Household appliance leakage alarm socket simple circuit

Household electricity (referring to 220V AC), safety first! The leakage alarm socket introduced here will automatically emit two alarm signals, sound and light, when the metal casing of household appliances such as washing machines, electric fans, rice cookers, electric irons, etc., will prompt the user to timely power off for maintenance. For those residents who are inconvenient to bury the electrical grounding wire, the use of this socket is definitely a good fit.
First, the working principle of the appliance leakage alarm socket circuit shown in Figure 1. Current limiting resistor (current limiting component, after the resistor is connected in the circuit, the resistance of the resistor is fixed. Generally, it is two pins, which can limit the current through the branch connected to it.) R1 and crystal diode (Crystal diodes in semiconductor electronic devices in both ends. These devices are characterized by non-linear current-voltage characteristics. Since then, with the development of semiconductor materials and process technology, different semiconductor materials, doping Distribution, geometric structure, the development of a variety of crystal diodes with a wide variety of structures and functional uses. The materials are germanium, silicon and compound semiconductors. Crystal diodes can be used to generate, control, receive, transform, amplify signals and perform energy conversion. VD1, Zener diode VD3, capacitor C, etc. constitute a simple half-wave rectification and voltage stabilization filter circuit, providing a stable 5V DC voltage to the alarm circuit; analog acoustic integrated circuit A and its external oscillating resistor R2, piezoelectric ceramic piece B constitutes an analog siren sound generator.

Usually, since the left end of R1 is connected to the ground terminal that is suspended in the three-hole socket XS, the alarm circuit has no working power, the light-emitting diode VD2 does not emit light, and B is silent.
Once the household appliance with leakage of the outer casing is connected to the three-hole socket XS, the leakage current will be formed by the XS phase line (hot line) hole, the metal casing of the household appliance, the XS grounding hole, the alarm circuit and the grid zero line (ground). Loop. The leakage current is rectified by R1 and VD1 is half-wave rectified to make VD2 light. At the same time, the leakage current is regulated by VD3, and 5V DC voltage is output at both ends. After C filtering, the simulation of A and R2 is made. When the sound generator works, B will sound a siren to remind the user to repair the appliance in time.
The alarm current of the leakage alarm circuit is less than 0.4mA, which is far lower than the national rated leakage current rating of less than 30mA.
Second, the component selection
VD1 selects 1N4004 or 2CP18 silicon rectifier diode; VD2 should use red high-brightness LED; VD3 uses 0.5W, 5V silicon Zener diode.
A selects KD-9561 four-sound analog sound alarm ASIC. The integrated circuit is in a flexible package with a chip size of 32.5 mm x 10 mm. SEL1 and SEL2 are two sound selection terminals, and the analog siren sound signal is generated according to Fig. 1; if SEL1 is connected to the VSS terminal, a simulated ambulance sound signal is generated; if SEL1 is left floating, SEL2 is connected to VDD. At the end, the simulated machine gun sound signal is generated; if both SEL1 and SEL2 are suspended, the simulated fire truck electric flute signal is generated. At the time of production, the reader can also choose one of the other three sounds according to each person's preference.
C uses CD11-10V type electrolytic capacitor. Both R1 and R2 use RTX type carbon film resistors, and the power dissipation is 1/2W and 1/8W, respectively. B uses HTD27A-1 or FT-27 piezoelectric ceramic sheets with a simple sound-assisting cavity. XS is a commercially available ordinary AC three-hole socket.
Third, production and use

Figure 2 shows the wiring diagram of the printed circuit board of the leakage alarm socket. The printed circuit board is made by knife cutting, and the actual size is about 34 mm × 34 mm. Except for the piezoelectric ceramic piece B and the three-hole socket XS, the other electronic components are soldered to the homemade printing plate. The integrated circuit chip is vertically soldered to the circuit board with three hard wires. Note when soldering: The soldering iron shell must be well grounded to prevent the AC induced voltage from penetrating the A internal CMOS integrated circuit!
There are two options for the assembly of the leakage alarm socket: one method is to install the alarm circuit board into a separate self-made insulating small box with a size of about 40mm × 40mm × 20mm, and the panel is respectively a piezoelectric ceramic piece B, The light-emitting diode VD2 opens the sound-releasing hole and the light-emitting hole, and the circuit board in the box is connected to the three-hole socket through two outer plastic-lead wires. The utility model is characterized in that the socket and the alarm box are self-contained, and the assembly and use are relatively convenient and flexible, and the disadvantage is that the appearance is poor. Another method is to select the three-hole socket XS as a commercially available multi-purpose rectangular socket, and remove the remaining two hole plugs other than the three-hole plug in the socket to open up space for the fixed installation alarm circuit. At this time, the unused plug hole on the panel is slightly processed, and it is subtly transformed into the sound-emitting hole of the piezoelectric ceramic sheet B and the light-emitting hole of the light-emitting diode VD2. Its characteristic is that the alarm circuit and the socket are integrated, and the appearance is the same as that of the ordinary socket, which is more convenient to use.
As long as the quality of the components of the leakage alarm is guaranteed, the welding is correct and can work normally without debugging. In order to verify the performance of the alarm circuit is good, you can introduce 220V AC (pay attention to safety!) into the middle hole (ground hole) and neutral (ground) hole of the three-hole socket. If the alarm circuit produces an acousto-optic signal, the line is normal; if there is no sound or no light, indicating that the alarm line is faulty, it is important to check whether the quality of the component is guaranteed, and whether there is any error in the welding until there is an acoustic or optical signal.
When in use, the alarm socket is connected to the 220V mains circuit in the usual way. Special attention should be paid to the phase line (hot line) and neutral line (ground line) of the power line. The position of the neutral line cannot be reversed. In addition, household appliances using ordinary two-pin plugs should be replaced with a three-jaw plug that matches the leakage alarm socket, and the metal casing of the household appliance is connected to the ground wire (non-220V mains zero line) inside the plug through the plastic wire. Serve.