The **MMBT3904-AL3-R** is a specific surface-mount version of the classic 2N3904 General Purpose Transistor. It is widely used in switching and amplification applications due to its versatility and high speed. --- ### 1. General Specifications The device is an **NPN Epitaxial Silicon Transistor**. Below are the key electrical characteristics: | Parameter | Symbol | Maximum Rating | Unit | | :--- | :--- | :--- | :--- | | Collector-Base Voltage | $V_{CBO}$ | 60 | V | | Collector-Emitter Voltage | $V_{CEO}$ | 40 | V | | Emitter-Base Voltage | $V_{EBO}$ | 6.0 | V | | Collector Current (DC) | $I_C$ | 200 | mA | | Total Power Dissipation | $P_D$ | 350 | mW | | Junction Temperature | $T_J$ | 150 | °C | --- ### 2. Package and Part Number Breakdown The "AL3-R" suffix typically refers to the specific packaging and tape-and-reel specifications from manufacturers like **UTC (Unisonic Technologies)**. * **MMBT**: Indicates a Surface Mount (SMT) package (Small Outline Transistor). * **3904**: The core NPN transistor type. * **AL3**: Refers to the **SOT-23** package type. * **R**: Generally signifies "Tape & Reel" packaging for automated assembly. ### 3. Key Performance Features * **High DC Current Gain ($h_{FE}$):** Typically ranges from 100 to 300, making it efficient for small signal amplification. * **Fast Switching:** It has a high transition frequency ($f_T$) of approximately 300 MHz, allowing it to be used in high-frequency pulse applications. * **Low Saturation Voltage:** $V_{CE(sat)}$ is usually less than 0.3V at $I_C = 50mA$, minimizing power loss when the transistor is fully "ON." --- ### 4. Typical Applications Because of its small footprint (SOT-23) and reliable performance, it is found in: 1. **Signal Logic Gates:** Used to invert signals or create basic logic circuits. 2. **LED Driving:** Switching small indicator LEDs on and off. 3. **Relay Driving:** Acting as a switch for small DC relays. 4. **Audio Preamplification:** Boosting low-level signals before further processing. ### 5. Pinout Configuration (SOT-23) ```text [ 3 ] <-- Collector / \ [ 1 ] --- [ 2 ] ^ ^ Base Emitter ``` ---