Gas furnace automatic igniter circuit design

As shown in the figure, the igniter uses 555 as the core, and uses the characteristics of the photoresistor to be sensitive to flare, to control the voltage of the reset terminal of 555, so that the 555 automatically starts or stops the oscillation and automatically ignites.
555 and R2, C3 form an astable multivibrator. When the gas valve switch is opened, the interlocking switch K is automatically closed. At this time, since the resistance of the photoresistor RG is extremely large, the 4 feet are at a high level, so one When the power is turned on, the SCR starts to oscillate continuously, so that the C4 continuously charges through R1 and L1, and continuously discharges through SCR and L1, and induces a high-voltage alternating current of about 10 kV in the secondary of the transformer T1, and the high-voltage passes through the discharge needle. Fire and discharge, automatically point the gas stove. After that, since the fire illuminates the RG to make it low impedance, the 4 pin is at a low level, the oscillator is forcibly reset, the vibration is stopped, and the SCR is turned off. When the fire extinguished for various reasons, RG showed high resistance, 4 feet were high, and 555 started to ignite again.
The pulse step-up transformer is the key component. U12 core can be used. The high-voltage line 2L2 uses a 12-inch TV high-voltage package, and the L1 uses a Φ0.5mm enameled wire to wind 20 turns.