GB1420387A - Overvoltage limiting circuit arrangement - Google Patents

Abstract

1420387 Overvoltage protective circuits SEMIKRON GES FUR GLEICHRICHTERBAU U ELEKTRONIK mbH 28 March 1973 [1 April 1972] 14854/73 Heading H2H [Also in Division H3] An overvoltage limiting circuit arrangement has two rectifier branches 2a, 2b each comprising one or more selenium rectifiers, the branches are connected in series opposition and a respective semi-conductor diode 4 is connected in parallel with each rectifier branch and each semiconductor diode 4 presents when its associated parallel rectifier branch is forwardly biased a lower impedance current path than does the parallel rectifier branch, so that the overvoltage is limited to a value near to the breakdown voltage of the rectifier branch which is reverse biased. The circuit provides overvoltage protection of a device such as a semi-conductor device connected in parallel to the arrangement and used in an A.C. circuit. When the rectifier section 2a conducts in the forward direction the voltage across this section is effectively short circuited to the lower voltage across the semiconductor diode 4 which may be a Si rectifier and the overvoltage across the device is limited by the voltage across the rectifier branch 2b which conducts in the reverse direction. The operation of the branches 2a, 2b reverses for the opposite polarity applied at 2. A construction of the circuit arrangement is disclosed (Fig. 3, not shown). A further embodiment is disclosed (Fig. 4, not shown) having three branches, each branch comprising a single selenium rectifier (2) and a parallel connected semi-conductor diode 4.