Two simple mains leakage alarm circuit and production

Crystal oscillator

Photocoupler

Two simple mains leakage alarm circuit and production

The two kinds of alarms introduced here are simple in circuit and sensitive in triggering. They can be directly loaded into the combined socket, which is suitable for leakage alarm of household appliances, and is cheap and easy to do. The two alarm circuits are shown in Figures 1(A) and (B), respectively. Figure (A) shows a leakage alarm made with a CMOS six-phase inverter CD4069. Normally, the audio oscillator composed of the gate A, the gates B, R2, and YD has no current passing through without sounding. When the electrical leakage of the outer casing is inserted into the three-hole socket, the leakage current flows from the power supply wire through the electrical casing to the grounding socket of the three-hole socket, and then returns to the power supply neutral line through the alarm to form a loop, and the leakage current is stepped down by R1 and VD rectified. The subsequent pulsating current causes the alarm to sound. The leakage alarm current of this circuit is less than 0.3mA.

Figure (B) uses a CW9300 music IC to make a leakage alarm. Since R1 and VT constitute a highly sensitive trigger circuit, the alarm has high sensitivity and its leakage alarm current is less than 10uA. The working voltage of the music IC is supplied by R2 step-down, VD rectification, and C filtering. Since the voltage is taken from the 220V mains hotline, compared with some alarm circuits that rely on leakage current and voltage to maintain the sound of the IC, not only the alarm volume is large, but also the shortage of the above-mentioned circuit volume with the leakage current is overcome.