how do you hook up/ use the flat square 4 pin leds?

I've never used them before but I need them to be flat and bright and they match the description...

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ac-dc7 years ago
It would be easier if we knew the exact LEDs you want to use.  Always pick LEDs you can find a datasheet for if you don't want to experiment on them to determine the pin functions.

Normally you'd look at the datasheet which tells you what the function of the LED's leads is.  Sometimes (if a single color LED) you may have two dies in the same package and could wire (or the trace on the PCB) them in parallel for higher current and lower voltage supply.  Other times you might want to wire in serial so it uses more voltage but less current, but in serial if one LED fails then the other is no longer lit. 

Downside of parallel wiring is you need precise current limiting if exact match in brightness between the two is required and by exact I only mean pretty close- there can still be a brightness difference.

High powered flat LEDs often have only one die but two connections for either anode or cathode.  On those you only need to connect to either of the two for anode and cathode.  Many high powered flat LEDs are designed such that to run at anywhere near their full current you have to heatsink the back of them.  Sometimes they are mounted on a metal "star" with laminations of insulating material and copper traces on top for power, or other times the designer of the circuit board puts traces under where the PCB is soldered, and often vias through the board to more copper on the back side of the PCB for heatsinking.

My answer is already too long so I end it here, but hopefully some of what was written helps.


The ones from Radio Shack (276-0027) are green 4 pin (not the multi-color type) there is one corner that looks flat (like some bridge rectifiers) and is the cathode side. The cathode is the side with two redundant pins that connect to the center light emitting element. The anode is the side that is like a narrow bar running across the top to connect to the other anode pin.

It's really just a standard 2 pin LED except it's flat and the 2 additional pins are just to hold it nice a tight on your board.

If you look at it close, you'll see that 2 pins go to anode, and the other two pins go cathode.

Hope this helps.

The ones from Radio Shack (276-0027) are green 4 pin (not the multi-color type) there is one corner that looks flat (like some bridge rectifiers) and is the cathode side. The cathode is the side with two redundant pins that connect to the center light emitting element. The anode is the side that is like a narrow bar running across the top to connect to the other anode pin.

It's really just a standard 2 pin LED except it's flat and the 2 additional pins are just to hold it nice a tight on your board.

If you look at it close, you'll see that 2 pins go to anode, and the other two pins go cathode.

Hope this helps.

I cant figure this out too!I'm trying to use a high-powered one that I got from radio shack and it has four pins and doesn't have specs other than how much electricity it needs.Haven't figured it out yet!
frollard8 years ago
As the others suggest - there are 2 types of led with 4 (or more) pins... RGB leds have 4 pins, one being the common anode or cathode, and the others being the individual colours. All 4 need to be hooked up to use all 3 colours. If it's just a white led - check the spec sheet of the led to find out what pads do what. Often they are marked on the casing with + -, sometimes they are not. Beware, some require reflow soldering to connect the center bottom ground plane!
klee27x8 years ago
That's true. But parts also sometimes have multiple pads that are really the same thing. Just connect 2 of the four. The other 2 are for stability and/or making routing pcb traces easier.
XOIIO8 years ago
usually multi-pin LEDs are multi-colored. One pin (usually the odd one out) will be positive (possibly negative) and the others opposite, for the different colors. You just hook them up like regular LEDs. Hope I helped!