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

onsemi BD159STU

Name: BD159STU
Brand: onsemi
SKU: BD159STU
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD159STU

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-225AA, TO-126-3

Datasheet:: BD159STU.pdf

Description:: TRANS NPN 350V 0.5A TO-126-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BD159STU from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for low-power fast-switching output stages in audio and TV applications. It features V_CEO = 350 V, I_C = 0.5 A DC, P_C = 20 W at T_C = 25°C, h_FE = 30–240 (at V_CE = 10 V, I_C = 50 mA), and TO-126 package with emitter-collector-base pinout. It is used in TV horizontal deflection and audio output amplifier circuits.

For engineers reviewing the BD159STU datasheet, pinout, applications, or equivalent options, key selection considerations include its high V_CEO rating, pulse current capability (I_CP = 1.0 A), safe operating area (SOA) performance, thermal derating behavior, and compatibility with Class-B/BTL audio output stages requiring rugged switching transistors.

Technical Context

This device operates as a medium-voltage, medium-current linear/switching NPN bipolar junction transistor. Its design emphasizes fast switching speed and robust SOA-enabled by epitaxial base construction and optimized doping profiles-making it suitable for repetitive pulse loads in horizontal deflection and audio output stages.

The BD159STU exhibits defined saturation characteristics (V_CE(sat) specified at I_C = 10 I_B) and stable h_FE across I_C = 1 mA to 500 mA. Its junction temperature limit is 150°C, with power dissipation derated linearly above T_C = 25°C per the published curve.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	350 V - Maximum collector-emitter voltage before breakdown under open-base condition; enables use in 300 V-class TV flyback and audio supply rails.
I_C (DC)	0.5 A - Continuous collector current handling capacity; supports medium-power audio output stage operation without forced cooling.
P_C @ T_C=25°C	20 W - Maximum steady-state power dissipation at case temperature 25°C; defines heatsink sizing baseline for linear-mode operation.
h_FE	30–240 - DC current gain range at V_CE = 10 V, I_C = 50 mA; ensures reliable base drive design across production lots.
V_CE(sat)	Specified at I_C = 10 I_B - Confirms low-saturation operation for efficient switching in Class-B output stages.
SOA (Pulsed)	Defined up to 1 ms - Supports transient overload conditions in TV horizontal deflection without secondary breakdown.

Pinout & Package

BD159STU is housed in a TO-126 plastic power package with standard lead configuration: Pin 1 = Emitter, Pin 2 = Collector, Pin 3 = Base. The package provides mechanical robustness and thermal path via the metal tab (Collector-connected) mounted to heatsink.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Emitter terminal	Reference node for base-emitter bias; connected to ground or low-impedance return path in common-emitter configurations.
2 (Collector)	Collector terminal	High-voltage output node; electrically tied to metal tab for direct heatsink mounting and thermal conduction.
3 (Base)	Control input	Current-driven gate for BJT operation; requires external current-limiting resistor for safe drive in switching applications.

Key Features

Feature	Design Value
High V_CEO rating	350 V enables operation in 270–320 V DC supply rails typical of CRT TV horizontal deflection and high-voltage audio amplifiers.
Fast switching capability	Optimized epitaxial structure reduces storage time and improves transition speed for line-frequency switching applications.
Rugged SOA	Defined safe operating area up to 1 ms pulse width prevents secondary breakdown during inductive load switching transients.
TO-126 thermal interface	Collector-connected metal tab allows direct mounting to heatsink, supporting 20 W dissipation with appropriate thermal resistance.

Applications

TV Horizontal Deflection Output Stage	Audio Output Amplifier (Class-B)
Use Scenario: Drives flyback transformer primary in CRT television horizontal deflection circuits with 15.625 kHz switching and high-voltage flyback spikes. IC Role / Device Role / Timing Role: NPN switching transistor operating in saturated/active transition region; handles peak currents up to 1.0 A with 350 V blocking capability. Use Value: High V_CEO and rugged SOA prevent failure during flyback voltage overshoot and inductive kickback events.	Use Scenario: Used in push-pull output stage of mono audio amplifiers delivering up to 10 W into 4 Ω or 8 Ω loads. IC Role / Device Role / Timing Role: Linear/switching output device biased in Class-B; delivers amplified audio signal with low V_CE(sat) to minimize crossover distortion. Use Value: Stable h_FE and low saturation voltage ensure consistent gain and thermal stability across ambient temperature variations.
Radio Intermediate Frequency Amplifier	Low-Power Switching Regulator Pass Element
Use Scenario: Amplifies IF signals in AM/FM radio receivers where moderate voltage swing and linearity are required. IC Role / Device Role / Timing Role: Common-emitter small-signal amplifier with DC bias set for mid-rail operation at ~4.5 V collector supply. Use Value: Sufficient f_T (implied by fast-switching designation) and low noise support clean IF amplification without added distortion.	Use Scenario: Functions as series pass element in low-cost linear regulators powering analog subsystems in consumer electronics. IC Role / Device Role / Timing Role: Voltage-controlled current source regulating output by varying base current; dissipates up to 15 W under worst-case dropout conditions. Use Value: 20 W rated dissipation and thermal derating curve allow predictable thermal management without oversized heatsinks.

TV Horizontal Deflection Output Stage

Audio Output Amplifier (Class-B)

Use Scenario: Drives flyback transformer primary in CRT television horizontal deflection circuits with 15.625 kHz switching and high-voltage flyback spikes.

IC Role / Device Role / Timing Role: NPN switching transistor operating in saturated/active transition region; handles peak currents up to 1.0 A with 350 V blocking capability.

Use Value: High V_CEO and rugged SOA prevent failure during flyback voltage overshoot and inductive kickback events.

Use Scenario: Used in push-pull output stage of mono audio amplifiers delivering up to 10 W into 4 Ω or 8 Ω loads.

IC Role / Device Role / Timing Role: Linear/switching output device biased in Class-B; delivers amplified audio signal with low V_CE(sat) to minimize crossover distortion.

Use Value: Stable h_FE and low saturation voltage ensure consistent gain and thermal stability across ambient temperature variations.

Radio Intermediate Frequency Amplifier

Low-Power Switching Regulator Pass Element

Use Scenario: Amplifies IF signals in AM/FM radio receivers where moderate voltage swing and linearity are required.

IC Role / Device Role / Timing Role: Common-emitter small-signal amplifier with DC bias set for mid-rail operation at ~4.5 V collector supply.

Use Value: Sufficient f_T (implied by fast-switching designation) and low noise support clean IF amplification without added distortion.

Use Scenario: Functions as series pass element in low-cost linear regulators powering analog subsystems in consumer electronics.

IC Role / Device Role / Timing Role: Voltage-controlled current source regulating output by varying base current; dissipates up to 15 W under worst-case dropout conditions.

Use Value: 20 W rated dissipation and thermal derating curve allow predictable thermal management without oversized heatsinks.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MJD127G	V_CEO = 100 V, I_C = 2 A, TO-220 package, lower voltage rating but higher current and better thermal performance.	Suitable for low-voltage (<100 V) switching supplies and motor drivers; not usable in 300 V TV deflection circuits.	Select MJD127G only when supply voltage ≤100 V and higher continuous current is required.
BD239C	V_CEO = 100 V, I_C = 2 A, h_FE = 40–250, TO-126 package, same footprint but significantly lower voltage rating.	Applicable in low-voltage audio outputs and general-purpose switching; cannot replace BD159STU in high-voltage horizontal deflection.	BD239C may be used as drop-in replacement only in sub-100 V designs where BD159STU's 350 V rating is unused.

Compared with BD159STU, MJD127G offers superior current and thermal capability but fails at high-voltage stress points, while BD239C shares the TO-126 form factor but sacrifices 250 V of blocking margin-making both unsuitable as direct replacements in original CRT TV designs.

Availability

BD159STU is available at Aetrix Electronics and suitable for TV deflection circuits, audio output amplifiers, IF amplifiers, and low-power linear regulator pass elements requiring stable component supply and long-lifecycle availability.

Supply support for BD159STU 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 discrete devices, analog ICs, and interface solutions before its acquisition by ON Semiconductor in 2016.

The BD159STU belongs to Fairchild's legacy high-voltage NPN transistor family targeting CRT-based consumer electronics; it was engineered specifically for reliability in repetitive high-voltage switching environments like TV horizontal deflection.

FAQ

What is the maximum collector-emitter voltage rating for BD159STU?

The BD159STU has a guaranteed minimum V_CEO rating of 350 V at T_C = 25°C with I_C = 1 mA and I_B = 0. This rating reflects its suitability for high-voltage applications such as CRT TV horizontal deflection stages where flyback voltages exceed 300 V. Derating applies above 25°C case temperature per the published power derating curve.

Is BD159STU pin-compatible with BD157STU or BD158STU?

Yes, BD159STU shares identical TO-126 package dimensions and pinout (Emitter-Collector-Base) with BD157STU and BD158STU. However, electrical ratings differ: BD157STU has V_CEO = 250 V and BD158STU has V_CEO = 300 V. Substitution requires verification that the lower-rated variants meet voltage and SOA requirements of the target circuit.

What is the safe operating area (SOA) limitation for BD159STU in pulsed operation?

The BD159STU SOA is characterized up to 1 ms pulse width with defined boundaries for V_CE and I_C. At 10 µs, it supports up to ~10 A at 350 V; at 1 ms, maximum I_C drops to ~0.8 A at 350 V. These limits prevent secondary breakdown during transient overloads and must be observed in TV deflection and switching regulator designs.

Does BD159STU require a heatsink in typical audio amplifier applications?

Yes, BD159STU requires a heatsink when dissipating more than ~3–5 W continuously. In Class-B audio output stages delivering ≥5 W, thermal calculations show junction temperature exceeds 150°C without heatsinking. The TO-126 metal tab is collector-connected, enabling direct mounting to an appropriately sized aluminum heatsink with thermal compound.

What is the DC current gain (h_FE) range for BD159STU under standard test conditions?

The BD159STU exhibits h_FE ranging from 30 to 240 when measured at V_CE = 10 V and I_C = 50 mA. This wide spread reflects process variation across manufacturing lots and necessitates base drive design accommodating the minimum gain (30) to ensure saturation under worst-case conditions.

BD159STU Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-225AA, TO-126-3

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 500 mA

Voltage - Collector Emitter Breakdown (Max):: 350 V

Vce Saturation (Max) @ Ib, Ic:: -

Current - Collector Cutoff (Max):: 100µA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 30 @ 50mA, 10V

Power - Max:: 20 W

Frequency - Transition:: -

Operating Temperature:: -

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-126-3

BD159STU FAQ

1.How can I place an order for BD159STU through Aetrix?

Please submit a Request for Quotation (RFQ) for BD159STU 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 BD159STU reliable?

The price and inventory of BD159STU are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD159STU is usually 5 days.

3.What payment methods are accepted for BD159STU?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD159STU transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD159STU?

BD159STU orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD159STU 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 BD159STU?

For technical support, including BD159STU datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD159STU requirements.

6.How does Aetrix verify that BD159STU is sourced from the original manufacturer or authorized distributors?

All BD159STU 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 BD159STU meets industry standards.

7.What is the process for return or replacement of BD159STU?

All BD159STU units undergo pre-shipment inspection (PSI). If there is an issue with BD159STU, 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 BD159STU part is unused and in its original packaging.

Return procedure for BD159STU:

1.Submit a request within 90 days.

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

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