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Last Updated on: Thursday, November 30, 2017 07:42 AM

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12v 24v AC and DC Day/Night Switch

 A Discover Circuits visitor contacted me a while back.  He needed a day/night switch which would work over a 12v to 24v range from both AC and DC sources.  He liked the idea of a solid state switching circuit instead of the usual relay.  He needed a switch which could handle up to 5 Amps of current.  I scratched my head a while and came up with the circuit below.

 The circuit uses a bridge rectifier circuit to convert AC into DC.  A 12v zener diode limits the operating voltage of the circuit to 12v.  A tiny Schmitt trigger inverter and a phototransistor detects the ambient light intensity.  If there is sufficient light, the inverter disables a push-pull oscillator circuit.  The oscillator, with a differential output, drives a charge pump circuit which when activated, provides sufficient gate-source voltage to a pair of n-channel FETs to turn them on fully.  The transistor switch can handle both AC and DC with a current in excess of 5 Amps.

 

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