SOLID_STATE_LATCHING_RELAY_CIRCUIT

Published:2009/7/17 4:07:00 Author:Jessie | From:SeekIC

A multitude of simple circuits perform switch debouncing because there are many ways to implement a toggling latch. The circuit illustrated here merges these functions into one topology, is extremely tolerant of power-supply variation (it works fine over more than a 3:1 range of supply voltage), and, most importantly, is unusual. The IC used in this case is the 4053B triple CMOS SPDT switch. Section B acts as a bistable latch and stores the current ON/OFF state of the relay. The 2.2-kΩ resistor between pins 1 (the ON terminal of the switch) and 10 (the control input) provides positive feedback that sustains the switch in whichever state it finds itself. Thus, if the latch is ON, pin 1 will be switched to pin 15 and, thereby, the positive rail. This will reinforce the positive state of pin 10 and the ON state of the switch. If, on the other hand, the latch is OFF, then the connection of pin 1 to pin 15 will be broken and the 10-kΩ pull-down resistor will drag pin 1 to ground. This will pull pin 10 low, in turn, holding the latch in the OFF state. Meanwhile, pin 2 will output the logic inverse of the signal appearing in pin 1. This signal communicates to pin 3 and, if the control push button is open, will connect to pin 4 and charge the capacitor to a state opposite that of the latch. There matters will rest until someone presses the button. This will connect the capacitor to pin 10 and toggle the Latch state. 4053B section A serves as an output buffer and has an output impedance of about 200 Ω when run with a 5-V supply and 100 Ω when run with a 12-V supply. If this is insufficient for the application, a transistor emitter-follower, like that illustrated, will boost output capability to beyond 0.1 A.



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