Noise attenuating circuit for mechanical relay including optical isolation

An electrical noise attenuating circuit, disposed to connect to a normally-open electro-mechanical relay having mechanical relay contacts and a relay coil, the relay contacts being electrically connected to an AC input terminal by a relay input lead and to an AC output terminal by a relay output lead, the relay coil being electrically connected to a DC input terminal by a coil input lead and to a common ground by a coil ground lead, said noise attenuating circuit comprising:

• at least two field effect transistors having gates, connected together in series and disposed to be inserted into the relay output lead between the relay contacts and the AC output terminal;
• rectifying means for producing a rectified voltage-stabilized direct current, disposed to be electrically connected between the relay input lead and the common ground;
• coupling means for providing electrically isolated coupling to the relay coil circuit, including a light-emitting diode and a photo-transistor, said photo-transistor being electrically connected by a first lead to the rectified direct current output of said rectifying means;
• current delay means for delaying the rise of current in said light-emitting diode, electrically connected to said light-emitting diode and disposed to connect to the coil input lead and to the coil ground lead;
• and
• voltage delay means for delaying the rise of voltage applied to the gates of said field-effect transistors, electrically connecting with said field-effect transistors and with a second lead of said phototransistor and with a floating ground of said rectifying means.