Issue link: https://resources.mouser.com/i/1437723
"Not only is the cost of lost time and repairs unacceptable, but the cost of customer confidence is almost the most important consideration of all. It is difficult to put a price on." Eddie Aho, Power Supply Design Engineer, KissAnalog These surge-suppression technologies are designed to block brief overvoltage power surges. They will not withstand sustained high currents. Under those conditions, the components can fail in ways that damage themselves and the protected circuit. For that reason, surge-suppression technologies are typically used along with other complementary overcurrent protection. For example, a properly rated fuse upstream from overvoltage surge protection will protect both the circuit and the surge suppressor if high current continues after the surge protection has blocked an initial voltage spike. Overcurrent protection technologies often used in conjunction with power surge suppression include the following: • Fuses. Provide slow, moderately accurate overcurrent protection against moderate to high currents. Fuses are self-sacrificial: After they do their job, they must be replaced. • Positive temperature coefficient (PTC) thermistors. PTC thermistors are temperature-dependent resistors whose resistance increases with temperature. If an overcurrent condition occurs that causes the PTC thermistor's temperature to rise, its resistance will increase. The greater its resistance, the hotter it gets, effectively blocking current to the protected circuit. When the PTC thermistor cools, it will reset and conduct once again. PTC thermistors have a slow response time and low current rating, but they are relatively accurate. Under the right conditions, they can be used instead of a fuse. • Electronic current limiters (ECLs). ECLs are self-contained electronic circuits that act as switches to open the series circuit when it detects a current over its maximum operating current. After the surge voltage has been removed, it returns to the low impedance conducting state. Clearly, there are many performance characteristics and technology configurations to consider when designing a surge-protection solution. Making the right choices for application-specific requirements is the essence of the engineering balancing act. 19 Understanding Surge-Suppression Technologies