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Basic battery charger

David Munzer
Prodigy 70 points
Other Parts Discussed in Thread: LM317

Hi there, 

I am working on a basic constant current source 3.7 V Li-Io battery charger. It consists of the LM317, a NPN transistor, some resistors, and capacitors. I set the open circuit voltage difference to be 4.1. However, when I connect the battery in I get no extra current draw compared to the 1mA the chip using while under no load. While testing in simulation, the circuit was able to draw the desired 700 mA to the battery. I have attatched in  a word document showing my working circuit in LTSpice and my implemented circuit to get the 4.1 voltage difference. Please let me know your thoughts.

Thanks,

David MunzerBattery Charger Schematics.docx

  • 0
    Prodigy 70 points

    The issue seems to be with the NPN transistor. When I disconnect the base of the BJT from the circuit, I get my desired open circuit voltage of 4.05 V and when given the battery load, I am able to get current flow through my battery, 600 mA. With the base connected of the NPN, the voltage drops to 1.95 V for no load and there is no change in current when the battery load is connected. I tried using higher resistor values with the base of the NPN connected. This allowed the open circuit voltage drop to be 4.1 V but I am pretty sure this messed up the feedback of the adjust pin since there was no extra current flow with the battery introduced.Battery Charger Schematic v2.docx

  • 0 in reply to David Munzer
    TI__Mastermind 24975 points
    David,

    My apologies for the delay in response, as I must have overlooked this post.
    Were you able to correct your issue?

    Best,
    Michael