How can I control the constant current block? What I need?
I need to calculate voltage with constant current load (I = 100maand after some time I need to calculate voltage without load (I = 0), for that I using BJT to control the constant current block from micro controller to turn off and on.
Can I achieve from this circuit? Why I am doing?
I need this for to calculate the voltage of the battery with cc load and without load
You can use a resistor with a value that can boost the 100mA load when the battery voltage is low, so the current limiter transistor (Q1) will act as a resistor when the battery voltage is high.
Otherwise, the transistor will dissipate the heat of this load, say it is 12V under 100mA, results in 1.2W. Your transistor must have ability to dissipate this power. and a sink, of course.
If the 12V battery can operate up to the lower limit of 10V, then we could define a load resistor that waits around 8V, to consider the voltage drop on the transistor series.
Being 8V and 100mA, we have V = R * I, R = V / I, R = 8 / 0.1, R = 80
Nearest commercial value for the resistor: 82 ohms.
Resistor power: P = V * I, P = 8 * 0.1, P = 0.8W
In this case, it is best to use a resistor of 2W or more to avoid long term damage.