A zero-crossing detection and power switch control circuit module

Abstract

The utility model discloses a zero -crossing detection and power switch control circuit module, include: mains input terminal for connecting alternating current source, set up in the front end of the mains input terminal input side's inhibition network, with zero -crossing detection circuit that the mains input terminal electricity is connected, electronic switch circuit, including second photoelectric coupler and with second photoelectric coupler control end connection's thyristor, mechanical switch circuit, set up in the relay contact both ends's contact inhibition network, including resistance and electric capacity, control circuit, with first photoelectric coupler, second photoelectric coupler with relay's control end electricity is connected, is used for according to zero -crossing detection signal control thyristor and the switch timing of relay. This zero -crossing detection and power switch control circuit module has the characteristics of accurate zero point switch control, low electromagnetic interference, high reliability and long life.

Description

Technical Field

[0001] This utility model relates to a zero-crossing detection and power switch control circuit module, which is particularly suitable for electrical equipment that requires frequent switching control, such as environmental protection equipment and industrial control equipment. Background Technology

[0002] In industrial control and environmental protection equipment, the switching control of mains power is a fundamental aspect. Traditional power switch control mainly includes two methods: relay mechanical switches and thyristor electronic switches. Relay control has the advantages of physical isolation and low conduction loss, but it has disadvantages such as large contact arc, limited lifespan, and high switching noise. Thyristor control has the advantages of being contactless and achieving precise zero-crossing switching, but it has relatively large long-term conduction loss and cannot achieve true physical isolation.

[0003] Especially in environmental protection equipment such as ozone generators, the loads often have strong inductive or capacitive characteristics, making them prone to generating large surge currents and electromagnetic interference during switching. This interference not only affects the normal operation of the equipment itself but can also propagate through the power grid, interfering with surrounding sensitive equipment. Furthermore, environmental protection equipment often requires frequent start-ups and shutdowns to adapt to different operating conditions, further exacerbating the stress and wear on switching components.

[0004] Existing zero-crossing detection circuits mostly employ single-half-wave or resistor divider designs, which suffer from low detection density, high susceptibility to power supply polarity, and weak anti-interference capabilities. Meanwhile, common power switch solutions often use only a single type of switching element, making it difficult to simultaneously meet the requirements of control accuracy, physical isolation, and long-term reliability.

[0005] Therefore, there is an urgent need for a power control solution that can simultaneously address multiple issues such as switching accuracy, electromagnetic interference, physical isolation, and component lifespan, in order to meet the high power control requirements of modern industrial control and environmental protection equipment. Utility Model Content

[0006] The purpose of this invention is to provide a zero-crossing detection and power switch control circuit module. This zero-crossing detection and power switch control circuit module features precise zero-point switching control, low electromagnetic interference, high reliability, and long lifespan.

[0007] The above-mentioned technical objective of this utility model is achieved through the following technical solution:

[0008] A zero-crossing detection and power switch control circuit module includes: a mains input terminal (CN2) for connecting to an AC power source; a front-end suppression network disposed on the input side of the mains input terminal (CN2), including a resistor (R54) and a capacitor (C16) connected in parallel; a zero-crossing detection circuit electrically connected to the mains input terminal (CN2), including a rectifier bridge (D3) and a first optocoupler (OK6) connected to the output terminal of the rectifier bridge (D3); and an electronic switch circuit, including a second optocoupler (OK5) and a control terminal connected to the second optocoupler (OK5). The circuit includes a thyristor (Q1); a mechanical switching circuit including a relay (K1), the contacts of which are connected in series between the mains input terminal (CN2) and the load output terminal; a contact suppression network disposed at both ends of the relay (K1) contacts, including resistors (R57 / R58) and capacitors (C18 / C19); and a control circuit electrically connected to the control terminals of the first optocoupler (OK6), the second optocoupler (OK5), and the relay (K1), used to control the switching sequence of the thyristor (Q1) and the relay (K1) according to the zero-crossing detection signal.

[0009] The present invention is further configured such that the zero-crossing detection circuit also includes a current-limiting resistor (R50 / R51), which is connected in series between the output terminal of the rectifier bridge (D3) and the input terminal of the first optocoupler (OK6).

[0010] The present invention is further configured such that the electronic switch circuit also includes a gate current limiting resistor (R53) disposed between the output terminal of the second optocoupler (OK5) and the gate of the thyristor (Q1).

[0011] The present invention is further configured such that the control circuit is configured to first control the thyristor (Q1) to conduct near the zero point of the power supply voltage, and then control the relay (K1) to close, forming a switching sequence of soft start followed by mechanical bypass.

[0012] The present invention is further configured such that the control circuit is configured to first control the relay (K1) to disconnect, and then control the thyristor (Q1) to extinguish at the next power supply voltage zero point, forming a switching sequence of first mechanical disconnection and then soft shutdown.

[0013] The present invention is further configured to include a status indicator circuit, which includes a capacitor (C15), a current-limiting resistor (R40), a light-emitting diode (LED1), and a rectifier diode (D5). The capacitor (C15) and the current-limiting resistor (R40) are connected in series and then in parallel across the mains input terminal (CN2). The light-emitting diode (LED1) and the rectifier diode (D5) are connected in series and then in series with the current-limiting resistor (R40).

[0014] The present invention is further configured such that: the status indication circuit also includes a discharge resistor (R39) connected in parallel across the capacitor (C15) for discharging the capacitor (C15) after power is cut off.

[0015] The present invention is further configured such that the front-end suppression network, the zero-crossing detection circuit and the contact suppression network are arranged in a stepped partition on the circuit board to form a multi-level electromagnetic interference suppression link from input to output.

[0016] The present invention is further configured such that: the mechanical switching circuit also includes a transistor (VT7) and a base resistor (R41), the collector of the transistor (VT7) is connected to the coil of the relay (K1), and the base resistor (R41) is connected between the base of the transistor (VT7) and the control circuit.

[0017] In summary, this utility model has the following beneficial effects:

[0018] Full-wave rectification zero-point detection structure: Full-wave rectification is performed using a rectifier bridge (D3), followed by detection via a first optocoupler (OK6), forming a detection mechanism unaffected by power supply polarity. Compared to traditional single / half-wave detection, the detection density is doubled (twice per cycle), significantly improving control accuracy; polarity influence is completely eliminated, making installation and wiring more convenient; and opto-isolation achieves physical separation of high-voltage and low-voltage circuits, effectively improving system safety and anti-interference capabilities.

[0019] Hybrid Switching Control Structure: This structure employs a hybrid switching architecture that combines a thyristor (Q1) and a relay (K1) to create a dual protection mechanism of soft switching and hard isolation. The thyristor is responsible for precise switching on and off at zero voltage, avoiding surge currents and electromagnetic interference during switching. The relay provides a low-impedance long-term path and reliable physical isolation, reducing long-term conduction losses. This structure fully leverages the advantages of both the thyristor and the relay, effectively extending system lifespan and improving reliability.

[0020] Multi-level EMI suppression chain: In terms of circuit spatial layout, a three-level suppression structure is formed from input to output: front-end suppression network (R54 / C16), zero-crossing control and contact suppression network (R57 / R58 / C18 / C19). This multi-level suppression structure forms a defense against electromagnetic interference. Compared with traditional single-point suppression schemes, the EMI suppression capability is improved, and interference to the power grid and peripheral equipment is significantly reduced.

[0021] Precisely controlled switching timing: Based on the zero-crossing detection signal, the control circuit implements an on-start timing sequence of soft start followed by mechanical bypass and an off-start timing sequence of mechanical disconnection followed by soft turn-off. This timing control minimizes the current stress on the relay contacts, significantly reduces contact arcing, and extends the relay's lifespan.

[0022] Safe and reliable indication and protection structure: The status indication circuit adopts a derating power supply structure with bleed protection, which not only provides intuitive power status indication, but also ensures that the capacitor (C15) discharges quickly after power failure through the bleed resistor (R39). After power failure, the residual voltage drops to a safe level quickly, which significantly improves maintenance safety. Attached Figure Description

[0023] Figure 1 This is the circuit schematic diagram of this utility model.

[0024] Reference numerals: 1. Mains input terminal (CN2); 2. Resistor (R54); 3. Capacitor (C16); 4. Rectifier bridge (D3); 5. First optocoupler (OK6); 6. Current-limiting resistor (R50 / R51); 7. Second optocoupler (OK5); 8. SCR (Q1); 9. Gate current-limiting resistor (R53); 10. Relay (K1); 11. Resistor (R57 / R58); 12. Capacitor (C18 / C19); 14. Capacitor (C15); 15. Current-limiting resistor (R40); 16. Light-emitting diode (LED1); 17. Rectifier diode (D5); 18. Bleeding resistor (R39); 19. Transistor (VT7); 20. Base resistor (R41); 21. Load output terminal (GUN_L / N). Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings.

[0026] like Figure 1 As shown, the zero-crossing detection and power switch control circuit module of this utility model includes an AC power input terminal 1 (CN2) for connecting to an AC power source.

[0027] A front-end suppression network is provided on the input side of the mains input terminal 1, including a resistor 2 (R54) and a capacitor 3 (C16) connected in parallel. The resistor 2 and capacitor 3 are installed in parallel near the mains input terminal 1 to form the first-level protection barrier for the input terminal.

[0028] The zero-crossing detection circuit, electrically connected to the AC input terminal 1, includes a rectifier bridge 4 (D3) and a first optocoupler 5 (OK6) connected to the output of the rectifier bridge 4. The four pins of the rectifier bridge 4 are connected to the AC input and DC output, respectively. The AC input of the rectifier bridge 4 is connected to the AC input terminal 1 via a trace. The DC output of the rectifier bridge 4 is connected to the input of the first optocoupler 5 via current-limiting resistors 6 (R50 / R51). The current-limiting resistors 6 are two parallel surface-mount resistors with a resistance of 33kΩ.

[0029] The electronic switching circuit includes a second optocoupler 7 (OK5) and a thyristor 8 (Q1) connected to the control terminal of the second optocoupler 7. The thyristor 8 is in a TO-220 package and is mounted on a heat sink. The heat sink is fixed to the circuit board with two M3 screws. A gate current limiting resistor 9 (R53) is provided between the second optocoupler 7 and the thyristor 8.

[0030] The mechanical switch circuit includes a relay 10 (K1), whose contacts are connected in series between the mains input terminal 1 and the load output terminal 21 (GUN_L / N).

[0031] A contact suppression network is provided at both ends of the relay 10 contact, including resistor 11 (R57 / R58) and capacitor 12 (C18 / C19). Resistor 11 consists of two surface-mount resistors with a resistance of 10Ω. Capacitor 12 consists of two surface-mount ceramic capacitors with a capacitance of 100nF and a voltage rating of 500V. Resistor 11 and capacitor 12 form two sets of RC networks, symmetrically arranged on both sides of the relay 10 contact.

[0032] The control circuit MCU is electrically connected to the control terminals of the first optocoupler 5, the second optocoupler 7, and the relay 10, and is used to control the switching timing of the thyristor 8 and the relay 10 according to the zero-crossing detection signal. The control circuit MCU contains a microcontroller and is located in the lower area of ​​the circuit board, maintaining appropriate physical isolation from the signal and power areas. This is prior art and will not be described further here.

[0033] The status indicator circuit includes capacitor 14 (C15), current-limiting resistor 15 (R40), light-emitting diode 16 (LED1), and rectifier diode 17 (D5). Capacitor 14 has a capacitance of 330nF and a withstand voltage of 500V. Current-limiting resistor 15 is a high-power resistor with a power rating of 1W and a resistance of 1.8kΩ. Light-emitting diode 16 is a standard 3mm diameter red LED. Rectifier diode 17 uses a DO-41 package. These components form an indication and capacitance drop circuit. The status indicator circuit also includes a bleeder resistor 18 (R39) connected in parallel across capacitor 14, with a resistance of 1MΩ.

[0034] The mechanical switch circuit also includes transistor 19 (VT7) and base resistor 20 (R41). Transistor 19 is in a TO-92 package, model number 2N2222. Base resistor 20 is a surface mount resistor with a resistance of 1kΩ. The collector of transistor 19 is connected to the coil of relay 10 via a trace, and base resistor 20 is connected between the base of transistor 19 and the control circuit MCU.

[0035] The control timing of a hybrid switch includes two phases: on and off.

[0036] The startup sequence is as follows: First, the control circuit MCU triggers the thyristor 8 to conduct near the zero point of the power supply voltage through the second optocoupler 7 based on the zero-crossing detection signal from the first optocoupler 5, thereby achieving zero-point soft start; after the current stabilizes, the control relay 10 is closed to form a low-impedance path.

[0037] The shutdown sequence is as follows: First, control relay 10 to disconnect to achieve physical isolation; then, at the next power supply voltage zero point, control thyristor 8 to turn off to achieve soft shutdown, which effectively reduces electromagnetic interference and electric arc of relay contacts during switching.

[0038] The working process of this utility model is as follows: AC power enters the circuit through AC power input terminal 1, and the front-end suppression network (resistor 2 and capacitor 3) initially suppresses the spike interference of the input power. The rectifier bridge 4 converts the AC power into pulsating DC, which drives the first optocoupler 5 through the current-limiting resistor 6. When the power supply voltage approaches zero, the output of the first optocoupler 5 changes, and the control circuit MCU accurately determines the zero point time accordingly.

[0039] When the load is turned on, the control circuit MCU first triggers the thyristor 8 to conduct near the detected zero point through the second optocoupler 7, achieving a zero-point soft start. After the current stabilizes, the control circuit MCU drives the transistor 19 to close the relay 10, forming a low-resistance path. At this time, the load obtains power through the relay 10 and the thyristor 8. Since the thyristor 8 is already conducting when the relay 10 closes, there is basically no current surge when the contacts close, which greatly reduces contact arcing and stress.

[0040] When the load is turned off, the control circuit MCU first controls relay 10 to open, achieving physical isolation. When relay 10 is open, the current is maintained through the already conducting thyristor 8, and no arc is generated when the contacts open. Then, near the next detected zero point, the control circuit MCU stops triggering thyristor 8, allowing it to extinguish naturally when the current crosses zero, achieving soft turn-off. This mechanism of first mechanically disconnecting and then softly turning off further reduces electromagnetic interference at the moment of turn-off.

[0041] Throughout the process, the contact suppression network (resistor 11 and capacitor 12) suppresses potential spike interference that may be generated when the relay 10 contacts operate, forming a multi-stage EMI suppression link from input to output. Meanwhile, the LED 16 in the status indicator circuit provides a clear indication of the power status, and the bleeder resistor 18 ensures that capacitor 14 discharges rapidly after power failure, achieving the purpose of maintenance safety.

[0042] This invention achieves precise zero-point control and physical isolation through a full-wave rectifier zero-point detection structure, a hybrid switching structure combining thyristors and relays, and a multi-layered EMI suppression link. This significantly reduces electromagnetic interference, extends component life, and improves system reliability, making it particularly suitable for environmental protection equipment and industrial control equipment that require frequent switching control.

[0043] Technical benefits of the zero-crossing detection and power switch control circuit module: improved electromagnetic interference suppression, extended lifespan of switching elements, and increased zero-crossing detection accuracy.

[0044] 1. A comparative testing method was used to compare the hybrid switch structure of this utility model with traditional single switch schemes (pure relays, pure thyristors). The test environment was a standard laboratory environment with a temperature of 25±2℃ and a humidity of 50±5%, using standard inductive loads (power factor 0.8) and capacitive loads (power factor 0.9 leading) as test loads. The measuring equipment included an EMI test receiver (9kHz-30MHz), a digital oscilloscope (1GS / s), a current probe (DC-100MHz), and a high-precision temperature recorder.

[0045] 2. Technical Effect Comparison Table

[0046] Performance indicators Traditional relay solution Traditional thyristor solution This utility model features a hybrid switch solution. Increase Improvement instructions EMI suppression effect (10kHz-1MHz) 75-85dBμV 60-70dBμV 50-55dBμV Reduce 20-30 dBμV The three-tiered suppression structure forms a three-dimensional defense, significantly reducing electromagnetic interference. Relay contact life 100,000 switching cycles not applicable 450,000 switching cycles Increase by 350% Zero-point soft switching and coordinated timing arc elimination significantly reduce contact stress. Load start-up surge current 5 times the rated current Twice the rated current 1.2 times the rated current 76% reduction Precise zero-point conduction effectively suppresses surge current, protecting the load and power supply. Zero-crossing detection accuracy ±3ms (single half-wave) ±2ms (voltage divider type) ±0.2ms (full-wave rectification) Increase by 90% The full-wave rectifier structure provides double the detection density, accurately capturing zero points. System long-term power consumption Low (contact voltage drop only) High (SCR on-state voltage drop) Low (relay bypass) Equivalent to a relay The relay provides a low-impedance path, avoiding the long-term conduction losses of the thyristor.

[0047] 3. Verification Methods and Results

[0048] EMI suppression effect test: The standard CISPR 16 test method was adopted, and an EMI receiver was used to measure the electromagnetic interference generated during switching in the 10kHz-1MHz frequency band. The test results show that the maximum interference level of this invention during inductive load switching is 55dBμV, which is 30dB lower than the 85dBμV of the traditional relay solution and 10dB lower than the 65dBμV of the traditional thyristor solution, verifying the effectiveness of the multi-stage suppression link.

[0049] Relay life testing: Accelerated life testing was conducted using an automated testing system, completing one switching cycle every 5 seconds and recording changes in contact resistance and failure states. Under the same load conditions, traditional relay solutions showed contact adhesion or burning after an average of 102,000 cycles; while the hybrid switch structure of this invention maintained normal operation after 455,000 cycles, with contact resistance increasing by no more than 20%, confirming a lifespan improvement of at least 350%.

[0050] Surge current test: A high-speed current probe is used to measure the peak current at the moment of inductive load startup. When a traditional relay is directly switched, the surge current reaches 5 times the rated current. The zero-point soft-start solution of this invention controls the surge current to 1.2 times the rated current, a reduction of 76%, which significantly reduces the impact on the load and power supply.

[0051] Zero-crossing detection accuracy test: The time relationship between the power supply zero point and the control signal was measured using a digital oscilloscope. The full-wave rectifier detection structure of this invention exhibits a zero-crossing detection error of less than ±0.2ms within a mains frequency fluctuation range of ±2Hz, while the error of the traditional single-half-wave scheme reaches ±3ms, and the error of the voltage divider scheme is ±2ms, verifying a significant improvement in detection accuracy.

[0052] 4. Verification Conclusion

[0053] Experimental results show that the zero-crossing detection and power switch control circuit module of this invention achieves significant improvements in EMI suppression, component lifespan, surge control, and detection accuracy through its full-wave rectified zero-point detection, thyristor and relay coordinated control, and multi-level EMI suppression structure. Especially under harsh operating conditions with frequent start-stop cycles of inductive loads, it has significant advantages over traditional solutions, effectively solving power control problems in environmental protection equipment and industrial control equipment, improving system reliability and electromagnetic compatibility, and demonstrating broad application prospects.

Claims

1. A zero-crossing detection and power switch control circuit module, characterized in that, include: The AC power input terminal (CN2) is used to connect to an AC power source; The front-end suppression network disposed on the input side of the mains input terminal (CN2) includes a resistor (R54) and a capacitor (C16) connected in parallel; The zero-crossing detection circuit electrically connected to the mains input terminal (CN2) includes a rectifier bridge (D3) and a first optocoupler (OK6) connected to the output terminal of the rectifier bridge (D3); An electronic switching circuit includes a second optocoupler (OK5) and a thyristor (Q1) connected to the control terminal of the second optocoupler (OK5); The mechanical switching circuit includes a relay (K1), the contacts of which are connected in series between the mains input terminal (CN2) and the load output terminal; The contact suppression network disposed at both ends of the relay (K1) contact includes resistors (R57 / R58) and capacitors (C18 / C19); The control circuit is electrically connected to the control terminals of the first optocoupler (OK6), the second optocoupler (OK5), and the relay (K1), and is used to control the switching timing of the thyristor (Q1) and the relay (K1) according to the zero-crossing detection signal.

2. The zero-crossing detection and power switch control circuit module according to claim 1, characterized in that, The zero-crossing detection circuit also includes a current-limiting resistor (R50 / R51), which is connected in series between the output terminal of the rectifier bridge (D3) and the input terminal of the first optocoupler (OK6).

3. The zero-crossing detection and power switch control circuit module according to claim 1, characterized in that, The electronic switching circuit also includes a gate current limiting resistor (R53) disposed between the output terminal of the second optocoupler (OK5) and the gate of the thyristor (Q1).

4. The zero-crossing detection and power switch control circuit module according to claim 1, characterized in that, The control circuit is configured to first control the thyristor (Q1) to conduct near the zero point of the power supply voltage, and then control the relay (K1) to close, forming a switching sequence of soft start followed by mechanical bypass.

5. The zero-crossing detection and power switch control circuit module according to claim 1, characterized in that, The control circuit is configured to first control the relay (K1) to disconnect, and then control the thyristor (Q1) to turn off at the next power supply voltage zero point, forming a switching sequence of mechanical disconnection followed by soft shutdown.

6. The zero-crossing detection and power switch control circuit module according to claim 1, characterized in that, It also includes a status indicator circuit, which includes a capacitor (C15), a current-limiting resistor (R40), a light-emitting diode (LED1), and a rectifier diode (D5). The capacitor (C15) and the current-limiting resistor (R40) are connected in series and then in parallel across the mains input terminal (CN2). The light-emitting diode (LED1) and the rectifier diode (D5) are connected in series and then in series with the current-limiting resistor (R40).

7. The zero-crossing detection and power switch control circuit module according to claim 6, characterized in that, The status indication circuit also includes a discharge resistor (R39) connected in parallel across the capacitor (C15) for discharging the capacitor (C15) after power is off.

8. The zero-crossing detection and power switch control circuit module according to claim 1, characterized in that, The front-end suppression network, the zero-crossing detection circuit, and the contact suppression network are arranged in a stepped partition on the circuit board to form a multi-level electromagnetic interference suppression link from input to output.

9. The zero-crossing detection and power switch control circuit module according to claim 1, characterized in that, The mechanical switching circuit also includes a transistor (VT7) and a base resistor (R41). The collector of the transistor (VT7) is connected to the coil of the relay (K1), and the base resistor (R41) is connected between the base of the transistor (VT7) and the control circuit.

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