ive seen some already made voltage refulators with pots for ajusting but they are limited to 1.5 - 3 amps with a heat sink so it says so i have some lm317 regulator transistor type things with 3 legs and you put a pot between 2 of the legs to ajust the vlotage going therw i would like to make one that can do the amprage ajustment to but for now i was wondering if you can piggy back the chips so they will handle more then just 3 amps so pearlle <(miss spelled im sure) the the legs to ecother and still have it ajust or is this going to cuase some resistance be tween them and the pot and things start to smoke ? also has and one used one of these chips with a transistor in stead of a pot and done the simple pwm from the arduino to the transistor to be able to program a vlotage level on the arduino to manage the lm 317 ? thanks for chcking this out !
It is not a good idea to run the adjustable LM317 in parallel mode for more current capacity. The best way to get more current is to 1) read the datasheet http://www.ti.com/lit/ds/symlink/lm317-n.pdf 2) follow one of the datasheet examples for more current capacity using an external power transistor. (such as: 5A Constant Voltage/Constant Current Regulator)
I have driven the LM317 with a PWM signal (using a LED coupled with an LDR in the ADJUST path to ground). It works. It's not "wonderful" and suffered from slow response (hysterisis) due to the behavior of the LDR. There are other ways (using an op amp) but my method was tried to have ISOLATION from the controlled supply.
good to know thank you for you in put ...
You should probably be looking at a switching design. A linear regulator (like the LM317) is easy to use, but it has to dissipate the "extra" power in the form of heat.
If you put 10V into a 5V linear regulator, the voltage is divided so both regulator & load both see 5V. And and since they they both pass the same current, the regulator and the load dissipate the same power. (Half the total power is wasted as heat in the regulator.) If you put more than 10V into that regulator, the regulator is wasting more power than is going to the load.
With a switching regulator, the "device" switches on & off (very-much like the Arduino's PWM outputs) so it doesn't "see" voltage and current at the same time and it dissipates (relatively) very little power/heat.
If you increase the voltage into a switching regulator, the current into the regulator will decrease although the current into the load remains constant. Since switching regulators are around 90% effecient, you typically get more current out of the regulator than you put in! (Less voltage, of course.)