KembaraXtra-Computer Science-Light-Emitting Diodes (LEDs)

KembaraXtra-Computer Science-Light-Emitting Diodes (LEDs)
1. Introduction to LEDs

What is an LED? A light-emitting diode is a special type of diode that emits light when current flows through it.
Diode Functionality: A diode allows current to flow in only one direction (low resistance) and blocks current in the opposite direction (high resistance).
LED Colors: LEDs are available in various colors.

2. LED Circuit Symbol

LED Symbol: (You should refer to Figure 3-16 for the actual symbol). It resembles a standard diode symbol with arrows indicating light emission.

3. Current and LEDs

Maximum Current: Exceeding the maximum rated current of an LED can damage it. Example: A standard red LED has a maximum current rating of about 25mA.
Target Current: Aim for a current slightly below the maximum (e.g., 20mA for a standard red LED) to ensure brightness without damaging the LED. Lower current = less brightness.
Current Limiting: A resistor is used in series with the LED to limit the current flowing through it.

4. Forward Voltage (Vf)

Definition: Forward voltage is the voltage drop across the LED when current is flowing through it.
Typical Vf: A typical red LED has a forward voltage (Vf) of about 2V.
Importance: Forward voltage is crucial for calculating the correct resistor value to limit current.

5. Basic LED Circuit Analysis (Refer to Figures 3-17 and 3-18)

Components:
- Battery (Voltage Source)
- LED (with forward voltage Vf)
- Resistor (R, to limit current)
Kirchhoff's Voltage Law: The sum of the voltage drops across the LED (Vf) and the resistor (VR) equals the battery voltage (Vbattery). Vf + VR = Vbattery.
Calculating VR: VR = Vbattery - Vf
Ohm's Law: R = V / I, where:
- R is the resistance of the resistor in ohms (Ω).
- V is the voltage drop across the resistor (VR) in volts (V).
- I is the current flowing through the circuit in amperes (A). (Note: 20mA = 0.020A)

6. Example Calculation (Based on the Text)

Given:
- Battery Voltage = 9V
- LED Forward Voltage (Vf) = 2V
- Target Current (I) = 20mA = 0.020A
Calculations:

i.VR = Vbattery - Vf = 9V - 2V = 7V
ii.R = VR / I = 7V / 0.020A = 350Ω

Conclusion: A 350Ω resistor is needed to limit the current to approximately 20mA in this circuit.

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