Select a Resistor to Drive an LED

Question

Problem: Select a Resistor to Drive an LED. Solve this hands-on electronics task on EWskills.

Accepted Answer

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

5. Filtered DigiKey Link

➡ View Matching Parts — 430Ω/470Ω, 2010, ±5%, Thick Film, 0.5W

5. Select a Resistor to Drive an LED