Help verify a charger circuit

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skjian

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Hi, experts!


I need to make simple charger circuit for 1 single NiMH battery. I design the circuit but since I am newbie to analog design, could anyone give a hand to verify this circuit or recommend other better circuit? The circuit target is to be as simple as possible with over temperature/voltage protection. Your kindness will be highly appreciated.
 

Comparing your circuit with the one in the BQ2000's data sheet, it is a good idea to replace 5.1V zener with 5V voltage regulator (you can use the L-version of the 7805), and one more thing, you should add an inductor just next to the Schottky diode - D4 .. see schematic diagram at: https://focus.ti.com/lit/ds/symlink/bq2000.pdf

Regards,
IanP
 

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    skjian

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thank you very much!
Another question. Is the Q2, D5 and C9 mandatory to turn-off Q1 during off-duty? What's its improvement compared with a single resistor?
 

skjian said:
thank you very much!
Another question. Is the Q2, D5 and C9 mandatory to turn-off Q1 during off-duty? What's its improvement compared with a single resistor?
Click to expand...
It actually works both ways: Ton and Toff are shorter, but if (in your circuit) you use R7≈4.7kΩ (or smaller) and R20≈470Ω (or smaller) the only main difference will be slightly warmer power transistor Q1 ..
One more thing, I don't see any reason behind connecting 100kΩ resistor between the collector of Q3 and THERM ..

Regards,
IanP
 

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