onsemi KSD794YSTU

Overview

KSD794YSTU from ON Semiconductor is an NPN epitaxial silicon power transistor in TO-126 package, rated for 45 V V_CEO, 3 A DC collector current, and 10 W collector dissipation at T_C = 25°C. It delivers h_FE of 30–70 at I_C = 20 mA and 60–100 at I_C = 0.5 A, with V_CE(sat) ≤ 2 V at I_C = 1.5 A / I_B = 0.15 A, suited for audio frequency power amplification stages.

For engineers reviewing the KSD794YSTU datasheet, pinout, applications, or equivalent options, key selection criteria include verified V_CEO/I_C ratings, h_FE classification (R/O/Y), saturation voltage under defined drive conditions, and thermal derating behavior across case temperature range.

Technical Context

This device operates as a linear-mode NPN power amplifier transistor with complementary pairing to KSB744/KSB744A. Its design supports Class AB audio output stages where low V_CE(sat) and stable h_FE over 0.02–1 A collector current range are critical for distortion control and thermal management.

The KSD794YSTU features f_T = 60 MHz at V_CE = 5 V / I_E = 0.1 A and C_ob = 40 pF at V_CB = 10 V, enabling operation up to mid-audio frequencies while maintaining predictable gain roll-off and output impedance characteristics.

Key Specifications

Pinout & Package

Package: TO-126 (3-lead plastic power package with metal tab connected to collector). Dimensions per Fairchild Rev. A1: 16.10 × 13.06 × 4.2 mm (L × W × H), mounting hole ø3.20 mm.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD794T4G and KSD794A, the KSD794YSTU offers optimal balance of compact TO-126 form factor, proven audio-band linearity, and cost-effective manufacturing for mid-power linear applications-whereas MJD794T4G trades size for thermal headroom, and KSD794A extends voltage capability without altering mechanical integration.

Availability

KSD794YSTU is available at Aetrix Electronics and suitable for audio power amplifiers, DC motor drivers, linear voltage regulators, and foldback protection circuits requiring stable component supply and consistent h_FE binning.

Supply support for KSD794YSTU 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

ON Semiconductor (formerly Fairchild Semiconductor) is a global semiconductor supplier specializing in energy-efficient power management, analog, sensors, and connectivity solutions for automotive, industrial, and consumer markets.

The KSD794YSTU belongs to ON Semiconductor's legacy power bipolar transistor family, designed specifically for linear audio amplification, motor control, and regulated power supply applications demanding reliability and consistent parametric performance.

FAQ

What is the maximum continuous collector current rating for KSD794YSTU?

The KSD794YSTU has a maximum DC collector current rating of 3 A at ambient temperature (T_A = 25°C). This value assumes adequate heatsinking and derates linearly with increasing case temperature per the published power derating curve. At T_C = 100°C, the usable I_C drops to approximately 5 A for pulsed operation but remains limited to ~1.5 A for sustained DC use. Always validate thermal design using the KSD794YSTU SOA graph and actual board-level thermal resistance.

Is KSD794YSTU pin-compatible with KSD794A?

Yes, the KSD794YSTU is fully pin-compatible with KSD794A - both use identical TO-126 package, pin 1 = emitter, pin 2 = collector, pin 3 = base, and share the same mechanical dimensions and solder pad layout. The only difference is V_CEO: 45 V for KSD794YSTU versus 60 V for KSD794A. No PCB changes are required when upgrading to KSD794A for higher voltage margin.

What h_FE classification does KSD794YSTU belong to?

The KSD794YSTU is manufactured in three h_FE classifications: R (60–120), O (100–200), and Y (160–320), all specified at V_CE = 5 V and I_C = 0.5 A. The suffix "YSTU" indicates it is part of the Y-class group, meaning its DC current gain falls within 160–320 under those test conditions - enabling tighter bias control in production amplifiers.

Can KSD794YSTU be used in switching applications?

The KSD794YSTU is characterized and optimized for linear operation (e.g., audio amplification), with published f_T = 60 MHz and SOA curves supporting safe operation in active region. While it can function as a switch, its relatively high V_CE(sat) (up to 2 V) and lack of specified switching time parameters (t_on/t_off) make it less efficient than purpose-built switching transistors like MJD122 or NSS12601. Use only in low-frequency (<10 kHz), low-duty-cycle switching where thermal limits permit.

Does KSD794YSTU require a heatsink in typical audio amplifier use?

Yes, the KSD794YSTU requires a heatsink in most audio amplifier applications. With 10 W collector dissipation at T_C = 25°C and typical power output of 5–8 W, junction temperature rises rapidly without thermal management. A minimum 2.5°C/W heatsink is recommended for continuous 5 W output; derating must follow the KSD794YSTU power derating curve if ambient or case temperature exceeds 25°C.