What happens if I apply 2,8 V to a led designed for 3,2 to 3,4 V?

Question

The led's spec.: VDC (a 20 mA) = 3,2V - 3,4 V. (1) If I supply 2,8V will I affect the life of the led? Will I damage it beside loosing brightness? (2) Will the led get damaged if the current exceeds 20 mA? Thank you.

Answer 1

You may find you get nothing at all out of the LED.  LED means Light Emitting Diode and if you are below the voltage drop of the diode, you do not get dim light, you get no light.  The voltage rating may be for use without an external resistor - for 3.2-3.4V you will be able to drop it right into the circuit.  I say this because most LED's have 1.5 volts drop and can be run off a 1.5 volt battery without a dropping resistor.

Answer 2

with regard to mike 1942 answer

1.5V battery is nominal voltage-normally measure 1.65V approx

common LEDs come as 20mA, 1mA and 2mA

this is maximum continuous current

as long as u don't exceed this as an average current, u can strobe them 10 to 50 times max (say at 10Hz or more)

for 20 mA red LEDs they normally show a little light  at 8 ma, significant at 12mA, and no really noticeable difference between 16 and 24 mA

the 'voltage drop' across an LED is fairly temperature and it is negatively dependent---the hotter the lower

google 'led specification' and look at graphs or more simply if u have a (voltage) variable power supply-slap a 1k resistor in series with LED and work on (roughly)

1k at 1v gives 1mA       use a milliamp meter for accuracy               and PLAY with it

Answer 3

You'll probably get a bit of a dim glow out of it.  Understand that the spec. says the voltage drop across the LED is 3.2 - 3.4 volts with 20 ma being passed thru the device.  Usually you drive it with something like 5V and then calculate the series (current limiting) resistor using the median value of the LED voltage.  So:

(5-3.3)/.02 = 85 ohms

And choose the next larger 'standard' value (91 ohms in a 5% resistor or 86.6 ohms if you want to spend the extra money for a 1% part ☺)

Pumping too much current thru the device will shorten its life (although some LEDs have a 'peak' current and a duty cycle value for use in multiplex-driven display systems).

HTH,

Doug

Answer 4

you should never apply a voltage to a LED, only a current, or they will be damaged, or not light at all. A voltage 2 volts or more above the VF spec via a resistor is the best way to do this.

If the spec on the LED is min-max operating voltage 3.2-3.4, then 2.8 volts is OK, but it probably won't light at all, or dimly.

Re 20mA, I don't know if the 20mA is a typical operating current or a maximum current. You have to read the spec sheet. If the latter, exceeding it will damage the LED, damage usually means it burns out.

Answer 5

LED  shall be dimmer. And you do not need any resistor to limit the current into 20ma,because the supply voltage is less than required voltage.

answer:

[1] It shall have a longer life,almost last forever.

[2] Exceed 20ma shall reduce the life of LED. It becomes brighter at the beginning,then dimmer then dead dark.