Foil fuses as opening switches for slow discharge circuits

Metal foil fuses embedded in various materials are widely used as opening switches in fast discharge circuits (approx. 1 (MU)s). Several technologies of current interest require opening switches in circuits which operate on a much longer time scale (approx. 100 (MU)s). We have investigated the behavior of aluminum and copper foil fuses for conduction times of 100 to 200 (MU)s. Reliable current interruption is obtained at the end of melting rather than at the end of vaporization. The ratio of initial to final resistance is 100. In general, the performance of slow fuses can be predicted by simple scaling from fast fuse behavior. For applications where the switching function depends critically on the resistivity versus input energy characteristic, the results presented can be used in the selection of proper fuse size and geometry.