onsemi KSE800STU

Overview

KSE800STU from onsemi is an NPN epitaxial silicon Darlington transistor in TO-126-3LD package, featuring monolithic construction with built-in base-emitter resistors (R1 ≈ 10 kΩ, R2 ≈ 0.6 kΩ), minimum DC current gain h_FE = 750 at I_C = 1.5 A, V_CE = 3 V, and rated for 4 A collector current and 40 W power dissipation at T_C = 25°C - used in high-gain switching and linear amplification stages of industrial motor drivers and relay interface circuits.

For engineers reviewing the KSE800STU datasheet, pinout, applications, or equivalent options, key selection considerations include its integrated bias resistors enabling single-base-drive operation, guaranteed V_CEO/V_CBO = 60 V breakdown rating, low saturation voltage (V_CE(sat) ≤ 3.0 V at I_C = 4 A, I_B = 40 mA), thermal derating profile, and Pb-free TO-126-3LD mechanical compatibility with legacy through-hole PCB layouts.

Technical Context

The KSE800STU implements a two-stage monolithic Darlington configuration with internal base-emitter resistors that provide self-biasing and eliminate external base resistor requirements. Its h_FE ≥ 750 at I_C = 1.5 A ensures high-current drive capability with minimal base drive current (I_B ≤ 30 mA).

It operates within a junction temperature range of −55°C to +150°C and exhibits V_BE(on) = 2.5–3.0 V at I_C = 1.5–4 A, supporting robust turn-on in high-noise industrial environments. The device's safe operating area (SOA) is defined up to 4 A DC with derated power above 25°C case temperature.

Key Specifications

Pinout & Package

Package: TO-126-3LD (Case 340AS), thermally enhanced through-hole plastic package with metal tab for heatsink mounting; pin 1 = Emitter, pin 2 = Collector (tab-connected), pin 3 = Base.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BD679A and MJD127G, the KSE800STU uniquely integrates base-emitter resistors in a thermally optimized TO-126-3LD package, delivering plug-and-play high-gain switching without layout redesign - critical for rapid prototyping and cost-sensitive industrial controls.

Availability

KSE800STU is available at Aetrix Electronics and suitable for industrial relay drivers, DC motor control stages, solenoid interface circuits, and linear amplifier stages requiring stable component supply and long-term manufacturing continuity.

Supply support for KSE800STU 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 specializing in energy-efficient power, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and IoT applications.

The KSE800STU belongs to onsemi's high-reliability discrete transistor product line, designed specifically for ruggedized industrial switching and amplification where integrated biasing, thermal robustness, and RoHS compliance are essential.

FAQ

What is the maximum continuous collector current rating for the KSE800STU?

The KSE800STU has a maximum continuous collector current (I_C) rating of 4 A at case temperature T_C = 25°C. This rating decreases with rising case temperature per the published power derating curve - at T_C = 100°C, the usable I_C drops to approximately 2.3 A. Operation beyond this limit risks thermal runaway and permanent damage. Always verify actual thermal conditions using the KSE800STU's R_θJC = 1.25°C/W and heatsink interface resistance.

Does the KSE800STU require external base resistors for operation?

No, the KSE800STU does not require external base resistors. It features monolithic construction with built-in base-emitter resistors (R1 ≈ 10 kΩ, R2 ≈ 0.6 kΩ), enabling direct drive from logic-level sources such as microcontroller GPIO pins. This eliminates the need for discrete bias components and simplifies circuit design - a key differentiator versus standard NPN transistors like the MJD127G or BD679A.

What is the collector-emitter saturation voltage V_CE(sat) of the KSE800STU under full-load conditions?

The KSE800STU specifies V_CE(sat) ≤ 3.0 V at I_C = 4 A and I_B = 40 mA, measured at T_C = 25°C. At lower currents (e.g., I_C = 1.5 A, I_B = 30 mA), V_CE(sat) is ≤ 2.5 V. These values reflect worst-case conduction loss during switching; actual performance may improve slightly at lower temperatures but must be validated in-system due to thermal feedback effects.

Is the KSE800STU pin-compatible with the KSE700 transistor?

Yes, the KSE800STU is the NPN complement to the PNP KSE700, and both share identical TO-126-3LD packaging and pinout (Emitter–Collector–Base). However, they are not functionally interchangeable in circuit - the KSE800STU is NPN and sinks current from load to ground, while the KSE700 sources current from supply to load. Their complementary pairing enables push-pull or H-bridge topologies requiring matched thermal and gain characteristics.

What is the junction-to-case thermal resistance (R_θJC) of the KSE800STU?

The KSE800STU has a junction-to-case thermal resistance (R_θJC) of 1.25°C/W, as derived from its 40 W power dissipation rating at T_C = 25°C and maximum junction temperature T_J = 150°C. This low value reflects the TO-126-3LD package's metal tab construction, which provides efficient heat transfer to an external heatsink. Proper mounting pressure and thermal interface material are required to achieve this spec in production.