5v to 1.25-2v

[stealth17]

I need a linear 5amp design that has ULTRA clean and stable power that is highly adjustable from 1.25-2v. I need the least droopage possible.

Ive got a design for 5v to 2.5-4.1v now. Its a switching design. I also need this 1.25-2v design though.

If someone could help me that woudl be SUPERB!

Ive attached a schematic of the switching design and the parts are quoted below. If you all see a mistake or see somewhere that needs improving, please tell me.

Thanks!!!
-Jordan

T = STP55NF03L
IC = TL431
C1, C3 = 3300uF/6.3V low-ESR
C2 = 100-470uF/16V low-ESR
R1 = 390ohm
R2 = 1.5Kohm
P = 1Kohm multiturn

[Ante]

Hi Jordan,

Why do you call the attached design “switching”?

[stealth17]

Hi Jordan,

Why do you call the attached design “switching”?

I thought it was becuase of the switching mosfet 

Told you Im a noob lol.

Now that you mention that, your right, its definatly linear. The guy said the mosfet gets very hot, and there arent any op amps. Do you think thats a good circuit for like 15amps of clean, stable power? Or, should I add a couple more caps and an inductor?

[Alun]

Just because it uses a MOSFET it doesn't make it a switching regulator, MOSFETs can be used in thier linear region too you know, in fact all transistors can, well apart from the unijunction but it's not a proper transistor anyway.

The MOSFET needs to be a low threashold type otherwise it will never turn on enough to provide the current you require.

[Ante]

Hi Jordan,

Anyway, you can change this circuit from the 2.5 – 4.1V range to 1.25 – 2V if you like but it will get even warmer than before! If you parallel some MOSFETs and put them on a big heatsink with a fan you just might get away with it! If the computer in question is equipped with water cooling you can use a smaller heatsink with a channel and run the water through it, this will save some space and secure the cooling of the MOSFETs.

[stealth17]

lol there isnt an easy way to do it without needing big heatsinks and stuff?

[Alun]

Yes there is a way to convert 5V to 1.25-2V without a fat heatsink, a switching regulator will do this but in your first post you stated that you need a stable and clean supply, however a switching regulator will not provide this as the output will be very noisy.

[stealth17]

what kind of circuit did this guy use?

http://www.xtremesystems.org/forums/showthread.php?t=73043

he had 2mv droop is all too

[Ante]

Hi Jordan,

A clean supply is not the same as a stable supply! Remember; all PSUs for computers are switchers and there are no problems getting a stable voltage from a switcher! I don’t think your computer will be disturbed by noise from a switching supply since every computer runs from one. The efficiency for a switcher might be as good as 90% or more but a linear supply can be as low as 15 – 20% depending on the difference between the input and the output voltage and the current needed. The rest will be heat whether you like it or not!