Smart fuse reduces cost, weight of automotive wiring harness: Page 3 of 6

September 14, 2017 //By Martin Jaiser, Manfred Brandl, ams
Smart fuse reduces cost, weight of automotive wiring harness
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.

But an intelligent fuse can provide even more benefits:

  • it can measure the temperature locally
  • it can enable intelligent power switching

This latter feature lets the system designer reduce even further the weight of copper in multi-function supply cables. Take the example of a front door. This has multiple electrical functions, including:

  • mirror positioning
  • mirror opening and closing
  • mirror heating
  • indicator lighting
  • electric window motor

All of these functions could operate simultaneously; in this case, the door’s power circuit would need to support a high peak load current, and this would call for a cable with a large diameter. The alternative is – at the cost of slightly compromising the user’s convenience – to disable certain functions by default. For example, the mirror heater may be disabled while the window motor is in operation. It might in fact only be necessary to stop the current to the heater for a few milliseconds, when the motor current spikes as it starts up. So the blocking of certain functions might either be minimal or, if prolonged, the user may be informed in the dashboard display.

In either case, precise and continuous current measurement, which is performed by default by an intelligent fuse, ensures that the current flowing through every single electrical sub-system is known, and so the power consumption and peak current requirement may both be managed in an intelligent and granular way. This will, of course, require the development of new and complex software.

Intelligent automotive fuses: a demonstration circuit

Now ams has developed a demonstration board which contains all the functional blocks required to realise an intelligent fuse (see Figure 1). In evaluating the circuit, automotive manufacturers are expected to assess:

  • whether the accuracy and precision of the current and temperature measurements are at the right level
  • whether the circuit offers the right number of channels

The feedback from manufacturers will influence the final specification of a chip-scale version of this demonstration circuit, now in development at ams.

The new fuse consists of a switching element and a current measurement element.

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