Automatic control starts loads softly

The components connected to 555 timer IC1’s pin 2 provide a trigger synchronized with the ac input’s zero crossing. In conventional 555 fashion, R1, R2, and Cdetermine IC1’s period. However, the RC delay network connected between IC1’s pins 1 and 5 causes IC1’s period to approach its full value only gradually, rather than instantly at power-on. Select a resistor-capacitor combination that suits your load. …

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http://www.edn.com/archives/1994/101394/21di7.htm

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