I’m an electronics newbie. I did a very simple project. In order to convert 12v dc to 6v dc I used one of those step down converters. Unfortunately what I’m trying to power is an AM radio. It power on without a problem but is completely unusable because of the EMI - RFI. Take in consideration that I usually run it using its ac power adapter (without any EMI – RFI). My question is: is there is a way to convert 12v dc to (smooth as if coming from a battery) 6v dc? The solution must be able to supply 0.4 amps (6v). Thank you very much.
The easiest way is to use a series pass regulator, like a 7806, to drop the 12V down to 6.
You'll waste about P = (Vin-Vout) x Iout = (12V - 6V) x 0.4A = 2.4 watts, so you'll need a heat sink on the regulator.
If you don't mind wasting a considerable amount of power, 2 resistors will do it.
12v -- resistor -- load -- resistor -- ground