malfunction, it is necessary to detect through the pulse output control loop access state detection circuit. The utility model has a simple circuit structure, strong applicability, and low cost. By adopting an AC positive feedback drive circuit, a control loop access state detection in a pulse output mode with low leakage current is realized.

[0055] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the utility model concept, or directly / indirectly used in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A pulse output control loop access state detection circuit, characterized in that: include: Current limiting unit, rectification unit, driving unit and isolation signal conversion unit; The current limiting unit is electrically connected to the rectifying unit and the relay through wires; the rectifying unit is electrically connected to the driving unit through wires; the driving unit is electrically connected to the isolation signal conversion unit through wires; The current limiting unit is used to limit the magnitude of the direct current; The rectifier unit is used to rectify the AC power supply connected to the input end into a stable DC; The driving unit is used for current amplification and for driving the isolation signal conversion unit; The isolation signal conversion unit is used for signal isolation and outputs a control loop access status detection signal.

2. A pulse output control loop access state detection circuit according to claim 1, characterized in that: The current limiting unit includes resistors R4, R5, R6, R11, R12, and R13; one end of the resistor R4 is connected to the RELAY_NO terminal of the relay, the other end of the resistor R4 is connected to the resistor R6 through the resistor R5, and the other end of the resistor R6 is connected to the rectifier unit; one end of the resistor R11 is connected to the RELAY_COM terminal of the relay, the other end of the resistor R11 is connected to the resistor R13 through the resistor R12, and the other end of the resistor R13 is connected to the rectifier circuit.

3. A pulse output control loop access state detection circuit according to claim 2, characterized in that: The rectifier circuit includes a rectifier bridge BR1, a capacitor C3 and a diode VD1; Pin 1 of the rectifier bridge BR1 is connected to the resistor R6, pin 2 of the rectifier bridge BR1 is connected to the resistor R13, pin 3 of the rectifier bridge BR1 is respectively connected to the capacitor C3 and the diode VD1, and pin 4 of the rectifier bridge BR1, the capacitor C3 and the other end of the diode VD1 are grounded.

4. A pulse output control loop access state detection circuit according to claim 3, characterized in that: The rectifier bridge BR1 includes a diode VD2, a diode VD3, a diode VD4 and a diode VD5; the cathode of the diode VD2 is connected to the cathode of the diode VD3, the anode of the diode VD3 is connected to the cathode of the diode VD4, the anode of the diode VD4 is connected to the anode of the diode VD5, and the cathode of the diode VD5 is connected to the anode of the diode VD2.

5. A pulse output control loop access state detection circuit according to any one of claims 1 to 4, characterized in that: The driving unit includes a capacitor C4, a voltage divider circuit, an acceleration circuit, a Darlington transistor V, a resistor R8, a resistor R10, a transistor VT1 and an AC positive feedback circuit; One end of the Darlington transistor V is connected to the acceleration circuit, and the other end of the acceleration circuit is respectively connected to the AC positive feedback circuit, the voltage divider circuit and the capacitor C4, and the other end of the capacitor C4 and the voltage divider circuit is grounded; one end of the Darlington transistor V is respectively connected to the voltage divider circuit and the isolation signal conversion unit; one end of the Darlington transistor V is connected to the resistor R8, and the other end of the resistor R8 is respectively connected to the resistor R10 and the base of the transistor VT1, the collector of the transistor VT1 is respectively connected to the AC positive feedback circuit and the isolation signal conversion unit, and the emitter of the transistor VT1 and the other end of the resistor R10 are grounded.

6. A pulse output control loop access state detection circuit according to claim 5, characterized in that: The Darlington transistor V includes a transistor V1 and a transistor V2; The emitter of the transistor V1 is connected to the voltage divider circuit, the base of the transistor V1 is connected to the emitter of the transistor V2, the collector of the transistor V1 is connected to the collector of the transistor V2 and the resistor R8 respectively, and the base of the transistor V2 is connected to the acceleration circuit.

7. A pulse output control loop access state detection circuit according to claim 6, characterized in that: The acceleration circuit includes a resistor R7 and a capacitor C2; one end of the resistor R7 is connected to the base of the transistor V2 and the capacitor C2, and the other end of the resistor R7 is connected to the voltage divider circuit, the AC positive feedback circuit and the other end of the capacitor C2.

8. A pulse output control loop access state detection circuit according to claim 6, characterized in that: The voltage divider circuit includes a resistor R3 and a resistor R9; one end of the resistor R3 is connected to the emitter of the transistor V1, and the other end of the resistor R3 is respectively connected to the capacitor C4, the resistor R9 and the acceleration circuit; the other end of the resistor R9 is grounded.

9. A pulse output control loop access state detection circuit according to claim 6, characterized in that: The AC positive feedback circuit includes a capacitor C5 and a resistor R14; one end of the resistor R14 is connected to the acceleration circuit, the other end of the resistor R14 is connected to the capacitor C5, and the other end of the capacitor C5 is connected to the collector of the transistor VT1.

10. A pulse output control loop access state detection circuit according to any one of claims 1 to 4, characterized in that: The isolated signal conversion unit includes an optocoupler D1, a resistor R1, a resistor R2 and a capacitor C1; pin 1 of the optocoupler D1 is connected to the resistor R2, and the other end of the resistor R2 is connected to the drive circuit; pin 2 of the optocoupler D1 is connected to the drive circuit; pin 3 of the optocoupler D1 is grounded; pin 4 of the optocoupler D1 is respectively connected to the resistor R1 and the capacitor C1, the other end of the resistor R1 is connected to the power supply end, and the other end of the capacitor C1 is grounded.

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