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Following circuit is a 220V touch switch from this website:

http://8085projects.info/m668-based-touch-sensitive-step-dimmer-circuit.html

I'm wondering how it works because the IC take its working voltage from + and - of diode bridge but when the thyristor switching the Load, voltage through the diode bridge become about 0.9V only and this voltage is lower than standard voltage to running the IC

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There are also another circuit by same concept and this time from this website:

https://www.homemade-circuits.com/220v-touch-lamp-circuit-with-delay-timer/

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So my question is:

1-Dose this method works?

2-If those circuits not correct so how motion switch with only 2 wires which available in the markets works?

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If you were able to safely monitor the signal on the lamp you would find a classic phase-controlled AC waveform.

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Figure 1. Triac control of AC power.

A dimmer will delay the power-on to achieve the required output power.

Any 2-wire electronic switch has two options for its self-power:

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  • If the turn-on of the thyristor (1) is delayed a few degrees after zero-cross then the voltage drop across the switch can be used to charge a capacitor - C1 (2). The chip is probably monitoring the zero-cross on pin 5 (3) and a time delay set by one of the other capacitors will initiate the thyristor trigger.
  • Another method would be to switch the output off for a full cycle and use the voltage drop to charge the capacitor. This has the major disadvantage that the flicker would be noticable.
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