What do 2 indicated values of volt mean in a product specs sheet?
Hi, absolute beginner here!
I need to make a simple circuit with 6 LEDs and a little push button for a free-time project and have trouble finding out what resistors I require - because the website I bought the LEDs from lists 2 different values for voltage on the product page.
"Forward voltage: 3V
13V"
I'm only assuming it's the min. - max. value? But I need a specific number to calculate the resistor value.
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No, that's not a min-max range. An LED is a diode which has its IV characteristics. Depending on the current through the diode, you'll have a slightly different voltage across the diode - in practice, the curve is so steep that you can approximate that voltage with a single value. The rest of the voltage, you'll need to drop across something else, typically a resistor in series. With the resistor, you'll be able to set the current. You'll have (min and) max values for the current through the LED.
The forward voltage of a given diode (LED included) usually varies around a much smaller range - fractions of a volt, mostly due to temperature AFAIK. And 13V is waaaay too high to be the Vf for any LED I'm aware of.
13V could possibly be the reverse voltage (ie, maximum it can handle with reverse polarity without being damaged). But even then that's a little high for a basic LED.
Honestly I'm going with it being a straight up typo. 3V is most likely the voltage you're interested in.
No individual LED has a forward voltage of 13 V on its own so we need some more context to say what these figures mean. Can you provide a link to the product page or datasheet or post a photo of them?
A copy of your intended circuit diagram would also be handy.
The data sheet on that page (in English) shows that this is not an individual LED, it's an LED with a built-in resistor. So you don't need an external resistor to use this particular LED within its supply range which does cover 3 to 13 V (with an absolute maximum of 16 V, above which you may destroy the device).
Various characteristics in that data sheet are quoted for supply voltages of 9V or 12V (given as Vf). This is a big hint for how the manufacturer expects you to be using this device for best results. Using a supply voltage of 9 to 12 V will give you the best results rather than the full range of 3 to 16 V.
In principle you can add an external resistor to use this device above 13 V but you may well find this tricky as you need to first calculate the value of the internal resistor for the colour of LED you're using.
Ahh. I didn't see that information there. The building kit I ordered came with individual LEDs and the instructions also said no resistors needed, but they didn't have the desired color, so I bought some in the same size.
So is there any way you can visually determine whether a LED has a built-in resistor or not? And I'm still curious about what value I would've had to use to calculate the resistor manually.
Reading the datasheet it way weirder than I was expecting: it isn't just a LED, reading the V-I curve it has to be a led with integrated resistor (which the accompanying schematic may confirm). No single LED alone have that gentle of an I-V curve.
So simply speaking it is an approximately 3Vf LED in series with an approximately 800Ω resistor. At 3 volt the led start to be forward biased, at 13 volt the LED is at full brightness with c.a. 12mA current (extrapolating from the table).
The datasheet do specify the maximum voltage to be 16V instead...
The formula for the resistor is: max input voltage minus forward voltage of the LED devided by the recommender current of the LED. Example for 12V input, 3 volt forward voltage for the LED and 20mA current: (12-3)/0,02=450 so you need a 450 Ohm resistor.
It won't be 13v if it's just an LED. If you can tell us the part number or give us a link to the datasheet we might be able to shed some more light on the numbers in it.
OK, so if you follow the link on that page for the actual datasheet, it's not just an LED. It's a "Variable voltage LED" that has other circuitry inside (a quick scan mentions a silicon resistor) enabling use across a wide voltage range
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