The invention relates to an undervoltage release, which comprises a capacitive charging
booster type starting power circuit, a
self feedback dual-limit detection circuit, a
relay switching circuit and an
electromagnet coil. The starting power circuit is connected with the
self feedback dual-limit detection circuit, the
relay switching circuit and the
electromagnet coil, and the control output end of the
self feedback dual-limit detection circuit is connected with the control input end of the
relay switching circuit; the relay switching circuit comprises a relay; when the
voltage of a
power grid is kept at a release
voltage or higher than the release
voltage after reaching a pull-in voltage, a relay coil and the
electromagnet coil form a serially connected loop; when the voltage of the
power grid is lower than the release voltage, the electromagnet coil is in a state of an open circuit; and when the voltage of the
power grid restores to the pull-in voltage or higher than the pull-in voltage, the relay coil and the electromagnet coil form a serially connected loop again. The undervoltage release has the advantages of low calorific power, big release instant starting torque, very
simple circuit, reliable work, high efficiency and the like.