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Turning on and off an AC Lamp With a Reed Switch (MIN079E)

The circuit shown in Figure 1 drives an incandescent lamp when plugged into the AC power supply line.


Figure 1 – The circuit
Figure 1 – The circuit


The builder must take care with this circuit because it is powered by the AC power line. The circuit must be inserted in a plastic or wooden box to avoid the possibility of causing shock. Remember that the sensor is also connected to the power supply line and therefore needs to be completely protected from accidental contact with the terminals. The circuit is very simple and can be mounted using a terminal strip, as shown by Figure 2.


Figure 2 – Mounting using a terminal strip
Figure 2 – Mounting using a terminal strip


This circuit is not self-latching, so when the mag- net is removed the SCR will automatically turn off. The SCR must be installed on a small heatsink, and the lamp should be limited to 300 watts.


SCR - TIC106B, MCR106-4 or equivalent SCR (110 AC power line With suffix D or 6 for the 220/240 AC power line)

D1 - 1N4004 silicon rectifier diode

R1, R2, R3 47 k x 1/8-watt resistors (yellow, violet, orange)

X1 - Reed switch

Terminal strip, wires, heatsink for the SCR, wires, power cord, etc.