5V for Picstep getting very hot !

[max_imum2000]

hello all
i just finished a picstep board
the board is running fine,
i connected it outside the pc so i attached a 7805 regulator. no caps or anything ,
now the 7805 is getting very hot with just 24volt input, i intend to use it up to 40volts so i guess it will even get hotter.

is there anything i can do to cool down this situation (heat sink would help as i already attached one).

maybe a current limiting resistor ? any value suggestion ?

thanks

[dtman2]

The best solution is not to run from the motor supply. Find an old 12V adapter and run from that. If the board were to draw 100mA (I'm not sure what it actually draws, probably less than that) then the regulator needs to dissipate 3.5W or so at 40V drive. That is way too much. If you put in an external resistor, you just move the problem to another component - there is still 3.5 W that needs to go somewhere.