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

onsemi BU406

Name: BU406
Brand: onsemi
SKU: BU406
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BU406

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BU406.pdf

Description:: TRANS NPN 200V 7A TO-220-3

Quantity:: RFQ Add To RFQ list

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Inventory:7,795

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Product details

Overview

BU406 from STMicroelectronics is a silicon epitaxial planar NPN switching transistor in TO-220 package, designed for horizontal deflection output stages in monochrome TV receivers with 110° CRTs. It delivers 7 A continuous collector current, 400 V collector-base voltage, 10 MHz transition frequency, 0.75 µs turn-off time, and 60 W total power dissipation at Tc ≤ 25 °C.

For engineers reviewing the BU406 datasheet, BU406 pinout, BU406 application, or BU406 equivalent, key selection criteria include high-voltage switching capability (VCEO = 200 V), fast turn-off performance (toff = 0.75 µs), second-breakdown robustness (Is/b = 4 A at VCE = 40 V), thermal resistance (Rthj-case = 2.08 °C/W), and TO-220 mechanical compatibility for heatsink mounting.

Technical Context

The BU406 operates as a high-voltage, high-speed switching transistor optimized for flyback energy recovery in CRT horizontal deflection circuits. Its design incorporates epitaxial planar structure to support repetitive 15 A peak collector current (tp < 10 ms) and withstand 400 V VCBO with low leakage (ICES ≤ 5 mA at VCE = 400 V).

It features pulsed saturation characteristics: VCE(sat) = 1 V at IC = 5 A/IB = 0.5 A and VBE(sat) = 1.2 V under identical conditions. Second breakdown limit is specified at 4 A for 10 ms at VCE = 40 V, confirming ruggedness for line-output duty cycles.

Key Specifications

Parameter	Value and Actual Design Meaning
VCBO	400 V - supports safe operation in high-voltage horizontal deflection flyback circuits without breakdown
IC (continuous)	7 A - sustains steady-state current in CRT line-output stage under full-load conditions
toff	0.75 µs - enables precise timing control and minimal switching loss during retrace interval
fT	10 MHz - ensures adequate gain-bandwidth for stable high-frequency switching up to line frequency harmonics
Rthj-case	2.08 °C/W - allows effective thermal management using standard TO-220 heatsinks at 60 W dissipation
Is/b	4 A @ VCE = 40 V, t = 10 ms - defines safe second-breakdown operating area for transient overload tolerance

Pinout & Package

Package: JEDEC TO-220 plastic housing with isolated tab; intended for through-hole mounting and heatsink attachment via screw or clip.

Pin/Terminal	Circuit Role	Design Meaning
Collector (C)	Main high-current, high-voltage output terminal	Connected to CRT deflection yoke and flyback transformer primary; carries full line current and flyback spikes
Base (B)	Control input for switching conduction	Driven by pulse transformer or driver IC; requires 0.5 A peak base current to saturate at 5 A collector load
Emitter (E)	Current return path and reference node	Ground-referenced in most designs; carries full collector current and must handle high di/dt during switching transitions

Key Features

Feature	Design Value
High-voltage blocking	400 V VCBO rating enables direct interface with CRT flyback voltages without external snubbing
Fast switching speed	0.75 µs turn-off time minimizes overlap loss and supports stable 15.625 kHz horizontal scanning
Rugged second breakdown	4 A safe operating area at VCE = 40 V ensures reliability during CRT retrace transients
TO-220 thermal performance	2.08 °C/W junction-to-case resistance supports 60 W dissipation with moderate heatsinking

Applications

Monochrome CRT Horizontal Deflection

High-Voltage Flyback Switching

Use Scenario: Horizontal output stage in 14–21 inch monochrome TV receivers driving 110° deflection angle CRTs.

IC Role / Device Role / Timing Role: Main switching transistor controlling yoke current and generating flyback pulse for EHT generation.

Use Value: 400 V VCBO and 0.75 µs toff ensure reliable retrace timing and voltage margin across CRT aging and line voltage variation.

Use Scenario: High-voltage DC-DC converter switch in legacy industrial flyback supplies requiring >200 V output.

IC Role / Device Role / Timing Role: Primary-side power switch managing energy transfer and voltage regulation via duty cycle control.

Use Value: 200 V VCEO and 7 A IC rating support stable operation at 100–250 kHz switching with minimal derating.

Legacy TV Repair Replacement

Line-Output Stage Prototyping

Use Scenario: Direct replacement for failed BU2508A, BU2520DX, or BU2525AF in field-service CRT monitors.

IC Role / Device Role / Timing Role: Drop-in compatible switching element preserving original timing, drive, and thermal behavior.

Use Value: Identical TO-220 pinout and matching VCEO/IC/toff specs eliminate redesign or board modification.

Use Scenario: Bench validation of horizontal deflection circuit topologies using discrete high-voltage transistors.

IC Role / Device Role / Timing Role: Test vehicle for evaluating base drive requirements, snubber design, and thermal layout before ASIC integration.

Use Value: Known fT (10 MHz) and Rthj-case (2.08 °C/W) enable accurate small-signal modeling and thermal simulation.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BU2508AX	VCEO = 250 V (vs. 200 V); fT = 8 MHz; Rthj-case = 2.5 °C/W	Higher voltage margin but slower switching and worse thermal resistance	Prefer when extended VCEO headroom is critical and switching frequency ≤ 15 kHz
BU2520DX	IC = 10 A; toff = 0.8 µs; Rthj-case = 1.9 °C/W; same TO-220 package	Higher current rating and marginally better thermal performance	Choose for upgraded deflection stages requiring >7 A peak or tighter thermal budgets

Compared with BU406, BU2508AX offers higher VCEO but reduced speed and thermal efficiency, while BU2520DX provides greater current capacity and improved heatsinking-both retain TO-220 compatibility but require verification of base drive and snubber tuning.

Availability

BU406 is available at Aetrix Electronics and suitable for monochrome CRT repair, legacy TV manufacturing, and high-voltage flyback converter development requiring stable component supply and documented thermal behavior.

Supply support for BU406 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, digital, and mixed-signal ICs and discrete power devices.

The BU406 belongs to ST's high-voltage bipolar transistor product line, engineered specifically for CRT horizontal deflection and industrial flyback applications demanding ruggedness, speed, and thermal reliability.

FAQ

Is BU406 still in active production?

No-BU406 is marked "Obsolete Product(s)" in ST's official datasheet revision (February 2003). It remains available through authorized legacy distributors and Aetrix Electronics' long-life inventory program for repair and maintenance of installed base equipment.

Can BU406 be used in modern switch-mode power supplies?

Yes, but with design constraints: its 10 MHz fT and 0.75 µs toff suit operation up to ~100 kHz. For >200 kHz designs, consider newer MOSFETs or IGBTs with lower gate charge and faster switching. Thermal design must account for Rthj-case = 2.08 °C/W and 60 W Ptot limit.

What is the safe base drive requirement for saturation?

For full saturation at IC = 5 A, apply IB = 0.5 A (hFE ≈ 10 typical in switching mode). Base resistor must deliver this peak current under VBB ≥ 12 V, accounting for VBE(sat) = 1.2 V. Pulse drive is recommended to avoid excessive base power dissipation.

Does BU406 have built-in protection features?

No-it is a bare bipolar transistor with no integrated protection. External components are required: base-emitter clamp diode (e.g., 1N4148), collector snubber network (RC or RCD), and heatsink with thermal cutoff if ambient exceeds 70 °C.

BU406 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-220-3

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 7 A

Voltage - Collector Emitter Breakdown (Max):: 200 V

Vce Saturation (Max) @ Ib, Ic:: 1V @ 500mA, 5A

Current - Collector Cutoff (Max):: 5mA

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

Power - Max:: 60 W

Frequency - Transition:: 10MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220-3

BU406 FAQ

1.How can I place an order for BU406 through Aetrix?

Please submit a Request for Quotation (RFQ) for BU406 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 BU406 reliable?

The price and inventory of BU406 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BU406 is usually 5 days.

3.What payment methods are accepted for BU406?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BU406 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BU406?

BU406 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BU406 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 BU406?

For technical support, including BU406 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BU406 requirements.

6.How does Aetrix verify that BU406 is sourced from the original manufacturer or authorized distributors?

All BU406 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 BU406 meets industry standards.

7.What is the process for return or replacement of BU406?

All BU406 units undergo pre-shipment inspection (PSI). If there is an issue with BU406, 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 BU406 part is unused and in its original packaging.

Return procedure for BU406:

1.Submit a request within 90 days.

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

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