Bel Power Solutions: The Future of Fuses

This article by Bel Power Solutions explores how a fuse is traditionally used within an electronic design and how it will need to change in a world of ever-increasing miniaturization. Learn more about the positive temperature coefficient (PTC) fuses offered by Bel and how they will improve the future of fuse design.

A traditional fuse consists of a piece of wire or other conductive link with a known current-carrying capacity placed in series with an electric circuit. The fuse functions solely as a safety device that is designed to melt and permanently interrupt further current flow.  By operating, fuses protect circuits from damage caused by overload or short circuit current, thereby preventing overheating and even fire if a fault condition should occur.

Depending on the circuit being protected, fuses can be rated from a few mA in small consumer electronic products to hundreds of Amps in industrial applications.  Current rating alone is not sufficient to specify a fuse for a particular application; fuses are also rated for voltage, AC and/or DC.  The voltage rating is a maximum and cannot be exceeded.  Once the fuse operates, there is no chance of arcing across the fuse.  Depending on whether the load is resistive or reactive, fuses are available that are designed to blow “fast” in the event of a current overload, or designed to allow a brief overload for a defined short time period before blowing, often called “time delay” or “slow” fuses.  Fuses also need to be selected according to circuit parameters.  Certain semiconductor circuits require a fuse to clear very quickly to avoid possible significant/expensive component damage. Conversely, highly inductive or capacitive circuits such as power supplies may generate brief inrush surges at “power-up”, where the circuit current is well above a fuse’s rating for a very short time. Circuits like this require a “Time Lag” or “Slow Blow” type fuse to allow it to ride out these brief but normal surges without causing what’s known as “nuisance clearing”.  This is also true for motor and transformer in-rush currents.

One thing all fuses have in common is that they are “one-time” devices. When any conventional fuse is forced to clear, installing an exact replacement after repairing the underlying fault is the only way to repower the protected circuit. But as electronic systems continue to shrink and evolve, the single use nature of the fuse has come under increasing pressure.



Apart from USB interfaces, other applications that benefit from PTC protection include:

-- IEEE 1394 Firewire
-- Power over Ethernet (PoE)
-- Lithium Ion Battery Packs
-- Battery Charger Circuits
-- PC Peripherals
-- Disk Drive Interface
-- Transformer
-- Telecom Line Interface
-- Motors
-- Power Supplies
-- Heaters
-- Toys