What voltage are LEDS? (AC/ DC/ either)? They don’t seem to be marked. (Obviously, quite a beginner in electronics here).
LEDs typically need 2 to 3 volts DC to light. Anything higher and they burn up. With a 12vdc supply, a 470 ohm resisitor (yellow-purple-brown) wired in series the LED will do ya.
Nick
Basicly this is it, most of the time you can use 1.5 to 3volts there are some that can operate on up to 5 volts, but not many. Your better off to buy them from someone who has them in a marked package to be sure of what your getting. I am pretty sure that they work on DC only as the they reqire current to travel in one direction only.
I’ve been using 1K resistors with my bigger LEDs, but I’m running a bit higher voltage, too. The 1K’s seem to work well for headlights on DCC locomotives.
Note that LEDs are very directional. They throw a “beam” forward, which is great for headlights but not particularly good for building interiors, for example.
LEDs are polarized and can be destroyed if you hook them up backwards to too high a voltage without the proper resistor, such as connecting a 1.2 Volt LED to a 12 Volt supply without a resistor. For LEDs with long leads coming out the back, the longer lead is the positive. If you can’t determine the polarity of the LED, it is usually safe to briefly connect one to a AAA battery for determining polarity.
Because an LED is a diode, it will pass current in only one direction, but they will light on either AC or DC.
In order to not burn one out, you need to know its Voltage and Milliamp rating, and the input voltage.
For a DC input, such as a 9 Volt battery, the Ohms law for computing the necessary resistor value is to subtract the LED’s voltage from the input voltage to determine how much voltage needs to be dropped, then divide by the milliamps. For example, an LED that needs 1.2 Volts at 15mA would be computed as needing 9 - 1.2, or 7.8 Volts dropped. Divide this figure by .015 (15 milliamps) to get a resistor value of 520 Ohms.
Resistors are also rated according to their degree of tolerance, as 1%, 5% or 10%. Most cheaper resistors are 10%, and the safe rule is to go to the next higher value of resistor. The value that you compute may not actually be a standard that is available, because resistors aren’t made in all possible values.
i use 12v filtered DC to drive an LED…the main thing is that you put in a resistor…(the resistor can go to either the cathode or anode side of the LED as long as there is one on either one of the posts)…I use from 380 to 560 ohm resistors depending on how many LED’s i’m driving in a particular circuit…chuck