Replacing a relay with transistors in this step down circuit
Try this:







simulate this circuit &ndash; Schematic created using CircuitLab

It's a simple voltage-follower circuit. The base of Q1 is held at 5.6V by D1, and the emitter is about 0.65V lower, or very close to 5.0V.

It'll deliver almost 2A at 5V, assuming you put a heatsink on Q1 that can handle the 15W of heat produced.