## Overview of the BD772-R Transistor The **BD772-R** is a specific variant of the **BD772**, which is a silicon Epitaxial Planar **PNP Power Transistor**. It is primarily designed for use in medium-power output stages, driver circuits, and high-fidelity (Hi-Fi) audio amplifiers. The suffix **"-R"** typically refers to the **hFE (DC Current Gain) classification**, indicating that this specific unit falls within a certain gain range (usually the higher end of the spectrum for this model). --- ### 1. Key Technical Specifications | Parameter | Symbol | Maximum Rating | Unit | | :--- | :--- | :--- | :--- | | Collector-Base Voltage | $V_{CBO}$ | -80 | V | | Collector-Emitter Voltage | $V_{CEO}$ | -80 | V | | Emitter-Base Voltage | $V_{EBO}$ | -5 | V | | Collector Current (DC) | $I_C$ | -4 | A | | Collector Current (Pulse) | $I_{CP}$ | -7 | A | | Total Power Dissipation ($T_c = 25^\circ C$) | $P_D$ | 25 | W | | Junction Temperature | $T_j$ | 150 | $^\circ C$ | --- ### 2. Physical and Structural Characteristics * **Package Type:** TO-220 (Plastic Lead-Formed Package). This allows for easy mounting to heat sinks. * **Polarity:** PNP (Requires negative voltage at the collector relative to the emitter to conduct). * **Complementary Pair:** The NPN counterpart to the BD772 is the **BD771**. These are often used together in Push-Pull amplifier configurations. --- ### 3. The "-R" Gain Classification In semiconductor manufacturing, transistors are binned based on their DC current gain ($h_{FE}$). While the standard BD772 has a wide range, the **R** rank usually specifies: * **$h_{FE}$ Range:** Approximately **40 to 80** (or **60 to 120** depending on the specific manufacturer like ROHM or ST). * **Test Condition:** Usually measured at $V_{CE} = -4V, I_C = -500mA$. --- ### 4. Common Applications 1. **Audio Amplifiers:** Used in the output or driver stage of Hi-Fi systems due to its linear gain characteristics. 2. **Voltage Regulation:** Acts as a pass transistor in linear power supplies. 3. **Relay Drivers:** Capable of switching inductive loads up to 4A. 4. **DC-DC Converters:** Used in medium-power switching applications. --- ### 5. Pin Configuration (TO-220) Looking at the front of the transistor (labels facing you): | Pin Number | Function | | :--- | :--- | | 1 | **Base** | | 2 | **Collector** (Connected to the metal tab) | | 3 | **Emitter** | ---