Need Help! Two Step Constant Voltage, Current Limited Charger

[waqas]

Hi Guys. I want to build this charger circuit. But i want to know how to calculate the values of R2, R6, and RS?
I calculated the values of RISW = 12ohm to turn Q2 transistor on at 50mA, and R3 = 0.2ohm to limit Max current to 3A.
I want to use bulk charge at 14.4V and then float charge to 13.6V.

Looking forward for good response.
Waqas

[waqas]

No help from experts? waiting for reply

[waqas]

77 views, not a single reply

[waqas]

No one can answer my question? 

[magic]

There are no experts here, only posers.

No one can answer my question? 

That may actually well be the case, as you have posted some weird circuit doing some weird things without much explanation.
Others may be put off by your constant whining


I suppose the way it's meant to work is that at high charging current, Q2 turns on and passes current through D3. Then R6 pulls up the ADJ voltage seen by LM317 and thus increases its output voltage. So R6 will determine how much the voltage increases during charging - less resistance is more boost.

R2 is in parallel with RS so it could be just one resistor. It determines "float" voltage. You will get ~2V for each 240Ω here, so maybe ~1.5kΩ is a good starting point for tuning.

I suppose D2 is some sort of thermal compensation, it should probably be kept at similar temperature as the battery.