My Rf reciever circuit on battery ,but not with a rectified xformer output as source


I just made a Rf circuit that turns on and off a relay depending on the transmitter's message

The circuit is working fine when i connect it to a 9v battery. But i cant get the circuit to work with 12v transformer with rectifiers and everything. I even tried a 6v adapter but it doesnt work.

The circuit components have a working range of 5v to 12v

What might be wrong? Anything like their is trace of ac ac or anything?

The circuit is consist of an rf transmitter and Ht12d decoder ic. The valid transmission pin of the ic is connected to bc547 transistor which powers a 5v relay. Everything works fine when a 9v battery is used
But when i use a 12v xformer as source it doesnt work.the way iam using xformer is xformer-bridge rectifier-capacitor

Then i tried adding a regulator ic 7805. It still doesnt work.

Best Answer

The circuit components have a working range of 5v to 12v

The output of a 12 volt transformer when fed through a bridge rectifier and smoothing capacitor will be: -

\$12 volts\times\sqrt2-1.4 volts\$ (diode drops in bridge) = 15.6 volts.

Maybe you have damaged your components. Maybe if you'd used the 7805 initially all might be well. However, if you are feeding the relay circuit also from 5 volts then maybe the relay won't operate properly because it might be a 12 volt version.

If you are lucky and haven't damaged the parts then use a 7812 regulator.