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SLA Charger

Tariq Ahmad
Prodigy 20 points
Other Parts Discussed in Thread: UC3906, BQ2031

I am designing a charger for 3 12V SLAs in series, a 36V system. The input voltage is 50V (nominal). The UC3906 has a Vin absolute max limit of 40V. Which part do you recommend for new designs?

Thanks.

 

  • 0
    TI__Mastermind 31120 points

    we typically target around 6 cells or 13.8V and the UC3906 is a linear charger so this would have to be for very current, low power.

    If you need higher power, use a switcher with the properly rated power stage, bq2031....best to use in pulse current mode.

    we really do not have an applications for higher voltage applications, but the bq2031 is scaleable when the proper rated components are chosen.

    Good Luck.

  • 0 in reply to Charles Mauney
    Prodigy 20 points

    Charles, thanks for your reply.

    Here's my problem: Raymond Mack in Marty Brown's book, "Power Sources & Supplies, World Class Designs, describes a charger ckt with the UC3906 charging 3 12V lead acid batteries in series. He is using a PNP Darlington pair in the charge path, with the Sink pin driving the base and the Source tied to the collector, and the emitter tied to the 50V drive through a  current sense resistor. That should take care of the higher current/power requirement. See Chapter 11.

    He has the Power pin tied to the 50V drive, which is violating the 40V absolute max limit. Presumably this is a tested and proven design by an industry expert.

    My question is: what insight does he have that is not apparent from the datasheet.?