Need a 5amp 1.25v-2.25v switching schematic

[stealth17]

Needs to be like the attached image. I need as clean and stable power as possible.

Ive searched the net for a long time for this and just really need help.

Thank you VERY much.

View attachment 37775

 

[audioguru2]

Hi Stealth,
Is your voltage reference clean and stable?
How much current can it provide?

A voltage divider can be made with two equal resistors from the reference. An opamp follower can buffer the half-reference voltage and have a power darlington transistor inside its negative feedback loop which provides the 5A output.
Power darlington transistors are much slower than opamps and therefore the circuit will need a capacitor for frequency compensation to avoid oscillation.

 

[stealth17]

Well I talked to the guy that made the DDR circuit and got this response:

Yeah the MOSFET can sustain 55A in certain conditions of temperature/heat disipation and continuous signal, but i wouldn't get that close to the limit in this application. Anyway, it's current handling capabilities are exceeeding by a large margin the necessary in this situation, and you should be more concerned by the limitations imposed by the wires and connectors (and even the PSU's 5V rail) rather than the transistor.
Referring to the idea you've proposed, first of all you'll need two power transistors, one for sourcing and one for sinking, with separate buffer circuits for each. The other problem is that a Darlington setup means a base-emitter voltage drop of at least 1.2V, wich is simply unacceptable cosidering your output voltage must have a minimum of 1.25V. You must use MOSFET transistors wich don't have such limitations, but a problem with the control circuit appears, as these need a high gate voltage to completely open.

I was thinking I could just make a whole new circuit that was adjusted by a pot so I can run it at any voltage I want. Then I dont have to go exactly half, maybe even run it a bit more than half...

Thanks!