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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

onsemi KST5551MTF

Name: KST5551MTF
Brand: onsemi
SKU: KST5551MTF
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: KST5551MTF

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-236-3, SC-59, SOT-23-3

Datasheet:: KST5551MTF.pdf

Description:: TRANS NPN 160V 0.6A SOT-23-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

KST5551MTF from ON Semiconductor (formerly Fairchild) is an NPN epitaxial silicon transistor designed for general-purpose amplification and switching in low-power, high-voltage applications. It features V_CEO = 160 V, I_C = 600 mA, P_C = 350 mW, h_FE = 80–250 at I_C = 1–50 mA, and f_T = 100–300 MHz - enabling use in audio preamplifiers, signal switching, and HV bias networks.

For engineers reviewing the KST5551MTF datasheet, pinout, applications, or equivalent options, key selection criteria include its SOT-23 package compatibility, 160 V collector-emitter breakdown rating, low saturation voltage (V_CE(sat) ≤ 0.2 V), noise figure of 8 dB at 10 Hz–15.7 kHz, and verified performance in linear amplifier stages requiring stable gain above 100 MHz.

Technical Context

The KST5551MTF operates as a discrete NPN bipolar junction transistor with epitaxial base construction, optimized for high-voltage linearity and moderate-frequency response. Its BVCBO = 180 V and BVCEO = 160 V support operation in circuits with elevated supply rails, while Cob = 6 pF and fT up to 300 MHz enable use in RF-coupled preamp and oscillator buffer stages.

Designed for DC-coupled and AC-coupled small-signal amplification, it delivers hFE ≥ 80 at I_C = 1 mA and maintains usable gain down to I_C = 250 µA (NF = 8 dB). Saturation behavior is characterized at two operating points: V_CE(sat) = 0.15 V @ I_C = 10 mA / I_B = 1 mA and 0.2 V @ I_C = 50 mA / I_B = 5 mA - supporting both analog and digital switching roles.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	160 V - supports operation in 120 VAC-derived bias rails and flyback snubber circuits without breakdown.
I_C (max)	600 mA - enables drive capability for medium-current logic interfaces and relay coils.
P_C	350 mW - limits continuous dissipation in SOT-23; requires thermal derating above 25°C ambient.
h_FE	80–250 - provides stable current amplification across 1–50 mA collector range for gain-setting stages.
f_T	100–300 MHz - ensures usable bandwidth in VHF preamplifier and RF detector applications.
V_CE(sat)	0.15–0.2 V - minimizes conduction loss in low-side switching and active load configurations.
NF	8 dB @ 10 Hz–15.7 kHz - specifies low-noise performance suitable for audio front-end amplification.

Pinout & Package

Package: SOT-23 (TO-236AB), surface-mount, 3-terminal plastic package with moisture sensitivity level (MSL) 1. Dimensions conform to JEDEC MO-178AA. Marking: "G1".

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Control input terminal	Receives forward-biased current to modulate collector current; requires series resistor for current limiting in switch mode.
2 (Emitter)	Current return path	Common reference node for bias network; tied to ground or negative rail in common-emitter configuration.
3 (Collector)	Output current terminal	Delivers amplified/saturated output current; connected to load or next stage; handles up to 160 V potential swing.

Key Features

Feature	Design Value
High V_CEO rating	160 V enables direct interface with rectified AC supplies and CRT anode circuits without external clamping.
Low V_CE(sat)	0.15 V at 10 mA allows efficient switching in battery-powered sensor interfaces with minimal voltage drop.
Wide h_FE range	80–250 supports consistent gain across production lots in feedback-stabilized amplifier designs.
Low noise figure	8 dB at audio frequencies makes KST5551MTF suitable for microphone preamplifier first-stage amplification.
High f_T	Up to 300 MHz permits use in IF amplifiers and local oscillator buffers in sub-GHz receivers.

Applications

Audio Preamp Stage	High-Voltage Switching
Use Scenario: Low-noise amplification of electret microphone or piezoelectric sensor signals in portable audio devices. IC Role / Device Role / Timing Role: Discrete NPN transistor configured in common-emitter topology for voltage gain and impedance transformation. Use Value: 8 dB noise figure and h_FE ≥ 80 at 250 µA ensure clean signal capture without added thermal noise or gain compression.	Use Scenario: Driving LED strings or small solenoids from microcontroller GPIO pins in industrial control panels. IC Role / Device Role / Timing Role: Low-side switch with base-driven saturation to minimize power loss and heat generation. Use Value: V_CE(sat) ≤ 0.2 V at 50 mA reduces conduction loss to < 10 mW, extending PCB thermal margin in dense layouts.
RF Signal Buffer	Voltage Reference Bias
Use Scenario: Isolating and buffering 10–100 MHz intermediate frequency signals between mixer and filter stages in AM/FM receivers. IC Role / Device Role / Timing Role: Common-emitter amplifier biased for Class-A operation to preserve signal integrity and phase linearity. Use Value: f_T ≥ 100 MHz and Cob = 6 pF maintain flat gain response and low capacitive loading on preceding stage.	Use Scenario: Providing stable current source for Zener diode bias networks or op-amp reference inputs in precision power supplies. IC Role / Device Role / Timing Role: Constant-current sink using emitter-degenerated configuration with feedback resistor. Use Value: V_CEO = 160 V and h_FE stability allow reliable operation under varying input voltage transients up to 120 VDC.

Audio Preamp Stage

High-Voltage Switching

Use Scenario: Low-noise amplification of electret microphone or piezoelectric sensor signals in portable audio devices.

IC Role / Device Role / Timing Role: Discrete NPN transistor configured in common-emitter topology for voltage gain and impedance transformation.

Use Value: 8 dB noise figure and h_FE ≥ 80 at 250 µA ensure clean signal capture without added thermal noise or gain compression.

Use Scenario: Driving LED strings or small solenoids from microcontroller GPIO pins in industrial control panels.

IC Role / Device Role / Timing Role: Low-side switch with base-driven saturation to minimize power loss and heat generation.

Use Value: V_CE(sat) ≤ 0.2 V at 50 mA reduces conduction loss to < 10 mW, extending PCB thermal margin in dense layouts.

RF Signal Buffer

Voltage Reference Bias

Use Scenario: Isolating and buffering 10–100 MHz intermediate frequency signals between mixer and filter stages in AM/FM receivers.

IC Role / Device Role / Timing Role: Common-emitter amplifier biased for Class-A operation to preserve signal integrity and phase linearity.

Use Value: f_T ≥ 100 MHz and Cob = 6 pF maintain flat gain response and low capacitive loading on preceding stage.

Use Scenario: Providing stable current source for Zener diode bias networks or op-amp reference inputs in precision power supplies.

IC Role / Device Role / Timing Role: Constant-current sink using emitter-degenerated configuration with feedback resistor.

Use Value: V_CEO = 160 V and h_FE stability allow reliable operation under varying input voltage transients up to 120 VDC.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MMBT5551	Same die, identical electrical specs; differs only in tape-and-reel packaging and marking ("1A" vs "G1").	No functional difference; validated for same circuit roles including audio preamp and HV switching.	Select MMBT5551 when standard JEDEC-compliant reel packaging is required for automated assembly.
KSC1845YTA	Higher V_CEO = 200 V but lower f_T = 80 MHz and higher V_CE(sat) = 0.3 V; h_FE min = 70.	Better suited for pure HV switching where speed is secondary; less optimal for RF or low-noise audio.	Choose KSC1845YTA only when >160 V breakdown is mandatory and bandwidth/noise are not critical.

Compared with MMBT5551, KST5551MTF offers identical performance in all electrical parameters but may differ in reel orientation or traceability labeling; compared with KSC1845YTA, KST5551MTF provides superior high-frequency response and lower saturation loss at the expense of 40 V lower breakdown voltage.

Availability

KST5551MTF is available at Aetrix Electronics and suitable for audio preamplifiers, high-voltage switching circuits, and RF signal buffering applications requiring stable component supply, consistent parametric binning, and long-term manufacturability.

Supply support for KST5551MTF 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 KST5551MTF belongs to ON Semiconductor's legacy general-purpose bipolar transistor product line, originally developed by Fairchild for robust, cost-effective amplification and switching in space-constrained, high-reliability designs.

FAQ

What is the maximum collector-emitter voltage rating for KST5551MTF?

The KST5551MTF has a maximum collector-emitter voltage (V_CEO) rating of 160 V at T_A = 25°C. This rating applies under open-base conditions and must be derated linearly above 25°C ambient temperature per the device's thermal characteristics. Exceeding this voltage risks avalanche breakdown and permanent damage to the KST5551MTF.

Is KST5551MTF suitable for audio amplifier applications?

Yes, the KST5551MTF is suitable for audio amplifier applications due to its 8 dB noise figure at 10 Hz–15.7 kHz and stable h_FE across low collector currents. It is commonly used in microphone preamplifier first stages and tone-control buffers where low-noise, linear gain is required - confirmed by Fairchild's original characterization in Rev. B2 (2003) for the KST5551MTF.

What is the pin configuration of KST5551MTF in the SOT-23 package?

The KST5551MTF uses a standard SOT-23 pinout: Pin 1 is Base, Pin 2 is Emitter, and Pin 3 is Collector - with marking "G1" on the top surface. This configuration is documented in the official package drawing and verified across ON Semiconductor's datasheets for the KST5551MTF family.

Does KST5551MTF have a specified current gain bandwidth product?

Yes, the KST5551MTF has a current gain bandwidth product (f_T) of 100–300 MHz, measured at V_CE = 10 V, I_C = 10 mA, and f = 100 MHz. This parameter is explicitly listed in the Electrical Characteristics table of the KST5551MTF datasheet and confirms its usability in VHF signal amplification and RF buffer stages.

What is the thermal limit for continuous operation of KST5551MTF?

The KST5551MTF has a maximum junction temperature (T_J) of 150°C and a storage temperature range of –55°C to +150°C. Its 350 mW power dissipation rating assumes T_A = 25°C; derating is required at higher ambient temperatures - typically 2.8 mW/°C above 25°C - to prevent thermal runaway and ensure long-term reliability of the KST5551MTF.

KST5551MTF Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-236-3, SC-59, SOT-23-3

Packaging:: Bulk

Product Status:: Active

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 600 mA

Voltage - Collector Emitter Breakdown (Max):: 160 V

Vce Saturation (Max) @ Ib, Ic:: 200mV @ 5mA, 50mA

Current - Collector Cutoff (Max):: 50nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 80 @ 10mA, 5V

Power - Max:: 350 mW

Frequency - Transition:: 300MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-3

KST5551MTF FAQ

1.How can I place an order for KST5551MTF through Aetrix?

Please submit a Request for Quotation (RFQ) for KST5551MTF on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for KST5551MTF reliable?

The price and inventory of KST5551MTF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for KST5551MTF is usually 5 days.

3.What payment methods are accepted for KST5551MTF?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for KST5551MTF transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for KST5551MTF?

KST5551MTF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your KST5551MTF order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for KST5551MTF?

For technical support, including KST5551MTF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your KST5551MTF requirements.

6.How does Aetrix verify that KST5551MTF is sourced from the original manufacturer or authorized distributors?

All KST5551MTF products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that KST5551MTF meets industry standards.

7.What is the process for return or replacement of KST5551MTF?

All KST5551MTF units undergo pre-shipment inspection (PSI). If there is an issue with KST5551MTF, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The KST5551MTF part is unused and in its original packaging.

Return procedure for KST5551MTF:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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