Electronics possible to not need resistors???

aight, i wanna light up 4 LEDs... all 4 run off of approx. 3 V... i was wondering if i could split all four from the 12 V+ of a molex and have no prob running them, or is there an easier way? oh and i wanna stick em on a switch... so do i run the 12 V+ lead into the switch then split on the output of the switch into the 4 LEDs???

 

Check the Vf and always use a resistor, leds do vary in Vf so you could end up with a high current if total Vf was only 11.5v.

General advice is to limit a series chain so total Vf is <80% Vs, so 4 @ 2.2v would be OK, but no more than 3 @3v.

 

yeah, i kinda had that in mind... the led's are actually 3.7 V... i figured at 3 V they'd still do the job i want them to do... anyone know of someone who's done something similiar? basically i'm looking for like a pic of this done or a diagram or something... cuz i'm not exactly sure if i'm thinking it right

 

You can't under-volt leds - below the forward voltage they're off, negligible current will flow.

Once voltage reaches Vf current increases and they light up.

Above Vf the series resistor takes the spare volts, a voltmeter check across the led will only show a slight increase over Vf for a large increase in supply voltage.

I'd draw you a graph but it's gone midnight

 

hmnmm... what about the 5 V+ lead? is there a way i can power up 4 lights from that? like have em break off at different points or something? i tried the leds at 5 V and they worked great

 

Just put them all in parallel. You will still want a resistor though.

 

I "relieved" my employer of an LED matrix. It consisted of 90 red LEDs (89 are working). From looking at the wiring they seem to be a bank of 10 in series and 9 of these banks in parallel. I don't know anything about the output values but the LEDs are about 3-4mm dia.

I'd seen it connected to a smallish 12V battery at work so I brought it home and plugged it into the 12V line of a molex.

This baby is as bright as the sun LOL. Lights my case up a treat.

I must say you got me bit worried about needing resistors as there was a resistor on there - a ceramic block of some sort of the V+ wire but it got broke. Doesn't seem to miss it though.