onsemi FJP5021

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). It delivers fast switching with typical fall time of 0.1 µs and operates reliably up to 150 °C junction temperature, commonly used in flyback converters and snubberless AC switchers.

For engineers reviewing the FJP5021 datasheet, pinout, applications, or equivalent options, key selection criteria include its 50 W power dissipation at TC = 25°C, wide forward-bias safe operating area (SOA), TO-220 package thermal performance, and verified hFE range of 15–50 at IC = 0.6–3 A.

Technical Context

The FJP5021 is a ruggedized NPN bipolar junction transistor optimized for high-voltage, medium-current switching in offline power supplies and industrial controls. Its design emphasizes high secondary breakdown immunity and clamped inductive switching capability, supported by VCEX(sus) = 500 V under IC = 2.5 A, IB1 = –IB2 = 1 A conditions with 1 mH load.

It exhibits low saturation voltages-VCE(sat) = 1 V and VBE(sat) = 1.5 V at IC = 3 A / IB = 0.6 A-and maintains usable gain (hFE ≥ 8) even at 3 A, enabling efficient base drive in hard-switched topologies without requiring Darlington buffering.

Key Specifications

Pinout & Package

Supplied in a through-hole TO-220 package with insulated tab, the FJP5021 features standard lead configuration: Pin 1 = Base, Pin 2 = Collector (connected to tab), Pin 3 = Emitter. The metal tab is electrically tied to the collector and must be isolated from heatsink unless circuit topology permits common-collector mounting.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD122 and BU508A, the FJP5021 uniquely balances 800 V blocking, 0.1 µs fall time, and TO-220 thermal performance-making it optimal for 200–500 V, 20–100 kHz industrial switching where both voltage headroom and switching efficiency matter.

Availability

FJP5021 is available at Aetrix Electronics and suitable for AC motor control, industrial relay drivers, flyback converter primary switches, and high-voltage DC power supplies 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 semiconductor company specializing in power management, analog, and discrete devices before its acquisition by ON Semiconductor in 2016.

The FJP5021 belongs to Fairchild's high-voltage bipolar transistor product line, engineered specifically for ruggedized switching in offline AC/DC conversion, motor control, and industrial actuation systems.

FAQ

What is the maximum collector-emitter sustaining voltage (VCEX(sus)) for the FJP5021?

The FJP5021 has a specified collector-emitter sustaining voltage VCEX(sus) of 500 V under test conditions of IC = 2.5 A, IB1 = –IB2 = 1 A, L = 1 mH, and clamped operation. This parameter confirms its suitability for snubberless inductive switching in AC load control and flyback topologies where voltage overshoot must be contained without external RC networks. The FJP5021 datasheet validates this rating in Figure 5 and the Electrical Characteristics table.

Does the FJP5021 have a built-in base-emitter resistor?

No, the FJP5021 is a standard three-terminal NPN bipolar transistor without any integrated base-emitter resistors. It requires external base drive circuitry-including current-limiting resistors and optional Baker clamp networks-to ensure proper saturation and prevent secondary breakdown. This discrete architecture allows full design flexibility in base biasing, unlike digital transistors which integrate resistors. The FJP5021 pinout (Base, Collector, Emitter) reflects this conventional configuration.

What is the safe operating area (SOA) limitation for the FJP5021 at 100 °C case temperature?

At TC = 100 °C, the FJP5021's maximum allowable power dissipation is approximately 30 W, derived from the linear derating curve in Figure 8 (50 W at 25 °C, zero at 175 °C). Its forward-bias SOA (Figure 6) shows that at 100 °C case, it can sustain 3 A at 50 V or 1 A at 250 V in DC operation. These limits assume adequate heatsinking and are critical for linear-mode applications like series regulators. The FJP5021 SOA data is explicitly plotted for DC and pulsed conditions in the Typical Characteristics section.

Can the FJP5021 replace the BU208A in a CRT flyback circuit?

The FJP5021 is not a direct replacement for the BU208A in CRT flyback applications. While both are TO-220 NPN transistors, the BU208A specifies higher fT (4 MHz vs. 18 MHz for FJP5021), different SOA contours, and is optimized for horizontal deflection linearity and high pulse current. The FJP5021's 0.1 µs tF and 500 V VCEX(sus) suit general-purpose 50–100 kHz flyback converters, but CRT timing-critical circuits require the BU208A's specific gain-bandwidth and switching symmetry. Always verify waveform fidelity and thermal stress when substituting the FJP5021 in legacy CRT designs.

What is the hFE classification group for the standard FJP5021 part number?

The standard FJP5021 is classified in the "Y" hFE group per the datasheet's hFE Classification table, meaning its DC current gain hFE1 ranges from 30 to 50 at VCE = 5 V and IC = 0.6 A. This grouping ensures consistent base drive requirements across production lots. The FJP5021 Y-grade variant is the most commonly stocked version and is explicitly referenced in the Absolute Maximum Ratings and Electrical Characteristics sections of the May 2003 Rev. A datasheet.