Smart fuse reduces cost, weight of automotive wiring harness

September 13, 2017 // By Martin Jaiser, Manfred Brandl, ams
The steady growth in the number of electronic, electrical and electro-mechanical functions in cars has given rise to many innovations in the design and operation of automotive power systems. In one domain, however, the car remains stuck in a technological Stone Age: the device of choice for circuit protection is still the fusible cut-out (fuse). Besides of being a very cheap component, there are numerous and serious drawbacks in using simple fuses. But there are alternatives.

From a system point of view, however, the implementation of a more intelligent, electronic fuse offers the potential to cut total cost, as well as to reduce the weight of the vehicle substantially. Now ams has introduced a reference design board which shows the industry a design concept for an accurate yet simple intelligent fuse, and which gives OEMs the opportunity to evaluate the concept, understand its advantages and cost, and simulate its operation in complex power systems.

The traditional fuse: slow, inconvenient, cumbersome

Thermal fuses are slow and inconvenient. The typical fuse in a car is blown after around 20-50ms when subject to 10x its nominal current. And because a fuse cuts out when triggered, it has to be replaced after every over-current event. This is why cars include a special housing at a central point, to provide the easiest possible access when a fuse needs to be replaced.

In fact, when today’s cars have so much modern technology inside them, such as touchscreens, voice recognition and sophisticated driver-assistance systems, the antiquated tool and obscure process for replacing a traditional fuse seem out of place.

A modern electronic fuse does away with this ancient technology. Instead, the dashboard can display diagnostic information on the potential location of the fault that caused the fuse to be triggered, and guidance on the way to repair it.

In addition, an electronic fuse is as much as four orders of magnitude faster, dramatically shortening the exposure of the circuit it protects to damaging current surges. It can also provide a much more precise maximum-current trigger point. This gives the potential to reduce cable diameter when compared to thermal fuse protection, which requires the designer to allow for a broadly defined maximum current range, rather than a specific – and lower – current value.

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