Buck-Boost coil current limiting

Discussion in 'The Projects Forum' started by CoolBeer, Aug 7, 2014.

  1. CoolBeer

    Thread Starter Active Member

    Mar 29, 2010
    So I'm working on a buck-boost supply that will be controlled from an MCU(AVR) as a battery charger(Lead Acid at first to work out the kinks before LiPo, they can be tempremental).

    In this regard I'm starting to think about current sensing/limiting, I can easy enough measure the current going into the battery, but avoiding inductor saturation that way is probably somewhat hard.

    I am thinking in the direction of putting a sense resistor just after the inductor and using that to cut the PWM short for the the remaining period. This seems to work fine in simulation, it is somewhat complex though and I wonder if I'm really overengineering something here or barking up the wrong tree(as in it may be different methods that are simpler).

    The circuit as it stands now in the simulator is a buck-boost stuck in boost mode(the buck switch is constantly on other than when it engages in over current).

    The current sense resistor is measured, voltage amplified, compared with the current maximum(REF1), that goes into a latch which latches on until the next pwm pulse, which resets the latch and on we go.

    Circuit as it stands now:

  2. crutschow


    Mar 14, 2008
    Yes, adding current limiting to a descrete design is somewhat complex. IC SMPC chips usually have current-limit built in as part of the circuitry. That's why ICs are simpler to use for building SMPCs as compared to using discrete parts.