Reading the value of a Surface Mount Device (SMD) capacitor typically involves interpreting a code printed on its small surface. For standard-tolerance SMD capacitors, a 3-digit code is used to mark the capacitance value on the part, providing a straightforward way to determine its electrical properties.
Understanding the 3-Digit Code
The most common method for marking standard SMD capacitors uses three digits. This code functions similarly to resistor color codes but in a numerical format.
- The first two numbers indicate the significant digits of the capacitance value.
- The third digit represents the multiplier, which is a power of 10.
The resulting value is typically in picofarads (pF).
Formula: Capacitance = (Significant Digits) * 10^(Multiplier) pF
Examples of the 3-Digit Code:
Let's look at a few common examples:
- 101: The first two digits are 10. The third digit is 1, meaning 10¹. So, 10 10¹ pF = 10 10 pF = 100 pF.
- 224: The first two digits are 22. The third digit is 4, meaning 10⁴. So, 22 10⁴ pF = 22 10,000 pF = 220,000 pF. To convert to nanofarads (nF), divide by 1000 (220 nF), or to microfarads (µF), divide by 1,000,000 (0.22 µF).
- 470: The first two digits are 47. The third digit is 0, meaning 10⁰. So, 47 10⁰ pF = 47 1 pF = 47 pF.
Using 'R' for Decimal Points
Sometimes, a decimal point is needed within the significant digits. In the coding scheme, 'R' is used to indicate the position of a decimal point.
- 'R' replaces the decimal point itself.
- Digits before and after 'R' form the significant digits.
Examples Using 'R':
- 2R2: This code means 2.2. Since there is no multiplier digit, the value is simply 2.2 pF.
- R10: This code means 0.10. The value is 0.10 pF.
- 4R7: This code means 4.7. The value is 4.7 pF.
Summary Table
Here's a quick reference for interpreting common codes:
| Code | Significant Digits | Multiplier (10^x) | Calculation (pF) | Value (pF/nF/µF) |
|---|---|---|---|---|
| 101 | 10 | 10¹ | 10 * 10 = 100 | 100 pF |
| 472 | 47 | 10² | 47 * 100 = 4700 | 4700 pF (4.7 nF) |
| 224 | 22 | 10⁴ | 22 * 10000 = 220000 | 220,000 pF (220 nF / 0.22 µF) |
| 105 | 10 | 10⁵ | 10 * 100000 = 1000000 | 1,000,000 pF (1 µF) |
| 2R2 | 2.2 | 10⁰ (implied) | 2.2 | 2.2 pF |
| R15 | 0.15 | 10⁰ (implied) | 0.15 | 0.15 pF |
Understanding this 3-digit code and the use of 'R' allows you to quickly identify the capacitance value of many common SMD capacitors directly from their marking. Keep in mind that very small SMD components might not have any marking due to space constraints.
