Digital pot for buck converter

Im trying to build a digital adjustable power supply using an arduino and a dc-dc cc cv buck converter. It uses 2 pots to control voltage and current.

I have every thing i need to moniter the voltage and current with the arduino but i would like to control the current and voltage with the arduino.

I have been searching on google for the last 2 days trying to find a digital pot that would work. The problem is the voltage at the pot is the same as the output voltage. So when outputting 14V the voltage at the pot is 14V. Most digital pots only allow around 5.5V. The ones that dont need a referance voltage of 10V or more.

Does anyone have any idea of a solution?

This one has separate inputs for VDD and VLOGIC -> http://www.mouser.com/Analog-Devices-Inc/Semiconductors/Digital-Potentiometer-ICs/AD5280-Series/_/N-4c498?P=1yxyv5nZ1yyh4l4

Thanks for that link. Unfortunatly the supply voltage max is 16.5V. I would like to go up to 30 if possible. As thats what my buck converter can do.

To start with i will only be powering it off a 19V laptop power supply but plan on building an ac-dc circuit later on with a transformer to get a 30vdc/10A, 12vdc/1A and 5vdc/2A out.

ADI has a few that go up to 33V. Check out the last two pages of this link -> http://www.analog.com/media/en/news-marketing-collateral/product-selection-guide/Choosing_the_Correct_Digipot.pdf

ok, thanks. looks like AD5293 will be my best bet.

i need a 5k and a 50k, but they only do 20k, 50k and 100k. so if i order 2x 50k, and put a 2K7 resistor between both pins A->W and another from B->W that should essentially make it 5K right?

if i understand correctly, i power the logic from 5V same as arduino. i then power it separately with with a voltage up to 33V, (eg from the 19V laptop power brick, and later on the 30V rectified AC) and then use it exactly the same as a standard pot?

Yes, you have the usage correct for that part. A $6 ePot from Mouser: high end stuff!

Do you have a schematic for your DC-DC? You could likely use one 20kΩ instead of playing games to get a 5kΩ.

I did something like this once, using just the 5 v. digital pot which gave me 100 steps between 0 and 5 v. I used a second 100 step D-pot to give an output of 0 - 0.25 v… I fed these into an opamp difference amplifier with a multiplication factor of 6, so I now had a reference voltage from 0 to 30 volts, in 0.025v steps. This output was used as the ground reference to an LM317, so I end up effectively with about 1.5 v. min, up to 30 volts output. This is my primary lab power supply, and has been working flawlessly for about a year.

The beauty of the small step size is that if you draw somewhat more current, and the voltage drops a little, you can auto-adjust it.

unfortunately i do not have the schematic, its a unit i have purchased from ebay

my initial use will be charging up some 12V lead acid car battery's, will also be using it as a lab supply, im still working on the schematic for the rest of it, happy to post it up when done.

i will be adding a relay on the output, temp probe for the battery, and am using a 20A acs712 current sensor for checking the current, a voltage divider before and after the output relay to check both the output of the converter and the charge of the battery. so i can program it to disconnect say every 30mins rest for a minute then check battery charge.

i went for the 1024 position one due to wanting to have as precise control as possible (and it was only like $1.50 AUD more then the 256), have a few rc car batts laying around i want to charge as well. not paying for one of those ridiculously expensive chargers for something i rarely use, same as the car battery.