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I feel this is going to be a stupid question-

  • TLC5940 is a 16-channel, constant-current sink LED driver.
  • ULN2004A is a high-voltage high-current Darlington transistor array.

Since the TLC5940 is sinking current, I take it you can't hook up the outputs to the inputs of the ULN2004A to drive something more demanding?

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You can use pull-ups on the output of the TLC5940 and this can form a voltage output device depending on what current is programmed for the sink. Say you programmed 10mA and the supply was 5V. If you used a 500 ohm pull-up resistor, the output would be close to 0V i.e. not driving the ULN2004A. If you programmed the current to be 1mA, the output would be about 4.5V and plenty to turn on the ULN2004A.

You've just got to remember the output is inverted.

If you found an PNP darlington array (common point to positive rail) then it wouldn't be inverted.

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  • \$\begingroup\$ ahaaaa, that makes sense. Though having the output from the darlington on by default (LEDs in this case) is not a great safety feature. You're right, should look for the opposite darlington array. Thanks! \$\endgroup\$
    – rom
    Dec 3, 2013 at 13:26

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