The design of a family of high-current switches with over-current and over-temperature protection

This paper describes the design and manufacture of a family of five high-current, high-voltage dc switches with over-current and over-temperature protection. The capacity of the switches ranged from 5 A, 163 V to 100 A, 400 V. Steps were taken to achieve stability in over-current and over-temperature trip thresholds with changes in supply voltage and ambient temperature. A small physical size was achieved, and the design of a ceramic and Kovar package is described. Difficulties arose in measuring circuit parameters while testing performance due to induced magnetic and electric noise, and solutions to these difficulties are discussed. In addition, difficulties achieving some of the design goals and subsequent solutions are described. Thick-film hybrid circuit processing was the chosen technology for circuit fabrication. Thermal management was a major area of design emphasis, and the use of aluminum nitride substrates in some of the networks offered a solution in maintaining output FET junction temperatures at a safe level. Suggestions for improvements are offered. It is clear that switching of many tens of kilowatts of power at high voltages with over-temperature and over-current protection is obtainable in a small package at a reasonable cost.