[sdiy] switching dc power sources

[Richie Burnett]

>> Then I thought: Screw it, I'll just take a ordinary adjustable 3
>> terminal LDO and switch one of the voltage defining resistors. That does
>> not work either because LDOs can only source current, not sink any. If I
>> switch from 3V to 1.8V the output voltage will just stay high until I've
>> consumed enough energy to drop it down.

Fit a bleeder resistor?  It will waste some power, but it's value could be 
quite large since you said that the voltage is permitted to take 250ms to 
settle.