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

STMicroelectronics BU508AW

Name: BU508AW
Brand: STMicroelectronics
SKU: BU508AW
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BU508AW

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-247-3

Datasheet:: BU508AW.pdf

Description:: TRANS NPN 700V 8A TO-247-3

Quantity:: RFQ Add To RFQ list

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Inventory:260

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Product details

Overview

BU508AW from STMicroelectronics is a high-voltage NPN power transistor designed for horizontal deflection output in standard-definition CRT TVs and switch-mode power supplies. It features V_CEO = 700 V, I_C = 8 A, P_TOT = 125 W at T_C = 25°C, R_thj-case ≤ 1 °C/W, and h_FE = 10–30 at I_C = 0.1–4.5 A, operating reliably up to T_J = 150°C.

For engineers reviewing the BU508AW datasheet, BU508AW pinout, BU508AW application, or BU508AW equivalent, key selection criteria include its 700 V collector-emitter sustaining voltage, low base-drive requirement (V_BE(sat) = 1.1 V at I_C = 4.5 A), rugged inductive switching capability (t_s = 2.5 µs, t_f = 0.2 µs), and TO-247 semi-insulated package thermal performance.

Technical Context

The BU508AW employs diffused-collector planar technology with an enhanced high-voltage structure optimized for horizontal deflection stage operation in CRT displays. Its design delivers stable h_FE across temperature and tight gain distribution at operating current, enabling consistent drive control in resonant flyback circuits.

It supports pulsed inductive switching at f_h = 16 kHz with L_BB(off) = 4.5 µH, exhibiting robust safe operating area (SOA) up to 1500 V and 15 A peak, and reverse-biased SOA compliance per Figure 10 - critical for horizontal output stage reliability under load transients.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	700 V - Sustaining voltage at I_C = 100 mA; defines maximum usable voltage in horizontal deflection switching
I_C	8 A continuous - Rated collector current at T_C = 25°C; supports typical CRT horizontal output load currents
P_TOT	125 W - Total dissipation at case temperature 25°C; enables high-power switching with minimal heatsink mass
R_thj-case	≤1 °C/W - Junction-to-case thermal resistance; allows efficient heat transfer to heatsink in compact TV chassis
h_FE	10–30 - DC current gain range at I_C = 0.1–4.5 A; ensures predictable base drive sizing across production lot
t_s/t_f	2.5 µs / 0.2 µs - Storage and fall time under specified inductive load; minimizes switching loss in 16 kHz flyback operation

Pinout & Package

BU508AW is housed in a TO-247 semi-insulated power package with three terminals: emitter (pin 1), base (pin 2), collector (pin 3). The package features a metal tab electrically connected to the collector, enabling direct heatsink mounting with electrical isolation via mica or silicone pad.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current return path for collector current	Low-inductance connection point for resonant tank ground reference; tied to CRT yoke return
2 (Base)	Control input for transistor conduction	Receives low-current drive signal (I_B ≤ 4 A); requires precise timing to avoid saturation delay in horizontal scan
3 (Collector)	Main high-voltage current output node	Connected to primary winding of flyback transformer; withstands 700 V sustained and 1500 V transient voltages

Key Features

Feature	Design Value
Diffused-collector "Enhanced generation" structure	Enables higher V_CEO and improved ruggedness vs. legacy horizontal output transistors without process scaling penalties
Tight h_FE range at operating I_C	Reduces need for batch-specific base resistor tuning in CRT deflection circuit production
Low base-drive requirement (V_BE(sat) = 1.1 V)	Lowers driver-stage power loss and simplifies pre-driver IC selection in cost-sensitive TV designs
Stable performance over temperature	Maintains SOA integrity and gain consistency from –65°C to +150°C junction, critical for sealed CRT enclosure environments

Applications

Horizontal Deflection Output

Switch-Mode Power Supply

Use Scenario: Horizontal scanning in standard-definition CRT television sets using resonant flyback topology.

IC Role / Device Role / Timing Role: High-voltage NPN switch controlling primary current in flyback transformer; turns on/off at ~15.625 kHz line frequency.

Use Value: Delivers precise timing edge control (t_s = 2.5 µs) and withstands 700 V sustain voltage during retrace, ensuring stable raster geometry and brightness.

Use Scenario: Primary-side switching element in offline SMPS for CRT TV auxiliary power rails (e.g., +12 V, +24 V).

IC Role / Device Role / Timing Role: Main power switch in quasi-resonant or fixed-frequency forward converter; handles 700 V DC bus and 8 A peak current.

Use Value: Supports high-efficiency conversion with low V_CE(sat) (1 V) and fast turn-off (t_f = 0.2 µs), reducing conduction and switching losses in compact power supplies.

Video Monitor Horizontal Output

Industrial CRT-Based Instrumentation

Use Scenario: Horizontal deflection stage in monochrome or color video monitors with analog RGB input.

IC Role / Device Role / Timing Role: High-reliability output transistor driving deflection yoke; operates continuously under varying ambient temperatures.

Use Value: Maintains consistent h_FE and SOA across –20°C to +70°C ambient, preventing image distortion or linearity drift in long-duration display operation.

Use Scenario: CRT-based oscilloscopes, radar displays, and medical imaging equipment requiring stable high-voltage pulse generation.

IC Role / Device Role / Timing Role: Precision timing switch for sweep generator and high-voltage anode supply modulation.

Use Value: Withstands repetitive 1500 V transients and exhibits low leakage (I_CES ≤ 0.2 mA at 1500 V), ensuring signal fidelity and measurement accuracy.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BU2508AX	V_CEO = 800 V, I_C = 8 A, h_FE = 15–40; same TO-247 package but higher V_CEO and wider gain spread	Supports higher line-voltage SMPS designs (e.g., 230 VAC universal input) where 700 V margin is insufficient	Select when >700 V blocking is required; verify base drive compatibility due to higher h_FE lower bound
2SC5027	V_CEO = 700 V, I_C = 7 A, P_TOT = 100 W; TO-3P package, R_thj-case ≈ 1.25 °C/W	Legacy alternative with lower power rating and larger footprint; used in older CRT service replacements	Acceptable for repair or low-volume legacy builds; not recommended for new designs due to thermal and packaging limitations

Compared with BU2508AX and 2SC5027, BU508AW offers optimal balance of 700 V rating, 125 W dissipation, and 1 °C/W thermal resistance in TO-247 - making it the preferred choice for cost-optimized, thermally constrained CRT horizontal deflection stages requiring proven field reliability.

Availability

BU508AW is available at Aetrix Electronics and suitable for horizontal deflection output, CRT TV switch-mode power supplies, and industrial CRT-based instrumentation requiring stable component supply and long-lifecycle support.

Supply support for BU508AW 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, Switzerland, designing and manufacturing analog, digital, and mixed-signal ICs and discrete power devices.

The BU508AW belongs to ST's high-voltage bipolar power transistor product line, engineered specifically for CRT display horizontal deflection and legacy SMPS applications demanding ruggedness, thermal efficiency, and long-term reliability.

FAQ

Is BU508AW RoHS-compliant and lead-free?

Yes. BU508AW is manufactured in ST's ECOPACK® package with lead-free second-level interconnect, compliant with JEDEC Standard JESD97 and EU RoHS Directive 2011/65/EU. The inner box label indicates the lead-free category and soldering profile limits.

What is the maximum safe operating voltage for BU508AW in continuous mode?

The absolute maximum V_CEO is 700 V at I_B = 0, and V_CES is 1500 V at V_BE = 0. For continuous operation in horizontal deflection, design must stay within the DC safe operating area (SOA) curve - limiting V_CE to ≤700 V at full I_C = 8 A, derated linearly above T_C = 25°C.

Can BU508AW replace BU2508DF in existing CRT designs?

No. BU2508DF is a Darlington pair (V_CEO = 1500 V, h_FE > 1000), while BU508AW is a single NPN transistor (h_FE = 10–30). Base drive requirements, switching speed, and SOA differ significantly; direct substitution would cause underdrive, overheating, or failure.

Does BU508AW require a heatsink in typical CRT horizontal output applications?

Yes. With P_TOT = 125 W and R_thj-case ≤ 1 °C/W, even modest power dissipation (e.g., 25 W) raises junction temperature by ≥25°C above case. A properly mounted aluminum heatsink (≥200 cm² surface area, thermal interface material) is mandatory to maintain T_J ≤ 150°C under worst-case line and temperature conditions.

BU508AW Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-247-3

Packaging:: Tube

Product Status:: Active

Transistor Type:: NPN

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

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

Vce Saturation (Max) @ Ib, Ic:: 1V @ 1.6A, 4.5A

Current - Collector Cutoff (Max):: 200µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 10 @ 100mA, 5V

Power - Max:: 125 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-247-3

BU508AW FAQ

1.How can I place an order for BU508AW through Aetrix?

Please submit a Request for Quotation (RFQ) for BU508AW 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 BU508AW reliable?

The price and inventory of BU508AW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BU508AW is usually 5 days.

3.What payment methods are accepted for BU508AW?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BU508AW transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BU508AW?

BU508AW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BU508AW 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 BU508AW?

For technical support, including BU508AW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BU508AW requirements.

6.How does Aetrix verify that BU508AW is sourced from the original manufacturer or authorized distributors?

All BU508AW 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 BU508AW meets industry standards.

7.What is the process for return or replacement of BU508AW?

All BU508AW units undergo pre-shipment inspection (PSI). If there is an issue with BU508AW, 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 BU508AW part is unused and in its original packaging.

Return procedure for BU508AW:

1.Submit a request within 90 days.

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

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