Alternating-current zero-cross detection circuit

Abstract

An alternating-current zero-crossing detection circuit comprises an alternating-current detection unit and an isolation output unit, the alternating-current detection unit comprises a sampling chip, an input pin of the sampling chip is connected with a live wire end through a plurality of divider resistors connected in series, a common grounding end is connected with a zero wire end, and an output end is connected with the common grounding end of the sampling chip through a fourth resistor and a first capacitor in sequence. The isolation output unit comprises an optical coupling isolator, the cathode of the input end of the optical coupling isolator is connected with the output end of the sampling chip, the anode of the input end of the optical coupling isolator is connected with a connection node of a fourth resistor and a first capacitor, and the collector of the output end of the optical coupling isolator is connected with a power supply and a signal output end. And the output end emitter of the optical coupled isolator is connected with the common ground. By monitoring the voltage between the live wire and the zero wire of the alternating current and sending a pulse signal through the capacitor, the problems of low precision, high cost and high power consumption of an alternating current zero-crossing detection circuit are solved.

Description

Technical Field

[0001] The utility model relates to the field of detection circuits, in particular to an AC zero-crossing detection circuit. Background Art

[0002] Zero-crossing detection is often used in control, modulation, protection and other fields. It is used to detect and track the position and time of the zero-crossing point of the positive half-wave and negative half-wave of the alternating current. Through zero-crossing detection, the instantaneous and long-term change information of the alternating voltage, such as phase, frequency, and jitter, can also be obtained. AC zero-crossing detection circuits are widely used in power carrier communication, power equipment, and home appliance access switching. In smart switches and smart switch products, zero-crossing detection technology is used to achieve zero-voltage switching, thereby suppressing startup surge current, arcing and instantaneous high temperature, and protecting relay contacts and other devices; in some smart lighting fields, dimming equipment uses zero-crossing detection technology to control the size of the AC conduction angle from zero point to achieve brightness adjustment; in the field of industrial control, synchronous signal output judgment is performed to achieve motor speed adjustment; it is also commonly used in power carrier communication and other power electronic equipment to achieve zero-crossing communication, phase recognition, reverse phase sequence judgment, zero-live reverse connection, station area recognition, power-off detection, etc. The current zero-crossing detection circuit usually connects the input end of the optocoupler isolator to the live wire and the neutral wire of the AC power respectively, and connects the output end of the optocoupler isolator to a signal flipping circuit. The output end signal of the optocoupler isolator is converted into a high and low level trigger signal through the charging and discharging of the capacitor in the signal flipping circuit and outputted to the signal port of the main control chip. However, this detection circuit that converts the accumulated electrical energy charging and discharging of the capacitor into high and low level output has poor detection accuracy and consistency.

[0003] The patent application with announcement number CN219997175U discloses a circuit for detecting AC voltage zero crossing. By adopting the method of transistor amplification current and capacitor power supply, the voltage difference between the live wire and the neutral wire is passed through the transistor amplification comparison circuit and then discharged by the capacitor to output a pulse. By outputting the pulse signal, the consistency and detection accuracy of the circuit detection can be improved to a certain extent. However, this zero-crossing detection circuit only sends out a pulse signal when the AC crosses the zero point, and the pulse signal needs to be connected to the main control chip through the output circuit, etc. This circuit that only monitors the zero point is not conducive to the main control chip to respond quickly; and the circuit for comparing and amplifying the voltage requires multiple components, the cost of the components is high, and the power consumption of the circuit is high, which is not conducive to reducing costs and increasing efficiency. How to solve this problem requires an AC zero-crossing detection circuit with high detection accuracy, low cost, and low power consumption. Summary of the invention

[0004] The purpose of the utility model is to provide an AC zero-crossing detection system to address the deficiencies in the prior art. The AC voltage is monitored by a sampling chip of an AC detection unit, and a pulse signal is output through an isolation output unit, thereby solving the problems of low accuracy, high cost, and high power consumption of the AC zero-crossing detection circuit and improving the circuit's anti-interference ability.

[0005] The purpose of the utility model is to adopt the following scheme to achieve: an AC zero-crossing detection circuit, including an AC detection unit and an isolation output unit, the AC detection unit includes a sampling chip, the input pin of the sampling chip is connected to the live wire end through a plurality of series-connected voltage-dividing resistors for connecting the AC live wire, the common ground terminal is connected to the neutral wire end for connecting the AC neutral wire, the output end is connected to the common ground terminal of the sampling chip through a fourth resistor and a first capacitor in sequence, the isolation output unit includes an optocoupler isolator, the cathode of the input end of the optocoupler isolator is connected to the output end of the sampling chip, the anode of the input end of the optocoupler isolator is connected to the connection node of the fourth resistor and the first capacitor, the collector of the output end of the optocoupler isolator is connected to the power supply and the signal output end, the signal output end is used to connect the signal input port of the main control chip, and the emitter of the output end of the optocoupler isolator is connected to the common ground.

[0006] Preferably, the common ground terminal of the sampling chip is connected to the neutral line terminal through a first diode, an anode of the first diode is connected to the common ground terminal of the sampling chip, and a cathode of the first diode is connected to the neutral line terminal.

[0007] Preferably, the number of the voltage-dividing resistors is 2 to 5.

[0008] Further preferably, the number of the voltage-dividing resistors is 3.

[0009] Preferably, a fifth resistor is arranged between the collector of the output end of the optocoupler isolator and the power supply, and is connected to a common ground via a second capacitor.

[0010] By adopting the above scheme, an AC zero-crossing detection circuit includes an AC detection unit and an isolation output unit, wherein the AC detection unit includes a sampling chip, an input pin of the sampling chip is connected to a live wire end through a plurality of voltage-dividing resistors connected in series for connecting an AC live wire, a common ground end is connected to a neutral wire end for connecting an AC neutral wire, and an output end is connected to a common ground end of the sampling chip through a fourth resistor and a first capacitor in sequence, and the isolation output unit includes an optocoupler isolator, a cathode of the input end of the optocoupler isolator is connected to an output end of the sampling chip, an anode of the input end of the optocoupler isolator is connected to a connection node of the fourth resistor and the first capacitor, a collector of the output end of the optocoupler isolator is connected to a power supply and a signal output end, the signal output end is used to connect to a signal input port of a main control chip, and an emitter of the output end of the optocoupler isolator is connected to a common ground. The sampling chip of the AC detection unit is used to detect the voltage between the live wire and the neutral wire of the AC power. When it is detected that the voltage drops to the voltage calibration value inside the chip, a pulse signal is emitted through the discharge of the first capacitor. Compared with the prior art for monitoring the zero-crossing point, the voltage before the AC power crosses the zero point is detected, and an early warning is given to the main control chip, so that the main control chip can make a judgment in advance; the sampling chip is used in conjunction with the energy storage capacitor to keep the circuit consistent and improve the detection accuracy; the output pulse signal is isolated through the isolation output unit to isolate the high and low voltages, and the anti-interference performance is good; a first diode is set between the neutral line end and the common ground end of the sampling chip to prevent the first capacitor from charging in the negative half cycle of the AC power, thereby saving electric energy and effectively reducing the power consumption of the circuit.

[0011] The utility model is further described below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the circuit structure of the utility model;

[0013] Figure 2 This is a schematic diagram of the zero-crossing pulse waveform of the utility model. DETAILED DESCRIPTION

[0014] See also Figure 1 to Figure 2, an AC zero-crossing detection circuit, including an AC detection unit and an isolated output unit. The AC detection unit includes a sampling chip U1, the sampling chip U1 collects the voltage between the AC live wire and the neutral wire, the input pin of the sampling chip U1 is connected to the live wire end L through a plurality of series-connected voltage-dividing resistors for connecting the AC live wire, the series-connected voltage-dividing resistors limit the current of the input pin of the sampling chip U1 to prevent the sampling chip U1 from being damaged by excessive current, the common ground terminal of the sampling chip U1 is connected to the neutral wire end N through a first diode D1, the anode of the first diode D1 is connected to the common ground terminal of the sampling chip U1, and the cathode is connected to the neutral wire end N, the neutral wire end N is used to connect the AC neutral wire, the output end is connected to the common ground terminal of the sampling chip U1 through a fourth resistor R4 and a first capacitor C1 in sequence; the first capacitor C1 is an energy storage capacitor, which provides electrical energy for the sampling chip U1 and the optocoupler isolator U2 in the isolated output unit.

[0015] The isolated output unit includes an optocoupler isolator U2, the cathode of the input end of the optocoupler isolator U2 is connected to the output end of the sampling chip U1, the anode of the input end of the optocoupler isolator U2 is connected to the connection node of the fourth resistor R4 and the first capacitor C1, the collector of the output end of the optocoupler isolator U2 is connected to the power supply VCC and the signal output end GLJC, a fifth resistor R5 is arranged between the collector of the output end of the optocoupler isolator U2 and the power supply VCC, the fifth resistor R5 is a pull-up resistor, and the collector of the output end of the optocoupler isolator U2 is connected to the common ground through the second capacitor C2, the second capacitor C2 is a filter capacitor, the signal output end GLJC is used to connect the signal input port of the main control chip, and the emitter of the output end of the optocoupler isolator U2 is connected to the common ground.

[0016] Preferably, the number of the voltage-dividing resistors is 2 to 5, and the number and parameters of the voltage-dividing resistors are adjusted according to the voltage of the input alternating current; by setting multiple voltage-dividing resistors, it is beneficial to reduce the voltage on the voltage-dividing resistor and protect the voltage-dividing resistor; multiple voltage-dividing resistors have a current limiting effect, which can not only protect the sampling chip from being damaged by excessive current, but also reduce circuit energy consumption. In this embodiment, the number of the voltage-dividing resistors is 3, including a first voltage-dividing resistor R1, a second voltage-dividing resistor R2, and a third voltage-dividing resistor R3.

[0017] In this embodiment, the resistance values ​​of the first voltage-dividing resistor R1, the second voltage-dividing resistor R2, and the third voltage-dividing resistor R3 are 1.5MΩ; the model of the sampling chip U1 is GS1102; the model of the first diode D1 is US1M; the resistance value of the fourth resistor R4 is 4.7KΩ; the capacitance of the first capacitor C1 is 47nF; the model of the optocoupler isolator U2 is PC817; the resistance value of the fifth resistor R5 is 10KΩ; and the capacitance of the second capacitor C2 is 1nF.

[0018] Working principle: The AC voltage is collected through the sampling chip U1. When the voltage of the AC is greater than the voltage calibration value in the sampling chip U1, the voltage calibration value of the sampling chip in this embodiment is 5.9V. The sampling chip U1 charges the first capacitor C1 to store energy; when the AC enters the negative half-cycle from the positive half-cycle, when the sampling chip U1 detects that the voltage drops from the high voltage to the voltage calibration value in the sampling chip U1, the discharge path from the output end of the sampling chip U1 to the ground is opened, the first capacitor C1 is discharged, and a loop is formed through the fourth resistor R4. The released voltage passes through the optical coupler isolator U2 to generate a zero-crossing pulse, and the signal output terminal GLJC outputs a low-level signal. The voltage calibration value is determined by the type of the selected sampling chip.

[0019] The voltage value of the AC power is monitored by the sampling chip U1. When the voltage drops from the high voltage of the positive half cycle, the first capacitor C1 is discharged in advance before the zero crossing point to output a pulse signal, so as to reserve preparation time for the subsequent zero crossing control of the main control chip. Figure 2 The figure shows a schematic diagram of the zero-crossing pulse waveform of the utility model, which can accurately detect the zero-crossing of AC power with good consistency; and the pulse signal is sent in advance before the zero-crossing point, reserving time for subsequent control of the main control chip, which is convenient for the control of the main control chip.

[0020] Zero-crossing detection only detects the zero-crossing point from the positive half-cycle to the negative half-cycle of the alternating current, so a first diode D1 is set on the line at the neutral line end. The first diode D1 is in a cut-off state in the negative half-cycle of the alternating current, and the first capacitor C1 cannot be charged, which effectively saves energy.

[0021] The utility model detects the voltage between the live wire and the neutral wire of the alternating current through a sampling chip. When the voltage drops to the voltage calibration value inside the chip, a pulse signal is discharged through a first capacitor before the alternating current passes through zero, so that the main control chip can make a judgment in advance. The sampling chip is used in conjunction with an energy storage capacitor to keep the circuit consistent and have high detection accuracy. The pulse signal is output by an isolation output unit to isolate high and low voltages and has good anti-interference performance.

[0022] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. An AC zero-crossing detection circuit, characterized in that: The invention comprises an AC detection unit and an isolation output unit. The AC detection unit comprises a sampling chip (U1). An input pin of the sampling chip (U1) is connected to a live wire end (L) through a plurality of voltage-dividing resistors connected in series for connecting to an AC live wire. A common ground end is connected to a neutral wire end (N) for connecting to an AC neutral wire. An output end is connected to a common ground end of the sampling chip (U1) through a fourth resistor (R4) and a first capacitor (C1) in sequence. The isolation output unit comprises an optocoupler isolator (U2). An input cathode of the optocoupler isolator (U2) is connected to an output end of the sampling chip (U1). An input anode of the optocoupler isolator (U2) is connected to a connection node between the fourth resistor (R4) and the first capacitor (C1). An output collector of the optocoupler isolator (U2) is connected to a power supply (VCC) and a signal output end (GLJC). The signal output end (GLJC) is used to connect to a signal input port of a main control chip. An output emitter of the optocoupler isolator (U2) is connected to a common ground.

2. The AC zero-crossing detection circuit according to claim 1, characterized in that: The common ground terminal of the sampling chip (U1) is connected to the neutral terminal (N) through a first diode (D1); the anode of the first diode (D1) is connected to the common ground terminal of the sampling chip (U1), and the cathode is connected to the neutral terminal (N).

3. The AC zero-crossing detection circuit according to claim 1, characterized in that: The number of the voltage-dividing resistors is 2 to 5.

4. The AC zero-crossing detection circuit according to claim 2, characterized in that: The number of the voltage-dividing resistors is 3.

5. The AC zero-crossing detection circuit according to claim 1, characterized in that: A fifth resistor (R5) is arranged between the output collector of the optical coupler isolator (U2) and the power supply (VCC), and is connected to a common ground via a second capacitor (C2).

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