# Wiring 4 LEDs in parallel with no resistors?

I will be wiring Four 3.3V 20mA UV LEDs for a project I am working on. This project involves using a computer's power supply to power several different components. My idea was to power the four LEDs with the orange 3.3V cable from the power supply in parallel skipping the 1ohm resistors. Does this seem like a sound idea or am I missing something here?

Jack A Lopez5 years ago
LEDs want constant current, not constant voltage.  Some sort of current limiting is always required.  For LEDs that use less than 30 mA, the usual trick for current limiting is to put a resistor in series with it.   For larger, more powerful, LEDs (100s of mA, or 1s of  A)  the usual trick is to use a regulator that supplies constant current.

Another trick is putting LEDs in series, since this guarantees that each LED shares the same current, and thus each LED gives the same brightness.

In contrast, putting LEDs in parallel with each other is a bad idea because then they don't have the same current.  There exists the possibility of the warmest LED stealing current from cooler LEDs it is in parallel with.

That being said, I have seen LEDs wired in parallel on the same chip, where they are close together, and in thermal equilibrium, same temperature, with each other.
frollard5 years ago
You're taking a huge risk - granted using a psu regulated to the correct voltage means it won't go over...

The way to remember is that a semiconductor (like a diode) acts like a resistor up to a certain voltage, over the (forward voltage) it doesn't offer (much) any extra resistance. so 3.3v - 3.3v = 0 and you're fine. If that psu spits out 3.4, then .1 volts sees virtually no resistance, and v=ir, i = v/r, and even a TINY overvoltage causes a MASSIVE current to flow (r = almost nil).

Use the resistors.
dcaballero (author) 5 years ago
Thanks for the reply Alex. The Forwards voltage is "3.3V (typical), 4.0V(max).
alexhalford5 years ago
Well, if you're sure the recommended forward voltage on the LEDs is 3.3V and your power supply is 3.3V then leave out the resistors.