Refrigerator power failure protector circuit design

PESD1CAN electrostatic protection SOT23-3 24V two-way

Household refrigerators are not afraid of power supply interruptions, and more often avoid short-term repeated power outages and calls. In order to avoid repeated starting and breaking of the compressor and protect it from damage, this short-time power-off protection circuit can be used. The circuit consists of a buck rectifier circuit, a 555 delay circuit and a thyristor trigger circuit, as shown in the figure.
The AC step-down and rectifier circuit consists of Cl and Rl bridge rectifiers Dl-D4 and C2. The rectified voltage is regulated by R2 and DW to a DC voltage of VDD=10V as the operating voltage of the suffix. 555 and C4, R3, RP1, etc. constitute an incoming call delay circuit. When the power is turned off after the power is off, since the voltage on C4 will not be abrupt, the incoming call is instantaneous, VDD acts on the 2 and 6 pins of 555, so that 555 is reset, that is, the output of the 3 pin is low, and the thyristor SCR has no trigger current. In the off state, the three-pin socket of the refrigerator connected in series with the SCR has no electricity, and the refrigerator stops running. As C4 is charged by R3 and RPl, when the lower end of C4 is charged to 1∕3VDD, the 555 is low. When the level is set, it is set to invert, and the output pin 3 has a logic level "1", and the high level can reach about 9V. This high potential causes the thyristor to trigger conduction, C2 is energized, the refrigerator starts running, and the "working" light LED is illuminated (green). C4 charges through R3 and RP1 to set the time of 1∕3VDD, that is, the delay after the incoming call, and its size is td=1.1(R3+RP1)C4.