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how to get a relay switch to latch?
i have overcurrent and thermal protection for my voltage regulator( this is a design project for electrical engineering year 2 ) connected to a relay switch via an OR gate using npn transistors and a 5v relay. but as the current cutoff circuit is based upon a comparator turning on a transistor... as soon as the transistor switches on and the relay trips the current in the circuit drops back down to 0 and the comparator instantaneously turns the transistor off and the n.c relay switch closes once more... i have been told that i can get the relay switch to latch by utilizing a normal push button n.c. switch and a l.e.d to notify me but i do not know how to implement this... any solutions is greatly appreciated.
You could implement the latch at the logic level - a set/reset latch using nand or nor gates, or a D type flip flop etc. A fault sets the latch, which is then used to drive the transistor as now. A push button resets the latch circuit.
Alternately, the relay has a separate contact that is connected in parallel with the driver transistor so it bypasses the transistor, holding the relay in. The release button would be a switch in series with that holding contact or the relay coil.
You could use an SCR instead of the driver transistor, with a pushbutton in series with the relay coil. You need appropriate damping on the relay coil, like a reverse diode or a snubber.
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