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As the title say, can you parallel the transistor pair in ULN2003? The datasheet of the IC say it has a max output current of 500 mA, but I need 1 A.

So is it possible? (if you know any other transistor array IC that can drive 1 A on each pair that would be a great help also)

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  • \$\begingroup\$ Even if you cascade them, that will not increase the current capability of a single one. Or did you mean parallel them? \$\endgroup\$ – PlasmaHH Sep 27 '18 at 14:51
  • \$\begingroup\$ Im sorry the word cascade is the wrong word to use. And yes i ment to parallel them. \$\endgroup\$ – Jake quin Sep 27 '18 at 15:01
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    \$\begingroup\$ please correct the wording of your question \$\endgroup\$ – jsotola Sep 27 '18 at 16:16
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As you now realise, you can parallel them rather than "cascade" them.

schematic

simulate this circuit – Schematic created using CircuitLab

Since transistors have a negative temperature coefficient of VCE (collector to emitter voltage) when on if one starts to run hot it will hog the current from the other, thereby getting hotter, etc., until it is destroyed.

The simplest way to prevent this is to add, say, 0.5 Ω series resistance to the collector (output) of each. That way if one starts to hog the current the voltage drop across its resistor will rise and limit the current.

Also, take care of the maximum current for the whole chip which, from memory, is 1.5 A. Remember that it all has to go through a tiny gold wire and out one little pin in the corner of the package!

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    \$\begingroup\$ Thermal runaway is certainly a problem, but hardly a problem when all the transistors are on the same silicon chip. \$\endgroup\$ – Jack Creasey Sep 27 '18 at 15:38
  • \$\begingroup\$ Good point. I don't have a good answer to that. \$\endgroup\$ – Transistor Sep 27 '18 at 15:39
  • \$\begingroup\$ Yes Thermal runaway is one of the drawbacks of paralleling transistors , Thank you for your wonderful response \$\endgroup\$ – Jake quin Sep 27 '18 at 15:47
  • \$\begingroup\$ Also datasheet says Total emitter-terminal current: –2.5 A just incase anyone is wondering the total chip current \$\endgroup\$ – Jake quin Sep 27 '18 at 15:52
  • \$\begingroup\$ @JackCreasey it can indeed be a problem even if the transistors are all on one chip. It can be a problem with a single transistor that develops hot spots and current is concentrated thru one small area of the device. It is a well-known phenomena and you shouldn't give the impression that devices sharing the same silicon are exempt from this. \$\endgroup\$ – Andy aka Sep 27 '18 at 16:23
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No, you can't "cascade" them, which would mean connecting the output of one to the input of another, but you can connect two or more transistors in parallel (with caveats) to handle more current.

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  • \$\begingroup\$ I am planning to drive a solenoid, what are this "caveats" that i should be aware of? \$\endgroup\$ – Jake quin Sep 27 '18 at 15:41
  • \$\begingroup\$ see @Transistor's answer \$\endgroup\$ – Dave Tweed Sep 27 '18 at 16:18

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