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diode series

Discussion in 'Electronic Components' started by [email protected], Jan 5, 2006.

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  1. Guest

    I'm looking for a component that has 12 or 15 silicon diodes in series,
    or an array with pinouts for diodes that I can connect in series. Low
    current application, a few milliamps. Might be able to work with
    led's, but the tempco on most led's is too low for the purposes of my
    project.
     
  2. Make up your mind! 8*) I take is this is last-year's project from
    12/29 about an array of LEDs with a different approach? Why not tell
    us what you are trying to do, you might get some good ideas.

    For instance, what voltage do you need on your reference, at what
    tolerance, and with what tempco?
     
  3. Guest

    I need a tempco of about -25 mV/deg C. I already built a prototype
    using diodes in series and don't like soldering lots of diodes. It
    exceeds the total number of components in the rest of the circuit, and
    consumes time. This is a voltage regulator with temperature
    compensation for charging 12 volt lead acid batteries, which call for
    temperature compensation between -18 and -33 mv/deg C, depending on the
    battery construction. The batteries in question undergo extreme
    temperature variations and have short lives if used on fixed voltage
    regulators. And no, it's not for a UPS.

    I decided against taking a small voltage reference, like a diode or
    two, and scaling it up using a resistive voltage divider. I prefer not
    to deal with touchy pot adjustments.
    I use a series of about a dozen diodes or so to get the tempco right
    and then stick a zener in the series to bring the voltage up the rest
    of the way.

    Now are you satisified?
     
  4. Franc Zabkar

    Franc Zabkar Guest

    Why not use a single IC solution with built-in temperature
    compensation, eg http://focus.ti.com/lit/ds/symlink/uc3906.pdf?

    The tempco of the internal 2.3V reference is -3.5mV/C which scales up
    to 13.8V and -21mV/C.

    There are other switchmode solutions which would be more efficient.

    - Franc Zabkar
     
  5. Guest

    I didn't think going into a long explanation would help, and it looks
    like I was right.
    This is a voltage regulator on a vehicle. Not an offline battery
    charger.
    Switchmode is too complicated. There's a max of about 2.3 amps field
    current to regulate, and I use hysteresis to keep the main switching
    element from heating up. Very simple circuit.
     
  6. Franc Zabkar

    Franc Zabkar Guest

    Years ago I built an alternator regulator using a Motorola MC3325. It
    has an on-chip string of diodes (including one zener) for setting the
    tempco, and it is linear. I don't know what is available today, but I
    believe ST Microelectronics has several single-chip solutions, both
    linear and switchmode. My old SGS Automotive Products databook lists
    the L9480VB which comes in a 3-pin TO220 package. You can't get any
    simpler than that. :)

    - Franc Zabkar
     
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