I have a small transformer. I want to connect it to mains in the US and take the other side, 12V, and use it at up to 500mA. Since my current is staying around half an amp, is it ok for me to use the transformer on regular breadboard?

Thank you

 

What is the transformer input voltage and output current rating?

 

Primary side voltage 115VAC, output current rating 400mA @ 12.6V, so I'll be using it up to around 350mA

 

It is better to have physical isolation in addition to the isolation the coils provide.

Such as a power board with the transformer, fuse, rectifier, and regulator on it (if it is a PCB Mount transformer), then run the low voltage wires to the "working" PCB. The two can be connected by standoffs, or you could super-glue one to the other so there is a 1/2" non-conductive gap between the power board and signal board. The 350 mA will be fine on standard copper traced perfboard/veroboard.

 

If you cannot make printed circuit boards, an alternative would be to use a non-PCB mount transformer, with insulated wire connections connected between the mains input, fuse, and the windings.

It may be acceptable to use a soldered breadboard for the low-voltage parts such as the rectifier onwards, provided that the current is not too big. I would not recommend a solder-less breadboard for any kind of power supply project, as the chances of something coming loose or shorting seem too great.

 

Maybe we do not understand the question. Is the question: "Is it ok to use an AC adapter (wall-wart) to power a circuit on a breadboard?" ?

I would say it is ok to use a 12VAC 400mA adapter. Put the bridge rectifiers, reservoir capacitor and voltage regulator on your board. You will need a heatsink for the regulator. Better still, build the components into a small metal box and put two banana jacks on the front of the box for the regulated DC output, with an LED and current limiting resistor to indicate when it is on. Maybe add a switch to turn off/on the DC voltage.

What DC voltage do you need? If it is 5VDC then I would choose a different transformer that outputs about 9V AC or DC so that you do not have to dissipate so much heat in the regulator. If you are building a standard regulated DC supply you can bolt the 78xx series regulator directly to the metal box to act as the heat sink.