Introduction : Here is an inexpensive auto cut-off circuit, which is fabricated using transistor and other discrete components.

It can be used to protect loads such as refrigerator, T.V., and VCR from undesirable over and under line voltages, as well as surges caused due to sudden failure/resumption of main power supply.

This circuit can be used directly as a standalone circuit between the mains supply and the load, or it may be inserted between an existing automatic/manual stabilizer and the load.

The over/under voltage cut-off with ON-Time delay provides various types of protection 1) Over-voltage protection. 2) Under-voltage protection. 3) Protection against transients. 4) Protection to load from frequent turning ON & OFF by providing time delay.

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