What would I need to buy so I would be able to connect LED's to a plug outlet? some kind of inverter, resistors etc.???? If you know would you be able to be a lil specific on the part If it would be hard to find? thanks in advance! Fargo:
leds typically run at about 3v~. First you need a DC plugpack/power brick/transformer, which has a low voltage output (12v DC for example) . Then you need a resistor in series with the led to further drop the current to the correct amount for your led. you can use Bit-tech's LED Caclulator to work out the value for a suitable resistor. Lets say for example, the plug pack outputs 12v DC, the led needs 3.7v forward voltage (typical for a blue led), and is rated for 40ma. we put those into the calculater, and.. so you use the closest valued resister you can find being:
If I'm not mistaken TMM is correct, But they do make inverters rated at 2 volts(most leds I have some across are 2) If I nead one I just go to a local radioshack I beleave they sell them for 6 bucks US.
For good LED control you need good current control. Every LED picks its own voltage for a given current. There are circuits to do the current regulation like: http://www.supertex.com/pdf/datasheets/CL1Datasheet.pdf To run off line voltage it is better to use a little transformer, for safety and because you don't loose so much power in resistors.
http://users.skynet.be/turbokeu/myprojects/acled/acled.pdf http://users.skynet.be/turbokeu/myprojects/acled.htm Make sure that the capacitor is rated to at least 240 volts, though. This is a must.
yeh that works aswell, but i find using an independant resistor for every led works out better then just supplying a fixed power source and running heaps of leds off that. Some Leds pull more current then others, which results in some being brighter then others (considering they are all rated for the same brightness), If you calculate the correct resister for each led, the brightness of every LED is about the same
I don't know how effective an inverter is to keeping a voltage since I'm used to playing with 12V car systems. So going with that, typically I suggest using a voltage regulator, not a resistor, to pull voltage down to what you need, as car charging systems have a tendency to spike up to 18volts, not very LED friendly if you're just using resistors. So voltage spikes are something to consider, and regulators don't cost much, and you won't need any resistors, they can also handle the load of quite a few LEDs.
An inverter is not really useful for this situation. An inverter takes a DC signal (often unregulated, as you have experienced) and converts it into an AC signal. We want the opposite, AC to DC, or at least, AC to a usable AC voltage. The regulator idea is good, but you would also need a step-down transformer and rectifier to convert 110 volts AC down to a voltage range that a typical regulator can work with, and it needs to be DC. Most regulators I've seen can't run off of straight 110 volts AC.
You still need current limiting though, voltage regulation is not enough for the reasons TMM specified - They'll all end up different brightnesses. A resistor per series string or per LED works best. Use some kind of transformer to lower the voltage to something safe/usable first though.
an AC adapter for something like a Sony CD player (I looked at mine, it dropped it to 4.5volts) into a regulator into a circuit of LEDs in parallel will give you equal brightness and the proper control needed to power quite a few LEDs. we had been talking about AC Adaptors, that's why I didn't specify that you'd need one to bring it down from 110AC to a lower DC voltage.
The thing is that LED brightness is a function of current, not voltage. It seems trivial, perhaps, but each LED has a slightly different I-V characteristic, so a given voltage will result in a different current sink per LED, which results in different brightnesses. What we need is a current source or transconductance source.
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=395616&Row=55233&Site=US 500mA, 3.3V, min voltage is 5.3V, however, so the input voltage would need to be higher than that (9V AC adapter would work, but it's working voltage is up to 25V) most LEDs I've used (from www.superbrightleds.com ) were 3.3V-typ. w/ 20-30mA current, 500mA is PLENTY for quite a few LEDs, all would get the current they needed to be the same brightness. if you're talking about each LED being slightly different from a manufacturing standpoint, yes, I understand what you're saying, each LED will be slightly different, and I emphasize slightly, i.e., unnoticeable if the company you're getting them from has any quality control whatsoever, but yes, each LED will have slight differences in the amount of flux used, and placement of the components in the epoxy, though very very slight. unless you're talking about wiring in series, then yes, the LEDs would be gradually dimmer as each one acts as a resistor through the circuit, I'm talking about wiring in parallel.
It seems apparent that you misunderstand the V-I characteristic of a diode. It's not possible for the LEDs to "get the current they needed to be the same brightness" from a voltage source - You need to limit the current to each LED. If each LED draws the same current then only then will they all be the same brightness. The difference is not so slight. You may not notice too much at full brightness, but bring the duty cycle down to 10% and the difference is more than noticable. I demonstrated this a year ago with some blue Kingbrights - it's the same old story... First, and LED is not an ohmic conductor, it's a semiconductor. An LED cannot act as a resistor. It's basic circuit theory to know that the current anywhere along a series circuit is the same, so the LEDs would NOT be gradually dimmer "as each one acts as a resistor through the circuit". They'd all be the same brightness, since they are all drawing the same current.
