onsemi KST5550MTF

Overview

KST5550MTF from ON Semiconductor is an NPN epitaxial silicon transistor designed for high-voltage switching and amplification in compact SOT-23 packages. It features 140 V V_CEO, 600 mA I_C, 350 mW P_C, and 100–300 MHz f_T, supporting use in DC-DC converters, relay drivers, and signal conditioning circuits.

For engineers reviewing the KST5550MTF datasheet, pinout, applications, or equivalent options, key selection criteria include breakdown voltage margin, saturation voltage at target drive current, DC gain linearity across collector current range, and SOT-23 thermal derating behavior in high-density PCB layouts.

Technical Context

This device operates as a general-purpose NPN bipolar junction transistor with fixed-emitter configuration and base-controlled conduction. Its 160 V V_CBO and 140 V V_CEO enable reliable operation in off-line auxiliary supplies and industrial sensor interfaces where transient overvoltage immunity is required.

The transistor delivers h_FE = 60–250 at I_C = 1–50 mA and V_CE = 5 V, with V_CE(sat) ≤ 0.25 V at I_C = 50 mA / I_B = 5 mA, supporting efficient low-side switching in 3.3 V–5 V logic-driven loads.

Key Specifications

Pinout & Package

SOT-23 package with standard 3-pin configuration: compact 2.9 mm × 1.3 mm footprint, 1.0 mm height, and gull-wing leads compatible with reflow soldering.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MMBT5551 and BC847C, the KST5550MTF uniquely balances high-voltage capability (140 V), moderate gain (60–250), and low saturation voltage (0.15 V) in SOT-23-making it optimal for cost-sensitive, space-constrained switching in 12–100 V systems where reliability under transient stress matters.

Availability

KST5550MTF is available at Aetrix Electronics and suitable for power supply auxiliary switching, industrial sensor interface, relay driver circuit, and LED current control requiring stable component supply across extended production lifecycles.

Supply support for KST5550MTF 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 is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The KST5550MTF belongs to ON Semiconductor's general-purpose bipolar transistor product line, engineered for robust high-voltage switching and amplification in space-constrained surface-mount designs.

FAQ

What is the maximum collector-emitter voltage rating for KST5550MTF?

The KST5550MTF has a maximum collector-emitter voltage (V_CEO) rating of 140 V at T_A = 25°C. This rating decreases with rising ambient temperature per the device's derating curve, and operation above this value risks avalanche breakdown. Designers must ensure transient voltages-including inductive kickback and ringing-remain within this limit during all operating conditions for KST5550MTF.

Does KST5550MTF support saturated switching at 50 mA collector current?

Yes, KST5550MTF supports saturated switching at 50 mA collector current with V_CE(sat) ≤ 0.25 V when driven with 5 mA base current (I_B = 5 mA). This is confirmed in the datasheet under test condition IC = 50 mA, IB = 5 mA. The resulting low saturation voltage ensures minimal power loss and thermal rise in KST5550MTF-based relay or LED driver circuits.

What package type does KST5550MTF use, and is it RoHS compliant?

KST5550MTF uses the SOT-23 surface-mount package with standard pinout (1 = Base, 2 = Emitter, 3 = Collector). It is RoHS compliant and halogen-free per ON Semiconductor's material declarations. The SOT-23 footprint measures 2.90 mm × 1.30 mm × 1.00 mm and supports standard reflow profiles, making KST5550MTF suitable for automated assembly in high-volume production.

How does the DC current gain (h_FE) of KST5550MTF vary with collector current?

KST5550MTF exhibits h_FE = 60 (min) at I_C = 1.0 mA, h_FE = 60 (min) at I_C = 10 mA, and h_FE = 20 (min) at I_C = 50 mA-all measured at V_CE = 5 V. This progressive reduction reflects typical BJT behavior, and designers should size base resistors accordingly to maintain saturation across the full operating range of KST5550MTF.

Can KST5550MTF replace older Fairchild KST5550 devices in existing designs?

Yes, KST5550MTF is the ON Semiconductor–branded successor to the Fairchild KST5550, retaining identical electrical specifications, pinout, package, and marking. The "MTF" suffix denotes tape-and-reel packaging per EIA-481 standards, and no layout or schematic changes are needed when migrating from legacy KST5550 to KST5550MTF in new production runs.