onsemi KSE803STU

Overview

KSE803STU from onsemi is an NPN epitaxial silicon Darlington transistor in TO-126-3LD package, featuring monolithic construction with built-in base-emitter resistors, h_FE ≥ 750 at I_C = 1.5 A, V_CEO = 60 V, and P_C = 40 W at T_C = 25°C. It serves as a high-gain power switch in DC motor control, relay drivers, and linear power supply pass elements.

For engineers reviewing the KSE803STU datasheet, pinout, applications, or equivalent options, key selection criteria include its guaranteed h_FE minimum of 750 at 1.5 A, V_CE(sat) ≤ 2.5 V at I_C = 1.5 A / I_B = 30 mA, and thermal derating to zero power at T_C = 175°C - critical for industrial load switching reliability.

Technical Context

The KSE803STU implements a monolithic Darlington pair with integrated R₁ ≈ 10 kΩ and R₂ ≈ 0.6 kΩ base-emitter resistors, enabling simplified biasing without external components. Its structure delivers high current gain while maintaining V_CEO and V_CBO ratings of 60 V each.

Designed for linear and switching operation, it supports continuous collector currents up to 4 A with safe operating area (SOA) defined up to 100 µs pulse width. Junction temperature is rated to 150°C, and storage range spans −55°C to +150°C.

Key Specifications

Pinout & Package

Package: TO-126-3LD (Case 340AS), surface-mount compatible through-hole package with integral heat slug; pin 1 = Emitter, pin 2 = Collector (connected to tab), pin 3 = Base.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN Darlington transistor applications.

Compared with MJD127G and TIP122, the KSE803STU offers optimized trade-offs for through-hole industrial controls: TO-126 mechanical robustness, guaranteed h_FE ≥ 750 without external components, and 60 V rating aligned with 48 V system standards - simplifying qualification and reducing bill-of-materials count.

Availability

KSE803STU is available at Aetrix Electronics and suitable for DC motor control, relay driving, linear power supply pass elements, and high-current LED driver applications requiring stable component supply, long-term industrial availability, and RoHS-compliant packaging.

Supply support for KSE803STU 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier focused on energy-efficient technologies for automotive, industrial, cloud, medical, and IoT applications.

The KSE803STU belongs to onsemi's general-purpose power bipolar transistor family, designed specifically for cost-sensitive, high-reliability industrial switching and linear regulation where simplicity, thermal robustness, and guaranteed gain are essential.

FAQ

What is the maximum continuous collector current rating for the KSE803STU?

The KSE803STU has an absolute maximum continuous collector current (I_C) rating of 4 A. However, this value assumes ideal thermal conditions - practical operation at 4 A requires substantial heatsinking and strict adherence to the power derating curve, which reduces allowable dissipation linearly from 40 W at 25°C case temperature to 0 W at 175°C. For reliable 4 A DC operation, thermal design must maintain T_C ≤ 75°C.

Does the KSE803STU require external base resistors for standard switching operation?

No, the KSE803STU does not require external base resistors for standard switching operation. It integrates monolithic base-emitter resistors (R₁ ≈ 10 kΩ, R₂ ≈ 0.6 kΩ) that provide self-biasing. This allows direct connection to logic-level sources (e.g., microcontroller GPIO) with only a series current-limiting resistor to set I_B, simplifying circuit design versus discrete Darlington configurations.

What is the guaranteed minimum DC current gain (h_FE) of the KSE803STU, and at what test conditions?

The KSE803STU guarantees h_FE ≥ 750 at V_CE = 3 V and I_C = 1.5 A, per onsemi's official datasheet. This minimum is tested and binned during production. At I_C = 4 A, h_FE drops to ≥ 100 - a critical design consideration when sizing base drive for full-rated current. The KSE803STU's h_FE specification ensures predictable gain behavior across its primary operating range.

How is the collector terminal of the KSE803STU physically connected in the TO-126-3LD package?

In the KSE803STU's TO-126-3LD (Case 340AS) package, pin 2 (Collector) is internally bonded to the metal tab/heat slug. This means the collector is electrically common with the exposed metal surface - requiring electrical isolation (e.g., mica washer or insulating pad) if mounted to a grounded or shared heatsink. Failure to isolate may cause short-circuit failure or unintended current paths in the system.

Is the KSE803STU suitable for use in automotive applications?

The KSE803STU is not AEC-Q101 qualified and is not recommended for automotive safety-critical or engine-compartment applications. While its 150°C junction rating and 60 V breakdown meet some automotive voltage requirements, onsemi positions it for industrial, commercial, and consumer equipment. For automotive use, designers should select AEC-Q101-qualified alternatives such as the NSS12601CF8T1G or MJD127G with full automotive qualification documentation.