AC load double-path parallel switch control circuit

Abstract

The present application belongs to the technical field of switch control circuit, especially relates to an alternating current load double-path parallel switch control circuit, which comprises a commercial power input line, an alternating current load, a relay switch branch and a thyristor switch branch. The commercial power input line comprises a live wire and a zero wire, and the zero wire (one end of the commercial power) is directly connected to one end of the alternating current load. The live wire (the other end of the commercial power) is divided into two parallel branches, and the output ends of the two parallel branches are connected to the other end of the alternating current load after being merged. The two parallel branches are respectively the relay switch branch and the thyristor switch branch, and the input ends of the relay switch branch and the thyristor switch branch are connected to the live wire, and the output ends are connected to the alternating current load, forming a double-path parallel power supply path.

Description

Technical Field

[0001] This invention belongs to the field of switch control circuit technology, and particularly relates to a dual-channel parallel switch control circuit for AC loads. Background Technology

[0002] Traditional electric heating appliance temperature control drive circuits are mainly divided into three categories. One category uses only a relay to drive the heating load. Relays have low conduction losses, low cost, and can handle high power, but they can only achieve on / off control and cannot continuously adjust the output power, resulting in poor temperature control accuracy and difficulty in meeting the needs of fine temperature control. Another category uses only a thyristor to drive the heating load. It can combine zero-crossing signals to achieve waveform loss control or periodic control for fine temperature control, which is advantageous when driving small power loads. However, it cannot operate at high power for extended periods when the heating load is large and space is limited, preventing the use of larger heat sinks. The third category uses a drive circuit that connects a relay and a thyristor in parallel (the same circuit described in this patent). Figure 4 However, while this design utilizes a relay to drive the heating load during high-power heating and a thyristor to drive the heating load during precise temperature control, the relay cannot be precisely controlled via a zero-crossing signal. This leads to arcing and electromagnetic interference during the switching process, resulting in poor circuit stability and safety performance. Although it can simultaneously meet the product design requirements of high-power heating, high-precision temperature control, miniaturized space layout, and low-cost production, it cannot solve the problems of short relay lifespan and poor system stability caused by arcing. Summary of the Invention

[0003] In view of the aforementioned problems, and in conjunction with the first aspect of the present invention, an embodiment of the present invention provides an AC load dual-path parallel switch control circuit, including a mains input line, an AC load, a relay switch branch, and a thyristor switch branch; The mains input line includes a live wire and a neutral wire, and the neutral wire (one end of the mains power) is directly connected to one end of the AC load. The live wire (the other end of the mains power) branches into two parallel branches, and the outputs of the two parallel branches are combined and connected to the other end of the AC load. The two parallel branches are a relay switch branch and a thyristor switch branch, respectively. The input terminals of the relay switch branch and the thyristor switch branch are connected to the live wire, and the output terminals are connected to the AC load. Both can be turned on in both directions without distinguishing between live and neutral, forming a dual-channel parallel power supply path. The main control module outputs independent control signals to drive the relay switch branch and the thyristor switch branch, and can conduct the relay switch branch, conduct the thyristor switch branch, or conduct both branches simultaneously. The thyristor switch branch is connected to a zero-crossing detection signal for triggering the thyristor to switch on or off at zero crossover.

[0004] Preferably, the AC load is a thermostat kettle heating plate, and the parallel output terminal of the live wire is provided with an OUT-H terminal, with the heating plate connected between the OUT-H terminal and the neutral wire; A varistor is connected in parallel between the live wire and the OUT-H terminal to form a circuit surge overvoltage protection.

[0005] Preferably, the relay switch branch includes a relay RLY1, a first driving transistor Q4, a freewheeling diode D5, a current-limiting resistor R19, and a pull-down resistor R20; One end of the relay RLY1 coil is connected to a +5V power supply, and the other end of the coil is connected to the collector of Q4. The freewheeling diode D5 is connected in parallel across the relay coil, with the cathode connected to +5V and the anode connected to the collector of Q4. The base of Q4 is connected to the main control signal terminal RLY-H via R19, and R20 is connected in parallel between the base and emitter of Q4. The emitter of Q4 is grounded. One end of the relay main circuit contact is connected to the live wire, and the other end is connected to the OUT-H terminal.

[0006] Preferably, the thyristor switch branch includes a bidirectional thyristor Q5, a second driving transistor Q6, a gate current limiting resistor R21, a voltage divider resistor R23, and a discharge resistor R22. The T1 terminal of the bidirectional thyristor Q5 is connected to the live wire, the T2 terminal is connected to the OUT-H terminal, and the gate G is connected to the collector of Q6 via R21. The base of Q6 is connected to the main control signal terminal SCR-H via R23, R22 is connected in parallel between the collector and emitter of Q6, and the emitter of Q6 is grounded.

[0007] Preferably, the circuit operating modes include high-power heating mode and fine temperature control mode; In high-power heating mode, the main control outputs RLY-H high level or RLY-H low level to control the relay to turn on or off. Before the relay is turned on or off, the thyristor is first controlled to conduct when the voltage of the neutral and live wires is zero, and then turned off after the relay completes the opening or closing action. In the fine temperature control mode, the thyristor drives the heat load independently, and the main controller can combine the zero-crossing signal to achieve wave drop control or periodic control to achieve fine temperature control. Preferably, it also includes a mains power front-end processing circuit, wherein the mains power front-end processing circuit shares the same mains power live wire and neutral wire input with the relay and the thyristor parallel drive circuit; The mains power front-end processing circuit includes a mains power input protection filter unit, a zero-crossing detection circuit unit, a rectification buffer unit, an OB2222MCPA switching power supply main control conversion unit, and a negative voltage output voltage regulator unit.

[0008] Preferably, the mains input protection filter unit includes a fuse FUSE, a varistor VDR1, an X capacitor CX1, a bleeder resistor R1 / R2, a common mode inductor LL1, an X capacitor CX2, and a Y capacitor CY1 / CY2. The neutral wire is connected in series with the fuse FUSE, and the live wire and the neutral wire are connected in parallel with VDR1 and CX1. The two ends of CX1 are connected in parallel with symmetrical discharge resistors R1 and R2. The live wire and neutral wire are connected to the common mode inductor LL1. The common mode inductor outputs COM1 and COM2. CX2 is connected in parallel between COM1 and COM2. COM1 and COM2 are connected to the protective ground PE through Y capacitors CY1 and CY2, respectively.

[0009] Preferably, the input terminal of the zero-crossing detection circuit unit is taken from the COM2 node, and includes voltage divider resistors R9, R10, R11, transistor Q1, pull-up resistor R13, current limiting resistor R14, filter capacitor C4, and RC snubber circuits R12 and C3. R9, R10, and R11 are connected in series to divide the voltage and then connected to the collector of Q1. The emitter of Q1 is connected to +5V. The base of Q1 is led out to the zero-crossing signal output terminal ZEO through R14. ZEO is connected in parallel with C4 and grounded. R13 is connected between +5V and the base of Q1, and R12 and C3 are connected in parallel between the collector and emitter of Q1. ZEO outputs a zero-crossing pulse signal synchronized with the mains power and sends it to the main control module for thyristor zero-crossing triggering.

[0010] Preferably, the rectifier buffer unit includes a power resistor R3, series rectifier diodes D1 and D2, a filter electrolytic capacitor EC1, and a discharge resistor R4; After COM1 is connected in series with R3, it is connected to D1 and D2 in series in the same direction. The output terminals of D1 and D2 are connected in parallel with EC1, and R4 is connected in parallel across EC1.

[0011] Preferably, the OB2222MCPA switching power supply main control conversion unit includes an inductor L1, a power chip U1, a start-up resistor R5 / R6, a current sampling resistor R7, and a Zener diode D3; After rectification, the DC power is connected to the high-voltage power supply pin of U1 via L1, and R5 and R6 are connected in series between the high-voltage side and the start-up pin of U1. The current sampling pin CS of U1 is connected in series with R7 to power ground, and the power ground pin of U1 is connected in parallel with D3 to the high voltage input node; The negative voltage output regulator unit includes an energy storage inductor L2, a rectifier diode D4, a filter capacitor C1, an electrolytic capacitor EC4, a thin film capacitor C2, feedback voltage divider resistors RJ1 and RJ2, and an adjustment resistor R8. One end of L2 is connected to the anode of D4, and the cathode of D4 outputs negative voltage. The connection point between L2 and D4 is connected in parallel with C1 to ground; the negative voltage output terminal is connected in parallel with EC4 and C2. One end of RJ1 is connected to the negative voltage output terminal, and one end of RJ2 is connected to the +5V reference. The midpoint of the connection between RJ1 and RJ2 is fed back to the feedback pin FB of U1. R8 is connected in parallel across RJ2 to adjust the feedback voltage division ratio. The negative voltage output regulator unit outputs a negative voltage power supply to provide working power for the main controller, relay driving transistor, and thyristor driving transistor. The thyristor switch branch (and relay branch) can be interchangeably placed between the neutral wire and the AC load, with the live wire directly and normally connected to the other end of the AC load, achieving equivalent dual-channel parallel switch control function. (Depending on the power supply scheme, such as...) Figure 3 The AC-DC power supply scheme shown uses a buck-boost topology to create a negative voltage, so the thyristor switch branch and the relay branch are placed between the live wire and the AC load.

[0012] Based on the above, a dual-channel drive structure of relay and bidirectional thyristor in parallel is adopted. During the high-power heating stage, the relay branch is mainly used, relying on the characteristics of low voltage drop and low steady-state heating of the relay contacts to handle the large current. During the period when the relay contacts are engaged or disengaged, the thyristor is briefly used to withstand the current, so as to eliminate the arc and electromagnetic interference generated during these two periods. During the fine temperature control stage, the thyristor branch is used separately. With the synchronous pulse output by the zero-crossing detection circuit at the front end, zero-crossing soft switching is achieved to complete the continuous fine adjustment of power, which greatly improves the temperature control accuracy.

[0013] This invention features an integrated mains power front-end processing circuit that combines input overcurrent, surge overvoltage, and EMI filtering protection functions, enhancing the overall circuit safety and anti-interference capabilities. The front-end circuit synchronously outputs a mains zero-crossing signal and a stable negative voltage operating power supply. A single mains input simultaneously provides trigger timing for the thyristor and power to the main controller and various drive transistors, eliminating the need for a separate power supply and a separate zero-crossing acquisition module. This simplifies the overall circuit layout, reduces the number of circuit components, and further optimizes the overall production cost and circuit reliability while meeting the requirements of high-power heating, precise temperature control, and miniaturized assembly. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the execution flow of an AC load dual-channel parallel switch control circuit provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the modular design of a relay-thyristor parallel drive AC electrical appliance in a dual-channel parallel switch control circuit for AC loads provided in an embodiment of the present invention. Figure 3 This invention provides an AC load dual-channel parallel switch control circuit integrated with zero-crossing detection and negative voltage output AC-CDC switching power supply mains front-end processing circuit. Figure 4This is a complete circuit diagram of an AC load dual-channel parallel switch control circuit provided in an embodiment of the present invention. Detailed Implementation

[0015] The present invention will now be described in detail with reference to the accompanying drawings; like Figure 1 As shown, this embodiment discloses a dual-circuit parallel switch control circuit for AC loads, which is applied to the on / off control scenario of AC appliances driven by 220V AC mains power. The mains power includes two power supply lines: live wire ACN1 and neutral wire ACL1. The AC appliance U2 is provided with power supply terminal 1 and power supply terminal 2.

[0016] The neutral wire ACL1 is directly connected to terminal 2 of the AC appliance U2 to establish a neutral wire constant power supply circuit; the live wire ACN1 is led out and divided into two independent branches connected in parallel. The two branches merge at the end and are connected to terminal 1 of the AC appliance U2. The two parallel branches are a relay branch and a solid-state relay / thyristor branch, respectively. The two branches work in parallel to realize the on / off control of the live wire to the load.

[0017] The first parallel branch is a mechanical relay branch. The main circuit input terminal of the mechanical relay is connected to the live wire ACN1, and the main circuit output terminal of the mechanical relay is connected to terminal 1 of the AC appliance U2. The mechanical relay is controlled by the output level signal of the independent drive control circuit to control the closing and opening of its internal contacts. When the contacts are closed, the branch is conducting, and the live wire can supply power to the AC appliance U2 through this branch; when the contacts are open, this branch cuts off the power supply path of the live wire.

[0018] The second parallel branch is a contactless switch branch. The switching device is a thyristor. The AC main circuit input terminal of the thyristor is connected to the live wire ACN1, and the AC main circuit output terminal of the thyristor is connected to terminal 1 of the AC appliance U2. The thyristor is equipped with a zero-crossing signal acquisition pin. The external circuit continuously inputs the zero-crossing signal of the AC mains to this pin. The zero-crossing signal is synchronized with the zero-crossing point of the AC mains sinusoidal voltage in real time. The thyristor's own drive circuit enables the contactless switch to complete the conduction and cut-off actions at the zero-crossing point of the AC mains voltage, avoiding the generation of arc and spike interference at the moment of switching on and off.

[0019] The two branches are electrically connected in complete parallel. Their input terminals are connected to the live wire ACN1, and their output terminals are connected to the AC appliance U2 terminal 1, forming a dual-channel redundant switching path. When the circuit is working, the mechanical relay branch can be used alone, the thyristor branch can be used alone, or both can be used in combination. When the mechanical relay branch is used alone, it relies on mechanical contacts to achieve stable high-power conduction. The conduction voltage is low and the long-term steady-state power consumption is low, which is suitable for the long-term high-power continuous operation of AC electrical appliances. However, the relay is affected by its own control error and external factors, and it cannot accurately switch on and off at the voltage zero point under the guidance of the zero-crossing signal. There is a problem of arcing and electromagnetic interference generated at the moment of relay switching. When the thyristor branch is conducting, it relies on the zero-crossing signal to achieve arc-free and impact-free soft switching. There is no electric spark at the moment of switching and the electromagnetic interference is weak. It is suitable for the conditions of frequent start-stop and high-speed adjustment of load power. When the two are used in combination, the mechanical relay shares the long-term continuous working current of AC electrical appliances, and the thyristor shares the working current of AC electrical appliances for a short time at the moment of relay switching. This eliminates the arcing and electromagnetic interference generated by the relay, extends the service life of the switching device, and improves the stability of the circuit. At the same time, it has the dual advantages of low steady-state loss of mechanical switches and no arcing impact of contactless switches.

[0020] The complete path of the AC power supply circuit is as follows: AC neutral wire ACL1, AC appliance U2 terminal 2, AC appliance U2 internal load, AC appliance U2 terminal 1, parallel switch branch (one or both of the relay branch and solid-state relay / thyristor branch are conducting), AC live wire ACN1. The controllable switching of the AC appliance power supply circuit is achieved through the on / off logic combination of the two parallel switch branches.

[0021] like Figure 2 As shown, this embodiment is a circuit for driving AC electrical appliances by a relay and a thyristor in parallel. It is applied to the scenario of driving the heating plate load of a thermostat kettle. The AC mains live wire is split into two parallel branches and then output to the OUT-H terminal. The OUT-H terminal is used to connect the external heating plate as an AC electrical appliance. The two parallel branches are a mechanical relay switch branch and a bidirectional thyristor contactless switch branch. The input terminals of the two branches are connected to the live wire, and the output terminals are connected to the OUT-H terminal. A varistor VDR2 is connected in parallel between the live wire and the OUT-H terminal to form an overvoltage protection circuit. The varistor model is 10D471K.

[0022] The mechanical relay selected is model HF3FF-5VDC-SA relay RLY1. One pin (pin 1) of the relay coil is connected to a +5V DC power supply, and the other pin (pin 2) is connected to the collector of transistor Q4. A freewheeling diode (model 1N4148) is connected in parallel across the relay coil, with its anode connected to the collector of Q4 and its cathode connected to +5V. This diode absorbs the reverse induced electromotive force generated when the relay coil is de-energized, protecting the driver transistor. The driver transistor Q4 is model S8050. The base of Q4 is connected to the main control signal terminal RLY-H through a current-limiting resistor R19 (4.7KΩ). A pull-down resistor R20 (10KΩ) is connected in parallel between the base and emitter of Q4. One end of R20 is connected to the base of Q4, and the other end is grounded. When there is no control signal, it pulls the base potential low, ensuring reliable transistor turn-off. The emitter of Q4 is directly grounded. Pin 3 of the relay main circuit is connected to the AC mains live wire, and pin 4 of the relay main circuit is connected to the OUT-H output terminal. The normally open contacts inside the relay form the first power supply path from the live wire to OUT-H. Working logic: When the main control outputs a high-level RLY-H signal, it flows into the base of Q4 through R19. Q4 is saturated and conducts. The +5V power supply forms a circuit through the relay coil and the conducting Q4. The relay coil is energized and closes, and the normally open contacts inside pins 3 and 4 are closed. The live wire supplies power to OUT-H through the relay contacts. When the main control removes the high level of RLY-H, R20 pulls the base potential of Q4 to ground, Q4 is cut off, the relay coil is de-energized, and the normally open contacts inside open, cutting off the power supply path of this branch.

[0023] The contactless switching device uses a bidirectional thyristor Q5, model BTB16-600C. The thyristor's main terminal T1 is connected to the AC mains live wire, and the main terminal T2 is connected to the OUT-H output terminal. The thyristor's gate G is connected to the collector of transistor Q6 via a current-limiting resistor R21 (100R / 1206 package). The driving transistor Q6 is model S8050. The base of Q6 is connected to the main control signal terminal SCR-H via a voltage divider resistor R23 (4.7KΩ). A bleeder resistor R22 (10KΩ) is connected in parallel between the collector and emitter of Q6, and the emitter of Q6 is grounded. Operating Logic: The main control outputs a high-level SCR-H signal, which flows into the base of Q6 through R23. Q6 is saturated and conducts. The AC potential of the live wire is connected to ground through the thyristor T1, the gate G, R21, and the conducting Q6, providing trigger current to the gate of the thyristor. The bidirectional thyristor Q5 is turned on, and the live wire supplies power to OUT-H through thyristors T1-T2. When the main control removes the high level of SCR-H, Q6 is turned off, and there is no continuous trigger current at the gate of the thyristor. It is automatically turned off when the AC mains power crosses zero, cutting off the power supply path of this branch.

[0024] A varistor VDR2 (10D471K) is connected in parallel between the live wire input terminal and the OUT-H output terminal, and is connected across the main contacts of the relay and the two ends of the triac. When a momentary high voltage surge occurs in the AC circuit, the resistance of the varistor drops sharply, dissipating the high voltage energy, absorbing the circuit peak voltage, and providing overvoltage protection for the relay contacts and the triac.

[0025] This circuit is a dedicated driver solution for the heating plate of a thermos kettle, with two parallel branches working together to control the heating plate: High-power heating mode: The main control output RLY-H is high or low to control the thyristor to conduct when the voltage between the live and neutral wires is zero before the relay is turned on or off, and to turn off after the relay completes the on or off action. The mechanical relay has a low on-state voltage and low steady-state loss, and mainly bears the continuous full-load operating current of the heating plate for a long time. It avoids the problem of large heat generation when a single bidirectional thyristor is turned on for a long time under full load. It does not require a large heat sink for the thyristor, saving internal installation space and reducing material and manufacturing costs. The bidirectional thyristor has high control accuracy and mainly bears the operating current at the moment of relay on and off, so as to eliminate the arc and electromagnetic interference generated by the relay.

[0026] Fine temperature control mode: In fine temperature control mode, the thyristor drives the heat load alone, and the main controller can combine the zero-crossing signal to achieve wave drop control or periodic control to achieve fine temperature control, which makes up for the shortcomings of pure relays that can only switch on and off, cannot finely adjust power, and have poor temperature control accuracy.

[0027] The AC mains power supply is divided into two paths: one path is transmitted to OUT-H via the main contact of the conducting relay RLY1, and the other path is transmitted to OUT-H via the triggered bidirectional thyristor Q5. The OUT-H terminal is connected to the heating plate load of the thermostat kettle, and the AC neutral line is directly connected to the other end of the heating plate, forming a complete AC power supply circuit. The main controller controls the two level signals of RLY-H and SCR-H respectively, and individually or simultaneously turns on and off the two parallel switch branches to achieve the dual control requirements of high-power rapid heating and low-power precise constant temperature of the heating plate.

[0028] like Figure 3 As shown, this embodiment discloses an AC-DC switching power supply front-end processing circuit that integrates a zero-crossing detection circuit and a negative voltage output type AC-DC switching power supply. The overall circuit consists of five parts connected in sequence: an AC input protection filter unit, a zero-crossing detection circuit unit, a rectification buffer unit, an OB2222MCPA switching power supply main control conversion unit, and a subsequent negative voltage output voltage regulator unit. The AC input includes two AC inputs: a live wire (ACN) and a neutral wire (ACL).

[0029] A fuse (model T6.3A) is connected in series with the neutral line ACL to provide overcurrent protection for the entire unit. A varistor VDR1 (model 10D471K) is connected in parallel between the live line ACN and the neutral line ACL to absorb high voltage surges from the mains input, providing overvoltage protection on the input side. An X capacitor CX1 (0.1uF) is connected in parallel between the live line ACN and the neutral line ACL, and symmetrical voltage divider resistors R1 and R2 (both 270K / 1206 package) are connected in series. The X capacitor filters out differential-mode electromagnetic interference, and R1 and R2 form a discharge circuit to release the residual charge in CX1 after the equipment is powered off, avoiding the risk of electric shock. The live wire ACN and the neutral wire ACL are connected to a common-mode inductor LL1 (30mH / 4A). The output terminals of the common-mode inductor are defined as COM1 and COM2 respectively. The common-mode inductor suppresses common-mode electromagnetic interference on the mains line. An X capacitor CX2 (0.1uF) is connected in parallel between COM1 and COM2. Y capacitors CY1 and CY2 (both with a capacity of 222K) are connected between COM1, PE protective ground, COM2, and PE respectively to further filter out high and low frequency common-mode interference and meet EMC safety filtering requirements.

[0030] The zero-crossing detection circuit input is taken from the COM2 node, and voltage divider resistors R9, R10, and R11 are connected in series. All three resistors are 150K / 1206 packaged resistors. The three-stage series resistors attenuate the 220V AC mains voltage to match the voltage withstand capability of the subsequent transistor. The voltage divider output node is connected to the collector of NPN transistor Q1 (model S8050). The base of Q1 is led out to the zero-crossing signal output terminal ZEO through the current-limiting resistor R14 (1K). The ZEO pin is connected in parallel with the filter capacitor C4 (103) to the signal ground to filter out ZEO output noise interference. A pull-up resistor R13 (10K) is set between the base of Q1 and the +5V DC power supply. When there is no AC input, the base of Q1 is pulled high, keeping Q1 in the off state. An RC snubber circuit is connected in parallel between the collector and emitter of Q1, including resistor R12 (10K) and capacitor C3 (102), to absorb the spikes generated when the AC waveform is switched. The emitter of Q1 is directly connected to the +5V DC power supply. Circuit operating logic: When the AC mains sine wave is in the non-zero-crossing range, there is an AC voltage difference in COM2. After being divided by R9, R10, and R11, an AC potential is formed at the collector of Q1. Q1 is periodically turned on / off, and the ZEO pin outputs a square wave zero-crossing pulse synchronized with the mains power. When the AC voltage crosses zero, the driving potential after voltage division disappears, Q1 remains off, and the ZEO level changes. The main control chip accurately identifies the zero-crossing moment of the mains sine wave by collecting the level change of the ZEO pin, providing a synchronous zero-crossing trigger reference signal for the preceding thyristor / solid-state relay.

[0031] After filtering, the COM1 circuit is connected in series with a power resistor R3 (22R / 2W) to limit the inrush current of the rectifier circuit; two identical rectifier diodes D1 and D2 (model M7) are connected in series after R3. The two diodes are connected in the same direction to form a full-wave rectifier branch, which converts the AC mains power into a pulsating DC voltage; an electrolytic capacitor EC1 (4.7uF / 400V) is connected in parallel at the rectifier output terminal to complete the first stage of filtering. A resistor R4 (4.7K / 1206) is connected in parallel across EC1 to discharge the residual voltage of the capacitor when the power is off.

[0032] The pulsating DC power after rectification and filtering is connected to inductor L1 (1mH / 0510 package). The output of L1 is connected to the high-voltage power supply terminals of pins 7 and 8 of the switching power supply control chip U1 (model OB2222MCPA). Startup voltage divider resistors R5 and R6, both 1M / 1206 packages, are connected in series between pins 5 and 6 of U1 and provide startup current for the chip upon power-up. Pin 4 of U1 is the current sampling CS pin, connected in series with sampling resistor R7 (2R / 1206) to power ground to collect the switching circuit current in real time, achieving overcurrent and peak current limiting protection. Pin 3 of U1 is the power supply VDD pin, pin 2 is the feedback FB voltage regulator pin, and pin 1 is the power ground GND. An electrolytic capacitor EC3 (4.7uF / 50V) is connected in parallel to ground on the VDD pin to provide a stable DC operating voltage for the chip; the FB feedback pin is connected to the output circuit of the subsequent stage to collect the output voltage amplitude in real time and adjust the duty cycle of the switch through the internal loop of the chip to stabilize the output voltage of the subsequent stage; a Zener diode D3 (model M7) is connected in parallel to the high voltage input node on the chip power ground pin to clamp the chip pin voltage and prevent the chip from being damaged by spikes.

[0033] The U1 switch converter is connected to the energy storage inductor L2 (1mH / 10*13) at the back end. One end of L2 is connected to the anode of rectifier diode D4 (model ES1J), and the cathode of D4 serves as the positive circuit for the negative voltage output. A filter capacitor C1 (105) is connected in parallel to ground at the connection point of L2 and D4. A large-capacity electrolytic capacitor EC4 (470uF / 10V) and a film capacitor C2 (104) are connected in parallel at the negative voltage output terminal to achieve high and low frequency composite filtering and smooth the output negative voltage. Voltage divider sampling resistors RJ1 and RJ2 are set at the end of the negative voltage output circuit. Both resistors are R1206 packaged. One end of RJ1 is connected to the negative voltage output terminal, and the other end of RJ2 is connected to the +5V reference potential. The midpoint of the connection between RJ1 and RJ2 is fed back to the FB pin of the U1 chip to form a closed-loop voltage regulation control circuit to continuously and stably output negative voltage. Resistor R8 (3.3K / 1206) is connected in parallel across RJ2 to assist in adjusting the feedback voltage division ratio and accurately match the target negative voltage output voltage.

[0034] The AC mains power is input through ACN and ACL, and after passing through the input protection EMI filter circuit, it is divided into two paths: one path, COM2, is divided and sent to the zero-crossing detection circuit, which outputs a synchronous zero-crossing pulse signal from the ZEO pin to provide the zero-crossing trigger timing for the thyristor drive circuit; the other path, COM1, is rectified into pulsating DC by a current-limiting resistor and a series diode, and sent to the OB2222MCPA switching power conversion circuit. After filtering by inductors, diodes, and multi-stage capacitors, it outputs a stable negative voltage power supply, providing negative operating power for the main control, drive transistors, thyristors, relays, and other downstream control devices. The zero-crossing detection circuit and the negative voltage AC-DC switching power supply share the same AC EMI filter front end and share the same live and neutral input circuits, realizing the simultaneous output of a zero-crossing synchronization signal and control negative voltage power supply from a single AC input, providing a matching timing reference and power supply for the relay + thyristor parallel AC load drive circuit.

[0035] It should be noted that, in order to simplify the description of the present invention and thus help to understand one or more embodiments of the invention, multiple features may sometimes be grouped into one embodiment, drawing or description thereof in the foregoing description of the embodiments of the present invention.

[0036] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A dual-channel parallel switch control circuit for AC loads, characterized in that: This includes mains power input lines, AC loads, relay switch branches, and thyristor switch branches; The mains input line includes a live wire and a neutral wire, and the neutral wire (one end of the mains power) is directly connected to one end of the AC load. The live wire (the other end of the mains power) branches into two parallel branches, and the outputs of the two parallel branches are combined and connected to the other end of the AC load. The two parallel branches are a relay switch branch and a thyristor switch branch, respectively. The input terminals of the relay switch branch and the thyristor switch branch are connected to the live wire, and the output terminals are connected to the AC load. Both can be turned on in both directions without distinguishing between live and neutral, forming a dual-channel parallel power supply path. The main control module outputs independent control signals to drive the relay switch branch and the thyristor switch branch, and can conduct the relay switch branch, conduct the thyristor switch branch, or conduct both branches simultaneously. The thyristor switch branch is connected to a zero-crossing detection signal for triggering the thyristor to switch on or off at zero crossover.

2. The AC load dual-channel parallel switch control circuit according to claim 1, characterized in that: The AC load is a thermostat kettle heating plate, and the parallel output terminal of the live wire is provided with an OUT-H terminal, with the heating plate connected between the OUT-H terminal and the neutral wire; A varistor is connected in parallel between the live wire and the OUT-H terminal to form a circuit surge overvoltage protection.

3. The AC load dual-channel parallel switch control circuit according to claim 2, characterized in that: The relay switch branch includes a relay RLY1, a first driving transistor Q4, a freewheeling diode D5, a current-limiting resistor R19, and a pull-down resistor R20; One end of the relay RLY1 coil is connected to a +5V power supply, and the other end of the coil is connected to the collector of Q4. The freewheeling diode D5 is connected in parallel across the relay coil, with the cathode connected to +5V and the anode connected to the collector of Q4. The base of Q4 is connected to the main control signal terminal RLY-H via R19, and R20 is connected in parallel between the base and emitter of Q4. The emitter of Q4 is grounded. One end of the relay main circuit contact is connected to the live wire, and the other end is connected to the OUT-H terminal.

4. The AC load dual-channel parallel switch control circuit according to claim 3, characterized in that: The thyristor switch branch includes a bidirectional thyristor Q5, a second driving transistor Q6, a gate current limiting resistor R21, a voltage divider resistor R23, and a discharge resistor R22. The T1 terminal of the bidirectional thyristor Q5 is connected to the live wire, the T2 terminal is connected to the OUT-H terminal, and the gate G is connected to the collector of Q6 via R21. The base of Q6 is connected to the main control signal terminal SCR-H via R23, R22 is connected in parallel between the collector and emitter of Q6, and the emitter of Q6 is grounded.

5. The AC load dual-channel parallel switch control circuit according to claim 4, characterized in that: The circuit operating modes include high-power heating mode and fine temperature control mode; In high-power heating mode, the main control output RLY-H is high or low to control the relay to turn on or off. Before the relay is turned on or off, the thyristor is first turned on when the voltage of the neutral and live wires is zero, and then turned off after the relay completes the opening or closing action. In the fine temperature control mode, the thyristor drives the heat load independently, and the main controller can combine the zero-crossing signal to achieve wave drop control or periodic control to achieve fine temperature control.

6. The AC load dual-channel parallel switch control circuit according to claim 1, characterized in that: It also includes a mains power front-end processing circuit, which shares the same mains power live wire and neutral wire input with the relay and the thyristor parallel drive circuit; The mains power front-end processing circuit includes a mains power input protection filter unit, a zero-crossing detection circuit unit, a rectification buffer unit, an OB2222MCPA switching power supply main control conversion unit, and a negative voltage output voltage regulator unit.

7. The AC load dual-channel parallel switch control circuit according to claim 6, characterized in that: The mains input protection filter unit includes a fuse FUSE, a varistor VDR1, an X capacitor CX1, a bleeder resistor R1 / R2, a common mode inductor LL1, an X capacitor CX2, and a Y capacitor CY1 / CY2. The neutral wire is connected in series with the fuse FUSE, and the live wire and the neutral wire are connected in parallel with VDR1 and CX1. The two ends of CX1 are connected in parallel with symmetrical discharge resistors R1 and R2. The live wire and neutral wire are connected to the common mode inductor LL1. The common mode inductor outputs COM1 and COM2. CX2 is connected in parallel between COM1 and COM2. COM1 and COM2 are connected to the protective ground PE through Y capacitors CY1 and CY2, respectively.

8. The AC load dual-channel parallel switch control circuit according to claim 7, characterized in that: The zero-crossing detection circuit unit has its input terminal taken from the COM2 node and includes voltage divider resistors R9, R10, R11, transistor Q1, pull-up resistor R13, current limiting resistor R14, filter capacitor C4, and RC snubber circuits R12 and C3. R9, R10, and R11 are connected in series to divide the voltage and then connected to the collector of Q1. The emitter of Q1 is connected to +5V. The base of Q1 is led out to the zero-crossing signal output terminal ZEO through R14. ZEO is connected in parallel with C4 and grounded. R13 is connected between +5V and the base of Q1, and R12 and C3 are connected in parallel between the collector and emitter of Q1. ZEO outputs a zero-crossing pulse signal synchronized with the mains power and sends it to the main control module for thyristor zero-crossing triggering.

9. The AC load dual-channel parallel switch control circuit according to claim 8, characterized in that: The rectifier buffer unit includes a power resistor R3, series rectifier diodes D1 and D2, a filter electrolytic capacitor EC1, and a discharge resistor R4. After COM1 is connected in series with R3, it is connected to D1 and D2 in series in the same direction. The output terminals of D1 and D2 are connected in parallel with EC1, and R4 is connected in parallel across EC1.

10. The AC load dual-channel parallel switch control circuit according to claim 9, characterized in that: The OB2222MCPA switching power supply main control conversion unit includes an inductor L1, a power chip U1, a start-up resistor R5 / R6, a current sampling resistor R7, and a Zener diode D3. After rectification, the DC power is connected to the high-voltage power supply pin of U1 via L1, and R5 and R6 are connected in series between the high-voltage side and the start-up pin of U1. The current sampling pin CS of U1 is connected in series with R7 to power ground, and the power ground pin of U1 is connected in parallel with D3 to the high voltage input node; The negative voltage output regulator unit includes an energy storage inductor L2, a rectifier diode D4, a filter capacitor C1, an electrolytic capacitor EC4, a thin film capacitor C2, feedback voltage divider resistors RJ1 and RJ2, and an adjustment resistor R8. One end of L2 is connected to the anode of D4, and the cathode of D4 outputs negative voltage. The connection point between L2 and D4 is connected in parallel with C1 to ground; the negative voltage output terminal is connected in parallel with EC4 and C2. One end of RJ1 is connected to the negative voltage output terminal, and one end of RJ2 is connected to the +5V reference. The midpoint of the connection between RJ1 and RJ2 is fed back to the feedback pin FB of U1. R8 is connected in parallel across RJ2 to adjust the feedback voltage division ratio. The negative voltage output regulator unit outputs a negative voltage power supply to provide working power for the main controller, relay driving transistor, and thyristor driving transistor. The thyristor switch branch (and relay branch) can be interchangeably placed between the neutral wire and the AC load, while the live wire is directly and continuously connected to the other end of the AC load, achieving the same dual-channel parallel switch control function. (Depending on the power supply scheme, the AC-DC power supply scheme shown in Figure 3 uses a buck-boost topology for negative voltage, so the thyristor switch branch and relay branch are placed between the live wire and the AC load.)

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