Unsure What Some "Maximum Ratings" Terminology Means
Jonathan Morrison
Posts: 23
I am having some trouble understanding the ratings on a component I just bought (a 10 segment LED). It has the following info - stuff in red (notice it's all red [noparse]:)[/noparse] ) - I have no clue about and would be really grateful if someone could shed some light on them:
Absolute Maximum Ratings (Per Element):
Power Dissipation: 75mW
Forward Current: 20mA
Reverse Voltage: 5V
Reverse Current: 100 uA
Electrical Characteristics:
Forward Voltage: 2.0V (typ) 2.8 (max)
Forward Current: 20mA
Peek Wavelength: 697 nm
Thanks for any clarifications on these. Are some of these ratings just synonyms for stuff I already know - like R V and I? Thanks!
Absolute Maximum Ratings (Per Element):
Power Dissipation: 75mW
Forward Current: 20mA
Reverse Voltage: 5V
Reverse Current: 100 uA
Electrical Characteristics:
Forward Voltage: 2.0V (typ) 2.8 (max)
Forward Current: 20mA
Peek Wavelength: 697 nm
Thanks for any clarifications on these. Are some of these ratings just synonyms for stuff I already know - like R V and I? Thanks!
Comments
·· The power rating in mW is based on the power and current.· 20mA is a standard upper range current draw in LEDs.· Most run at 20mA fine.· In your case, since you have the forward voltage and the current, you can easily calculate the resistor required to run this from a 5V source, such as a Stamp I/O pin.
·· So for an LED with a Forward Voltage of 2V on a 5V power supply drawing 20mA would require a 150 ohm resistor in series.· Although you could easily use a 220 aqnd draw less current.· Most of the other information like wavelength you won't need to worry about.· That's it's color output in the visible spectrum.· If it's red, it's red, if it's green, it's green.· Most people don't need to worry about the exact wavelength.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
Post Edited (Chris Savage (Parallax)) : 7/21/2005 4:26:15 PM GMT
In reverse bias, the LED will take up to 5 volts before destroying itself, and will 'leak' 100 micro-amps in that condition. We don't usually reverse bias LED's, but there are some clever designs (bi-color LED's for instance) which take advantage of this. "Reverse Bias" here meaning you turn the diode around, put +5 on the cathode and ground on the anode.
·· Actually those meanings are meant to be intuitive...Forward voltage and current are the voltage drop and current consumption when the device is connected properly.· As for the remaining items, instead of explaining, I will send you a link that might explain it in more detail so you understand.
http://www.americanmicrosemi.com/tutorials/diode.htm
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Chris Savage
Parallax Tech Support
csavage@parallax.com