onsemi KSE172STU

Overview

KSE172STU from Fairchild Semiconductor is a PNP epitaxial silicon transistor rated for -100 V collector-base voltage, -80 V collector-emitter voltage, and -3 A continuous collector current, with 12.5 W collector dissipation at TC=25°C; it serves as a high-voltage, medium-power switching and low-frequency audio amplification device in industrial power supplies and relay drivers.

For engineers reviewing the KSE172STU datasheet, pinout, applications, or equivalent options, this part supports design of robust DC-DC converter stages, linear regulator pass elements, and discrete PNP output stages where V_CEO ≥ -80 V, I_C ≤ -3 A, and f_T = 50 MHz are required under TO-126 thermal constraints.

Technical Context

The KSE172STU operates as a single PNP bipolar junction transistor with epitaxial base construction, optimized for linear amplification and saturated switching. Its DC current gain (h_FE) ranges from 12 to 250 depending on collector current, and saturation voltages are specified at multiple operating points including V_CE(sat) = -1.7 V at I_C = -3 A / I_B = -600 mA.

Thermal performance is defined by 12.5 W maximum collector dissipation at case temperature T_C = 25°C and 1.5 W at ambient T_A = 25°C, reflecting its TO-126 package's reliance on heatsinking. Junction temperature is rated to 150°C, with storage range spanning -65°C to +150°C.

Key Specifications

Pinout & Package

Package: TO-126 - Three-lead, through-hole plastic power package with integral metal tab for heatsinking; mounting hole Ø3.20 mm; outline conforms to JEDEC TO-126 standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD122G and BCP53-16, the KSE172STU occupies a mid-tier position: higher voltage than SOT-223 PNP transistors but less current and power than TO-220 devices, making it optimal for 2–3 A, 48–60 V applications using through-hole assembly and moderate heatsinking.

Availability

KSE172STU is available at Aetrix Electronics and suitable for industrial relay drivers, linear voltage regulator pass elements, and low-frequency audio amplifier output stages requiring stable component supply and long-term obsolescence management.

Supply support for KSE172STU 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 components before its acquisition by ON Semiconductor in 2016.

The KSE172STU belongs to Fairchild's legacy general-purpose PNP transistor family designed for industrial control, power conversion, and audio signal path applications where reliability, voltage headroom, and thermal robustness are prioritized.

FAQ

What is the maximum collector-emitter voltage rating for KSE172STU?

The KSE172STU has a maximum collector-emitter voltage (V_CEO) rating of -80 V at T_C = 25°C with open base. This rating ensures safe operation in 48 V DC systems with margin for inductive transients. Exceeding this voltage risks avalanche breakdown and permanent device failure. The KSE172STU datasheet specifies this value under standardized test conditions (I_C = 10 mA, I_B = 0), and derating is required at elevated temperatures.

Does KSE172STU support linear amplification applications?

Yes, the KSE172STU supports linear amplification, particularly in low-frequency audio output stages. Its h_FE of 50 at I_C = -100 mA and f_T of 50 MHz provide sufficient gain-bandwidth for <20 kHz signals. The device exhibits low output capacitance (C_ob = 50 pF), minimizing high-frequency phase shift. The KSE172STU is explicitly characterized in the datasheet for "Low Power Audio Amplifier" use, confirming its linearity under Class-A or Class-AB biasing.

What is the pin configuration of KSE172STU in the TO-126 package?

The KSE172STU uses a standard TO-126 pinout: Pin 1 is Emitter, Pin 2 is Collector, Pin 3 is Base - with the metal tab (attached to collector) facing outward when viewed from the front (leads down, flat side toward viewer). This configuration is confirmed in the Fairchild datasheet diagram and matches JEDEC TO-126 mechanical drawings. The KSE172STU's pin assignment is identical across the KSE170/171/172 family and must be observed to avoid reverse-bias damage during PCB layout.

Can KSE172STU replace KSE171STU in an existing design?

Yes, the KSE172STU can directly replace KSE171STU in most designs due to identical pinout, package, and electrical behavior except for higher voltage ratings: KSE172STU offers -100 V V_CBO and -80 V V_CEO, versus -80 V and -60 V for KSE171STU. No circuit changes are needed unless the original design relied on tighter V_CEO tolerance. The KSE172STU maintains compatible h_FE, V_CE(sat), and thermal characteristics, making it a safe upgrade for enhanced voltage margin.

What thermal considerations apply to KSE172STU in continuous operation?

For continuous operation, the KSE172STU requires heatsinking to maintain T_C ≤ 25°C for full 12.5 W dissipation; at ambient T_A = 25°C, its derated power drops to 1.5 W without heatsink. Thermal resistance from junction-to-case is ~2.0°C/W (calculated from 12.5 W and 25°C ΔT), so a heatsink with ≤ 10°C/W junction-to-ambient resistance is recommended for 5 W continuous dissipation. The KSE172STU's maximum junction temperature is 150°C, and exceeding this causes irreversible degradation.