Variable Resistor Led Circuit. For example a volume knob can be a variable resistor. So if we have a 12v battery powering a 3 5v 25ma led our formula becomes.
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12 3 5 25 1000 340ohms. Substituting these values in the above equation we can calculate the value of series resistance as. They can also be used to control the voltage across devices in a circuit too.
A variable resistor is very important.
It allows you to build a circuit with some degree of control. So if we have a 12v battery powering a 3 5v 25ma led our formula becomes. Power supply voltage led voltage current in amps desired resistor value in ohms we end up with a resistor value of 48 ω. Our version of the formula now looks like this.
