How to find the resistor value for different types of LED circuits
The following step-by-step guide will help you find the correct value of a resistor (or resistor).resistors) for one or more LEDs and LED string circuits to design and connect to the battery and power supply.
The following guide will show you how:
- Calculate the value of the resistors for different LED circuits.
- Calculate the forward current of the LEDs.
- Calculate the forward voltage for various LED circuits.
- Connect the LEDs in series with a battery.
- Connect the LEDs in parallel to a battery.
- Connect LEDs in series-parallel combination circuits.
Update:you can use this tooLED Resistor Calculatorfor the same purpose, i. h to determine the value of the exact or nearest standard value of resistance for LED circuits.
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table of Contents
Typical LED symbol, structure and line identification
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Formula to find the resistance value for an LED circuit
resistance value= (VDelivery– V.F) ÷ yoF
- VDelivery= supply voltage
- VF= forward voltage
- IF= direct current
The following formula can be used to calculate the value of the power rating of the resistor.
resistance classification= yoF2× resistance value
Find the value of a resistor to connect to an LED
Before going into details, let's try to evaluate the following simple circuit. This makes it easy to determine the value of resistors for other complex circuits.
Click to enlarge the image
In the above simple LED circuit, the supply voltage is 6 V, the forward voltage of the LED (VF) is 1.3 volts and the forward current (IF) is 10mA.
The value of the resistor (which we put in series with the LED) for the previous circuit would now be:
resistance value= (VDelivery– V.F) ÷ yoF = (6 – 1,3) ÷ 10mA =470 Ω
current draw =20mA
Resistor power formula for this circuit
Resistance Rating = IF2× resistance value
= (10mA)2× 470 Ω = 0.047W =47 mW
ButThis is the minimum resistor value required to ensure that the resistor does not overheat. Therefore, it is recommended to double the resistance rating you have calculated. So for this circuit, choose a resistor of 0.047 W × 2 = 0.094 W = 94 mW. Rated power of the resistor (the value is doubled) = 0.094 W = (94 mW)
Good to know:
- It's too hard to find the exact power-rated resistors you calculated. Resistors generally come in 1/4 watt, 1/2 watt, 1 watt, 2 watt, 5 watt, etc. Therefore, choose the next highest power rating. For example, if the calculated value of the resistor's power rating is 0.789 W = 789 mW, you would select a 1 W resistor.
- It's too hard to get the exact value of the resistors you calculated. In general, resistors are supplied in standard values. If you can't find the exact value of a resistor you calculated, select the value closest to the resistor you calculated. For example, if the calculated value is 313.5 Ω, you would use the closest standard value, which is 330 Ω. If the closest values are not close enough, you can achieve this by connecting resistors in a series - parallel configuration.
- IF= direct current of the LED:This is the maximum current that an LED can draw continuously. For long life and stability, it is recommended to provide 80% of the forward current of the LED. For example, if the LED's current rating is 30mA, you should drive that LED at 24mA. A current value that exceeds this value will shorten the life of the LED or it may start to smoke and burn.
- If you still can't find the forward current of the LED, assume it is 20mA, since typical LEDs run at 20mA.
- VF= forward voltage of the LED:This is the forward voltage of the LED, i.e. h the voltage drop when we supply the rated forward current. You can find this data on LED packages, but it varies between 1.3V and 3.5V depending on type, color, and brightness. If you still can't find the forward voltage, just connect the LED above 200Ω with a 6V battery. Now measure the voltage across the LED. It is 2V and this is the forward voltage.
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Find the value of a resistor for series connection with LED
Another simple LED circuit (LEDs connected in series) is shown below. In this circuit we connect 6 LEDs in series. The supply voltage is 18 V, the forward voltage (VF)of the LEDs is 2V and the direct current (IF)is 20mA each.
Resistance value for LEDs in series= (VDelivery– (VF× number of LEDs))÷IF
Click to enlarge the image
In the LED series circuit above, the total forward voltage (VF) de 6 LED = 2 × 6 = 12V
and direct current (IF) is equal (i.e. 20 mA)
(Use: This is a series circuit, so the current in the series circuit is the same at all points, while the voltages are additive.)The value of the resistor (for the series connection) would now be:
= (VDelivery– (VF× Number of LEDs)) ÷ IF = (18 – (2 × 6)) ÷ 20mA
= (18 – 12) ÷20 mA =300Oh
Total current consumption = 20mA
(This is a series circuit, so the currents are equal)resistance classification
= yoF2× resistance value= (20mA)2× 300 Ω = 0.12 = 120 mW
ButThis is the minimum resistor value required to ensure that the resistor will not blow. In this way, it is recommended to double the rated power of the calculated resistor. So for this circuit, choose a resistor of 0.12 W × 2 = 0.24 W = 240 mW.Rated power of the resistor (the value is doubled) = 0.24 W = (240 mW).
Find the value of a common resistor to connect LEDs in parallel
Click to enlarge the image
In this circuit we connect LEDs in parallel with a common resistor. The supply voltage is 18 V, the forward voltage (VF) of the LEDs is 2 V and the forward current (IF) is 20 mA each.
Common resistor value for LEDs connected in parallel=(VDelivery– V.F) ÷ (yoF× number of LED)
Here the total forward current (IF) of 4 LEDs = 20 mA × 4 = 0.08 A and forward voltage (VF) is equal (ie 2V)
(Use:This is a parallel circuit, i. h the voltage is the same at all points, while the currents add.
The value of the resistance (for a parallel circuit with a common resistance) would now be:
= (Vdelivery– V.F)÷(IF× number of LED)
= (18 – 2)÷0,08
Total current draw = 20mA × 4 = 80mA
(This is a parallel circuit, so the currents add up)
Resistance Rating = IF2× resistance value = (20mA)2× 200 Ω = 0,08 W = 80 mW
As previously,This is the lowest required resistor value that will not overheat or explode. Therefore, it is recommended to double the power rating of the calculated resistor. So choose a 1.28 W × 2 = 2.56 W resistor for this circuit. Resistor power rating (value is doubled) = 2.56 W (280 mW).
Find the value of a separate resistor for parallel connection with LED
Click to enlarge the image
This is another way to connect LEDs in parallel with separate resistors. In this circuit we have connected 4 LEDs in parallel with separate resistors. The supply voltage is 9V and the forward voltage (VF) of the LEDs is 2 V and the forward current (IF) is 20 mA each.
Separate resistor value for LEDs connected in parallel=(VDelivery– V.F) ÷ yoF
In this case, the total forward voltage (VF) of LED = 2 and direct current (IF) 20mA (also 20mA)
(Use:This is a parallel circuit, but we are finding the resistance value for each section, not the entire circuit. Therefore, in each section, the circuit is in series connection (see formula for series connection or 1callesimple circuit above, you will find that these are the same)
The resistor value (for parallel connection with separate resistors) would now be:
= (VDelivery– V.F)/ IF= (9 – 2)÷20mA = 350 Ω
Total current draw = 20mA × 4 = 80mA (This is a parallel circuit, so the currents add up)
Resistance Rating = IF2× resistance value = (20mA)2× 350Ω = 0.14 =140 mW
same as abovescenarios, the calculated value of the resistor is theMinimum value required for a safe connection in the LED circuit. To be safe, it's a good idea to double the power rating of the calculated resistor. So for this circuit, choose a resistor of 0.14 W × 2 = 0.28 W = 280 mW. Rated power of the resistor (the value is doubled) = 0.28 W (280 mW).
There is another way to connect LEDs to batteries in a series and parallel combination and yes, you will also need a suitable resistor or resistors for this purpose. But if you understand this simple calculation based tutorial, I'm sure you can easily determine the value of resistors also for LED connections and circuits based on a series-parallel combination.
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If you know the total current and the voltage across the whole circuit, you can find the total resistance using Ohm's Law: R = V / I. For example, a parallel circuit has a voltage of 9 volts and total current of 3 amps. The total resistance RT = 9 volts / 3 amps = 3 Ω.What is the formula used for calculating the current-limiting resistor value in an LED circuit connected to an Arduino's digital output? ›
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The point here is that you generally don't want to use only one current-limiting resistor because you can't ensure that the LEDs will equally share current; furthermore, it is possible that one LED will get much more current than the others.How do you know how much current a resistor can handle? ›
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Required components for this 220V LED circuit:
560-ohm 1-watt resistor. 1M 0.25-watt resistor.
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- Wattage of power supply ÷ Wattage of LED strip = Total metres you can run off that strip.
- Amps x voltage = wattage.
- Wattage ÷ voltage = amps.
50" Bar comes with 12" of flood reflectors on the outsides of the light and 26" of spot reflectors on the inside half of the light. This will optimize both functional light spread and light distance for increased visability. General Specs. Watts 195 Amp Draw 14.44 Lumens 18000 # of LEDs 100.Why use 330 ohm resistor for LED? ›
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= (3.7 - 3.3)/100 = 0.4/0.1 = 4 ohms. The required wattage would be 0.4 x 0.1 = 0.04W, so a 1/4 watt resistor would be more than enough.
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It doesn't matter! The resistor can go before – or after – the LED, and it will still protect it. the current that flows out of a battery is always equal to the current that flows back into the battery.
|Power Supply Voltage||LED Color||Resistor (rounded)|
|5 V||Red, Yellow, or Yellow-Green||150 Ω|
|5 V||Red, Yellow, or Yellow-Green||56 Ω|
|9 V||Red, Yellow, or Yellow-Green||75 Ω|
|9 V||Blue, Green, White, or UV||100 Ω|
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In extreme cases the excessive power can even melt or catch on fire. One cause of failure in many applications is temporary exposure to unexpectedly high current peak, or short but severe overload (STOL).