onsemi KSE801STU

Overview

KSE801STU from onsemi is an NPN epitaxial silicon Darlington transistor in TO-126-3LD package, designed for medium-power switching and linear amplification. It delivers minimum DC current gain (h_FE) of 750 at I_C = 1.5 A, supports V_CEO = 60 V and I_C = 4 A continuous collector current, and integrates monolithic base-emitter resistors (R₁ ≈ 10 kΩ, R₂ ≈ 0.6 kΩ) for simplified biasing - used in relay drivers and motor control stages.

For engineers reviewing the KSE801STU datasheet, pinout, applications, or equivalent options, key selection factors include its built-in resistor network, safe operating area up to 40 W at T_C = 25°C, thermal derating curve, V_CE(sat) ≤ 3 V at I_C = 4 A/ I_B = 40 mA, and Pb-free TO-126-3LD mechanical compatibility with legacy KSE800-series designs.

Technical Context

This Darlington pair integrates two NPN transistors and two on-chip resistors (R₁ ≈ 10 kΩ, R₂ ≈ 0.6 kΩ) in a single die, enabling self-biasing without external components. It operates as a high-gain, medium-voltage switch with V_CEO = 60 V and junction temperature rating up to 150°C.

The device exhibits V_BE(on) = 2.5–3 V at I_C = 1.5–4 A, V_CE(sat) ≤ 3 V under rated drive, and I_CBO ≤ 500 nA at 100°C - confirming stable leakage performance in thermally demanding industrial environments.

Key Specifications

Pinout & Package

Package: TO-126-3LD (Case 340AS), surface-mountable through-hole package with integral metal tab for heatsinking. 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 KSE801STU uniquely combines integrated bias resistors, TO-126-3LD mechanical compatibility, and guaranteed h_FE ≥ 750 - making it optimal for cost-sensitive, space-constrained relay and motor driver PCBs where component count reduction is critical.

Availability

KSE801STU is available at Aetrix Electronics and suitable for relay driver stages, motor speed control circuits, linear regulator pass elements, and industrial 4–20 mA sensor interface outputs requiring stable component supply across production lifecycles.

Supply support for KSE801STU 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, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The KSE801STU belongs to onsemi's legacy bipolar power transistor family, engineered specifically for robust, low-component-count switching in industrial control, automation, and power management systems.

FAQ

What is the maximum continuous collector current rating for KSE801STU?

The KSE801STU is rated for 4 A continuous collector current (I_C) at case temperature T_C = 25°C. Derating is required above 25°C per the published power derating curve - e.g., ~0.33 W/°C reduction beyond 25°C. At T_C = 75°C, usable dissipation drops to ~23 W, limiting practical I_C to approximately 2.8 A depending on V_CE. Always verify thermal design using the KSE801STU's SOA chart.

Does KSE801STU have built-in base resistors, and what are their values?

Yes, the KSE801STU integrates two monolithic base-emitter resistors: R₁ ≈ 10 kΩ between base and first transistor's base, and R₂ ≈ 0.6 kΩ between first transistor's emitter and second transistor's base. These enable direct logic-level drive without external bias components - confirmed in the device's equivalent circuit diagram and marking diagram documentation.

Is KSE801STU pin-compatible with KSE800STU?

Yes, KSE801STU and KSE800STU share identical TO-126-3LD packaging, pinout (Emitter–Collector–Base), and mechanical dimensions. Both devices are specified with same absolute maximum ratings and electrical characteristics - including V_CEO = 60 V, I_C = 4 A, and h_FE ≥ 750 - making them functionally interchangeable in existing designs.

What is the typical V_CE(sat) of KSE801STU under full-load conditions?

The KSE801STU specifies V_CE(sat) ≤ 3.0 V at I_C = 4 A and I_B = 40 mA. At lighter loads (I_C = 1.5 A / I_B = 30 mA), V_CE(sat) is ≤ 2.5 V. These values are measured per JEDEC test conditions and reflect actual conduction loss - critical for calculating thermal rise and efficiency in motor or relay driver stages using KSE801STU.

Can KSE801STU be used in linear regulator applications?

Yes, the KSE801STU is suitable as a series pass element in linear regulators due to its 40 W power dissipation capability at T_C = 25°C, 150°C junction limit, and stable h_FE across operating current. Its integrated base resistors simplify bias network design, and TO-126 metal tab allows direct heatsink attachment - verified in onsemi's application guidance for medium-power linear supplies using KSE800-series transistors.