# 4A 16bit? digital power supply

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#### MrDEB

##### Well-Known Member
Got to looking at different bench power supplies and using an LM317 seems the easiest method but only 1 Amp unless you follow the data sheet design.
A simple pot on the adjustment pin is really all that is needed but lets enhance the power supply with a pic and an LCD.
This schematic is my first draft and maybe needs adjustments here and there.
AND yes 4 amps as per data sheet page 17
Reason for this is I purchased two of the tiny power supply modules off of Ebay and one won't change the voltage. Stuck on 10v.
Just need an LM317 to bread board circuit.
Thinking of using all 1/2w resistors??

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#### MikeMl

##### Well-Known Member
You mean 16 steps; not 16 bits, right?

#### MrDEB

##### Well-Known Member
the mosfets are logic level p channel mosfets that are controlled by the pic, thus IMO are not overkill.
I need to adjust the resistor values accordingly but this is a starting point. The 2k pot is for fine adjustment if desired. Thinking of putting a resistor in series with the pot to prevent the LM317 adjustment from going too low.
Plan to use two tactile switches for UP/DOWN to select desired voltage. For accuracy, 1% resistors should be used as well as add more steps.

#### MikeMl

##### Well-Known Member
What is the minimum output voltage (when port value =1111)?
What is the maximum output voltage (when port value=0000)?
Presumably you want 15 equal steps between Vmin and Vmax?

the mosfets are logic level p channel mosfets that are controlled by the pic...
The IRLZ44N you show is an NFET. Since the source will need to be tied to PICground, you should be using NFETs.

To make a true R-2R ladder, the inputs need to be switched from 0V to some other reference Voltage, not just either ground or floating.

I would use a true 8bit Dac driven directly from the PIC port pins, and then buffer that to make a true linearly-variable power supply. The 1.25V offset created in the LM317 is going to be a pain in the backside...

#### MrDEB

##### Well-Known Member
I purchased two of the small modules Jonsea posted and they work but one of them is stuck on 10v. need to disassemble and maybe just on of the tactile switches is stuck.