New Power Key to raspberry PI 

This new version has a tip120 to driver the output power, the tip127, but the great change in this version is the step Down I designed 2 schematics one using a stepDOWN converter  in the circuit input and another one in the circuit output, the differences betwen them is that you can change the tip127 to another smaller transistor because the current in the input of the converter will be smaller, I left the tip127 in both design but this is not mandatory.

As raspberry PI needs 5v with 3amp we have 15w in the output of the stepdown so in the input we will need only 1,25amp this permits we use a smaller transistor to substute tip127, or if you continue using tip127 you can use it without heatsink.

 

Fig.01