I have 12v DC and want to lower this to between 4-5v DC 3A (pulsed < 3ms with a 20% duty cycle) with as small a footprint as possible, I have always used linear or switch mode regulators before but ideally want it smaller than these packages.
I looked at a zener but one that is 15w is huge, any other way of doing this?
The load is resistive, a digital circuit MCU etc, as for vsag I suspect 2v max, it will be the MCU that dictates this and I have not selected this as yet. looking at a Attiny13 it's voltage range is 1.8-5v
If you are switching the MCU's Vdd supply on-off, you will have to be careful with supply bypassing. If the bypass caps are large, then the surge current to charge them at the beginning of each pulse will be huge. Is that where the 3A requirement comes from? Surely the MCU will not require 3A?
Why turn off the power supply to the MCU at all? Just put it in a sleep state.