newbie question - Electronic Circuits Projects Diagrams Free

raphaelriv · 13th March 2008, 08:21 PM

hello all, sorry for the newbie question but this is just to get something clear:

this website: http://www.iguanalabs.com/1stled.htm

states that you must use a resistor with an LED to not burn it out. However if I use this LED:

Digikey Part number: 67-1131-ND
Product Photos SSL-LXA227ID-5V
Standard Package 1,000
Category Optoelectronics
Family LEDs - <75mA, Discrete
Color Red
Lens Style/Size Round, 1.8mm
Millicandela Rating 8mcd
Voltage Rating 5.0V
Wavelength 635nm
Current - Test 20mA
Viewing Angle 60°
Lens Type Diffused, Red Tinted
Luminous Flux -
Catalog Page 2412
Other Names 67-1131

and hook it directly to a power supply and i fixed the voltage at 5volts the LED worked and the current it pulled was 0.012Amps. It didn't burn out or anything.

The formula in other tutorials to find the appropiate resistors are:

Vled + Vresistor = Vsupply

Vresistor = V supply - Vled

Vresistor = If x Rresistor

Rresistor = Vsupply - Vled / Ir

----------------------------------------------------------------

the question is should I be using a resistor? with this particular LED ? from what i read i can see that the answer is yes to limit the current to a safe value. But then the Foward voltage spec seems to high to take it into account. 5volts?

i'll appriciate some advice. thanks

kjennejohn · 13th March 2008, 09:35 PM

Hi. This LED has a resistor built into it that sets it for use in a 5V circuit. You can't overdrive it unless you subject it to a higher voltage that leads to a current greater than its rated max. You can typically use these with a slightly higher voltage, like up to 12V, where it gets real bright, and lower voltages like 3.3V, where it's dim. The tipoff is the "-5V" at the end of the part number. A 12V part will have "-12V" at the end, etc. This isn't true for all LEDs, however. You'll have to check the data sheets. The interesting thing is, I couldn't find the data sheet using the given part number at the manufacturer's site. Go figure!

Later!
kenjj

raphaelriv · 13th March 2008, 10:20 PM

where did u ended up finding the datasheet, i tried mfg and googling it and nothing came up

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13th March 2008, 08:21 PM
raphaelriv Experienced Member	newbie question hello all, sorry for the newbie question but this is just to get something clear: this website: http://www.iguanalabs.com/1stled.htm states that you must use a resistor with an LED to not burn it out. However if I use this LED: Digikey Part number: 67-1131-ND Product Photos SSL-LXA227ID-5V Standard Package 1,000 Category Optoelectronics Family LEDs - <75mA, Discrete Color Red Lens Style/Size Round, 1.8mm Millicandela Rating 8mcd Voltage Rating 5.0V Wavelength 635nm Current - Test 20mA Viewing Angle 60° Lens Type Diffused, Red Tinted Luminous Flux - Catalog Page 2412 Other Names 67-1131 and hook it directly to a power supply and i fixed the voltage at 5volts the LED worked and the current it pulled was 0.012Amps. It didn't burn out or anything. The formula in other tutorials to find the appropiate resistors are: Vled + Vresistor = Vsupply Vresistor = V supply - Vled Vresistor = If x Rresistor Rresistor = Vsupply - Vled / Ir ---------------------------------------------------------------- the question is should I be using a resistor? with this particular LED ? from what i read i can see that the answer is yes to limit the current to a safe value. But then the Foward voltage spec seems to high to take it into account. 5volts? i'll appriciate some advice. thanks Last edited by raphaelriv : 13th March 2008 at 09:14 PM.

13th March 2008, 09:35 PM
kjennejohn Experienced Member	Hi. This LED has a resistor built into it that sets it for use in a 5V circuit. You can't overdrive it unless you subject it to a higher voltage that leads to a current greater than its rated max. You can typically use these with a slightly higher voltage, like up to 12V, where it gets real bright, and lower voltages like 3.3V, where it's dim. The tipoff is the "-5V" at the end of the part number. A 12V part will have "-12V" at the end, etc. This isn't true for all LEDs, however. You'll have to check the data sheets. The interesting thing is, I couldn't find the data sheet using the given part number at the manufacturer's site. Go figure! Later! kenjj __________________ All my pencils used to have erasers!

13th March 2008, 10:20 PM
raphaelriv Experienced Member	re: where did u ended up finding the datasheet, i tried mfg and googling it and nothing came up