Overview
This lecture explains how to determine the correct resistor value needed for an LED circuit to ensure safe operation.
Required Information for Resistance Calculation
- Identify the electronic component (e.g., LED) needing the resistor.
- Determine the voltage of your power source (e.g., 9V battery).
- Find the forward voltage (voltage drop) of your component, usually from manufacturer data sheets.
- Find the current (amps) used by your component, also from the data sheet.
Steps to Calculate the Resistor Value
- Use the formula: Resistance (R) = (Power Source Voltage - Forward Voltage) / Amps.
- Example: For a 9V battery, an LED with 3.2V forward voltage, and 24mA (0.024A) current:
- R = (9 - 3.2) / 0.024
- R = 5.8 / 0.024 ≈ 240 ohms
Practical Tips and Considerations
- Always check your LED's data sheet for accurate forward voltage and current.
- If the exact resistor value is unavailable, use the next highest standard value to protect your LED.
- Using a resistor slightly higher in value is safe; too low can damage the LED.
- If you lack manufacturer info, start with a 1.5 kΩ resistor for basic LED protection.
- Add battery voltages together if using multiple batteries.
Key Terms & Definitions
- Forward Voltage — The voltage drop across a component (like an LED) while operating.
- Amps (A) — Unit of electric current; LEDs often specify usage in milliamps (mA).
- Resistor — A component that limits current flow in a circuit.
- Ohm (Ω) — Unit of electrical resistance.
Action Items / Next Steps
- Write down the resistor calculation formula for future use.
- Look up or save your component's data sheets for forward voltage and current ratings.
- Practice calculating required resistor values with different components and power sources.