First of all im sorry for the grammar because english is not my 1st language,so bear with me.

So im trying to power up 100 0603 red smd led,its a generic brand and all data i could gather was its 1.8 - 2.0V and 20ma

I tried to powering all of them for a diorama (mostly plastic) with a 5v 1A phone charger (its just laying around and easy option),parallel with 100ohm resistor (at first i though every led was rated 3v,i bought pack of them and realized it was wrong,i used it anyway) at each one of them.

Everything light up perfectly and so bright,but sh*t happens when i let them on too long,its melting some of my diorama especially the one that i glued on tight place,i never really try to touch the led (i though if its light up then its fine),so i touch it and its fells like its sting me,its hot to the level you cant hold it but not enough to kill the led but i think the life span would shorted.

Then i tried to power it up directly from my pc USB port,its rated 5v 500ma,led became cooler,just warm but its okay to touch. On another try i just double the 100ohm resistor (at first i though it would dim the led,turn out not much) and the led seems fine,no overheat or noticeable dim at all only warm just like usb pc but it would be my last option since i already wired everything and to add another resistor one by one again woulf be hassle.

Any idea i could solve the heat problem without too much hassle? Also a thing bugging me is every answer on google said i could put 1 billion amperage on 20ma led and it still gonna take 20ma from it so it would be fine,but why i notice a significant temperature change when i switch from the charger to the usb port with less amperage? Too much current or too much voltage? Oh btw im not yet to wire all of them together,only a small pack like 20 - 30 at a time for testing,i wonder what happen if i wire all them up and put it on,should it be pulling 2000ma at once?



1 Answer 1



simulate this circuit – Schematic created using CircuitLab

If you choose 20mA then result is 50x2x20mA=2A total for 100 LEDs in 2S string. But 1A charger will only work for 25x2 strings.

  • \$\begingroup\$ Thanks tony,already thinking about similar schematic,too bad i just wish i didnt wire all of them,every led got 100ohm R NEXT to each other lol my bad design,but it saves me so much space,so dumb yet working,mayble i need to rewire them,thanks anyway! \$\endgroup\$
    – user194312
    Commented Jul 24, 2018 at 5:31
  • \$\begingroup\$ well since you only have 1A run 50x2 at 10mA and keep the 100 Ohm R in half of them \$\endgroup\$ Commented Jul 24, 2018 at 6:16
  • \$\begingroup\$ Thanks again tony,but maybe i will change the 1A charger with the 2A one,my only concern is would it still heat up if i do 2A and 100x20ma correctly since the current is almost perfect \$\endgroup\$
    – user194312
    Commented Jul 24, 2018 at 7:44
  • \$\begingroup\$ If you keep it under 20mA , in my schematic , it is perfect \$\endgroup\$ Commented Jul 24, 2018 at 11:31

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