Latch-up describes the process of moving a component or product by means of an electrical force into a state, that it cannot leave without external intervention.
A typical example is the triggering of an SCR (ger.: Thyristor), that is supplied by a voltage exceeding its holding voltage. As long as the externally supplied voltage does not drop below its holding voltage, the SCR remains turned on. As a result of the power being dissipated in this state, often irreversible damage is caused to the SCR.
Latch-up may also occur on functional level of a product. For example, in hysteresis comparators, a controlled latch-up is used to achieve a certain functionality of the given comparator. However, an uncontrolled functional latch-up can often only be resolved by a RESET or a power-supply cycling of the given product.