I am working on a circuit for a home make home security system. I bought the following wall transformer to power my circuit. I was going to use with a 5VDC Linear voltage regulator to get 5 volts for my digital circuitry.
I couldn't find any documentation on this transformer. When I plug it into the wall and measure the voltage at the output I get zero volts. I tried attaching it to a couple different loads (with fairly small resistance) but I still couldn't measure any voltage at the output. I realize this is probably because the transformer is not regulated and thus requires a load for the output to be 12V but I am still not sure if I can use this transformer with my design. Does this thing only output 12VDC if it has the exact right load? Or since I will be connecting this to a linear voltage regulator will that handle it all for me? The total current draw of my circuit will typically be less than 200mA unless the alarm is sounding, and then it will go up some.
Also, I was planning on using the 12V from the transformer to power the horn(siren) directly and switch it on with a power Mosfet. The 12 Volts will not be regulated so do I need to add a big resistor in series with the horn so that it will have the proper 12 Volts across it?
I guess I should have just spent a little more and got a regulated supply!