An automatic switching circuit with enhanced phase-cut compatibility, characterized by comprising a leading edge phase-cut/trailing edge phase-cut intelligent identification circuit, which internally includes an input interface circuit, a signal detection circuit, a holding current control circuit, a current-limiting protection circuit and a control chip U1, and further comprising a leading edge phase-cut/trailing edge phase-cut conversion circuit;
- The input interface circuit comprises a diode D1 and a diode D3, the anode of diode D1 is electrically connected to terminal L, the anode of diode D3 is electrically connected to terminal N, and the cathodes of diode D1 and diode D3 are commonly connected to an internal high-potential node of the circuit;
- The signal detection circuit comprises a resistor R1, a resistor R2, a capacitor C1, a resistor R5, a diode D2 and a Zener diode Z1;
- one end of resistor R1 is electrically connected to the 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, 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;
- The holding current control circuit comprises a transistor Q1, a diode D4, a resistor R3, a resistor R4, a resistor R7 and a resistor 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 and Zener diode Z2, and the other end of resistor R3 is electrically connected to the output terminal of the signal input interface;
- the other end of Zener diode Z2 is grounded;
- the other end of resistor R6 is electrically connected to the anode of diode D4 and the collector of transistor Q2;
- the cathode of diode D4 is electrically connected to the base of transistor Q1;
- under the control of pin 3 of control chip U1, transistor Q1 conducts current from the input interface circuit through resistor R4, transistor Q1, resistor R7 and resistor R8 to ground, and this current flows through the phase-cut dimmer in the external main circuit as a holding current to prevent its false turn-off;
- The current-limiting protection circuit comprises a transistor Q2, a resistor R7 and a resistor R8;
- one end of resistor R7 is electrically connected to the emitter of transistor Q1 and the base of transistor Q2, the other end is electrically connected to one end of resistor R8, and the other end of resistor R8 is grounded;
- when the current flowing through resistor R7 and resistor R8 exceeds a set threshold, the voltage drop generated at the other end connected to resistor R7 and resistor R8 triggers transistor Q2 to conduct, and after transistor Q2 conducts, it pulls down the base voltage of transistor Q1, keeping the flowing current at the set value to realize current-limiting protection;
- Pin 4 of control chip U1 is electrically connected to capacitor C2, the other end of capacitor C2 is grounded, pin 7 of control chip U1 is the output terminal NO-OFF of the leading edge phase-cut/trailing edge phase-cut intelligent identification circuit, used for algorithm identification and control of the leading edge phase-cut and trailing edge phase-cut conversion circuit;
- The leading edge phase-cut/trailing edge phase-cut conversion circuit comprises a capacitor C3, a resistor R9, a resistor R10, a resistor R11, a resistor R12, an optocoupler triac U2 and a 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 triac U2, pin 3 of optocoupler triac U2 is electrically connected to input terminal ACN, pin 1 of optocoupler triac U2 is electrically connected to resistor R10, the other end of resistor R10 is connected to power supply VCC, pin 2 of optocoupler triac U2 is electrically connected to the D pole of field-effect transistor Q3, resistor R11 is electrically connected to the G pole of field-effect transistor Q3 and resistor R12, the other end of resistor R12 and the S pole of field-effect transistor Q3 are connected to ground, and one end of resistor R11 is electrically connected to the output terminal NO-OFF of the leading edge phase-cut/trailing edge phase-cut intelligent identification circuit.