Patent ID: 7359175
Filing Date: 2008-04-15
Classification: H01H

Abstract:
1. A relay drive circuit for controlling, based on ON/OFF operation of a relay switch, power supply to a coil of an electromagnetic relay in order to control power supply to a load, the relay including: the coil; a core inserted in the coil; a plate including magnetic material, the plate magnetically drawn to come in contact with a head of the core when the coil is supplied with electric power, the plate getting apart from the bead when the coil is not supplied with electric power; a movable contact moving along with the plate; and a fixed contact installed to the coil, the relay drive circuit comprising: a first drive portion for setting a coil current to be supplied to the coil to a first current value with which the plate is drawn to the head of the coil and the movable contact comes in contact with the fixed contact; a second drive portion for setting the coil current to a second current value which is smaller than the first current value set by the first drive portion, so that the movable contact and the fixed contact are kept in contact with each other; a current switching portion for switching between supplying the coil with the coil current having the first current value set by the first drive portion and supplying the coil with the coil current having the second current value set by the second drive portion; and a plate-OFF detecting portion for detecting, based on change of a potential at an end of the coil, an OFF-tendency in which the plate is about to get apart from the head of the coil the detecting being made before the plate gets apart from the head of the coil, wherein the current switching portion switches to supplying the coil with the coil current having the first current value set by the first drive portion to prevent the relay from turning to OFF, when the plate-OFF detecting portion detects the OFF-tendency.