### BCX55 NPN Medium Power Transistor The **BCX55** is a high-performance NPN epitaxial silicon transistor designed for medium power amplification and switching applications. It is commonly found in surface-mount circuits due to its compact SOT-89 package. --- ### 1. Key Technical Specifications Below are the typical electrical characteristics for the BCX55: | Parameter | Symbol | Maximum Rating | | :--- | :--- | :--- | | Collector-Emitter Voltage | $V_{CEO}$ | 60 V | | Collector-Base Voltage | $V_{CBO}$ | 60 V | | Emitter-Base Voltage | $V_{EBO}$ | 5 V | | Collector Current (DC) | $I_C$ | 1 A | | Peak Collector Current | $I_{CM}$ | 1.5 A | | Total Power Dissipation | $P_{tot}$ | 1.3 W (on PCB) | | Junction Temperature | $T_j$ | 150 °C | --- ### 2. Physical Characteristics The BCX55 is primarily manufactured in the **SOT-89** (Small Outline Transistor) package. This package is specifically designed for better heat dissipation compared to smaller SOT-23 packages. #### Pin Configuration: 1. **Emitter (E)** 2. **Collector (C)** (Connected to the large heat-sink tab) 3. **Base (B)** --- ### 3. Gain Grouping The BCX55 often comes in different "Gain Selection" versions, which indicate the DC Current Gain ($h_{FE}$) range: * **BCX55:** General range (approx. 40 to 250) * **BCX55-10:** $h_{FE}$ range of 63 to 160 * **BCX55-16:** $h_{FE}$ range of 100 to 250 --- ### 4. Common Applications Due to its 1A current handling and medium power rating, it is used in: * **Output stages** of audio amplifiers. * **Driver circuits** for relays, lamps, and small motors. * **Voltage regulators** for power management. * **High-side switching** in industrial electronics. --- ### 5. Complementary Part The PNP (negative) counterpart to the BCX55 is the **BCX52**. These two are often used together in "Push-Pull" amplifier configurations.