Modifications in the charger circuit for 4,6 & 8 volts

[rajultra]

Hello sir :o

Here i ve got a charger circuit diagram for 12 volts battery . .

7255
Now i want to design the same thing for

1) 4 volts
2) 6 volts
&
3) 8 volts

So what modifications does component's value need in above 3 cases ?

please tell ! thanks :)

[ardhuru]

Here's all the math you need:

http://www.eleccircuit.com/lm338-lm350-lm317-voltage-regulator-calculator/

Best Regards.

[Sherbrook]

With P1 centered the circuit should give output of 14v or about 2.3v per cell. For a 6v battery you will need an output of 7v, 8v - 9.3v, 4v - 4.7v. The output voltage is set by potential divider R3 and R4/P1.
Here is what I would do.
Replace R4 with a 47k pot set at 47k and set P1 mid position. Power on the circuit and decrease the setting of the pot until the output voltage is the required value. Replace the pot with the nearest value fixed resistor. Adjust P1 to get the exact voltage required.

Phil