Automotive Semiconductors and Functional Safety
Which correctly describes "load dump," a problem in automotive power supplies?
- AA phenomenon in which a large current flows into the starter motor at engine start, causing the battery voltage to drop sharply
- BA phenomenon in which the battery is disconnected while the alternator (generator) is charging, producing a large surge voltage on the supply line
- CA phenomenon in which lightning strikes the vehicle body and a large current flows into the supply line, destroying components
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Answer: B. A phenomenon in which the battery is disconnected while the alternator (generator) is charging, producing a large surge voltage on the supply line
Load dump is a phenomenon in which the battery is disconnected, for example by a terminal coming loose, while the generator is charging at high current, and the energy with nowhere to go makes the supply line voltage spike. Even in a 12 V system, without suppression circuitry it can reach roughly several tens of V to about 100 V and last for tens to hundreds of ms. For this reason, many ICs connected directly to the battery have a voltage rating of about 40 V or more, and they are protected with TVS diodes and similar devices. The voltage drop at engine start is a different phenomenon called cranking.
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