well i was thinking of useing one of my 2 options to get power from 1 a hp printer transformer with a 32v leg at 4 amps...and the second leg 15v with 8amps option 2 is a computer power supply with the standard 5 and 12 volt out puts its a smaller compact model but the amps are like around 18 6 and .4 and some of my stuff i would like to control these legs better then the giant steps. in current and volts
When dealing with adjustable linear regulators, certainly at the 3 amp output and greater the limit is going to be how large a voltage range you wish, as the lower the output voltage selected with a fixed DC voltage input feeding the regulator the higher the heat dissapation will be for the chip and will most likely be hitting automatic temperature shutdown well before you hit the devices maximum output current rating. So after you design in the needed heat management cost, size, noise, etc, you will wish you had started with using a switching regulator to begin with.
So state your total voltage range desire, and maximum current output desired. The highest output voltage sets the required filted DC input value needed for the circuit and the minimum output voltage running a maxium output current rating will determine the heat load.
Bottom line, don't use a linear regulator, buy an Asian adjustable Switching regulator and build a power supply around it, they are cheap and work great.
Lefty
@retrolefty thank you that is a better idea i guess so do you know if this creates any heat or just less loss ?
and @johnwasser and DVDdoug thanks for the info i may change my direction to this no linear regulator then i just have make it adjustable and building the supply around some already made circuits sounds fun enough to get the project going ...