Hello ,
I recently bought one 2868 Step up/down and it works fine.
https://www.pololu.com/product/2868
But just because i am very new generally on electronics
i can not well understand the tunning process for the cutt of potensiometer.
(Admins…Feel free to combine/move this post according best forum readability)
So…i have a battery pack 3AA rechargables that gives apporximatelly 4.35 Volt on start up
and i ve set the primary/basic potensiometer to give me 4.0 Volts.
And i want to cut of at 3.3 Volt meaning no less than 1.1 for each rechargable AA
According the formula
EN / 0.7 = VIN / VIN cutoff
i must have(with the secondary potensiometer)
EN adjusted @
= (4.35 / 3.3 ) * 0.7 = 0.92
Now the problem is that ok…i am doing like this and lets say working perfect.
But what will happen if sometime that i will go to replace the batteries
…the starting voltage (for some reason) is not 4.35 but lets say 4.2
Then finding cutt off with formula
EN / 0.7 = VIN / VIN cutoff
VIN cutoff = (VIN * 0.7) / EN
= (4.2 * 0.7 ) / 0.92
= 3.20
If all those i wrote untill now are ok,then
Can you please clarify if
this is “as it is”?
and …is not possible to have a
STABLE Cutt off voltage
(as i was imagine (as newby))
???
I mean …i though i could exactly set up the cutt off coltage.
Ah.!..and not only this …but the question
(sorry if i am confused and confusing you)
Lets say…that ok have it started at VIN=4.35
and EN=0.92 meaning cutt off at 3.3
But if i switch off my application
when the batteries are 4.0 volts
and after 2 days switch on (without recharge batteries)
then the cuttof will be less that 3.2 ??? !!!?
(Is there somekind of internal
"hold in 2868 memory the start voltage)?
VIN cutoff = (VIN * 0.7) / EN
= (4.0 * 0.7 ) / 0.92
= 3.04 ???
Is this 3.04 / 3AA =1 Volt will “destroy” the efficiency of my batteries?
Thank you in advance and sorry if i am not very clear…