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I am building a circuit with 6 parallel LEDs, powered by 5 volts through a transistor array which can provide 300ma. If each LED is allowed 20ma (by setting the correct resistance for each), I should be able power each LED without a problem. I could even power 12... or 45 LEDs with 1 amp.

Is there anything that limits the number of parallel LEDs that I can power in this manner (besides power consumption?)

Will the voltage drop of one LED impact the others at any point (or would this ever be an issue?)

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ You missed the LED symbol in the editor! Depending on the LEDs you may be able to put two per string to double the maximum number of LEDs or halve the current for the original number. The R values would have to be adjusted. \$\endgroup\$ – Transistor Apr 12 '16 at 17:28
  • \$\begingroup\$ Nothing limits it, you are good to go. Or show us the actual circuit, if you have troubles.. \$\endgroup\$ – Eugene Sh. Apr 12 '16 at 17:29
  • \$\begingroup\$ if it is truly parallel each resistor is the same value and each led, then one led or resistor in theory wont affect the other paths more than the accuracy of the components selected would affect it. if they all vary then sure one path may affect the other paths, how much? just do the math. \$\endgroup\$ – old_timer Apr 12 '16 at 17:36
  • \$\begingroup\$ Side note: You do not write what kind of LED you are using. If the forward voltage of the used LED type(s) is below 2.5V, you could put two LEDs in series with one resistor which halves the power consumption and the number of resistors. \$\endgroup\$ – ndim Apr 16 '16 at 17:42
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Basically no, there isn't a theoretical limit. Though there are some practical ones:

  1. How lossy your power supply cables are - the associated resistance will cause a voltage drop proportional to the current. The more branches you chain off the supply cable, the higher the current, and so the more the voltage drops.

  2. How much power the supply can provide - if you try and drive a million LEDs from a 1A supply, clearly things aren't going to go well.

  3. Your wallet - for example a million LEDs would cost a fair amount. But then I suppose you are unlikely to go for that many :)

  4. Time - wiring them all up takes a fair bit

  5. Thermal considerations - stick a large number of LEDs and resistors in a small space with inadequate consideration for the amount of power being dissipated, and the whole thing will heat up until something gives in.

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