An enhanced phase-compatible automatic switching circuit

Abstract

This invention relates to the field of phase-cut control circuit technology, specifically an automatic switching circuit that enhances phase-cut compatibility. It includes a leading-edge / trailing-edge phase-cut intelligent identification circuit, comprising an input interface circuit, a signal detection circuit, a sustaining current control circuit, a current-limiting protection circuit, and a control chip U1. It also includes a leading-edge / trailing-edge phase-cut conversion circuit. Pin 7 of U1 is the NO-OFF output terminal of the leading-edge / trailing-edge phase-cut intelligent identification circuit, used for algorithmic identification and control of the leading-edge and trailing-edge phase-cut conversion circuit. This invention, through multi-mode adaptive algorithms, intelligent detection and compensation, collaborative control, and dynamic sustaining current adjustment, achieves stable current compensation while controlling dimmers of different brands and models. It also improves dimming compatibility, eliminates flicker under low-power loads, identifies and controls the leading-edge and trailing-edge phase-cut conversion, and enhances dimming accuracy. Furthermore, the circuit is simple and low-cost.

Description

Technical Field

[0001] This invention relates to the field of phase-cutting control circuit technology, specifically an automatic switching circuit that enhances phase-cutting compatibility. Background Technology

[0002] Phase-cut dimming technology is widely used in diode LED dimming due to its advantages of low cost and simple circuitry. However, existing phase-cut dimming power supply technology has the following shortcomings:

[0003] Unstable maintenance current control: Traditional phase-cut maintenance current circuits have problems such as high power consumption, high heat generation, and uncontrollable maintenance current, which can easily lead to dimmer oscillation noise and cannot adapt to the needs of different phase-cut controllers.

[0004] Poor dimming compatibility: Although existing phase-cut dimming technology can adjust the dimming curve, it is not coordinated with the holding current circuit for control. As a result, some phase-cut controllers do not have enough holding current to allow the dimmer to work properly at the minimum / maximum conduction angle, resulting in flickering and limited compatibility.

[0005] Flickering under low power load: Low-power diode LED lamps are prone to flickering when phase-switching dimming. Existing technologies suffer from complex control, inflexibility, and high cost.

[0006] Unable to distinguish between leading-edge and trailing-edge phase cutting: Existing technology simply converts the phase-cut sine wave into a square wave through diodes and transistors and transmits it to the subsequent stage. It cannot distinguish between leading-edge and trailing-edge phase cutting. The freewheeling current required for leading-edge and trailing-edge phase cutting is different, and the maximum and minimum conduction angles of leading-edge and trailing-edge phase cutting are inconsistent. The inability to distinguish between leading-edge and trailing-edge phase cutting limits the compatibility of phase-cut dimming power supplies.

[0007] Poor dimming effect: Due to power grid fluctuations, the phase cutting angle control is inaccurate. Limited by the current provided by the freewheeling circuit, the phase cutting dimmer will exhibit a disordered phase cutting waveform during dimming. Traditional zero-crossing detection circuits will directly convert this disordered waveform into a square wave and transmit it directly to the subsequent circuit. The subsequent circuit will suffer from poor dimming effect due to this disordered square wave.

[0008] Therefore, it is urgent to improve the phase-cutting control circuit to solve the above-mentioned problems. Summary of the Invention

[0009] The purpose of this invention is to provide an automatic switching circuit that enhances phase-cut compatibility. Through multi-mode adaptive algorithms, intelligent detection and compensation, collaborative control and dynamic maintenance current adjustment, it can maintain stable current compensation when controlling dimmers of different brands and models, improve dimming compatibility, eliminate flicker under low power loads, identify and control the phase-cutting transitions before and after the phase and the phase-cutting transition at the trailing edge, improve dimming accuracy, and the circuit is simple and low in cost.

[0010] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0011] An enhanced phase-cut compatibility automatic switching circuit includes a leading-edge phase-cut / tail-edge phase-cut intelligent identification circuit, which includes an input interface circuit, a signal detection circuit, a sustaining current control circuit, a current limiting protection circuit, and a control chip U1, and also includes a leading-edge phase-cut / tail-edge phase-cut conversion circuit.

[0012] The input interface circuit includes diodes D1 and D3. The anode of diode D1 is electrically connected to the L terminal, and the anode of diode D3 is electrically connected to the N terminal. The cathodes of diodes D1 and D3 are connected to a high-potential node inside the circuit.

[0013] The signal detection circuit includes resistors R1 and R2, capacitor C1, resistor R5, diode D2, and Zener diode Z1. One end of resistor R1 is electrically connected to a high-potential node, and the other end is electrically connected to one end of resistor R2. The other end of resistor R2 is electrically connected to the anode of diode D2. The anode of diode D2 is electrically connected to the cathode of Zener diode Z1, one end of capacitor C1, pin 1 of control chip U1, and one end of resistor R5. The anode of Zener diode Z1, the other end of resistor R5, the other end of capacitor C1, and pin 2 of control chip U1 are grounded.

[0014] The current-maintaining control circuit includes transistor Q1, diode D4, resistors R3, R4, R7, and R8. The collector of transistor Q1 is electrically connected to one end of resistor R4; the other end of resistor R4 is electrically connected to the output terminal of the signal input interface; the emitter of transistor Q1 is electrically connected to one end of resistor R8 through resistor R7; the other end of resistor R8 is electrically connected to ground; one end of resistor R3 is electrically connected to pin 3 of control chip U1; one end of resistor R6 is connected to the Zener diode Z2; and the resistor R3... The other end is electrically connected to the output terminal of the signal input interface; the other pin of the Zener diode Z2 is grounded; the other end of the resistor R6 is electrically connected to the anode of the diode D4 and the collector of the transistor Q2; the cathode of the diode D4 is electrically connected to the base of the transistor Q1; under the control of the third pin of the control chip U1, the current of the transistor Q1 flows from the input interface circuit through the resistor R4, the transistor Q1, the resistor R7, and the resistor R8 to ground. This current flows through the phase cut dimmer in the external main circuit as a holding current to prevent it from being turned off accidentally.

[0015] The current limiting protection circuit includes transistor Q2, resistor R7, and resistor R8. One end of resistor R7 is electrically connected to the emitter of transistor Q1 and the base of transistor Q2, and the other end is electrically connected to one end of resistor R8, with the other end of resistor R8 grounded. When the current flowing through resistors R7 and R8 exceeds a set threshold, the voltage drop generated at the other end of resistors R7 and R8 triggers transistor Q2 to conduct. After transistor Q2 conducts, it pulls down the base voltage of transistor Q1, keeping the current flowing through it at the set value, thus achieving current limiting protection.

[0016] Pin 4 of control chip U1 is electrically connected to capacitor C2, and the other end of capacitor C2 is grounded. Pin 7 of control chip U1 is the NO-OFF output terminal of the leading edge phase-cutting / tail-edge phase-cutting intelligent identification circuit, which is used for algorithm identification and control of the leading edge phase-cutting and tail-edge phase-cutting conversion circuit.

[0017] The leading-edge / trailing-edge phase-cutting conversion circuit includes capacitor C3, resistors R9, R10, R11, R12, optocoupler SCR U2, and field-effect transistor Q3. The input terminal ACL is electrically connected to fuse F1 and then to capacitor C3. The other end of capacitor C3 is electrically connected to resistor R9. The other end of resistor R9 is electrically connected to pin 4 of optocoupler SCR U2. Pin 3 of optocoupler SCR U2 is electrically connected to input terminal ACN. Pin 1 of optocoupler SCR U2 is electrically connected to resistor R10. The other end of resistor R10 is connected to power supply VCC. Pin 2 of optocoupler SCR U2 is electrically connected to the drain (D) terminal of field-effect transistor Q3. Resistor R11 is electrically connected to the gate (G) terminal of field-effect transistor Q3 and resistor R12. The other end of resistor R12 is connected to ground via the source (S) terminal of field-effect transistor Q3. One end of resistor R11 is electrically connected to the NO-OFF output terminal of the leading-edge / trailing-edge phase-cutting intelligent identification circuit.

[0018] The present invention has at least the following beneficial effects:

[0019] Through multi-mode adaptive algorithms, intelligent detection and compensation, collaborative control and dynamic maintenance current adjustment, it can maintain stable current compensation when controlling dimmers of different brands and models, improve dimming compatibility, eliminate flicker under low power load, adaptive front and rear phase switching and trailing edge phase switching, improve dimming accuracy, and the circuit is simple and low cost. Attached Figure Description

[0020] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0021] Figure 1 This is a circuit diagram of the present invention;

[0022] Figure 2This is a circuit diagram of the present invention. Detailed Implementation

[0023] The following will describe in detail the implementation of this application with reference to the accompanying drawings and embodiments, so that the implementation process of how this application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0024] Example 1:

[0025] like Figure 1 As shown, the enhanced phase-cut compatibility automatic switching circuit provided in this embodiment has its input terminals ACL and ACN connected to the AC voltage after phase cutting by the phase-cut dimmer. It includes a leading-edge phase-cut / trailing-edge phase-cut intelligent identification circuit, which includes an input interface circuit, a signal detection circuit, a sustaining current control circuit, a current limiting protection circuit, and a control chip U1. It also includes a leading-edge phase-cut / trailing-edge phase-cut conversion circuit.

[0026] The input interface circuit includes diodes D1 and D3. The anode of diode D1 is electrically connected to the L terminal, and the anode of diode D3 is electrically connected to the N terminal. The cathodes of diodes D1 and D3 are connected to a high-potential node inside the circuit. This input interface circuit is used to convert the phase-cut AC signal output by the phase-cut dimmer into a phase-cut wave and introduce it into the circuit as the input for signal detection and maintenance current loop.

[0027] The signal detection circuit includes resistors R1 and R2, capacitor C1, resistor R5, diode D2, and Zener diode Z1. One end of resistor R1 is electrically connected to a high-potential node (i.e., the cathode connection point of D1 and D3), and the other end is electrically connected to one end of resistor R2. The other end of resistor R2 is electrically connected to the anode of diode D2, and the anode of diode D2 is electrically connected to the cathode of Zener diode Z1, one end of capacitor C1, pin 1 of control chip U1, and one end of resistor R5. The anode of Zener diode Z1, the other end of resistor R5, the other end of capacitor C1, and pin 2 of control chip U1 are grounded (GND).

[0028] The function of this circuit is to acquire the phase-cut waveform signal output from the input interface circuit and input the signal to the control chip U1. The control chip U1 can sample the data through one of the following methods: ADC, IO high and low level, internal comparator, analog watchdog, and fuse the data through the algorithm to realize waveform reconstruction. It also extracts waveform features through the algorithm, parses the conduction angle information (dimming brightness) and leading and trailing edge information of the current phase-cut dimmer, and generates control data for the sustaining current circuit to control the sustaining current circuit.

[0029] The current-maintaining control circuit includes transistor Q1, diode D4, resistors R3, R4, R7, and R8. The collector of transistor Q1 is electrically connected to one end of resistor R4; the other end of resistor R4 is electrically connected to the output terminal of the signal input interface (i.e., the cathode connection point of D1 and D3); the emitter of transistor Q1 is electrically connected to one end of resistor R8 through resistor R7; the other end of resistor R8 is electrically connected to ground (GND); one end of resistor R3 is electrically connected to pin 3 of control chip U1; one end of resistor R6 is connected to the Zener diode Z2; and the resistor R3... The other end is electrically connected to the output terminal of the signal input interface (i.e., the cathode connection point of D1 and D3); the other pin of the Zener diode Z2 is grounded (GND); the other end of the resistor R6 is electrically connected to the anode of the diode D4 and the collector of the transistor Q2; the cathode of the diode D4 is electrically connected to the base of the transistor Q1; under the control of the third pin of the control chip U1, the current of the transistor Q1 flows from the input interface circuit through the resistor R4, the transistor Q1, the resistor R7, and the resistor R8 to ground. This current flows through the phase cut dimmer in the external main circuit as a holding current to prevent it from being turned off accidentally.

[0030] The current limiting protection circuit includes transistor Q2, resistor R7, and resistor R8. One end of resistor R7 is electrically connected to the emitter of transistor Q1 and the base of transistor Q2, and the other end is electrically connected to one end of resistor R8, with the other end of resistor R8 grounded (GND). When the current flowing through resistors R7 and R8 exceeds a set threshold, the voltage drop generated at the other end of resistors R7 and R8 triggers transistor Q2 to conduct. After transistor Q2 conducts, it pulls down the base voltage of transistor Q1, keeping the current flowing through it at the set value, thus achieving current limiting protection.

[0031] Pin 4 of control chip U1 is electrically connected to capacitor C2, with the other end of capacitor C2 grounded. Pin 7 of control chip U1 is the NO-OFF output terminal of the leading-edge phase-cutting / trailing-edge phase-cutting intelligent identification circuit, used for algorithm identification and control of the leading-edge phase-cutting and trailing-edge phase-cutting conversion circuit. Capacitor C2 serves as a power supply bypass filter capacitor for control chip U1. Control chip U1 receives input from the signal detection circuit, outputs control signals to the sustaining current control circuit, and outputs the phase-cutting phase calculated by the algorithm. The final phase output can be selected from one of the following signals: PWM signal, serial port signal, or other digitally encoded signals such as Manchester encoding, output to pin 6 (OUT) of control chip U1. The power supply for control chip U1 is provided by an external circuit.

[0032] The leading-edge / trailing-edge phase-cutting conversion circuit includes capacitor C3, resistors R9, R10, R11, R12, optocoupler SCR U2, and field-effect transistor Q3. The input terminal ACL is electrically connected to fuse F1 and then to capacitor C3. The other end of capacitor C3 is electrically connected to resistor R9. The other end of resistor R9 is electrically connected to pin 4 of optocoupler SCR U2. Pin 3 of optocoupler SCR U2 is electrically connected to input terminal ACN. Pin 1 of optocoupler SCR U2 is electrically connected to resistor R10. The other end of resistor R10 is connected to power supply VCC. Pin 2 of optocoupler SCR U2 is electrically connected to the drain (D) terminal of field-effect transistor Q3. Resistor R11 is electrically connected to the gate (G) terminal of field-effect transistor Q3 and resistor R12. The other end of resistor R12 is connected to ground via the source (S) terminal of field-effect transistor Q3. One end of resistor R11 is electrically connected to the NO-OFF output terminal of the leading-edge / trailing-edge phase-cutting intelligent identification circuit.

[0033] The working principle of the multifunctional novel phase-cutting control circuit provided in this embodiment is as follows:

[0034] When an external phase-cut dimmer is connected, a phase-cut voltage appears at the input terminals ACL and ACN. The signal detection circuit consisting of diodes D1 and D3, and subsequent resistors R1, R2, D2, Zener diode Z1, capacitor C1, and resistor R5 is used by the control chip U1 to analyze the current conduction angle information (dimming brightness) and leading and trailing edge information of the phase-cut dimmer through algorithm calculation based on the waveform characteristics of the signal, and calculate the sustaining current control data.

[0035] Based on the calculated conduction angle information (dimming brightness), sustaining current control data, and rising and falling edge information of the phase-cut dimmer, the sustaining current control circuit is dynamically controlled on demand. Pin 3 of the control chip U1 outputs a high-level drive signal, which passes through resistor R6 and diode D4 to the base of transistor Q1, turning on transistor Q1. After transistor Q1 is turned on, the current flows from the phase-cut AC voltage (L, N) output by the phase-cut dimmer through (diode D1, diode D3), resistor R4, transistor Q1, resistor R7, and resistor R8 to ground (GND). This current flows through the phase-cut dimmer in the external main circuit, ensuring that the total current is not lower than the sustaining current and preventing the dimmer from being turned off accidentally.

[0036] During normal operation, when the voltage drop across resistors R7 and R8 reaches a level that causes transistor Q2 to enter amplification mode, transistor Q2 is in amplification mode, which pulls down the base potential of transistor Q1, forcing a reduction in the current flowing through transistor Q1, thus achieving rapid overcurrent protection and effectively solving the compatibility and reliability issues in phase-cutting dimming.

[0037] The intelligent identification circuit for leading-edge / trailing-edge phase cutting uses an algorithm to analyze and confirm whether a phase-cut dimmer is currently connected, based on the signal provided by the signal detection circuit connected to pin 1 of the control chip U1, and identifies whether the connected dimmer is a leading-edge or trailing-edge phase cut dimmer. Pin 7 of the leading-edge phase cut control chip U1 outputs a high level. Pin 7 of the trailing-edge phase cut control chip U1 outputs a low level.

[0038] In the leading-edge / trailing-edge phase-cutting conversion circuit, one end of resistor R11 receives a control signal from pin 7 of control chip U1. When the signal is high, MOSFET Q3 is turned on, pins 4 and 3 of optocoupler SCR U2 are connected, and the RC absorption circuit consisting of capacitor C3 and resistor R9 is activated, absorbing the voltage spikes generated during chopping by the leading-edge phase-cutting dimmer, ensuring good conduction of the leading-edge phase-cutting dimmer. When one end of resistor R11 receives a low signal from pin 7 of control chip U1, MOSFET Q3 is turned off, pins 4 and 3 of optocoupler SCR U2 are disconnected, the RC absorption circuit consisting of capacitor C3 and resistor R9 is deactivated, and the waveform generated during chopping by the trailing-edge phase-cutting dimmer remains unchanged, ensuring good conduction of the trailing-edge dimmer.

[0039] Example 2:

[0040] This embodiment provides a method for implementing the novel multifunctional phase-cutting control circuit in Embodiment 1, including the following steps:

[0041] Signal Acquisition and Processing: The phase-cut AC voltage (L, N) output from the phase-cut dimmer is introduced through diodes D1 and D3, and after being divided by resistors R1, R2, and R5, it reaches pin 1 of the control chip U1. Capacitor C1 is used for filtering, diode D2 is used for clamping voltage, and Zener diode Z1 is used for voltage regulation. After filtering by the clamping voltage of diode D2, Zener diode Z1, and capacitor C1, the final detection signal is input to pin 1 of the control chip U1. The control chip U1 uses an algorithm to fuse the data based on the waveform characteristics of the signal, realizes waveform reconstruction, extracts waveform features, and parses the conduction angle information (dimming brightness) and leading and trailing edge information of the current phase-cut dimmer. At the same time, it generates control data for the sustaining current circuit to control the sustaining current circuit.

[0042] Dynamic adjustment of sustaining current: Control chip U1 analyzes the current conduction angle information (dimming brightness) of the phase-cut dimmer, sustaining current control data, and load status information (leading and trailing edge information). Based on this information, pin 3 of control chip U1 controls transistor Q1 to automatically and dynamically adjust the sustaining current to ensure that the external phase-cut dimmer is not accidentally turned off or has poor conduction. Specifically, pin 3 of control chip U1 outputs a high-level drive signal, which passes through resistor R6 and diode D4 to the base of transistor Q1, turning on transistor Q1. After the circuit is turned on, the current flows from the phase-cut AC voltage (L, N) output by the phase-cut dimmer to ground through diode D1, diode D3, resistor R4, transistor Q1, resistor R7, and resistor R8. This current flows through the phase-cut dimmer in the external main circuit to ensure that the total current is not lower than the holding current and to prevent the dimmer from being turned off accidentally. At the same time, the phase-cut phase calculated by the algorithm is output from pin 6 of the control chip U1. The final phase output can be selected from one of the following signals: PWM signal, serial port signal, or other digital encoded signals such as Manchester encoding.

[0043] Overcurrent protection operation: During the conduction of transistor Q1, current flows through sensing resistors R7 and R8. Under normal operation, the voltage drop across resistors R7 and R8 is close to the conduction threshold of transistor Q2, and the currents in transistors Q2 and Q1 are in equilibrium. If a circuit fault causes an abnormal increase in the current of transistor Q1, the voltage drop across resistors R7 and R8 will exceed the conduction threshold of transistor Q2. At this time, transistor Q2 will quickly conduct, pulling the base potential of transistor Q1 down to ground potential, forcing transistor Q1 to turn off, cutting off the sustaining current loop, and protecting the circuit components.

[0044] The present invention has at least the following beneficial effects: by using a multi-mode adaptive algorithm, intelligent detection and compensation, collaborative control and dynamic maintenance current adjustment, it can maintain stable current compensation when controlling dimmers of different brands and models, improve dimming compatibility, eliminate flicker under low power load, adapt to front and rear phase cutting and trailing edge phase cutting, improve dimming accuracy, and the circuit is simple and low cost.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An automatic switching circuit with enhanced phase-cut compatibility, characterized in that, It includes a leading-edge phase cut / tail-edge phase cut intelligent identification circuit, which includes an input interface circuit, a signal detection circuit, a sustaining current control circuit, a current limiting protection circuit, and a control chip U1, as well as a leading-edge phase cut / tail-edge phase cut conversion circuit; The input interface circuit includes diodes D1 and D3. The anode of diode D1 is electrically connected to the L terminal, and the anode of diode D3 is electrically connected to the N terminal. The cathodes of diodes D1 and D3 are connected to a high-potential node inside the circuit. The signal detection circuit includes resistors R1 and R2, capacitor C1, resistor R5, diode D2, and Zener diode Z1. One end of resistor R1 is electrically connected to a high-potential node, and the other end is electrically connected to one end of resistor R2. The other end of resistor R2 is electrically connected to the anode of diode D2. The anode of diode D2 is electrically connected to the cathode of Zener diode Z1, one end of capacitor C1, pin 1 of control chip U1, and one end of resistor R5. The anode of Zener diode Z1, the other end of resistor R5, the other end of capacitor C1, and pin 2 of control chip U1 are grounded. The current-maintaining control circuit includes transistor Q1, diode D4, resistors R3, R4, R7, and R8. The collector of transistor Q1 is electrically connected to one end of resistor R4; the other end of resistor R4 is electrically connected to the output terminal of the signal input interface; the emitter of transistor Q1 is electrically connected to one end of resistor R8 through resistor R7; the other end of resistor R8 is electrically connected to ground; one end of resistor R3 is electrically connected to pin 3 of control chip U1; one end of resistor R6 is connected to the Zener diode Z2; and the resistor R3... The other end is electrically connected to the output terminal of the signal input interface; the other pin of the Zener diode Z2 is grounded; the other end of the resistor R6 is electrically connected to the anode of the diode D4 and the collector of the transistor Q2; the cathode of the diode D4 is electrically connected to the base of the transistor Q1; under the control of the third pin of the control chip U1, the current of the transistor Q1 flows from the input interface circuit through the resistor R4, the transistor Q1, the resistor R7, and the resistor R8 to ground. This current flows through the phase cut dimmer in the external main circuit as a holding current to prevent it from being turned off accidentally. The current limiting protection circuit includes transistor Q2, resistor R7, and resistor R8. One end of resistor R7 is electrically connected to the emitter of transistor Q1 and the base of transistor Q2, and the other end is electrically connected to one end of resistor R8, with the other end of resistor R8 grounded. When the current flowing through resistors R7 and R8 exceeds a set threshold, the voltage drop generated at the other end of resistors R7 and R8 triggers transistor Q2 to conduct. After transistor Q2 conducts, it pulls down the base voltage of transistor Q1, keeping the current flowing through it at the set value, thus achieving current limiting protection. Pin 4 of control chip U1 is electrically connected to capacitor C2, and the other end of capacitor C2 is grounded. Pin 7 of control chip U1 is the NO-OFF output terminal of the leading edge phase-cutting / tail-edge phase-cutting intelligent identification circuit, which is used for algorithm identification and control of the leading edge phase-cutting and tail-edge phase-cutting conversion circuit. The leading-edge / trailing-edge phase-cutting conversion circuit includes capacitor C3, resistors R9, R10, R11, R12, optocoupler SCR U2, and field-effect transistor Q3. The input terminal ACL is electrically connected to fuse F1 and then to capacitor C3. The other end of capacitor C3 is electrically connected to resistor R9. The other end of resistor R9 is electrically connected to pin 4 of optocoupler SCR U2. Pin 3 of optocoupler SCR U2 is electrically connected to input terminal ACN. Pin 1 of optocoupler SCR U2 is electrically connected to resistor R10. The other end of resistor R10 is connected to power supply VCC. Pin 2 of optocoupler SCR U2 is electrically connected to the drain (D) terminal of field-effect transistor Q3. Resistor R11 is electrically connected to the gate (G) terminal of field-effect transistor Q3 and resistor R12. The other end of resistor R12 is connected to ground via the source (S) terminal of field-effect transistor Q3. One end of resistor R11 is electrically connected to the NO-OFF output terminal of the leading-edge / trailing-edge phase-cutting intelligent identification circuit.

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