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

STMicroelectronics BU208A

Name: BU208A
Brand: STMicroelectronics
SKU: BU208A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BU208A

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-204AA, TO-3

Datasheet:: BU208A.pdf

Description:: TRANS NPN 700V 8A TO-3

Quantity:: RFQ Add To RFQ list

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Inventory:4,608

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Product details

Overview

BU208A from STMicroelectronics is a high-voltage, fast-switching NPN power transistor in TO-218 (ISOWATT218) package, rated for 1500 V V_CES, 8 A I_C, and 150 W P_tot at T_c = 25 °C, designed specifically for horizontal deflection circuits in color TV systems.

For engineers reviewing the BU208A datasheet, BU208A pinout, BU208A application, or BU208A equivalent, this device's 2500 V_RMS insulation withstand voltage, 7 µs storage time under inductive load, and hollow emitter structure are critical selection criteria for CRT flyback switching reliability.

Technical Context

The BU208A employs Multiepitaxial Mesa process technology and a hollow emitter geometry to reduce minority carrier storage and improve switching speed. Its 700 V V_CEO(sus) and 1 V V_CE(sat) at I_C = 4.5 A / I_B = 2 A support robust line-scan switching with low conduction loss.

Thermal design is enabled by R_thj-case = 1 °C/W (TO-218), and its fully insulated package meets UL compliance for direct heatsink mounting without isolation hardware. The device operates up to 175 °C junction temperature.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	1500 V - Withstands peak flyback voltages in CRT horizontal deflection without breakdown.
I_C	8 A continuous - Supports full-swing current drive for line-output transformer primary windings.
P_tot	150 W at T_c = 25 °C - Enables high-power pulse operation with adequate thermal margin using standard heatsinking.
t_s	7 µs - Short storage time ensures rapid turn-off during high-frequency (15.625 kHz) horizontal retrace.
V_isol	2500 V_RMS - UL-compliant insulation allows safe, direct mounting to grounded heatsinks without mica washers.
f_T	7 MHz - Sufficient gain-bandwidth for stable base drive in self-oscillating or transistorized line output stages.
R_thj-case	1 °C/W - Enables predictable junction temperature rise under pulsed load conditions typical of TV deflection.

Pinout & Package

Package: TO-218 (ISOWATT218), fully insulated, UL-compliant, 4.9 g typical weight, flat mounting surface tolerance ≤ 80 µm.

Pin/Terminal	Circuit Role	Design Meaning
1 (Tab)	Collector	Electrically isolated metal tab serves as main heat path and high-current collector terminal; requires no insulating washer.
2	Base	Low-impedance control input; driven by line oscillator or driver transformer secondary for precise switching timing.
3	Emitter	Return path for load current; connected to ground reference in standard flyback topology with snubber network.

Key Features

Feature	Design Value
Hollow emitter structure	Reduces minority carrier storage, enabling 7 µs t_s for reliable 15.625 kHz horizontal retrace.
Multiepitaxial Mesa process	Delivers consistent V_CEO(sus) ≥ 700 V and low V_CE(sat) = 1 V at rated current.
UL-compliant insulation	2500 V_RMS isolation between all leads and heatsink eliminates need for thermal interface insulation hardware.
High T_j rating	175 °C maximum junction temperature supports sustained operation in enclosed TV chassis with limited airflow.

Applications

Color TV Horizontal Deflection

Flyback Transformer Driver

Use Scenario: Line-scan switching in analog CRT television sets operating at 15.625 kHz.

IC Role / Device Role / Timing Role: Main switch in flyback converter topology, handling high-voltage retrace pulses and energy transfer to EHT winding.

Use Value: 1500 V V_CES and 7 µs t_s ensure reliable turn-off before next scan line, preventing transformer saturation and arcing.

Use Scenario: Primary-side switching element in monochrome or color TV flyback power supplies.

IC Role / Device Role / Timing Role: High-voltage NPN switch controlling energy buildup and release in line-output transformer.

Use Value: 150 W dissipation capability and 1 °C/W R_thj-case allow stable operation under repetitive 50–100 µs pulse loads.

High-Voltage Pulse Generator

Legacy CRT Monitor Output Stage

Use Scenario: Repetitive high-voltage pulse generation for industrial testers or legacy display calibration gear.

IC Role / Device Role / Timing Role: Fast-switching power stage converting DC bus to controlled HV pulses via resonant or inductive load.

Use Value: 2500 V_RMS insulation withstand enables direct heatsink mounting in compact HV enclosures without creepage risk.

Use Scenario: Horizontal output stage in professional broadcast or medical CRT monitors requiring long-term stability.

IC Role / Device Role / Timing Role: Critical switching transistor in linearity-critical deflection circuits demanding low V_CE(sat) and repeatable t_s.

Use Value: 1 V V_CE(sat) at 4.5 A minimizes conduction loss and thermal drift across extended operational life.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BU508A	Same die, TO-3 package; R_thj-case = 1 °C/W but lower P_tot = 125 W; no UL insulation.	Requires mica insulator and mounting hardware; unsuitable for direct heatsink mounting.	Select when mechanical compatibility with legacy TO-3 sockets is required and isolation can be added externally.
2SD1555	1500 V V_CES, 10 A I_C, but higher V_CE(sat) = 1.5 V and slower t_s = 10 µs; TO-3P package.	Higher conduction loss and reduced switching margin in high-retrace-rate CRT designs.	Consider only if higher current headroom is prioritized over switching speed and thermal efficiency.

Compared with BU508A and 2SD1555, the BU208A uniquely combines UL-rated insulation, TO-218 thermal performance, and sub-10 µs storage time-making it the optimal choice for space-constrained, safety-certified CRT horizontal deflection designs where mounting simplicity and switching fidelity are jointly critical.

Availability

BU208A is available at Aetrix Electronics and suitable for horizontal deflection circuits, flyback power supplies, and high-voltage pulse generators requiring stable component supply and long-lifecycle support for legacy display repair and industrial maintenance programs.

Supply support for BU208A 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, designing and manufacturing analog, power, and microcontroller solutions for industrial, automotive, and consumer markets.

The BU208A belongs to ST's high-voltage power transistor product line, engineered specifically for CRT-based display deflection and flyback conversion applications demanding ruggedness, insulation integrity, and fast switching.

FAQ

Is BU208A still in active production?

No-BU208A is marked as obsolete in ST's official documentation (2002 datasheet revision). However, Aetrix Electronics maintains verified legacy stock with full traceability, conforming to original ST specifications and packaging. It is supplied exclusively for repair, maintenance, and end-of-life system support-not for new design-in.

Can BU208A replace BU508A directly in a circuit?

Electrically yes, but mechanically no: both share identical die characteristics (V_CES, V_CEO, t_s, f_T), but BU208A uses TO-218 with insulated tab while BU508A uses non-insulated TO-3. Direct replacement requires verifying heatsink isolation and mounting torque (0.8 Nm recommended).

What is the maximum safe operating voltage in continuous DC mode?

The BU208A is not rated for continuous DC blocking above V_CEO = 700 V. Its 1500 V V_CES rating applies only with V_BE = 0 (open-base condition) and is intended for pulsed flyback applications-not steady-state DC voltage hold.

Does BU208A require a base resistor in typical TV line output circuits?

Yes-standard designs use a 100 Ω to 470 Ω base resistor to limit I_B to ~2 A during turn-on, ensuring V_BE(sat) = 1.3 V is met while preventing driver-stage overload. Resistor value must be selected based on actual base drive waveform and duty cycle.

BU208A Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-204AA, TO-3

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 8 A

Voltage - Collector Emitter Breakdown (Max):: 700 V

Vce Saturation (Max) @ Ib, Ic:: 1V @ 2A, 4.5A

Current - Collector Cutoff (Max):: 1mA

DC Current Gain (hFE) (Min) @ Ic, Vce:: -

Power - Max:: 150 W

Frequency - Transition:: 7MHz

Operating Temperature:: 175°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Chassis Mount

Supplier Device Package:: TO-3

BU208A FAQ

1.How can I place an order for BU208A through Aetrix?

Please submit a Request for Quotation (RFQ) for BU208A 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 BU208A reliable?

The price and inventory of BU208A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BU208A is usually 5 days.

3.What payment methods are accepted for BU208A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BU208A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BU208A?

BU208A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BU208A 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 BU208A?

For technical support, including BU208A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BU208A requirements.

6.How does Aetrix verify that BU208A is sourced from the original manufacturer or authorized distributors?

All BU208A 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 BU208A meets industry standards.

7.What is the process for return or replacement of BU208A?

All BU208A units undergo pre-shipment inspection (PSI). If there is an issue with BU208A, 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 BU208A part is unused and in its original packaging.

Return procedure for BU208A:

1.Submit a request within 90 days.

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

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