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I am currently using BC 547 transistor and an Arduino Uno to turn a low power switch on and off. I have successfully achieved this with one of the Arduino output pins, but would like to replicate this over 13 of the pins. This would require 13 transistors and resistors, one for each pin, which seems like overkill. I want to know if there is a neater way of doing this with an IC?

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    \$\begingroup\$ Yes, they are called transistor arrays. It is common to find them in dual, quad, and octal configurations. Same with resistors, they come in arrays of all common, all independent, etc. \$\endgroup\$
    – rdtsc
    Jul 11 '16 at 14:58
  • \$\begingroup\$ This is a good question as it stands, if you're really only looking for a transistor array. However, if you add more details about your particular system, you may get alternative solutions. \$\endgroup\$
    – pipe
    Jul 12 '16 at 4:00
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The ULN2003 Arrary contains 7 darlington transistors connected with common emitter.

enter image description here

There is even a base resistor included. You could choose which voltage level you desire, such as ULN2002, 2003 or 2004

enter image description here

EDIT #1 : as pointed out by Peter Green, the saturation voltage (Collector to emitter voltage) when transistor is on is higher with Darlington than with a single transistor. Where typical transistor saturation voltage might be 0.3 to 0.8 volts. The ULN2003 saturation voltage can be from 1.1 volts to 1.6 volts. Resulting in significantly more power dissipation of a single transistor.

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    \$\begingroup\$ Be aware that darlingtons have a high collector-emmiter voltage. Without knowing the OPs application we can't tell if it's ok to use darlingtons instead of regular transistors. \$\endgroup\$ Jul 11 '16 at 15:19
  • \$\begingroup\$ good point @PeterGreen. As usual, power dissipated is important. \$\endgroup\$
    – Marla
    Jul 11 '16 at 15:21
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    \$\begingroup\$ and so is making sure the load gets the voltage it needs. \$\endgroup\$ Jul 11 '16 at 15:28
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You are looking for the ULN2003, High-Voltage, High-Current Darlington Transistor Arrays.

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Fiugre 1. ULN2003.

The base resistors and snubber diodes are even built-in!

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  • \$\begingroup\$ Ha ! transistor, you beat me to it by a small time :) \$\endgroup\$
    – Marla
    Jul 11 '16 at 14:18
  • \$\begingroup\$ Thank you for the incredibly fast response - I will try this out. \$\endgroup\$ Jul 11 '16 at 14:19
  • \$\begingroup\$ @Marla: It's tough in here! You've got a bit more depth in covering the different voltage ranges. That more than justifies the longer response time. \$\endgroup\$
    – Transistor
    Jul 11 '16 at 14:31

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