Hello everyone - I have a Li-ion charge controller PCB that I'm hoping to modify to include a charge completion LED. I believe I need to use a simple FET based circuit to achieve this but don't know where to start choosing parts and working out what resistors I need etc... I have the desire but not the knowledge sadly!
The charger is based on the S8254A charge controller IC. When charging is complete pin 1 is pulled high to stop the charge via this P channel charging MOSFET.
I hoped to use an N channel MOSFET on that same pin to switch on a charge completion LED when the pin is pulled high. However reading the datasheet for the charge controller (links above) tells me this would mean the LED remained illuminated when the battery and charge controller were disconnected from the power supply. It would stay illuminated as long as the battery is in a fully charged state and over time this would obviously drain the battery while in storage until the voltage fell enough to release the IC from the overcharged state.
The battery is a 4 x 18650 Li-ion pack with a fully charged voltage of 16.8v across the input/output pins of the pcb. The wall plug power supply I use supplies the charge controller board with 18v 500mA to those same input/output pins.
I hope to use some simple logic to illuminate the charge completion LED only when both the following conditions are met:
1) charge controller IC pin 1 is high (18v) indicating the cell voltages have all reached 4.2v
2) pcb is connected to power supply (not sure how to detect this. there is only a slight voltage difference when charger is connected 17.9v vs 16.8v!)
The whole setup of cells and charge controller has to fit inside a small canister of the bike light that it drives. There is some room for additional circuitry to control the charging led. Wall charger connects via a standard centre positive round DC jack - I could maybe modify the socket to detect when the charger is attached?
Any suggestions to help me out?
The charger is based on the S8254A charge controller IC. When charging is complete pin 1 is pulled high to stop the charge via this P channel charging MOSFET.
I hoped to use an N channel MOSFET on that same pin to switch on a charge completion LED when the pin is pulled high. However reading the datasheet for the charge controller (links above) tells me this would mean the LED remained illuminated when the battery and charge controller were disconnected from the power supply. It would stay illuminated as long as the battery is in a fully charged state and over time this would obviously drain the battery while in storage until the voltage fell enough to release the IC from the overcharged state.
The battery is a 4 x 18650 Li-ion pack with a fully charged voltage of 16.8v across the input/output pins of the pcb. The wall plug power supply I use supplies the charge controller board with 18v 500mA to those same input/output pins.
I hope to use some simple logic to illuminate the charge completion LED only when both the following conditions are met:
1) charge controller IC pin 1 is high (18v) indicating the cell voltages have all reached 4.2v
2) pcb is connected to power supply (not sure how to detect this. there is only a slight voltage difference when charger is connected 17.9v vs 16.8v!)
The whole setup of cells and charge controller has to fit inside a small canister of the bike light that it drives. There is some room for additional circuitry to control the charging led. Wall charger connects via a standard centre positive round DC jack - I could maybe modify the socket to detect when the charger is attached?
Any suggestions to help me out?
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