Circuit guards amplifier outputs against overvoltage

To protect audio amplifiers and other automotive electronic circuits in the event of an accidental direct connection to the car battery voltage, add the circuitry shown in this application note (a shunt regulator, diodes, and an n-channel MOSFET in series with each audio path).

A universal requirement for automotive electronics is that any device with direct connections to the wiring harness must be able to withstand shorts to the battery voltage. Though brutal, this requirement is necessary for reliability and for safety. One example of the need for this protection is the audio amplifier that produces indicator noises in the automotive interior. Though operating from a lower voltage (3.3V or 5V), it must be able to stand off the full battery voltage. A protection network appropriate for these amplifiers can be used for other automotive circuits as well.

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