The designation **120-R** (or **120R**) is a common nomenclature used in electronics to describe components with a specific value of **120 Ohms**. The "R" acts as both a decimal point placeholder and a unit symbol for Ohms ($\Omega$). --- ## 1. Common Types of 120-R Components The most frequent application of "120-R" is in resistors. Depending on the circuit requirements, they come in various packages: | Component Type | Package Style | Description | | :--- | :--- | :--- | | **SMD Resistor** | 0603, 0805, 1206 | Surface-mount chips labeled "1200" or "121" (12 + 1 zero). | | **Through-Hole** | Axial (Cylindrical) | Traditional resistors with color bands: **Brown-Red-Brown-Gold**. | | **MELF Resistor** | Metal Electrode Leadless | High-precision cylindrical SMD components. | | **Network Resistor** | SIP / DIP | Multiple 120-ohm resistors in a single integrated package. | --- ## 2. Technical Specifications When selecting a 120-R part, you must consider the following electrical characteristics: ### A. Power Rating (Wattage) - **1/8W or 1/4W:** Standard for signal processing. - **1W to 5W:** Used in power supplies or LED current limiting. - **High Power:** Often housed in ceramic or aluminum casings for heat dissipation. ### B. Tolerance - **±5% (Gold band):** Standard consumer electronics. - **±1% (Brown band):** Precision circuits (CAN Bus termination). ### C. Temperature Coefficient - Measured in **ppm/°C**, indicating how much the resistance changes as the part heats up. --- ## 3. Key Application: CAN Bus Termination The most "famous" use of a **120-R** resistor is in **Controller Area Network (CAN Bus)** communication, used extensively in automotive and industrial automation. * **Function:** To prevent signal reflection. * **Placement:** One 120-ohm resistor is placed at each physical end of the bus (between CAN-High and CAN-Low). * **Result:** The parallel combination of two 120-R resistors results in a **60-ohm** total bus impedance, which matches the characteristic impedance of the twisted-pair cable. --- ## 4. How to Identify 120-R (Color Codes) If you are looking at a 4-band through-hole resistor, the colors will be: 1. **Band 1:** Brown (1) 2. **Band 2:** Red (2) 3. **Band 3:** Brown (Multiplier: x10) 4. **Band 4:** Gold (Tolerance: ±5%) ```text Calculation: 12 x 10 = 120 Ohms ``` ---