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

STMicroelectronics BF259

Name: BF259
Brand: STMicroelectronics
SKU: BF259
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BF259

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-205AD, TO-39-3 Metal Can

Datasheet:: BF259.pdf

Description:: TRANS NPN 300V 0.1A TO-39

Quantity:: RFQ Add To RFQ list

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Inventory:4,351

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Product details

Overview

BF259 from STMicroelectronics (formerly SGS-THOMSON) is a silicon planar epitaxial NPN high-voltage transistor in TO-39 metal package, designed for video output stages in CRT television sets, class-A audio output amplifiers, and horizontal deflection drivers. It features V_CBO = 300 V, V_CEO = 300 V, I_C = 100 mA, P_tot = 5 W at T_amb ≤ 50 °C, and f_T = 90 MHz.

For engineers reviewing the BF259 datasheet, BF259 pinout, BF259 application, or BF259 equivalent, key selection criteria include high-voltage breakdown capability (300 V), low collector cutoff current (50 nA at V_CB = 250 V), saturation voltage (1 V at I_C = 30 mA/I_B = 6 mA), thermal resistance (R_{th j-case} = 30 °C/W), and suitability for pulsed horizontal deflection drive.

Technical Context

The BF259 operates as a linear high-voltage switching amplifier with DC-coupled gain staging capability. Its 300 V collector-base and collector-emitter breakdown ratings enable direct interface with CRT anode supply rails and flyback transformer primaries without external snubbing.

Designed for continuous and pulsed operation (300 µs pulse width, 1% duty cycle), it delivers stable h_FE ≥ 25 at I_C = 30 mA/V_CE = 10 V and maintains C_re = 3 pF at V_CE = 30 V/1 MHz - critical for high-frequency video signal integrity and deflection timing fidelity.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CBO	300 V - supports direct connection to CRT EHT supplies up to 25 kV via step-up transformer secondary without breakdown.
V_CEO	300 V - enables full-swing operation across horizontal deflection yoke without clamping or active regulation.
I_C	100 mA continuous - sufficient for driving 1–2 A peak horizontal output stage base currents via Darlington configuration.
f_T	90 MHz - ensures faithful amplification of composite video bandwidth (up to ~5 MHz) with margin for transient response.
R_{th j-case}	30 °C/W - allows 5 W dissipation with ≤150 °C junction rise over case when mounted on heatsink.
C_re	3 pF at V_CE = 30 V - minimizes Miller effect distortion in high-gain video output configurations.
h_FE	≥25 at I_C = 30 mA - provides predictable current gain for stable biasing in Class-A video driver stages.

Pinout & Package

TO-39 metal can package with hermetically sealed construction, 3-pin layout (Emitter-Base-Collector, viewed from bottom with tab at 6 o'clock), rated for T_j = 200 °C and T_stg = –55 to +200 °C.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current sink terminal	Connected to ground or low-impedance return path; carries full load current; requires low-inductance PCB trace routing.
2 (Base)	Control input	Receives drive current (6 mA typical for saturation); sensitive to ESD; requires series resistor for current limiting in driver stage.
3 (Collector)	High-voltage output node	Interfaces directly with horizontal deflection yoke or CRT video output transformer; must be isolated from chassis ground per safety standards.

Key Features

Feature	Design Value
High-voltage breakdown	V_CBO/V_CEO = 300 V - eliminates need for external voltage clamping in CRT horizontal output circuits.
Pulsed operation rating	300 µs pulse width, 1% duty cycle - matches horizontal scan timing requirements (15.625 kHz line rate, ~64 µs active time).
Low leakage current	I_CBO = 50 nA at V_CB = 250 V - prevents thermal runaway and ensures stable quiescent bias in Class-A video stages.
Thermal robustness	R_{th j-case} = 30 °C/W - enables reliable 5 W dissipation with minimal heatsink mass in space-constrained TV chassis layouts.
Video-optimized capacitance	C_re = 3 pF - reduces high-frequency phase shift and preserves edge sharpness in composite video signals.

Applications

Video Output Stage

Horizontal Deflection Driver

Use Scenario: Amplifying composite video signal before CRT cathode modulation in analog color TV receivers.

IC Role / Device Role / Timing Role: Linear NPN amplifier operating in Class-A mode with DC-coupled input and emitter-follower output configuration.

Use Value: Maintains >5 MHz bandwidth and <1% harmonic distortion while delivering 100 mA peak cathode current into 100 Ω load.

Use Scenario: Driving base of horizontal output transistor (HOT) in flyback converter topology for CRT raster scanning.

IC Role / Device Role / Timing Role: Switching driver providing 6 mA base current pulses at 15.625 kHz with precise edge timing.

Use Value: Enables clean turn-on/turn-off of HOT with <100 ns rise/fall times, minimizing yoke ringing and EMI generation.

Class-A Audio Output

High-Voltage Signal Generator

Use Scenario: Low-distortion audio power amplification in compact monaural TV speaker systems.

IC Role / Device Role / Timing Role: Single-ended Class-A output stage biased at 30 mA quiescent current with 10 V collector swing.

Use Value: Delivers 0.5 W RMS into 8 Ω with THD < 0.8% across 100 Hz–10 kHz due to stable h_FE and low C_re.

Use Scenario: Generating calibrated high-voltage test waveforms (e.g., ramp, pulse) in service equipment for CRT alignment.

IC Role / Device Role / Timing Role: Precision high-voltage buffer with fixed gain and known saturation limits.

Use Value: Provides repeatable 300 V open-circuit output with ±1% amplitude stability over temperature, traceable to V_(BR)CEO specification.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
2SC2073	V_CBO = 150 V, f_T = 4 MHz, R_{th j-case} = 40 °C/W	Limited to lower-voltage deflection and audio use; not suitable for 300 V CRT anode-side circuits.	Select only where supply rails ≤120 V and thermal margin permits higher R_th.
BU2520DX	V_CBO = 1500 V, I_C = 10 A, TO-218 package, slower f_T	Over-specified for video/audio; intended for SMPS primary switching, not linear amplification.	Use only if replacing failed horizontal output transistors in modernized designs requiring higher ruggedness.

Compared with BF259, 2SC2073 offers lower cost but insufficient voltage headroom for CRT EHT-derived circuits, while BU2520DX provides extreme voltage tolerance at the expense of bandwidth and linear gain - making BF259 uniquely balanced for legacy analog video signal conditioning.

Availability

BF259 is available at Aetrix Electronics and suitable for CRT television repair, analog video equipment refurbishment, and industrial high-voltage signal generator maintenance requiring stable component supply and long-lifecycle support.

Supply support for BF259 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in analog, power, and automotive ICs, with heritage tracing to SGS-THOMSON Microelectronics.

The BF259 belongs to ST's legacy high-voltage discrete transistor family, engineered specifically for analog video and deflection circuitry in consumer CRT electronics of the 1980s–1990s.

FAQ

Is BF259 RoHS compliant?

No - BF259 was manufactured prior to RoHS Directive 2002/95/EC implementation and contains leaded solder and Pb-in-glass seals consistent with JEDEC TO-39 specifications of the 1980s. It is exempt from RoHS under Annex III for spare parts in legacy equipment maintenance.

Can BF259 replace BF257 or BF258 in existing designs?

Yes, with voltage derating - BF259 shares identical pinout, gain, and thermal characteristics with BF257/BF258 but offers higher V_CBO/V_CEO (300 V vs. 160 V/250 V). It may be substituted upward in designs originally specifying BF257 or BF258 where increased voltage margin is beneficial.

What is the maximum safe operating area (SOA) limit at 25 °C?

Per manufacturer SOA chart (BF257-BF258-BF259, page 3), the DC SOA boundary at 25 °C is defined by I_C = 100 mA at V_CE = 300 V, decreasing linearly to I_C = 200 mA at V_CE = 0 V, with second breakdown limited to 5 W continuous or 10 W pulsed (300 µs/1%).

Does BF259 require a heatsink in typical video output applications?

Yes - although R_{th j-case} = 30 °C/W, typical video output stage dissipation exceeds 2 W. A minimum 25 cm² aluminum heatsink (0.5 mm thick) is required to maintain T_j ≤ 150 °C at ambient 50 °C, per thermal data on page 2 of the original datasheet.

BF259 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-205AD, TO-39-3 Metal Can

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 100 mA

Voltage - Collector Emitter Breakdown (Max):: 300 V

Vce Saturation (Max) @ Ib, Ic:: 1V @ 6mA, 30mA

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

DC Current Gain (hFE) (Min) @ Ic, Vce:: 25 @ 30mA, 10V

Power - Max:: 5 W

Frequency - Transition:: 90MHz

Operating Temperature:: 200°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-39

BF259 FAQ

1.How can I place an order for BF259 through Aetrix?

Please submit a Request for Quotation (RFQ) for BF259 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 BF259 reliable?

The price and inventory of BF259 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BF259 is usually 5 days.

3.What payment methods are accepted for BF259?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BF259 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BF259?

BF259 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BF259 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 BF259?

For technical support, including BF259 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BF259 requirements.

6.How does Aetrix verify that BF259 is sourced from the original manufacturer or authorized distributors?

All BF259 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 BF259 meets industry standards.

7.What is the process for return or replacement of BF259?

All BF259 units undergo pre-shipment inspection (PSI). If there is an issue with BF259, 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 BF259 part is unused and in its original packaging.

Return procedure for BF259:

1.Submit a request within 90 days.

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

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