need some help with a little math

[Silent Soldier]

I'm trying to figure out which resistors I need to get a range of 3.7-6.5v with these chips but I'm not that great with math to begin with and all the numbers and values on spec sheets are information overload for me. Any chance someone with experience can help me out? Heck, the longer I look at this the more confused I get, I'm not even sure now if these chips will work for PV's now.. I dunno, too many numbers, my brain hurts

http://focus.ti.com/lit/ds/slus215b/slus215b.pdf

 

[Hogwart]

Maybe this will help
http://www.e-cigarette-forum.com/fo...ustable-voltage-box-mod.html?highlight=Ucc283

 

[breaktru]

UCC383-ADJ

VOUT=(1.25 V x (R1+R2)) / R1

(1.25v x (200ohms+500ohms)) / 200 = 4.375 volts output

For voltage of 6.25v
(1.25v x (200ohms+800ohms)) / 200 = 6.25 volts output
Not sure if this reg will go over 5v.

Tweak to taste

 

[Silent Soldier]

VOUT=(1.25 V x (R1+R2)) / R1

(1.25v x (200ohms+500ohms)) / 200 = 4.375 volts output

For Max voltage of 6.25v
(1.25v x (200ohms+800ohms)) / 200 = 6.25 volts output

Tweak to taste

Ok now that's a little easier to understand. Ok so If I'm understanding this correctly I would use that formula to set the max voltage and and I'm stuck with the 1.25v as the min output?

 

[breaktru]

Ok now that's a little easier to understand. Ok so If I'm understanding this correctly I would use that formula to set the max voltage and and I'm stuck with the 1.25v as the min output?

I was just to post that exact statement. No matter what you do, the low end will always be 1.25volts
For the high end, you can use many alternative resistors.
Here's another for 6.25volts: R1=5k and R2=20k

for 6.5v, R2 should be 21k which will be hard to find. Keep playing with the values to work it out.

 

[Silent Soldier]

I was just to post that exact statement. No matter what you do, the low end will always be 1.25volts
For the high end, you can use many alternative resistors.
Here's another for 6.25volts: R1=5k and R2=20k

Well crap on a stick.. Do they even make adj regulators with a low out of 3.7'ish? I haven't seen any, I never go below that so being able to drop down to 1.25v seems kinda pointless. Now for my next question, how the heck do you know which pot to use? As I understand it, the wattage rating doesn't matter much since there's not much current going through it, but how do you determine the ohm rating it needs to have?

 

[CapeCAD]

1.25V is the reference voltage measured where R1 and R2 meet, not the output voltage. Your output voltage range can be adjusted between 3.7V and the maximum voltage of the regulator (5V).

R1 at 200 ohm and R2 as a 400 ohm resistor (set minimum voltage of 3.7) in series with a 200 Ohm pot (adjustable to maximum voltage of 5V) would get the range you desire.

 

[breaktru]

DUH... what was I thinking? yes series a fixed with the pot so not to Zero out the resistance.
Thanks Cape, brain fog or senility sinking in.

 

[Silent Soldier]

Bah! Neither Mouser, Jameco, or digi-key have 400ohm resistors I hope 402 ohm will work lol cause thats as close as I can get.

 

[CapeCAD]

Bah! Neither Mouser, Jameco, or digi-key have 400ohm resistors I hope 402 ohm will work lol cause thats as close as I can get.

Yes, close is good enough, they don't have to be exact. You could also use (2) 200Ohm in series if you want to stick with one value.

 

[Silent Soldier]

Thanks alot guy's, this has been very helpful. Now another question (sorry) I'm working on a new mod and the enclosure already has a power button in it but it's a membrane switch so I'm guessing I'm going to need a n-channel mosfet to use it with the 4050 chip?

 

[Silent Soldier]

Ugh, I'm frazzled now. I got my breadboard today and the rest of my parts so I've been playing around with the resistances on this chip and no matter what value the resistors or what combo they are in the potentiometer still adjusts from the chips minimum to maximum voltages. I even tried pulling all the resistors out and only using the pot, same thing. I have no idea whats going on but at least it works... sorta.

 

[breaktru]

S.S. did you forget about my schematic on the 04050?
Also: I would go with a P-Channel

 

[Silent Soldier]

S.S. did you forget about my schematic on the 04050?
Also: I would go with a P-Channel

I haven't forgot, I have it saved to my hard drive lol. Will the same resistor values for the 4050 work for the UCC283t? Like I said it works, just not as intended. if I run the 200 and 400 resistors and pull out the pot then it's a steady 3.7 volts. If the pot is in then it adjusts through the chips full voltage range regardless of what other resistors are in there, it has me rather confused as to why/how that is. I'm trying to get one of my 100k digi pots wired up to try now.