220Ω Resistor
The standard current-limiting resistor for a 5V-powered red or yellow LED — one of the two values (with 330Ω) every beginner kit includes.
How this component works
A resistor opposes the flow of electric current. The relationship between voltage, current, and resistance follows Ohm's Law: V = I × R. The higher the resistance in ohms (Ω), the less current flows for a given voltage.
Resistors are used to limit current to protect other components (like an LED), to divide voltage between two points, or to set bias points in transistor circuits. Real resistors are also rated for power dissipation (commonly 1/8W, 1/4W, 1/2W, 1W) — exceeding this rating causes the resistor to overheat and fail.
Fixed resistors have a color-coded value that doesn't change. A potentiometer is the variable version of a resistor, and both use the same underlying physics in CircuitForge's solver.
Deep Dive: 220Ω Resistor
The 220Ω resistor is the cornerstone of 5V LED circuits. If you have a standard red LED with a 2V forward voltage (Vf), placing a 220Ω resistor in series with a 5V supply leaves 3V across the resistor (Vr = 5V - 2V = 3V). Applying Ohm's Law (I = V/R), this results in a current of exactly 13.6mA (3V / 220Ω = 0.0136A). This sits perfectly within the safe, bright operating range of typical 20mA indicator LEDs without pushing them to their thermal limits.
Because it drops a relatively high amount of current compared to the 1kΩ or 10kΩ parts, power dissipation must be kept in mind. At 3V across the resistor, it dissipates about 41mW (P = V×I = 3V × 13.6mA). This is well below the 250mW (1/4W) rating of a standard through-hole resistor, so it remains comfortably cool to the touch.
While often used as a pull-up or pull-down resistor in high-speed digital lines where parasitic capacitance must be charged quickly, it draws over 22mA when pulled directly across a 5V rail. This makes it a poor choice for battery-powered static logic pull-ups compared to a 10kΩ resistor, as the constant current draw would quickly drain the battery.
Common Use Cases
- Current-limiting resistor in series with a red/yellow/green LED on a 5V supply
- Pull-down or pull-up resistor where a lower value is needed for faster switching
- Base resistor for driving a small-signal NPN transistor from a 5V logic pin
Frequently Asked Questions
Will a 220Ω resistor work for any LED?
It works safely for most low-power red, yellow, and green LEDs on 5V, but blue and white LEDs have a higher forward voltage and draw less current through the same resistor — 330Ω is more common for those on higher-voltage supplies. Check the LED's forward voltage first.
What happens with a lower resistance, like 100Ω?
Less resistance means more current reaches the LED. If it pushes the LED past its rated forward current, the LED will run hotter and its lifespan drops — in the simulator you can raise the source voltage and watch the current climb to see this directly.
Comparison Notes
Compared to a 330Ω resistor, 220Ω allows roughly 50% more current to flow. On a 5V supply, this makes LEDs visibly brighter but cuts into the safety margin if driving components directly from a microcontroller pin with a strict 20mA current limit. For 3.3V systems, a 220Ω resistor is often a bit too high for LEDs (yielding only ~6mA for a 2V LED), making lower values like 100Ω or 150Ω more common.