DETECTION CIRCUIT FOR INSTANTANEOUS VOLTAGE DROP AND VEHICLE-MOUNTED DIAGNOSTIC SYSTEM

A detection circuit for instantaneous voltage drop and an on-board diagnostic system. The detection circuit comprises two RC circuits (11, 12), wherein each of the RC circuits (11, 12) comprises a first resistor (R1, R2), a second resistor (R3, R4), and an energy storage capacitor (C1, C2); a first end of the first resistor (R1, R2) is used for receiving a to-be-detected voltage (VBATT), and a second end thereof is connected to a first end of the second resistor (R3, R4); the energy storage capacitor (C1, C2) is connected in parallel with the second resistor (R3, R4); the first end of the second resistor (R3, R4) forms an output end of the RC circuit (11, 12), and the output end is connected to an input end of the comparator (13); an output end of the comparator (13) is connected to the determination unit (14); in the two RC circuits (11, 12), the resistance ratios of the second resistors (R3, R4) to the first resistors (R1, R2) are different, the capacitances of the energy storage capacitors (C1, C2) are different, and the capacitance of the energy storage capacitor (C1, C2) in the RC circuit (11, 12) with a larger resistance ratio of the second resistor (R3, R4) to the first resistor (R1, R2) is smaller; and the determination unit (14) is configured to determine that the to-be-detected voltage drops instantaneously when at least it is detected that the comparator (13) is inverted.