Induction protection safety power socket circuit diagram

In real life, accidents involving personal injury or electric shock often occur due to unintentional contact with the metal part  　　of the plug when unplugging or plugging in the power plug. In order to ensure the safety of electricity use, we made a gap between the original power plug and the socket. A control circuit can automatically disconnect the internal power supply of the socket when the human hand approaches the socket (about 5cm ~ 6cm away), and automatically restore the power connection inside the socket after the human hand leaves the socket. No human operation is required. It is simple and convenient. And practical, it can be said that it is a new type of power socket with "fool-type" safety protection function . The schematic block diagram of the socket is shown in Figure 1.

　　working principle

　　The circuit schematic diagram of the safety power socket is shown in Figure 2. Normally, the junction field effect transistor VT1 is in a zero-bias state, the resistance between its drain and source is small, and the potential of the non-inverting input terminal V+ of the integrated operational amplifier IC (voltage comparator working mode) connected to the drain D is also low. . Use the potentiometer RP1 to adjust the potential of the inverting input terminal V- to slightly higher than V+. In this way, V+V-, the op amp output terminal Vo changes from 0 to 1, VT2 is turned on, and the relay K immediately closes, and the two groups The moving pieces are all connected to the normally open point, and the power socket connected to the normally closed point is in a power-off state, and the power indicator LED goes out. In this way, even if human hands touch the metal part of the plug, there will be no electric shock. C3 functions to buffer clutter interference and accumulate a certain barrier voltage to improve the sensitivity of relay K when it is closed. When the plug is inserted and the human hand leaves the socket, the field effect tube cannot sense the electrical signal of the human body (or the sensitivity is not enough), the circuit returns to normal working condition, the relay is released again, and the external power supply and neutral line connected to the moving piece are restored again. An electrical outlet provided for normally closed contact connections .

　　Selection and production of components

Field effect transistor VT1 uses 3DJ6 or 3DJ7, and a thin metal sheet 　　with an area of ​​about 1cm can be welded to the gate G to increase the sensing effect.

　　DC relay K should use two sets of contacts, and the rated load of the contacts should be ≥220V/3A to meet the needs of general electrical appliances.

　　Other component parameters can be found marked in the figure.

　　In this example, the potential of the drain D of the field effect transistor, that is, V+, is usually about 0.8V, V- is about 1.8V, and the sensing distance (relay K pull-in) is 5cm to 6cm.

　　Since the field effect transistor relies on the width of the conductive channel to control the size of the current, it is easily affected by the environment (noise, temperature, etc.). After a capacitor C2 is connected in parallel between the drain and the source, the pulsating component of the drain voltage can be reduced. Decrease to improve its stability.

　　In the actual measurement, the V-potential should be carefully adjusted (change the sliding end position of the potentiometer RP1) according to the sensing distance (the hand is the sensed source, and the pull-in of the relay K is the mark), so that the relay K can be stably pulled in without It is better to be too sensitive and cause tremor (about 6cm~7cm).

　　The position of the field effect tube should be as far away from other components as possible to avoid or reduce electromagnetic interference. It should be placed on the side or above, and ensure that the relay K can reliably close when the plug is 5cm to 6cm away from the socket.

　　During normal operation, the current of the whole machine is about 10mA~15mA.