LM7812 power regulator 28v to 12 dc-dc converter wrong output
I don't know how you burned the 7812; it has both short-circuit and thermal overload protection.  

Anyway, you have 16 V input-output difference, and that's a lot. A 60 mA load will already cause 1 W dissipation. I would suggest to place a power resistor in series with the 28 V to decrease the 7812's voltage drop. You can afford at least 10 V across the resistor, so if you want 1 A output you need a 10 &Omega;/ 10 W resistor. The 7812 still will dissipate 6 W then, so will need a considerable heatsink.