I have voltage source of 7v 250mA. Question is, when I apply it to regulator do I get 5v and 1.5A on the output of regulator?Or do I need 1.5A for a linear regulator ? How much current would I need to get 1.5A out when using a buck regulator?
Considering Vin=7V and Iin=250 mA and if you are using switching regulator, in that case Pin = 1.75 W ( ~ Vin* Iin), So for Vo=5V and considering 100 % efficiency ( which is not possible practically ), you can get 0.35A at output.
n ( efficiency )= Po/Pin
If 95% efficiency, Po=1.66W and Io=0.33A.
So depending upon efficiency of your regulator, you will get output current capability of your regulator.