Powering a RAMPS set up from a 19V supply

Background
I have a RepRapPro Huxley which is powered by a 19V laptop type power supply rated at 6A. The electronics is currently a MELZI board which controls the RepRapPro PCB heatbed via one of the MELZI expansion pins. The MELZI is also driving a cooling fan.
What I want to do
I would like to keep the cooling fan and heated bed and add an LCD panel plus controller - but do not have enough spare I/O lines available on my current electronics.
Solution
Got to be RAMPS as this will provide the additional control lines.
The Problem with this idea
The power supply. I don't want to replace the laptop brick PSU as to do so and go to a 12V supply would reduce the power available to the heat bed currently running from 19V. However, if I plug in 19V to the RAMPS, I am going to run the risk of blowing my Arduino Mega board - and I don't want to do that. :-)
How does this sound?
Remove the D1 component on the RAMPS board and replace it with a 7812 regulator: connecting its input pin to where the diode anode used to go, its output to where the diode cathode was and its ground pin to a convenient place on the circuit board.
Question
Does the above sound practical, reasonable and the best way of solving the problem? Not sure of how I would physically locate the 7812 but I don't think I would need to bother with a heatsink for it given that it is only being used to provide power for the Arduino - not the steppers, heat bed or hot end.

Thank you,
Alan

As long as the PSU is up to it, the idea should work.

Are you sure that 19V @ 6.5A is enough to run everything (particularly with a heatbed?).

Cefiar Wrote:
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> As long as the PSU is up to it, the idea should
> work.
>
> Are you sure that 19V @ 6.5A is enough to run
> everything (particularly with a heatbed?).

Yes - It does seem relatively low I agree but it has been running without any problems for almost a year now. The power supply came with the kit of parts from RepRapPro and has an output current rating of 6.32A at 19V. The heater resistor will take a large chunk of that when cold - 6R8 will draw almost 3A on its own. However, the bed size is only 140mm square and although I don't know how much current this draws, it works! (Struggles a bit to go much beyond 100C without covering it over during warm up).

Thanks for the reply,
Alan