dplatt@coherent.com (Dave Platt) (10/20/88)
In the 10/13/88 issue of Electronic Design, there's an article
concerning power drivers (electronic switches capable of handling
high-current loads such as motors, etc.). On page 59:
"Because of the problem of electrochemical corrosion (rust), most
switches in automotive applications must be connected between the
load and the positive power source despite the difficulty of driving
high-side switches. Corrosion is accelerated when an electrical
component is at a high potential when it's not powered.
Consequently, the component must be kept at the lowest possible
potential when it's off."
It seems that car-makers who want to use "smart power" circuitry (in
which the switching is performed via low-level logic signals that drive
power MOSFETs) have a difficult choice to make. If they place the
switches between the load and ground, the load device will "float" at
the battery's voltage when not in use, and may be subject to corrosive
effects due to leakage currents. If they place the switches between
the load and the battery, then the load will float at ground potential
when not in use, and won't suffer from corrosion... but the circuitry
needed to build a "high side" switch is substantially more expensive
and complex than a "low side" switch.
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