Surface Mount Device (SMD) resistors are often marked with a numerical code to indicate their resistance value. The markings on SMD resistors typically consist of numbers and sometimes letters, and they are usually printed on the top surface of the resistor. Here's how you can read a standard SMD resistor:
Three-Digit Code:
The most common SMD resistors have a three-digit code. The first two digits represent significant figures, and the third digit represents the multiplier.
For example, if you see "473" on an SMD resistor, it means 47 * 10^3 ohms, or 47 kΩ.
Four-Digit Code:
Some SMD resistors have a four-digit code. The first three digits represent significant figures, and the fourth digit represents the multiplier.
For example, "1023" would mean 102 * 10^3 ohms, or 102 kΩ.
Letter Codes:
In some cases, a letter may follow the numerical code. This letter typically indicates the tolerance of the resistor.
Common tolerance codes include:
F for ±1%
G for ±2%
J for ±5%
K for ±10%
Examples:
If you see "221" on an SMD resistor, it means 22 * 10^1 ohms, or 220 ohms.
If the resistor has a tolerance letter, like "221J," it means 220 ohms with a tolerance of ±5%.
Metric Prefixes:
Sometimes, you may encounter SMD resistors with metric prefixes, especially in smaller sizes. Common prefixes include:
R for ohms (e.g., 4R7 means 4.7 ohms).
K for kilohms (e.g., 4K7 means 4.7 kΩ).
Remember that these are general conventions, and it's always a good practice to check the manufacturer's datasheet or specifications for any specific resistor to ensure accurate interpretation of the markings. Additionally, the size and style of the SMD package can vary, so it's essential to consider those factors when identifying SMD resistors.
