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HL PS TM 03.02.99
Anps039e.doc Dr. A. Graf
Page 1. H. Estl
HL application note
Dr. Alfons Graf Siemens AG, HL PS TM
Hannes Estl Siemens AG, HL PS TM2
Fuse Function with PROFET Highside Power Switches
Abstract:
The protection functions originally incorporated in smart power switches for self-protection
have become so sophisticated that they are now capable of protecting not only themselves but
also the connected load including leads and plug-in contacts. Although in the past this was
primarily the task of fuses, the reduction in the number of fuses in new vehicle generations
from approx. 80 to the present 40 is evidence of the trend towards replacing fuses by
semiconductors.
This article shows how correct dimensioning and placement of smart power switches not only
enables fuses to be replaced but can also significantly improve protection behavior. In the
case of thermal operation of the protection functions, for example, a similar but in some
applications more favorable behavior can be achieved than with the current vehicle fuse,
whereas active current sensing allows virtually any fuse behavior to be implemented.
We then examine the various influencing factors such as manufacturing variations or
temperature, but also the magnitude of the operating voltage which is important particularly
for the new 42V electrical system. Finally, the unlikely event of destruction of the
semiconductor and the associated failure of the protection function will be analyzed in greater
detail. Correct dimensioning for lamp or motor load switching will be clarified with the aid of
a number of practical examples.
