Current through an LED circuit – Learning electronics lesson 0002

The Amount of current flowing through a simple LED protected by a resistor circuit depends on the forward voltage of the LED and the resistance of the resistor. The LED drops some of the supply voltage from the resistor, and then the resistor sets the current based on the voltage across the resistor and it’s resistance. Series components have the same current flowing through them.

LED protected by a resistor circuit voltage resistance and current ohms law calculations diagram by electronzap
LED protected by a resistor circuit voltage resistance and current ohms law calculations diagram by electronzap
Rectifier diode and LED schematic symbols and common appearance with forward biased polarity diagram by electronzap electronzapdotcom
Rectifier diode and LED schematic symbols and common appearance with forward biased polarity diagram by electronzap electronzapdotcom
  • Forward biased (FB) diode/LED: Anode more positive than cathode.
  • Reverse biased (RB) diode/LED: Cathode more positive than Anode.
  • LED is a Light Emitting Diode

You can estimate the voltages if you know approximately how much the forward voltage (voltage needed to get a FB diode to start conducting current) of the LED is. Red and other warm colors tend to have close to a 2V forward voltage, whereas blue, green and white tend to have close to 3V forward voltage.

Voltage measurement locations

Make sure and set the meter to measure a higher voltage that you can expect to come across. Some meters are auto ranging and you only have to set it to measure voltage.

Measuring voltages of a simple circuit
Measuring voltages of a simple circuit

The 2 lines coming out of the circled V (for voltage measurement) go to the measurement locations points. Usually you put the black probe on the more negative side of the circuits, and the red probe to the more positive side of the circuit. If you connect red probe to more negative and black probe to more positive, you will get a negative voltage on the display.

Video:

Resistor protecting LED circuit calculations for limiting current and power dissipation

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Current through a resistor – Learning electronics lesson 0001