What Are Semiconductor Fuses?

Geisha A. Legazpi

Semiconductor fuses are current protection devices that will disconnect a circuit or device when a predefined current limit is reached. They are a very popular replacement for alternating current (AC) and direct current (DC) fuses in many areas. Any excess currents will cause a semiconductor fuse to open the circuit and prevent circuit damage. Semiconductor fuses are mostly used for semiconductor protection wherein they protect electronic components, such as diodes, transistors, and integrated circuits (ICs).

A semiconductor fuse protects the semiconductor’s circuitry from either short circuiting or overloading.
A semiconductor fuse protects the semiconductor’s circuitry from either short circuiting or overloading.

Early electrical or wire-type fuses used a piece of conductor inside a protective shielding, such as glass or other protective and fire-retardant material. When the fuse rating was exceeded, the fuse conductor vaporized and cut power from the protective circuit, and the fuse was replaced. This mechanism is still being used for non-critical applications.

Circuit breakers are electromagnetic and resettable AC and DC protection devices. A 30-ampere (A) circuit breaker may be designed to trip or break the circuit at more than 30 A. In most cases, a circuit breaker may be reset by flipping the rocker switch to the “on” position again. If an attempt is made to reset a circuit breaker that still has a current overload, the circuit will not energize. This makes the circuit breaker very popular for all locations, including homes.

Semiconductor fuses are smaller than glass fuses, which have a glass tube with connecting covers at each end. A glass tube is about an inch (2.54 cm) long with a visible fuse material that makes it simple to inspect if a glass fuse is still going to work. The conducting material on a glass fuse may be thinner than a strand of human hair. Like glass fuses, semiconductor fuses may be mounted on printed circuit boards (PCBs), or they may be inside special fuse holders. Semiconductor fuses could be less than five times the equivalent glass fuse.

In general, semiconductor fuses have advantages over wire-type fuses and circuit breakers because the fast response time saves electronic and electrical equipment from damage. Older fuses are also rated based on response times. Fast-blow fuses quickly open when the current limits are reached, while slow-blow fuses are used to tolerate momentary overcurrents, such as during motor start-ups and cold starts of electronic equipment. Starting an electric motor involves transient start-up currents that may be about 30% more than steady running current, and the electrical resistance of most devices falls with drops in temperature. Depending on local climate, some electronic devices have a defined pre-start pre-heat sequence to manage the potential overcurrents on start-up.

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