5. Select a Resistor to Drive an LED
1. Component Purpose & Calculation
The red LED has a forward voltage of 2V and needs 22mA to light up properly. The supply is 12V. Without a series resistor, the full 12V would destroy the LED instantly. The resistor limits the current to a safe value.
Resistor Calculation:
R = (Vsupply − Vf) / If = (12V − 2V) / 22mA = 10V / 0.022A = 454.5Ω
The nearest standard resistor values are 430Ω and 470Ω. Both are acceptable:
- 430Ω → I = 10/430 = 23.3mA (slightly brighter, within safe range)
- 470Ω → I = 10/470 = 21.3mA (slightly dimmer, perfectly safe)
Power dissipation: P = I² × R = (0.023)² × 470 = 0.25W. A ≥0.5W resistor provides safe margin.
Required: 430Ω to 470Ω · ±5% · ≥0.5W · 2010 package · Thick Film · −55°C to +125°C · RoHS
2. How to Find It on DigiKey
Go to DigiKey.com → Resistors → Chip Resistor - Surface Mount
Apply these filters:
- Resistance → 430 Ohms or 470 Ohms
- Tolerance → ±5% or tighter
- Power (Watts) → 0.5W (1/2W)
- Composition → Thick Film
- Package / Case → 2010
- Part Status → Active
Tip: The task accepts any value from 430Ω to 470Ω. Search for both 430Ω and 470Ω separately, or use DigiKey’s multi-select to pick both values at once.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Resistance | 430Ω to 470Ω | Limits LED current to ~21–23mA. |
| Tolerance | ±5% | Acceptable for LED drive; not precision. |
| Power Rating | ≥0.5W | Actual dissipation ~0.25W; 2× margin. |
| Type | Thick Film | Standard, cost-effective for this use. |
| Package | 2010 | Handles 0.5W; fits the board layout. |
| Temp Range | −55°C to +125°C | Standard industrial range. |
| RoHS | Yes | Compliance required. |
4. Selecting a Safe, Production-Ready Part
The filtered list will show many matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?
Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide