🎄 Do I Need A Resistor For Led

1 Answer. Forward voltage is a voltage necessary for LED to conduct electricity. If the voltage across your LED is 3.4V, it will draw as much current as it can, and burn out eventually. So you need to limit this current to 300 mA. If you have power source of 9V, it means you can fit 2 LED comfortably in series as they will need 6.8 V together. So by putting the 150 ohm resistor in there there will be a maximum current of 20 mA through the LED. Let's also say that we want the LED current to go down to 1 mA. Unless the pot has a super high resistance, it won't go down to 0 mA, and 1 mA seems like a reasonable lower limit. To make that work, our pot needs to be about 2K Ohms. Then run the wire from the splice to the resistor. With motion and airflow, the resistor will cool. Signal lights don't stay on long enough, for a load resistor to heat up enough, to start a fire. You can mount them anywhere you want. Pick a spot with good airflow. Maybe the front of the bike. You need to know the forward voltage (Vf) and current requirement (A) of the LED. Then, calculate if the 1.5kΩ resistor results in enough (and not too much) current for the LED. AND as dl324 said, the LED may load the output line to the point the MCU cannot detect the output of the PIR… As the voltage of the 9v battery drops, eventually only the RED component of the rainbow leds will light up. … also wiring rainbow leds in series can be problematic as the driver chip for one led can mess up the others in series. You really need to run them in Parallel with current limit resistors on each one independent on the others. Good As one LED fails, the others will take more current and the rest of the LEDs will start to self-destruct. The reason why they take more current is this: the current-limit resistor will have been designed so that say 60mA will flow when 3 LEDs are in parallel. When one LED fails, the remaining LEDs will take 30mA each. Choosing the resistor to use with LEDs As you can see from the chart above, there are two forward voltages typically used. The red, yellow, and orange LEDs fall into the 1.8 V category, and the white, blue, green, pink, UV, fall into the 3.2 V category. The transistors are used as switches (assuming the base resistor is low enough), and the current in the LEDs is determined mainly by the value of the resistors, the "12V" supply voltage and the voltage drop of the LEDs. Schematic A is rather different, the resistor and transistor form a voltage controlled current sink. Calculate the resistor value using ohm's law, which states: voltage = current times resistance. The required voltage drop is four volts, as the battery provides nine volts and five volts is needed to power the LED. Putting the voltage drop and an example LED current of 20 milliamps into the equation gives: 4 = 0.02 x R. At that current this LED has a Vf forward voltage of: See left graph: 2.2V. That means if the LED is next to a resistor and a 9V output; R=V/I R=9-2.2/0.020 = 340 Ω. At least. A resistor is a current limiter, the LED is not. It can use practically unlimited current and without resistor it will brighten very much for a very short moment. To determine the current-limiting resistor for an LED, you need to know its forward voltage (Vf) and desired current (I). Use Ohm’s Law (R = Vf / I) to calculate the resistor value. For a 5V supply and a standard 2V LED, a 150-ohm resistor (nearest standard value) would limit the current to around 20 mA, a common choice for LED applications. OK, let's do the calculation. A simplified model for a LED is a fixed voltage source in series with a small resistor. Let's pick this LED from Kingbright. The slope is 20mA/100mV, so the internal resistance is 5\$\Omega\$. The the intrinsic LED voltage is 1.9V. Let's assume that the LEDs need 20mA and that our power supply is 5V. .

do i need a resistor for led