hello,

I am not able to glow an LED with two batteries of 1.5V each. Please help me.
P.S: i believe the LED rating is 1.5V. The same LED glows when connected to 9V Batery. Please expalin me this.





sudhakar.N

 

Hello,

Can you give us more details on the led.
1.5 Volts is very unlikely.
See this table for some examples of forward voltages of leds:
http://www.theledlight.com/technical3.html

This link comes from the EDUCYPEDIA page on leds:
http://educypedia.karadimov.info/electronics/composemiconductorsled.htm

Bertus

 

If it glows on 9V and doesnt lite on 3V, it means that the LED needs more than 3V. Try with 4.5V then.

Allen

 

check current requirement for that particular LED>

 

In general, you should not simply connect an LED up to a battery, as there will be nothing but the internal resistance of the battery to limit current through the LED. This usually results in the rapid destruction of the LED, and in some cases, can lead to the forceful rupturing of the housing of the battery.

The most simple way to limit the current is to use a resistor in series with the LED.
You calculate the current limiting resistor by:
Rlimit >= (+V - Vf_LED) / Iled
where:
Rlimit = The resistance required to limit the current.
+V = The voltage supply.
Vf_LED = The forward voltage of the LED when the rated current is flowing through the LED, generally obtained from the datasheet as Vf(typ) (typical forward voltage) or by testing.
Iled = The rated forward current of the LED; obtained from the datasheet.

 

thank u all

 

A local tutorial on LEDs I wrote a while back. You really need at least 4.0V for a few LEDs (usually blue and white), most can use 3.0V (red and green) and under. IR can use 1.5.

LEDs, 555s, Flashers, and Light Chasers