This Month's Design Tip: Circuit Protection, an alternative approach

When the output terminals of a DC-DC converter are short circuited, excessive current flows. Such excessive current usually results in overheating, smoke, fire and other potentially serious problems. Critical circuit failure is sure to follow! Traditional short circuit protection circuits have typically consisted of a transistor, Zener diode, and a resistor but Murata's POSISTOR® product offers a simple and more elegant alternative.

When using Murata's POSISTOR®, in short circuit (failure) conditions, its resistance sharply increases thereby decreasing current flow offering protection to the circuit in question. See diagram.

The benefits in POSISTOR® include: single component solution, reduced component costs, reduced production costs, real estate savings, recovers original low resistance once short circuit condition is corrected, fucntions as a "resettable" fuse and is simple to use.