I want to measure an AH of Ni-MH battery. range of this type of battery is between 1v-1.4v , So I need this circuit to sink fixed current from battery for measurement AH.
I want to measure an AH of Ni-MH battery. range of this type of battery is between 1v-1.4v , So I need this circuit to sink fixed current from battery for measurement AH.
Like I said - if we don't get enough information, then we can't make sensible replies.
Your entire premise is incorrect, you don't power the constant current load from the battery under test, it's powered from a separate supply (such as a 9V battery), so your 'problems' don't exist.
This assumes you even want to use a constant current - I tested various batteries decades ago - using two AA in series, and a torch bulb as a load (this is a far more reasonable load for batteries than a constant current which would never happen in reality).
I'd assumed that the op had a 1v reference not a 1v supply.
Nifty op amp working from less than a volt.
I have a battery tester, its a dc motor of all things, it is stalled by a spring at one end and a pointer on the other, I spose its similar to a meter movement but low impedance.
to power a constant current source, you would use a 5V-12V supply to feed the reference side of the current source (the base circuit with the diodes) and the battery would go to the collector and emitter resistor. the bottom of the emitter resistor would be common between the bias supply negative rail and the battery negative terminal.
google "howland current source".... better yet, go to www.ti.com and do a search for "AN-1515 howland current source". a Howland current source is an op amp used as a current source with no external transistors, and will work well with the op amp listed above.