The battery charger circuits above have been in use for quite some time during my 26/battery fetish period. Making chargers for my B+ battery stack left me melancholic with the thought of repeating the soldering task up to 35 times. Looking through some old datasheet books I discovered a little critter that combines the circuits above into a single chip. Granted, it only removes the BC547 from the picture, but it makes soldering so much easier as there are less routes to be made. Just solder on the desired resistor values and you’re off.
The chip in question is the L200. It can supply up to 2A of output current (plenty for any battery) and is setup almost the same as a regular LM317, it just has two extra pins (3 and 5).
Pin 1 : Input supply
Pin 2 : Output
Pin 3 : Ground
Pin 4 : Voltage refference (used to set output voltage)
Pin 5 : Current-limit sense input
The output voltage is calculated as follows:
2.77V x (1 + (Pot / 1K))
The current limit is calculated as follows:
Imax = 0.45V / R1
Say you want 1A of maximum output, you would need a 0.45 ohm resistor (0.45V / 1A). The 0.45V is a given taken from the datasheets (V5 – 2).
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