Push ON, Push OFF for AC voltages
Stephen Woodward’s DI, “Flip ON Flop OFF” does a wonderful job for DC voltages. I thought of extending this idea to much-needed AC voltages, as all our gadgets work with AC voltages.
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Figure 1 shows the compact circuitry using a simple counter IC. This circuit utilizes a single push-button (PB) to switch between ON and OFF states for AC voltages. When you push PB once, the output terminal J2 gets 230V/110V AC. For the next push, output at J2 becomes zero. This action continues for subsequent pushes. Accordingly, the gadget connected to J2 will be ON or OFF.
Figure 1 Pushbutton circuit that switches on ON and OFF for AC voltages using electromechanical relay (RL1).
In Figure 1’s circuit, when PB is momentarily pushed once, U1’s(counter 4024) Q1 goes HIGH, counting one input pulse, which makes the Darlington pair Q1 and Q2 conduct. Relay RL1 gets energized. Its NO contact closes and passes 230V/110V AC connected to J1 to J2. The gadget connected to J2 turns ON.
When you push PB again, the second pulse is generated and counted by U1. It’s Q1 (LSB of counter) becomes LOW, making Q1 and Q2 OFF. The relay gets de-energized, and the AC voltage to J2 gets disconnected, making the gadget turn off. R2 and C2 are for the power-on reset of U1.
If you prefer not to use an electromechanical relay, a solid-state relay can be used, as shown in Figure 2. In this circuit, when you push PB once, the Q1, Q2 pair starts conducting, current flows through the LED of U3, an optically coupled TRIAC, causing it to conduct. Due to this, U4 TRIAC conducts, passing 230V/110V to J2. When you push PB again, the Q1, Q2 pair opens, stopping current flow through the LED of U3. The TRIACs of U3 and U4 stop conducting, disconnecting power to J2.
Figure 2 Circuit switches AC power on and off for output-connected gadgets using a solid-state relay formed by U3 and U4.
Jayapal Ramalingam has over three decades of experience in designing electronics systems for power & process industries and is presently a freelance automation consultant.
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