How to Use a 9-Volt Battery to Power LEDs
- 1). Examine the data sheet for the LED you wish to use. Identify the specifications for maximum current (Imax) and typical forward voltage (Vf typ).
Example: 9-volt battery
LED Imax = 20milliamps (mA)
Vf typ=2 Volts (V) - 2). Determine the voltage drop across the resistor (Vr). This voltage will equal the battery voltage (Vbatt) minus the Vftyp for the LED.
Example: Vr=Vbatt-Vftyp
Vr=9 volts - 2 volts = 7 volts - 3). Calculate a working current (Iwork) for the LED---typically about 75 percent of the maximum current.
Example: Iwork= Imax x 0.75
Iwork=20mA x 0.75 = 15mA - 4). Choose a resistor value to allow 15mA of current to flow across.
Example: I=V/R ( Ohm's Law: Current = Voltage/Resistance)
15mA = Vr/R
15mA = 7 volts/R
R=466 ohms - 5). Select a 466-ohm resistor, or the next highest value of standard resistor.
- 6). Connect one end of the resistor to the positive terminal of the battery.
- 7). Connect the other end of the resistor to the positive (anode) terminal of the LED.
- 8). Connect the cathode of the LED to the negative terminal of the battery. The LED should illuminate.
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