Simple leakage alarm circuit

Simple Leakage Alarm The two alarms introduced here have simple circuits and sensitive triggering. They can be directly installed into the combined socket. They are suitable for leakage alarms of household appliances. They are cheap and easy to make. working principle 　　　　　　

The circuits of these two alarms are shown in Figure 1(a) and (b) respectively. Picture (a) is a leakage alarm made with a CMOS six-inverter CD4069. Normally, the audio oscillator composed of gate A, gate B, R2, and YD does not produce sound when no current passes through it. When an electrical appliance with a leaky shell is inserted into a three-hole socket, the leakage current flows from the live wire of the power supply through the electrical shell to the ground jack of the three-hole socket, and then returns to the neutral wire of the power supply through the alarm to form a loop. The leakage current is stepped down by R1 and rectified by VD. The pulsating current behind makes the alarm sound. The leakage alarm current of this circuit is less than 0.3mA. Figure (b) uses a piece of CW9300 music IC to produce a leakage alarm. Since R1 and VT form 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 live wire, compared with some alarm circuits that rely on leakage current and voltage to maintain IC sound, not only the alarm volume is larger, but also it overcomes the shortcomings of the above-mentioned circuit volume changing with the leakage current. Component Selection and Production Components are selected according to the schematic diagram. During production, a circuit can be selected according to the specific situation, and the two electrodes of a two-eye socket at the lower end of the combined socket are cut off to accommodate the circuit components and be installed in the empty space inside. After the installation is completed, you can use a 200Ω resistor, connect one end to the live wire of the power supply, and the other end to the ground end of the socket to simulate a leakage test. The circuit should work normally. The withstand voltage of the diode in the picture should be >400V, YD can be Φ27mm, the β of the transistor VT should be ≥100, and the resistors should all be 1/8W.