Onsemi FQB5N90TM 900V N-Channel MOSFET: Datasheet, Application Circuit, and Design Considerations

The Onsemi FQB5N90TM is a high-voltage N-Channel MOSFET designed to deliver robust performance in demanding power conversion applications. With a drain-to-source voltage (V_DSS) rating of 900V and low on-resistance, this MOSFET is engineered for high efficiency and reliability in circuits such as switch-mode power supplies (SMPS), power factor correction (PFC), and motor controllers.

Datasheet Overview

Key parameters outlined in the datasheet define the device’s operational limits and characteristics. The 900V V_DSS ensures suitability for off-line applications, including those with high-voltage transients. The device features a maximum continuous drain current (I_D) of 4.3A at 25°C and a low on-resistance (R_DS(on)) of 1.8Ω (max) at 10V V_GS, which helps minimize conduction losses. The super-TO-220 package offers improved isolation and mechanical durability, supporting better thermal performance and creepage distance. Additionally, the MOSFET is characterized by fast switching performance, though designers must carefully manage parasitic inductances to avoid voltage overshoot.

Application Circuit Example

A typical application for the FQB5N90TM is in a flyback converter for AC-DC power supplies. In such a circuit, the MOSFET serves as the main switch controlled by a PWM IC. The schematic includes:

- A gate drive circuit with a series resistor (e.g., 10Ω) to suppress ringing and optimize switching speed.

- A clamp network (e.g., RCD snubber) across the primary winding to absorb leakage inductance energy and protect the MOSFET from voltage spikes.

- A bootstrap circuit for high-side driving if used in half-bridge configurations.

Proper layout is critical: keep high-current loops tight and place decoupling capacitors close to the drain and source pins to reduce parasitic inductance.

Design Considerations

1. Gate Driving: Ensure a sufficient gate drive voltage (recommended 10V-12V) to fully enhance the MOSFET and minimize R_DS(on). Use a dedicated gate driver IC to achieve sharp rise and fall times.

2. Thermal Management: The super-TO-220 package supports efficient heat dissipation. Always use a heatsink during continuous operation near maximum ratings. Monitor junction temperature to avoid exceeding the 175°C maximum.

3. Voltage Spikes: In high-frequency circuits, voltage spikes due to stray inductance can exceed the 900V rating. Implement snubbers or clamp circuits for protection.

4. Body Diode Usage: The intrinsic body diode has slow reverse recovery. For applications requiring frequent diode conduction (e.g., in bridge circuits), consider an external anti-parallel diode if reverse recovery time is critical.

ICGOOODFIND: The Onsemi FQB5N90TM is a high-voltage MOSFET optimized for efficiency and reliability in power electronics. Its high breakdown voltage, low R_DS(on), and robust package make it ideal for SMPS and industrial systems. Careful attention to gate driving, thermal design, and voltage transient suppression is essential for maximizing performance.

Keywords:

900V MOSFET

Switch-Mode Power Supply

Power Factor Correction

Thermal Management

Gate Drive Circuit