This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance; and it doesn`t generate very much heat.The circuit draws about 30ma AC. Always use a fuse and/or a fusible resistor to be on the safe side. The values given are only a guide. There should be more than enough power available for timers, light operated switches, temperature controllers etc, provided that you use an optical isolator as your circuit`s output device.
If a relay is unavoidable, use one with a mains voltage coil and switch the coil using the optical isolator.C1 should be of the `suppressor type`; made to be connected directly across the incoming Mains Supply. They are generally covered with th