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Darlington Arrays

Discussion in 'Electronic Basics' started by Michael, Dec 1, 2007.

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  1. Michael

    Michael Guest


    Am I right in thinking that the ULN2003A has built in base resistors meaning
    I can drive a bank (6) of relays with the only external components being one
    diode per relay? I assume a 1N4001 is good enough?


  2. ian field

    ian field Guest

    First hit on google..............
  3. John Larkin

    John Larkin Guest

    The ULN even has the diodes.

  4. Michael

    Michael Guest

  5. ian field

    ian field Guest

    Read further down the data sheet - it shows the internal diagrams for each
    darlington stage for 01,02 & 03 versions.
  6. From a logic designer's viewpoint, these parts are groups of
    inverters, as shown in the logic diagram on page 2 of that data sheet.
    Page 3 shows the actual circuit of one inverter, for each of the
    varieties of the part.

    The 2003 input circuit makes it TTL-compatible. The 2002 and 2004 are
    designed to be driven from other sources. An old Motorola datasheet
    (perhaps Freescale now) listed the intended driving sources for each

    By the way, there's an 8-channel version: ULN2803.

    These parts include diodes, so you don't need an external one.

    Peter Bennett, VE7CEI
    peterbb4 (at)
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  7. Chris

    Chris Guest

    Yup. There's a diode for every output on the ULN2003. Remember -- to
    take advantage, though, you have to connect pin 16 to Vcc (or the
    power source for the relay coils).

    Good luck
  8. Jamie

    Jamie Guest

    All the outputs are open collector and pull to the (E) pin when on.
    the (E) pin needs to be connected to your supply's common/(-)

    They all have an internal diode for each already, also, it has
    a diode array tied to a "COM" common pin. With that control, you can
    connect the "COM" to the (-) rail and all of
    the outputs will turn on or, connect "COM" to the (+) rail and they'll
    aid in protection.

    One leg of each relay are joined all together to the (+) of your
    supply. Each remaining leg of the relays will connect to a single

    Hope that was clear enough.
  9. ehsjr

    ehsjr Guest

    Pin 9, not 16.
  10. Chris

    Chris Guest

    Oops, right. Thanks -- hope the OP took a look at the .pdf above and
    got it right.

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