Positive Feedback and Latching

The circuit of Fig. 12.6 illustrates positive feedback, and it can also be used to construct a circuit breaker. The experimenter can use the 5K pot as a rheostat in this hookup, beginning by using the full 5,000 ohms capability (with the arrow 

When the normally open clip lead switch (horizontal in the diagram) is momentarily closed, the relay pulls in (operates), and the relay contacts then start sending current to the coil, so that the coil stays energized even after the horizontal switch opens again. 

The phrase positive feedback means that, when a device like a relay operates, a signal of some sort is sent back to the beginning of its circuit, to continue its operation, or make its operation stronger. Another description of this circuit is latching relay, although that can also mean a strictly mechanical means of keeping the armature down, via a ratchet. 

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