The **MMBT3904-AE3-R** is a widely used General Purpose NPN Epitaxial Silicon Transistor. It is the surface-mount (SMD) equivalent of the classic through-hole 2N3904 transistor. --- ### 1. Key Technical Specifications Below are the primary electrical characteristics of the MMBT3904-AE3-R: | Parameter | Symbol | Value | 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 | | **DC Current Gain** | $h_{FE}$ | 100 - 300 | (at 10mA) | | **Transition Frequency** | $f_T$ | 300 | MHz | --- ### 2. Pin Configuration (SOT-23 Package) The "AE3" suffix typically refers to the **SOT-23** package type. The pinout is standard for this series: 1. **Pin 1 (Base):** Controls the flow between Collector and Emitter. 2. **Pin 2 (Emitter):** Where the current exits the transistor. 3. **Pin 3 (Collector):** Where the current enters the transistor. --- ### 3. Core Functions The MMBT3904-AE3-R is designed for two primary modes of operation: #### A. Switching It acts as a digital "on/off" switch. Because of its fast response time, it is ideal for: * Driving LEDs or small relays. * Pulse Width Modulation (PWM) control. * Logic gate interfacing. #### B. Amplification It can amplify small AC signals or DC currents. * **Low Noise:** Suitable for the first stages of audio pre-amplifiers. * **High Frequency:** With a 300MHz transition frequency, it can be used in RF (Radio Frequency) oscillation and small signal amplification. --- ### 4. Part Number Breakdown The suffixing follows specific manufacturer nomenclature (often UTC - Unisonic Technologies): * **MMBT3904:** The core model (NPN General Purpose). * **AE3:** Denotes the **SOT-23** package. * **R:** Indicates **Tape & Reel** packaging for automated assembly. --- ### 5. Common Applications * **Signal Processing:** Shifting voltage levels between different circuit parts. * **Inverters:** Creating logic NOT gates. * **Sensor Interfacing:** Amplifying weak signals from sensors to be read by a Microcontroller (MCU).