Design and Principle Analysis of a Small Contactless Refrigerator Delay Protector

The contactless refrigerator protector has few components, low cost, small size, and no need for debugging. The bidirectional thyristor replaces the relay.

How it works

The circuit of the protector is shown in Figure 1 (click here to download the schematic diagram). The 220V AC power supply is stepped down by capacitor C1, half-wave rectified by VD1, and stabilized by VDW before being supplied to the time base circuit 555 as the working power supply. After about 5 minutes of power supply, the output terminal of the time base circuit ③ changes from low level to high level, and the bidirectional thyristor VS is turned on to supply power to the refrigerator. At this time, the light-emitting diode LED lights up, indicating that the power supply is normal.

Component selection and production

See the attached table for component selection.
 No. Name Model Quantity R1 Resistor 1M 1W 1R2 Resistor 1K 1/8W 1R3 Resistor 2M 1/8W 1C1 Metallized paper dielectric capacitor 0.47u/400V 1C2, C3 Electrolytic capacitor 100uF/16V 2C4 Polyester capacitor 100n 1VD1, VD2 Rectifier diode IN4007 2VDW Zener diode 2CW19 (12V) 1LED Light-emitting diode 1VS Bidirectional thyristor 3A/400V 1IC1 Timing circuit NE5551

This circuit uses few components and is easy to install. As long as the connections are correct, it can generally work normally without debugging.