I a working on a circuit that has components that need 3.3V and 5V. My power input is 12VDC and can not be changed. The 3.3V components use about 510mA of current and the 5V components use about 155mA. My first attempt at a circuit used two linear voltage regulators in SOT-223 packages. The 5V reg use 12V as it's input voltage and the 3.3V reg used 5V as it's input. Of course the 5V regulator get's extremly hot and then shuts off (luckily it has thermal protection!)
I have read some other posts on this forum about how to dissipate the heat with the PCB traces and also to do it using the case (which is a possibility in my case), however it would be much preferable for this design for the enclosure to not get warm. People using it may complain. So I am considering using a switching-mode voltage regulator like this AD1509. My concern is with the noise. My board has a WiFi module on it and I am wondering if the performance will be affected by the switching noise. The AD1509 switches at 150kHz and I think WiFi is in the 2.5GHz range so I should be okay right?
Also, do you think the switching voltage regulator will also get hot or if I just a big copper pad under it will it be okay?