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Silicon Carbide Non-ohmic Resistors

Nature volume 158, page 742 (23 November 1946) | Download Citation



DURING the pastk dejfKde, resistors having silicon carbide again and characterized by a striking law-the current passed Aing proportional to the fourth or fifth power of have become available com-mRciatfly and are now widely used in many fields of ectrical engineering. Their development was first stimulated by the requirements of surge diverters (lightning arresters) for overhead power transmission lines, but success in this application had led to their use for the protection at much lower voltages, of the highly inductive coils found in electrical machinery, contactors, clutches, brakes, relays, etc. An important advantage arising from the limitation of the peak voltage developed when such coils are disconnected from the supply is the reduction of the sparking at opening contacts, and of the radio interference) to which such sparking gives rise. This method of spark quenching has received particular attention in connexion with telephone relays, where the preservation of contacts is of great importance. Silicon carbide resistors have also found application for the> protection of radio transmitting and receiving circuits and of electrical instruments, and for scale modification in the latter; in metadyne systems, where they permit practically any desired main motor characteristic to be obtained; and in non-linear bridge circuits. The characteristics and limitations of these resistors, and the principles governing their application, are discussed in a recent paper by Messrs. F. Ashworth, W. Needham and R. W. Sillars (J. Inst. Elect. Eng., 93, Part 1, No. 69; Sept. 1946), with which is associated an extensive discussion.

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