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Progress update!
I put together a PCB board for the power section and opto-isolated it from the control board.
The test mentioned earlier was performed : Use a pot to control PWM from the micro; have a second pot to increase the duty cycle by 1 bit in order to determine the change in amps due to a single increment in duty cycle.
The micro was run with a 16 mhz crystal in fast pwm mode with 9 bit resolution (512 total divisions). In this mode, the switching frequency is about 31 khz.
Results:
Up to ~5 amps, the charger was in discontinuous current mode and was not sensitive to a small change in duty cycle.
Above 5 amps, a single increment in duty cycle increases the output current by about .5 amps.
I think this'll be ok. Towards the end of charge, the charger should be able to control current finely , if needed. Otherwise, during bulk charging, I think half an amp is enough resolution to control current.
One thing I had thought about was dithering the duty cycle - like, one cycle would have dutycycle = 100, and the next would have dutycycle=101, and duty cycle would alternate between the 2 every cycle. might provide some finer resolution?
pictures in the next post...
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