i donno how your transistor is connected but as you write it outputs the voltage and don wanna use series register , you are having an emmiter follower loaded between gnd and emmiter.

Ve = Vb-0.7

you just have to control the base voltage, you can connect either a voltage devider at base cicuit, or a resistance/zener pair to drop the base voltage. this will reduce your power waste down by factor 1/beta.


abhishek