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| Both sides previous revisionPrevious revisionNext revision | Previous revision |
| en:electronics:led_resistor [2010/03/28 11:33] – Helen | en:electronics:led_resistor [2020/07/20 09:00] (current) – external edit 127.0.0.1 |
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| ====== LED resistor calculation ====== | ====== LED Resistor Calculation ====== |
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| If the supply voltage is higher than LEDs voltage the resistor have to be included into the circuit in series. The resistor limits the current and produces the required voltage drop. To find the correct value for the resistor the following equation is derived from Ohm's law: | If the supply voltage is higher than the LED's voltage, the resistor has to be included in the circuit in series. The resistor limits the current and produces the required voltage drop. To find the correct value for the resistor, the following equation is derived from Ohm's law: |
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| [{{ :images:electronics:led_resistor:led_resistor_schematics.png?180|LED with series resistor}}] | [{{ :images:electronics:led_resistor:led_resistor_schematics.png?180|LED with series resistor}}] |
| where: | where: |
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| * R is resistor. | * R is resistance. |
| * U<sub>in</sub> is supply voltage. | * U<sub>in</sub> is supply voltage. |
| * U<sub>f</sub> is LED voltage. | * U<sub>f</sub> is LED voltage. |
| * I<sub>f</sub> is LED current. | * I<sub>f</sub> is LED current. |
| * U<sub>r</sub> is voltage drop on the resistor. | * U<sub>r</sub> is voltage drop on the resistor. |
| * P<sub>r</sub> is power of the resistor what is transformed to the heat. | * P<sub>r</sub> is power of the resistor that is transformed into heat. |
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| The current limiting resistor of a LED has to be not smaller than R and at least with the power of P<sub>r</sub>. | The current limiting resistor of an LED has to be not smaller than R, and at least with the power of P<sub>r</sub>. |
