Izhar Fareed
Description
The above pictured schematic diagram is just a standard constant current model with a added current limiter, consisting of Q1, R1, and R4. The moment too much current is flowing biases Q1 and drops the output voltage.
The output voltage is: 1.2 × (P1+R2+R3)/R3 volt. Current limiting kicks in when the current is about 0.6/R1 amp.
For a 6-volt battery which requires fast-charging, the charge voltage is 3 × 2.45 = 7.35 V. (3 cells at 2.45v per cell). So the total value for R2 + P1 is then about 585 ohm. For a 12 V battery the value for R2 + P1 is then about 1290 ohm.
For this power supply to work efficiently, the input voltage has to be a minimum of 3V higher than the output voltage.
P1 is a standard trimmer potentiometer of sufficient watt for your application.
The LM317 must be cooled on a sufficient (large) coolrib.
Q1 (BC140) can be replaced with a NTE128 or the older ECG128 (same company).
Except as a charger, this circuit can also be used as a regular power supply.
Parts List
|
R1 |
0.56 Ohm, 5W, WW |
|
R2 |
470 Ohm |
|
R3 |
120 Ohm |
|
R4 |
100 Ohm |
|
C1 |
1000uF/63V |
|
C2 |
220nF |
|
Q1 |
BC140 |
|
Q2 |
LM317, Adj. Volt Reg. |
|
C3 |
220nF (On large coolrib!) |
|
P1 |
220 Ohm |
PCB
