Onsemi FDPF4N90C N-Channel MOSFET: Datasheet, Application Circuit, and Replacement Guide

The FQP4N90C from Onsemi is a high-voltage N-Channel MOSFET designed for demanding switching applications. This robust transistor combines high voltage capability with excellent switching characteristics, making it a popular choice in power supply designs, electronic ballasts, and other high-voltage circuits.

Datasheet Overview and Key Specifications

The FQP4N90C is characterized by its 900V drain-to-source voltage (Vdss) rating, which allows it to handle significant voltage spikes and operate reliably in off-line power supplies. A key feature is its low on-resistance, typically 4.0 Ohms max (Rds(on)), which helps to minimize conduction losses and improve overall efficiency. The device is packaged in the TO-220F-3L (fully isolated) package, which offers enhanced creepage distance and allows for easier mounting to a heatsink without an insulating washer. Other critical parameters include a continuous drain current (Id) of 1.5A at 25°C and a fast switching speed that is essential for high-frequency operation.

Typical Application Circuit: Switched-Mode Power Supply (SMPS)

A common use for the FQP4N90C is as the primary side switch in a flyback converter topology. In this circuit:

The MOSFET is connected in series with the primary winding of a transformer and the high-voltage DC bus.

A PWM (Pulse Width Modulation) controller IC drives the MOSFET's gate through a series resistor, which controls the switching speed to minimize ringing.

A simple zener diode and resistor clamp network is often used to protect the gate from overvoltage transients.

The fast body diode of the MOSFET aids in clamping voltage spikes caused by transformer leakage inductance, often in conjunction with an RCD (Resistor-Capacitor-Diode) snubber network across the primary winding.

This setup efficiently converts a high-voltage DC input to a regulated lower-voltage DC output, leveraging the MOSFET's high voltage tolerance and switching capability.

Replacement and Cross-Reference Guide

When seeking a replacement for the FQP4N90C, it is crucial to match the core electrical parameters to ensure system reliability and performance.

Direct Equivalents: The best replacements are often from the same manufacturer. Check Onsemi's current portfolio for the latest versions or direct equivalents like the FQP5N90C (with a lower Rds(on)).

Suitable Replacements from Other Manufacturers: When cross-referencing, key specifications to match are:

Vdss ≥ 900V

Continuous Drain Current (Id) ≥ 1.5A

Rds(on) of a similar or lower value

TO-220F or standard TO-220 package (note: standard TO-220 is not isolated)

Comparable gate charge (Qg) for similar driving characteristics.

Potential Replacements: Devices like the STMicroelectronics STF4N90K5, Infineon IPP4N90N, or Toshiba TK4P90E may serve as potential substitutes, but a thorough design review is mandatory to confirm compatibility in the target application, especially concerning switching performance and safe operating area (SOA).

ICGOODFIND: The Onsemi FQP4N90C remains a reliable and robust high-voltage MOSFET for power conversion. Its high 900V rating and low on-resistance make it well-suited for SMPS designs. When replacing it, meticulous attention to voltage, current, and switching parameters is essential for maintaining system integrity and performance.

Keywords: High-Voltage MOSFET, SMPS, 900V, Cross-Reference, On-Resistance