Reverse/forward voltage explained?


i am looking to buy some LED's for an upcoming project but I have been confused by the terms reverse voltage and forward voltage.

Which one reffers to the voltage required if the LEd is corrected in the right way.

for example, buying some LED's from ebay it saisd this
"Forward Voltage typ/max: 2.2V/2.8V
Reverse Voltage: 5V "

Does that mean with the LED connected (anode positive and cathode negative) i would need 5volts of power? or would i need 2.2/2.8volts?


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fkyc9 days ago

i want to put UV LED (Fv=3.3V) to my bluetooth keyboard that runs on 3.3V LiPO internally. My plan is to connect the LED and the battery in series with a 3 prong on/off switch between the positive (+) terminal of the battery and the LED's anode. Since the forward voltage of the LED and the battery are the same (3.3V), is this configuration (without resistor or diode) fine or is it ALWAYS better to use a resistor with any LEDs and if it is, what is the safe / recomended value should it be?

DJman2303 months ago

Hey all. I want to use these led

http://grobotronics.com/led-infrared.html?sl=en to build an IR board for a cctv camera. I have connected 19 leds. How much voltage and amperage do they want??

The FORWARD voltage is the volt drop through the LED, when the nominal current is flowing, when the ANODE is more positve than the CATHODE. Here, you will see betwen 2.2 and 2.8V in normal operation.

REVERSE voltage is the maximum the LED can stand the other way round without damage.
joearkay (author)  steveastrouk5 years ago
So how do i determine what voltage power supply to use for the LEDS?
iceng joearkay5 years ago
As steveastrouk points out,
The Power supply needs to be greater then the forward voltage plus
an extra minimum of two more volts.   Six or nine volts are favorite values.
You must plan to put a resistor in series with the LED.
Pay attention, not to exceed the recommended LED current,
or the longevity will be cut down fast !

If I have more than two LED in series, will the power supply need to go up as well? E.g. 3 LEDs with Forward Voltage at 3V each; does that require min of 11V power supply?

Yes over 9V

Take the FORWARD voltage, as the critical parameter and the rated forward current.

The rest depends on how many you want to deploy, and what voltage you have available to drive them.


as someone who found this on a google search, this answer is flipping awesome and clear, thankyou!

Your welcome ;-)

Good answer, one thing to remember with any LED of any Type or Colour, is the brightness and longevity varies with the forward Voltage. In the example given 2.2 Volts would light it at decent functional brightness and last literally for Years, but running it at anywhere above 2.8 V will make it very bright but not for nearly as long.

You've seen this picture:

Because that's usually part of the story of the diode, a graph of current versus voltage, the so-called i-v characteristic.  Forward voltage and current are on the right hand side of this graph, and reverse voltage and breakdown are shown on the left hand side.

If you feel up to it,  you can even read the section of the article on diodes that refers to this graph, here:

Anyway, mostly I just wanted you to see the picture, because the folkore of diodes is really incomplete without it.  It's part of the story, and I'd feel like I wasn't really doing my job, as an educator, or storyteller,  if I didn't at least show you the picture.