Led Resistor Calculator Free Download

The following are tools to calculate the ohm value and tolerance based on resistor color codes, the total resistance of a group of resistors in parallel or in series, and the resistance of a conductor based on size and conductivity.

An electronic color code is a code that is used to specify the ratings of certain electrical components, such as the resistance in Ohms of a resistor. Electronic color codes are also used to rate capacitors, inductors, diodes, and other electronic components, but are most typically used for resistors. Only resistors are addressed by this calculator.

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The color coding for resistors is an international standard that is defined in IEC 60062. The resistor color code shown in the table below involves various colors that represent significant figures, multiplier, tolerance, reliability, and temperature coefficient. Which of these the color refers to is dependent on the position of the color band on the resistor. In a typical four-band resistor, there is a spacing between the third and the fourth band to indicate how the resistor should be read (from left to right, with the lone band after the spacing being the right-most band). In the explanation below, a four-band resistor (the one specifically shown below) will be used. Other possible resistor variations will be described after.

In a typical four-band resistor, the first and second bands represent significant figures. For this example, refer to the figure above with a green, red, blue, and gold band. Using the table provided below, the green band represents the number 5, and the red band is 2.

The fourth band is not always present, but when it is, represents tolerance. This is a percentage by which the resistor value can vary. The gold band in this example indicates a tolerance of 5%, which can be represented by the letter J. This means that the value 52 M can vary by up to 5% in either direction, so the value of the resistor is 49.4 M - 54.6 M.

Coded components have at least three bands: two significant figure bands and a multiplier, but there are other possible variations. For example, components that are made to military specifications are typically four-band resistors that may have a fifth band that indicates the reliability of the resistor in terms of failure rate percentage per 1000 hours of service. It is also possible to have a 5th band that is the temperature coefficient, which indicates the change in resistance of the component as a function of ambient temperature in terms of ppm/K.

More commonly, there are five-band resistors that are more precise due to a third significant figure band. This shifts the position of the multiplier and tolerance band into the 4th and 5th position as compared to a typical four-band resistor.

On the most precise of resistors, a 6th band may be present. The first three bands would be the significant figure bands, the 4th the multiplier, the 5th the tolerance, and the 6th could be either reliability or temperature coefficient. There are also other possible variations, but these are some of the more common configurations.

Resistors are circuit elements that impart electrical resistance. While circuits can be highly complicated, and there are many different ways in which resistors can be arranged in a circuit, resistors in complex circuits can typically be broken down and classified as being connected in series or in parallel.

This tool is used to decode information for color banded axial lead resistors. Select the number of bands, then their colors to determine the value and tolerance of the resistors or view all resistors DigiKey has to offer.

There are tools on the web like -denshi.jp/en/teikokeisan.htm but keep in mind that E-Series are built such that tolerances overlap. E.g. E24: a 470k 5% resistor can have from 446.5 to 493.5, the next bigger one, 510k can have from 484.5 to 535.5k and in practice may even be lower than the 470k so combining resistors to get more precision is very limited. It is better to switch to a higher, finer graded E-Series to get precision you can rely on.

I often parallel or series resistors. Mostly for flexibility tweaking regulator output voltages. I think the main decision is whether you want a high or low resistance value. If you want to get to 2.03 Meg ohms, it will probably be cheaper/easier with series connections. Start with the highest available value which is lower than the target, and then tweak it with a lower value in series.

This calculator is based on the Ohms Law Calculator, but takes into consideration the voltage drop from the LED. To use the calculator, enter any three known values and press "Calculate" to solve for the others.

i recently got those high powered led's, but the problem is there is no datasheet whatsoever, so i tested them out ,i found out that at 3v it takes about 45ma, and does not require a resistor(led voltage=power source).now i want to run 5 of them at 6v,what resistor value would i need??? i tried figuring this out by a potentiometer but i burned it.........

Most LEDs are not at all fussy about what current they need, but as long as you keep thinking about supplying 'voltage' to an LED you are doomed to failure. You do NOT apply some specific voltage voltage to an LED to get it to work. The 'forward voltage' value specified (or measured) for an LED is the result of somehow getting the correct current to flow through the diode. We typically use a fixed voltage supply and a current limiting resistor to do this, but the constant current supply mentioned by Mike is a better choice if you have one.

So to deal with an LED you start with the forward current that you need, typically about half it's maximum rated value (lets use 20 mA). Next you estimate what the forward voltage drop will be with that current flowing through the LED. If you have a datasheet for the LED you may be able to get a fairly accurate value, otherwise you take a guess based upon your experience or the experience of others as in reply # 2 (I usually use 1.7v for a red LED). Next you pick out a supply voltage which must be higher than the voltage you just determined (I'll use 5v). Now you can use Ohm's law to determine the required resistance. The voltage across the resistor will be the difference between the supply voltage you decided to use and the voltage that you guessed would be across the LED (5v - 1.7v = 3.3v). The current through the resistor will be the same as the current through the LED (20mA). Ohm's law for the resistor says that R = V/I (R = 3.3/0.020 = 165 ohms). You then pick the closest value resistor that you happen to have and stick that in your circuit. Most likely the current won't be exactly what you desired and the LED voltage won't be what you guessed would be there but you won't see any smoke either and you will see light from the LED.

This will happen whenever you use a potentiometer as a rheostat and don't use a fixed current limiting resistor as well. Your potentiometer had a relatively fixed voltage across it (the supply voltage less the forward voltage of the LED). Now look at Ohm's law for your rheostat (I = V/R). You had a fixed voltage divided by a variable resistance. As the resistance went down the current went up. Each time the resistance was halved the current doubled. What was the current just before the resistance got to zero? Answer: a lot (theoretically almost infinity). In your case the potentiometer burned out before the LED but it could have gone the other way or you may have hit the jackpot and destroyed both of them.

If you trust the guy you bought them from, with the 0.5W rating, you could use some variable power supply, a few fixed resistors and a voltmeter to find out what what voltage current value the LED works at 0.5W. with a serial resistor, say 300ohm, increase the power supply voltage and measure voltage across the resistor until you get V_led*I_led~=0.5W and stop there. I made my students do this on regular diodes but they could use a function generator and a two-channel oscilloscope. I wouldn't waste that much time for cheap LEDs.

You really don't have to 'test' anything. You just keep the current below it's maximum rated value and the power will automatically be less than the maximum rated value. The only reason to be at all concerned with the forward voltage is (1) to make sure your supply is greater than this value, and (2) to have a ballpark value from which to start calculating the series resistor.

got them working,with a resistor ,and they dont heat up, the problem was that the two same type of led ,were different but they looked same; one type required 145ma and the other type 30-40ma, so i fixed a pot and got the 30-40ma one working perfectly, the voltage drop i measured was 3.10v and the current was 35ma,with a resistor of around 81 ohm.

I remember there being a calculator for when you need non-standard resistor values, which you can input the value you need and it tells you the closest matches you can achieve by paralleling and putting resistors in series. But now, I can't find it anymore. Thanks!

Color-coding is a method used to indicate the resistive value, tolerance, and temperature coefficient of resistors with low wattage rating because of their small size. Color bands are used because they can be easily and cheaply printed on a small electronic component. Color-coding is also used for capacitors, inductors and diodes.

When the resistor body surface is large enough, as in large wattage resistors, the resistance value, tolerance, and wattage are usually printed on the body of the resistor. Surface mounted resistors (SMD) use another coding system that uses alphanumeric codes printed on its surface instead of color codes.

In a three-band resistor, the first two bands represent the first two significant digits followed by one band for the multiplier. Since no tolerance band is available, the tolerance will always be 20%.

In a four-band resistor, which is the most common, the first two bands also represent the first two significant digits. The third band represents the multiplier. The fourth band represents the tolerance. ff782bc1db