LED circuit with current-limiting resistor in PCB Design - Real Business Scenario

Scenario Mode

👤 Your Role: You are an electronics technician working on a new product prototype.

📋 Request: Your manager wants a clear report showing how to design an LED circuit with a current-limiting resistor to ensure the LED operates safely.

📊 Data: You have data on LED forward voltage (Vf), desired current (I), and supply voltage (Vs).

🎯 Deliverable: Create a report with calculations for the resistor value, a simple schematic diagram, and a summary dashboard showing the resistor value and expected LED current.

Sample Data

LED Color	Forward Voltage (Vf)	Desired Current (mA)	Supply Voltage (Vs)
Red	2.0	20	5
Green	2.2	20	5
Blue	3.0	20	5
White	3.2	20	5

1

Step 1: Calculate the resistor value for each LED color using the formula R = (Vs - Vf) / I, where I is in Amps.

For Red LED: R = (5V - 2.0V) / 0.02A = 150 ohms For Green LED: R = (5V - 2.2V) / 0.02A = 140 ohms For Blue LED: R = (5V - 3.0V) / 0.02A = 100 ohms For White LED: R = (5V - 3.2V) / 0.02A = 90 ohms

Expected Result

Resistor values: Red=150Ω, Green=140Ω, Blue=100Ω, White=90Ω

2

Step 2: Create a simple schematic diagram showing the supply voltage connected to the resistor, then to the LED, and finally to ground.

Draw: Vs (+5V) -> Resistor (calculated value) -> LED (color) -> Ground

Expected Result

A clear schematic with correct resistor values for each LED color

3

Step 3: Build a dashboard table summarizing LED color, resistor value, and expected current.

Table columns: LED Color, Resistor Value (Ω), Expected Current (mA) Values from step 1 calculations

Expected Result

Dashboard table: Red | 150Ω | 20mA Green | 140Ω | 20mA Blue | 100Ω | 20mA White | 90Ω | 20mA

4

Step 4: Explain why the resistor is important to limit current and protect the LED.

Text explanation: The resistor limits current to prevent LED damage by dropping excess voltage and controlling current flow.

Expected Result

Clear understanding that resistor prevents LED burnout by controlling current

Final Result

Resistor

↓

Resistor

✓Each LED color requires a different resistor value due to different forward voltages.

✓Using the correct resistor ensures the LED receives the desired 20mA current.

✓Without the resistor, the LED could draw too much current and burn out.

✓The simple circuit with resistor and LED connected to 5V supply is effective and safe.

Bonus Challenge

Design a circuit with two LEDs of different colors connected in series with one resistor. Calculate the resistor value and expected current.

Show Hint

Add the forward voltages of both LEDs, then use R = (Vs - (Vf1 + Vf2)) / I to find the resistor.