Here is the simple and low cost NiCd and NiMH battery charger circuit which can be used for various battery type and size. This battery charger use a regulator IC of LM317.
Schematic diagram:
NiCd – NiMH Battery Charger circuit diagram
The charge will start if a battery is connected between pins JP1-JP4 or JP2-JP4 or JP3-JP4. For example, if a battery is connected to JP1-JP4 pins then the current that flows cause a voltage drop to R1, then D1 causes a voltage drop of 0,7 volts and ?1 conducts. Then through transistor’s emitter flows a current that comes from Adjustment pin of LM317.
NiCd – NiMH Battery Charger Circuit Notes:
- I is 1/10 of the battery’s charging capacity. For example if battery has a rated capacity of 1700mA then ?=170.
- Diode D4 prevents current to flow from battery back to the charging circuit. Resistors R1,R2 and R3 adjusts the charging current and it’s value is given from : Rx=(1,25 + 0,1) / I , where x = 1,2,3.
- The input voltage must be at least 3 times the battery’s voltage. For example an input voltage of 25V can charge a 8,4V (9V) battery.
- R3 is 1/2 Watt and R1 and R2 it’s 1/4 Watt.
- Pins distribution:
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Pins
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Battery type
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JP1 – JP4
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AAA
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JP2 – JP4
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AA
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JP3 – JP4
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PP3 & 6F22
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PCB top and bottom layout:
I have a few doubts on this NiMH battery charger circuit.
>Is there any battery full auto cutt off protection in this circuit?
If not can you tell how can i implement this?