By its very nature, a surge stopper protects the downstream electronics from load dump as well as the other conditions in ISO 16750-2 and ISO 7637-2 without relying on the internal resistance of the alternator. The surge stopper solution shown in Figure 8 provides uninterrupted power while operating from a clamped alternator. Furthermore, if it is subjected to load dump from an unclamped alternator, it will not be damaged. In the unclamped scenario, it may shut off to protect itself and then automatically reapply power to the load after a cool-down period. It is important to note that power is only shut off in the presence of multiple simultaneous faults: an improper unclamped alternator is installed and the battery connection is lost during charging.
Operation of the Surge Stopper Protection Solution
The design in Figure 8 protects downstream electronics from ISO 16750-2 and ISO 7637-2 transients while providing up to 4A of output current. At the same time, it protects the upstream system from overcurrent events caused by conditions such as short-circuit faults in the downstream electronics. As it does this, it consumes a miserly 35µA of quiescent current, an important consideration in modern automobiles featuring countless battery-draining loads while the vehicle is not running.