onsemi FJP5021O

Overview

FJP5021 from Fairchild Semiconductor is an NPN silicon power transistor designed for high-voltage switching applications, featuring 800 V collector-base breakdown voltage (BVCBO), 500 V collector-emitter sustaining voltage (VCEX(sus)), and 5 A DC collector current (IC), commonly used in flyback converters and snubberless AC-switching circuits.

For engineers reviewing the FJP5021 datasheet, pinout, applications, or equivalent options, key selection criteria include its 500 V VCEO rating, 1 µs typical turn-on time (tON), 0.1 µs typical fall time (tF), wide forward-bias safe operating area (SOA), and TO-220 package thermal performance under pulsed and DC loads.

Technical Context

The FJP5021 employs a planar epitaxial base structure optimized for rugged high-voltage switching, with specified clamped-inductive switching performance at IC = 4 A, VCC = 200 V, and RL = 50 Ω. Its hFE classification "O" denotes DC current gain of 20–40 at IC = 0.6 A and VCE = 5 V.

It supports fast switching via low saturation voltages-VCE(sat) = 1 V and VBE(sat) = 1.5 V at IC = 3 A / IB = 0.6 A-and exhibits 18 MHz fT at VCE = 10 V / IC = 0.6 A, enabling stable operation in kHz-range SMPS topologies without oscillation risk.

Key Specifications

Pinout & Package

Package: TO-220 (3-lead, straight lead, insulated tab). Dimensions per Fairchild Rev. A: 15.90 mm × 10.08 mm × 18.95 mm max height; mounting hole ø3.60 mm; thermal resistance junction-to-case (RθJC) = 1.5°C/W (typ., data inferred from TO-220 standard).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage NPN switching transistor applications.

Compared with MJD122 and BU508A, the FJP5021 uniquely balances 500 V blocking, 0.1 µs tF, and hFE classification "O" in TO-220-making it optimal for compact, high-efficiency 50–150 kHz flyback and AC-switching designs requiring ruggedness without oversized packaging.

Availability

FJP5021 is available at Aetrix Electronics and suitable for switch-mode power supplies, AC motor control systems, and industrial solenoid drivers requiring stable component supply and long-term industrial lifecycle support.

Supply support for FJP5021 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Fairchild Semiconductor was a U.S.-based analog and power semiconductor manufacturer, acquired by ON Semiconductor in 2016; known for rugged discrete power devices and industry-standard packaging.

The FJP5021 belongs to Fairchild's high-voltage bipolar transistor family, engineered specifically for reliability-critical industrial switching applications where SOA, clamped-inductive ruggedness, and consistent hFE grouping are mandatory.

FAQ

What is the maximum continuous collector current rating for the FJP5021?

The FJP5021 has a maximum DC collector current (IC) rating of 5 A at case temperature TC = 25°C. Derating is required above 25°C per the power derating curve in the datasheet-e.g., ~3.5 A at TC = 75°C. This rating assumes adequate heatsinking and accounts for both conduction and switching losses in real-world layouts.

Does the FJP5021 support snubberless AC switching applications?

Yes, the FJP5021 supports snubberless AC switching: its VCEX(sus) = 500 V is explicitly tested under clamped-inductive conditions (IC = 2.5 A, IB1 = –IB2 = 1 A, L = 1 mH), confirming ruggedness against inductive turn-off stress without external snubbers-key for solid-state relay and AC dimmer designs.

What is the hFE classification of the FJP5021 and why does it matter?

The FJP5021 carries hFE classification "O", meaning its DC current gain ranges from 20 to 40 at VCE = 5 V and IC = 0.6 A. This tight grouping ensures predictable base drive requirements across production lots-critical for consistent switching behavior and thermal management in volume-manufactured power supplies.

Can the FJP5021 replace the BU508A in existing designs?

The FJP5021 is not a direct replacement for BU508A: while both offer 500 V VCEO, the FJP5021 has lower peak current (5 A vs. 8 A) and faster tF (0.1 µs vs. 0.3 µs), but uses TO-220 instead of TO-218. Layout and thermal design must be revalidated; it suits higher-frequency, space-constrained upgrades-not drop-in swaps.

What is the recommended base drive configuration for reliable FJP5021 switching?

For reliable FJP5021 switching, apply ≥0.6 A base current (IB) to achieve full saturation at IC = 3 A, with VBE(sat) = 1.5 V. Use a low-impedance driver (e.g., complementary BJT pair or dedicated gate driver IC) and keep base trace short and wide to minimize inductance-critical to avoid oscillation during fast turn-off.