When the gas stove accidentally turn off, by C6 and R15 added to the flame detection pin on the 150V AC pulse voltage appears open state, IC1 comparator negative side due to the role of R19 and make the potential higher than the positive comparator, forcing IC1 Inversion, from the original high-level reversal to low state, the output of the low-level signal to the microcontroller's flame signal detection input. When the flame detection pin serious leakage or flame detection pin and the body short-circuit, T1 secondary winding 150V AC pulse voltage through the R15 and C7 constitute a loop, because the capacitance of the AC short-circuit, IC1 comparator negative due to R19 The role of higher than the positive terminal potential, so that the comparator inversion, the output low, the low-level signal input to the microcontroller's flame signal detection port, so that the microcontroller through the flame signal detection input level can determine the level of flame.

    The use of the circuit of the AC flame detection method to improve the reliability of the flame detection to prevent the occurrence of control errors.