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Current-limited constant voltage?

Discussion in 'Electronic Design' started by Mark Tranchant, Jul 16, 2003.

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  1. My first post to this group. Having read some of the wildly off-topic
    discussions here I was a little wary posting, until I saw the venerable
    Winfield Hill posts here. It was a gift copy of TAoE that confirmed my
    interest in EE, since lapsed somewhat...

    I need to make a current-limited constant voltage circuit for charging a
    Li-Ion cell. I know that these things can be dangerous, and mine will be
    encased in a non-airtight die-cast box for safety.

    Are there any problems with simply cascading a simple LM317 current
    source circuit with an LM317 voltage source circuit? I realise I'll have
    to account for the regulator voltage drops, and I know I'll also need a
    CV cut-off timer.

    Thoughts?
     
  2. Ralph Naylor

    Ralph Naylor Guest

    Hi Mark,
    Though I'm a bit reluctant to take the fun out of your project, there are
    tons of ICs out there that directly address what you want. Here's one -
    http://www.maxim-ic.com/quick_view2.cfm?qv_pk=3915
    and another - http://www.linear.com/prod/datasheet.html?datasheet=961
    and there are plenty more from these and other semi companies.
    Regards,
    Ralph in NH
     
  3. Thanks - but I'm struggling to find a suitable one.
    Small 3mm x 3mm 8-Pin Thin DFN Package, 0.8mm High
    Complete Linear Charger in ThinSOT™ Package (5-pin (2+3 "DIL"), with as
    little as 500um gap between pins)
    Are there any in DIL/TO22 packages or anything I'm going to be able to
    solder? I also need to be able to buy a single IC in the UK - can't find
    a suitable source for the above suggestions.
     
  4. Wong Sy Ming

    Wong Sy Ming Guest

    Why not try the MAX1811, it's as simple as it gets and they come in SO-8
    packages.
     
  5. Fred Bloggs

    Fred Bloggs Guest

    Yeah- if you ask this question then you lack the ability to do the
    above-mentioned accounting. Pick-a-chip from either Maxim or Linear
    Technology, one that's designated Li-ion charger, and build the exact
    application circuit illustrated- using parts ordered from Digi-Key. The
    Li-ion charge is critically dependent on termination voltage and this
    requires precision- if you don't blow something up, then at best you end
    up with a half-assed charger otherwise. Your post is not of the wildly
    off-topic variety but it does indicate a lot of dumbness.
     
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