Automatic power-off switch circuit during power outage

In some areas with frequent power outages, electrical appliances are not turned off after the power outage. Once the power comes, they will be powered on by themselves. At the least, it consumes electricity and shortens the life of electrical appliances, and at worst, it causes major accidents such as fires (such as various electric heating appliances). If the automatic power-off switch introduced in this article is installed, the electrical device will automatically be in a power-off state when the power comes back after a power outage. Only manual intervention to press the switch can the electrical device be energized. This device can be used to do To be foolproof. working principle 　　　　　　　　　　　

(a) in the figure is an automatic power-off switch for capacitor voltage reduction. The 220V AC voltage is stepped down by capacitor C1, rectified by VD2, and stabilized by VD1 to supply the DC working voltage of the relay J coil. Note that the normally open contact S is used in the relay. When a call comes, since S is disconnected, the relay coil has no DC working voltage, which in turn cannot close S, so the power output socket CZ has no power; when you need to power up the appliance, you need to press the button switch AN. Then the relay coil gets the working voltage and S is closed. Afterwards, although AN has been disconnected, the closing of S allows the relay to still be powered and continue to work. This is called the "self-protection" function of the relay. When there is a power outage, S is disconnected; when the power comes back, the circuit repeats the above process. The circuit in Figure (b) is more concise, eliminating a series of components such as voltage reduction, rectification, and voltage stabilization in Figure (a), but it requires the use of a 220V AC relay. First, it is more expensive, and second, there are sometimes annoying problems during operation. Power frequency hum. You can choose according to the components on hand and your own hands-on ability. Component Selection and Production In Figure 1(a), it is best to select a relay with a coil working voltage of 24V or 48V, so that the corresponding coil current should be smaller to reduce the requirement for C1 capacity. The contact current should be appropriately selected according to the load size. . VD1 should be selected based on the working voltage of the relay. Generally, a Zener diode with a voltage stabilization value slightly higher than 1W of the working voltage of the relay coil is selected. The withstand voltage of C1 should not be less than 400V, 630V is better. The withstand voltage of C2 should also be based on the voltage stabilization of VD1. Select the value appropriately.