Infineon BUZ21 Power MOSFET: Datasheet, Application Circuits, and Replacement Guide

The Infineon BUZ21 is a classic N-channel power MOSFET that has established itself as a reliable workhorse in the world of power electronics. Renowned for its robustness and straightforward design, it continues to be a popular choice for switching and amplification tasks in various applications, from power supplies to motor control.

Datasheet Overview and Key Specifications

Understanding the BUZ21 begins with its datasheet. This document outlines the critical electrical characteristics that define the component's performance and limitations.

Drain-Source Voltage (V_DSS): The BUZ21 is rated for a maximum of 500V, making it suitable for off-line switch-mode power supplies (SMPS) and other high-voltage circuits.

Continuous Drain Current (I_D): It can handle a continuous current of up to 3.5A at a case temperature of 25°C.

On-Resistance (R_DS(on)): A crucial parameter for efficiency, its typical on-resistance is 1.5 Ohms (max. 2 Ohms). This resistance determines the voltage drop and power loss when the MOSFET is fully switched on.

Gate Threshold Voltage (V_GS(th)): Typically between 2-4V, this defines the voltage required to start turning the device on. It is designed to be driven directly by standard logic-level signals or common driver ICs.

Package: The device is housed in a TO-220 package, which offers a good balance of size, cost, and thermal performance, allowing for easy mounting on a heatsink.

Common Application Circuits

The BUZ21's primary function is as a high-speed switch. Here are two typical circuit configurations:

1. Low-Side Switch: This is the most common configuration. The MOSFET is placed between the load and ground. When a sufficient voltage (typically 10-15V) is applied to the gate relative to the source (which is at ground), the device turns on, completing the circuit and powering the load (e.g., a motor, solenoid, or lamp). This setup is simple to drive as the gate voltage is referenced to ground.

2. Simple Switch-Mode Power Supply (SMPS): In a basic flyback or forward converter design, the BUZ21 acts as the main switching element. It is controlled by a PWM (Pulse Width Modulation) controller IC to rapidly turn on and off, regulating the energy transfer from the primary side of a transformer to the secondary, isolated output. Its 500V rating is essential for handling voltage spikes inherent in these inductive circuits.

Replacement and Modern Substitute Guide

While still available, the BUZ21 is a older technology. Newer MOSFETs often offer superior performance. When seeking a replacement, consider these key parameters for cross-reference:

V_DSS: Must be equal to or higher than 500V.

I_D: Should be at least 3.5A.

R_DS(on): Look for a value that is equal or lower to ensure equal or better efficiency and reduced heat generation.

Package: Must be compatible (TO-220 is standard).

Excellent modern substitutes often come from Infineon's own newer generations or other manufacturers like STMicroelectronics, ON Semiconductor, and Vishay. For instance, the STP4NK50Z (500V, 3.8A, R_DS(on)=1.2Ω) or the IRFBA40N50K (500V, 40A, R_DS(on)=0.065Ω) are potential upgrades, with the latter offering significantly lower conduction losses. Always consult the latest datasheets to ensure compatibility in your specific circuit, particularly regarding gate charge and switching speed.

ICGOODFIND: The Infineon BUZ21 remains a valid and robust 500V power MOSFET for various medium-power switching applications. While newer components offer enhanced efficiency, understanding its specs and common circuit configurations provides a solid foundation for both maintaining existing equipment and designing new solutions. When replacing it, focus on matching or improving its key parameters like voltage, current, and on-resistance.

Keywords: Power MOSFET, Datasheet, Switch-Mode Power Supply (SMPS), On-Resistance (RDS(on)), TO-220 Package.