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I'm confused about led current draw, my understanding of through hole LEDs was that whatever current is going through one, is going through the others. By that I mean if I had 3 1.5v 20mA LEDs I would only require a 4.5v supply with 20mA output.

So the reason I'm confused is that I read my led strip requires .4A per meter... What does that even mean, do I need a whole amp for 2 meters now?

My application is in actuality driving 1 meter strip of rgb LEDs. So what current output would I need per channel on an led driver chip? 400mA I suppose...?

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  • \$\begingroup\$ Electrically, the LEDs are no different in the two cases. What is different is that your LED strip consists of several rows of three LEDs plus resistor in series, making it suitable for a constant voltage source, i.e. 12 V. \$\endgroup\$ – winny Aug 1 '16 at 22:09
  • \$\begingroup\$ I read somewhere that they still can be susceptible to overheating even with the resistors. Would it be worth my time hooking up led drivers? I want to dim them, but I could do that with a MOSFET and pwm. That leaves current limiting as the only benefit of the driver? As I already have a 12v source, no need for boost. \$\endgroup\$ – Aaron Aug 1 '16 at 22:13
  • \$\begingroup\$ Yes, but an LED driver won't make any difference to that. It's just due to the Chinese LED strip market going south and quality is at an all time low. My old 3*50 mA 5050 chip based LED strip from 2009 is still going very strong. My 2015 strip, not so much. \$\endgroup\$ – winny Aug 1 '16 at 22:35
  • \$\begingroup\$ Thanks a bunch, your position as my top responder is retained haha \$\endgroup\$ – Aaron Aug 1 '16 at 22:39
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    \$\begingroup\$ Well, if you dim it, regardless how, it will improve the situation drastically. My point is that a LED driver is not required. You can dim it by just hooking it up to 10 or 11 V. You are welcome. @pipe answer below is excellent by the way. \$\endgroup\$ – winny Aug 2 '16 at 7:01
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You're totally right that you have the same current running through every LED when they're connected in series. Your confusion comes from not knowing how the typical LED strip is constructed. I have drawn one possible construction here:

schematic

simulate this circuit – Schematic created using CircuitLab

Each LED in the first column will draw I1 amperes, each LED in the second column will draw I2 amperes, etc. The longer your LED strip is, the more "columns" it will have. Thanks to Kirchhoff's current law, the individual currents will be added together to form I0 in my schematic. That's your total current.

They could have constructed it as one long series-connected chain. For a LED strip with 200 white LEDs you would need to feed this with about 600 volts. This is completely unpractical, even if the amount of current is low.

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