Reducing 12v DC to 0.5V DC no more than 1A draw

[irving2008]

The problem with just using a resistor divider is that the output volts will vary with input voltage, and the O2 sensor heater voltage may vary from 10v under cranking to 14.4v when charging from the alternator.

I'm guessing this is to simulate a post-CAT sensor when using a straight thru exhaust (obviously for track use only as it wouldn't be road legal :) )

Where does the 1A requirement come from? And how accurate does the 0.5v need to be? And are you sure you want a DC voltage as many O2 sensors actually have a pulse output, the frequency of the pulse representing the O2 level.

Assuming you do want a DC voltage, then the correct way to do this is a resistor, a zener diode and a trim pot (variable resistor). A 560ohm 1/2w resistor from the nominal 12v supply connected to a 1.5v zener diode which is then connected to the ground side. A 500ohm trim pot is then connected across the zener diode and the output voltage taken from the centre of the trim pot and ground. The pot can then be adjusted to give a suitable output between 0 and 1.5v