Discussion
Basicly after the above, on most searchers i do it doesnt come up, also went to the local electronics shop and he was useless, will mapplin have these in, or is there a different name or way to identify them. Its to put in a games console, to replace the old standard bulb. not really wanting to order of the internet, just wanting to pop out tomorow and pick one up, thanks.
In short, there is no such thing. LEDs don't have voltage rating like filament lamps. Each LED tends to have a particular voltage drop according to the materials it is made from, in the approximate range 1.8-2.8V. Yes, there are 12V ones, but these have a built-in regulator and probably wouldn't work down at 3.3V. Some blue LEDs will be around 3.0V, but I wouldn't connect them directly to 3.3V.
However, you can use pretty much any LED you want on a 3.3V supply, with the addition of a series resistor. It shows the standard of shop staff now that they didn't tell you this rather basic fact.
To calculate the resistor value, you need to know the voltage drop of the LED, and the amount of current it draws.
Resistor value (in ohms) = (3.3V - LED_voltage) / current_in_amps
So if your LED voltage is 2.4V, and draws 20mA (=0.02 Amps)
=(3.3-2.4) / 0.02
=55 Ohms (the lowest value you can use)
There isn't a standard 55 Ohm resistor, the nearest is 56 Ohms, so I would use that. LEDs can be fearsomely bright at full power, so you might like to experiment with values up to 200 Ohms or so. Resistors are extremely cheap.
However, you can use pretty much any LED you want on a 3.3V supply, with the addition of a series resistor. It shows the standard of shop staff now that they didn't tell you this rather basic fact.
To calculate the resistor value, you need to know the voltage drop of the LED, and the amount of current it draws.
Resistor value (in ohms) = (3.3V - LED_voltage) / current_in_amps
So if your LED voltage is 2.4V, and draws 20mA (=0.02 Amps)
=(3.3-2.4) / 0.02
=55 Ohms (the lowest value you can use)
There isn't a standard 55 Ohm resistor, the nearest is 56 Ohms, so I would use that. LEDs can be fearsomely bright at full power, so you might like to experiment with values up to 200 Ohms or so. Resistors are extremely cheap.
That resistor value seems awfully low - I use 470R for 5V, and 1K for 12V - I think I used 390R for 3.3V the last time.
However, I don't use maths to back up my values
- I tried 390R for 5V the other day (I wondered why I had a bag of 390Rs, and I wanted to see if they could be used for LEDs), and the green LED I was using was yellow.
I'll have to have a think/search to see what's sensible...
However, I don't use maths to back up my values
- I tried 390R for 5V the other day (I wondered why I had a bag of 390Rs, and I wanted to see if they could be used for LEDs), and the green LED I was using was yellow.I'll have to have a think/search to see what's sensible...
Well, http://led.linear1.org/1led.wiz shows about the same value (47R). I'd go and find out the specs for the LED I was using if it wasn't one that I've had for several years!
wow thaks for the replies, just sort of learnt alittle something,so what do you lot think i should get, ive got a vid on how to install
http://uk.youtube.com/watch?v=eU9IusZKs-E
http://uk.youtube.com/watch?v=eU9IusZKs-E
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