The **BUT33** is a high-voltage, high-speed NPN power transistor designed primarily for switching applications. It belongs to a class of bipolar junction transistors (BJTs) often used in power supplies and industrial control circuits. --- ## 1. Core Specifications The BUT33 is known for its ability to handle significant voltage levels and moderate current. Below are the typical technical parameters: | Parameter | Symbol | Typical Value | | :--- | :--- | :--- | | **Collector-Emitter Voltage** | $V_{CEO}$ | 400V - 450V | | **Collector-Base Voltage** | $V_{CBO}$ | 850V - 1000V | | **Collector Current (DC)** | $I_C$ | 10A | | **Total Power Dissipation** | $P_{tot}$ | 100W | | **Package Type** | - | TO-3 (Metal Can) | | **Operating Temperature** | $T_j$ | -65°C to +200°C | --- ## 2. Key Features * **High Voltage Capability:** Designed to operate safely in circuits with high mains voltages (e.g., 220V/240V AC rectified). * **Fast Switching:** Optimized for high-frequency switching, reducing energy loss during the transition between "on" and "off" states. * **Thermal Robustness:** Usually packaged in a **TO-3** metal case, which allows for excellent heat dissipation when mounted to a heatsink. --- ## 3. Common Applications The BUT33 is typically found in "heavy-duty" electronic environments: 1. **Switch Mode Power Supplies (SMPS):** Used as the primary switching element to convert high-voltage DC into high-frequency AC for transformers. 2. **Motor Controllers:** Employed in DC motor speed control circuits. 3. **Horizontal Deflection:** Historically used in CRT (Cathode Ray Tube) monitors and television sets. 4. **Inverters:** Part of the circuitry that converts DC power (from batteries or solar panels) into AC power. --- ## 4. PIN Configuration (TO-3 Package) When looking at the bottom of a TO-3 metal package with the pins positioned toward the bottom: * **Pin 1 (Left):** Base (B) * **Pin 2 (Right):** Emitter (E) * **Case (Body):** Collector (C) > **Note:** Because the metal case is the Collector, it is vital to use an insulating mica washer and thermal paste if the heatsink needs to be grounded or isolated. ---