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Mains OFF senseing


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I need a circuit that composed from a 220 to say 12 volts transformer then I rectify this to DC and then connectes to some transistor citcuit. this transistor citcuit must sense the existing or not of the 220vAC.
if there is no 220volts the circuit o/p is high and vice versa.
thank you for your help.

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Dear walid

It is a little bit confusing. when there is no Mains power your cicuit will go off.
maybe you use a battery, when there is power, your citcuit wil use the power from 12V rail, and also charges the battery. and when ther is no 220V, your circuit will use the Battery power.

HTH -Shahriar

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That's the whole point, tnk2k was suggesting using a NORMALLY CLOSED RELAY. When the power's on the relay contacts are open as the coil is powered, this disconnects the load (lamp buzzer etc.) from the supply. If the power is interrupted  the contacts will close and connect the load to the capacitor. You'll need to design the circuit carefully though to stop the relay being powered from the capcaitor. ;D

I personally wouldn't use a relay, I'd use a cheaper componant like a comparator or transistors.

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