Electronic device disconnect circuit

摘要

An electronic disconnect circuit protects an electronic device, such as a radio, installed in a motor vehicle from overvoltage condition in which the normal internal protection is inadequate. A normally closed relay includes 2 sets of terminals connected in the ground conductor and in the voltage conductor of the power cable connected to the electronic device. The relay coil is connected through a diode which becomes conductive if the voltage in the ground conductor rises above the voltage in the other conductor, thus protecting the radio or similar electronic device from a reversal of polarity as would occur when a battery charger or similar device is improperly connected to the vehicle. A switching transistor responds to an over voltage condition to turn on the relay coil when an over voltage condition occurs, such as during a high voltage jump start or a high voltage transient condition.