Patent ID: 6697243
Filing Date: 2004-02-24
Classification: H02H

Abstract:
An undervoltage release for monitoring the voltage of a power supply system, comprising:an electromagnet for tripping a switching device when the voltage of the power supply system falls below a predetermined magnitude; and a driver circuit feeding the electromagnet, the driver circuit including, a rectifier circuit for obtaining a direct current, an auxiliary voltage source arranged downstream from the rectifier circuit, for supplying voltage to electronics, a pulse transmitter for producing a holding current which, provided the power supply system voltage is sufficiently high, is essentially independent of the power supply system voltage, and a threshold value circuit, provided with an undervoltage detector, for interrupting the holding current which holds the electromagnet in the pulled-in state, wherein the pulse transmitter includes, an operational amplifier, a first electronic switch, controlled by the operational amplifier and connected in series with a resistor in the holding circuit of the electromagnet, which is connected to a freewheeling diode, and with a feedback path to allow the voltage which is dropped across the resistor to act on the input of the operational amplifier, and wherein a self-holding circuit, which is formed from the electromagnet and the freewheeling diode, contains a further electronic switch which is driveable as a function of the output signal from the undervoltage detector and which is arranged between the electromagnet and the first electronic switch, and wherein a timer is provided for driving the further electronic switch, with one of its poles being coupled to the auxiliary voltage source via a diode circuit.