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Hello, I am trying to design a simple battery charger. It is supposed to
charge 4x AA (2000mAh) rechargeable batteries off of a 5 volt supply. Right
now what I have designed has an op-amp is tied to a 4.76 volt reference and
the positive battery terminal. When the battery's voltage is below the
reference it switches on a NPN transistor with a 35 ohm resistor at its
emitter. When fully on the batteries will receive about 140mA. The charger
will continue to remain on until the voltage rises above the reference.

I believe I'll be using a dual op amp, which leaves room for expansion.

What do you suggest for fuses ? advice on resettable fuses, temperature
sensors, and other safety features would be appreciated.
What Is the recommended charge voltage cutoff ? (RTFM ?)
Is the voltage reference method described a viable mean of charging
batteries ?
What other cheap/low part count methods are there to safely charge batterie=
s
?


Note: This is not a production design, it is meant to be simple and cheap.
Though I don't want it to destroy the batteries or leave them uncharged.

--=20
Jason White

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