Visual doorbell circuit

Circuit working principle: The entire circuit
consists of four parts: flasher, pulse trigger, oscillator and power supply. When the doorbell switch is pressed, the circuit is energized and works. The 220 V
alternating current is divided into two channels after passing through the doorbell switch . One channel is sent to the primary of 9V power transformer Tl
, and passes through T. Buck and VD. A VD. After bridge rectification, the output low-voltage DC power is added
to the oscillation circuit. Another route VD. After half-wave rectification, the capacitors C3 and C4 are charged through the current-limiting resistors M and R respectively,
so that the voltage at both ends of C3 and C4 reaches about 300 V. The flash tube SC is filled with high-voltage xenon gas. Normally, it is non-conductive when a voltage of about 300 V is applied . By single-junction transistor VT. etc. form a pulse oscillation circuit, which outputs a 1 Hz sharp pulse and is amplified by transistor VT2 to push the one-way thyristor vs. When a trigger pulse is sent to the control electrode of vs, vs is triggered to conduct, causing the capacitor C4 to discharge through the Lz of T2 . Since ￡,, L: form a step-up transformer, a high-voltage pulse of about 1000 V is induced on /, and is applied to the trigger end of the flash tube SG, which ionizes the gas in the tube , and SG is turned on, causing the capacitor C, The electric energy stored on the SC is discharged by the SG, and the SC will produce a strong flash in a very short period of time. The oscillator continuously sends out pulses, and the SG flashes continuously following the pulse frequency. Adjusting the month, or C, changes the flash frequency. The duration of the flash is determined by the size of C.