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STMicroelectronics BU508AFI
- Part No.:
- BU508AFI
- Manufacturer:
- STMicroelectronics
- Category:
- Single Bipolar Transistors
- Package:
- ISOWATT-218-3
- Datasheet:
-
BU508AFI.pdf
- Description:
- TRANS NPN 700V 8A ISOWATT-218FX
- Quantity:
- Payment:
- Shipping:
Inventory:6,752
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Product details
Overview
BU508AFI from STMicroelectronics is a high-voltage, fast-switching NPN power transistor in an ISOWATT218 (TO-218) fully insulated package, rated for VCES = 1500 V, IC = 8 A, and Ptot = 50 W at Tc = 25 °C, with 2500 VRMS insulation withstand voltage - designed specifically for horizontal deflection circuits in color TV systems.
For engineers reviewing the BU508AFI datasheet, BU508AFI pinout, BU508AFI application, or BU508AFI equivalent, key selection factors include its 1500 V collector-emitter blocking capability, 7 µs storage time under inductive load, 550 ns fall time, hollow emitter structure for enhanced switching speed, and U.L.-compliant insulated mounting.
Technical Context
The BU508AFI employs Multiepitaxial Mesa technology and a hollow emitter structure to achieve fast switching performance while maintaining high-voltage robustness. Its safe operating area is defined up to 150 °C case temperature, with Rthj-case = 2.5 °C/W enabling thermally constrained designs in compact CRT deflection stages.
It operates as a primary horizontal output switch in flyback-based deflection systems, where VCEO(sus) = 700 V (at IC = 100 mA) and VCE(sat) = 1 V (at IC = 4.5 A, IB = 2 A) ensure low conduction loss and reliable sustain during retrace intervals.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCES | 1500 V - Enables direct use in 110–240 VAC-fed CRT horizontal deflection without external snubbing for peak line-voltage transients. |
| IC | 8 A continuous - Supports high peak current demands of horizontal scan yoke drive with margin for thermal derating. |
| Ptot | 50 W at Tc = 25 °C - Defines maximum steady-state power dissipation before thermal shutdown in ISOWATT218 package. |
| ts / tf | 7 µs / 550 ns - Fast storage and fall times reduce switching losses and enable stable operation at ~15.735 kHz horizontal frequency. |
| Visol | 2500 VRMS - Allows direct mounting to grounded heatsinks without insulating washers, simplifying mechanical assembly and improving thermal reliability. |
| fT | 7 MHz - Confirms sufficient gain-bandwidth for stable base drive in self-oscillating or IC-controlled horizontal output stages. |
Pinout & Package
BU508AFI uses the ISOWATT218 (TO-218) package: a fully insulated, U.L.-compliant 3-lead power transistor housing with integrated ceramic isolation between leads and metal mounting flange. Mounting torque must not exceed 1 Nm; flatness tolerance on heatsink side is ≤80 µm.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (Collector) | Main high-current, high-voltage output node | Connected to horizontal deflection yoke and flyback transformer primary; carries full scan current and withstands 1500 V transient spikes. |
| 2 (Base) | Control input for turn-on/turn-off | Receives current-driven drive signal (typically 2 A peak); low VBE(sat) = 1.3 V minimizes driver stage power loss. |
| 3 (Emitter) | Reference and return path for collector current | Returned to ground or damper network; low-inductance layout critical to suppress voltage overshoot during turn-off. |
Key Features
| Feature | Design Value |
|---|---|
| Hollow emitter structure | Reduces minority carrier storage time to 7 µs, enabling clean turn-off in high-frequency horizontal deflection. |
| Fully insulated ISOWATT218 package | 2500 VRMS isolation eliminates need for mica washers or silicone pads when mounted to chassis-grounded heatsinks. |
| Multiepitaxial Mesa process | Delivers consistent VCEO(sus) = 700 V and tight parameter distribution across production lots for CRT BOM stability. |
| Low VCE(sat) | 1 V at IC = 4.5 A ensures <1.5 W conduction loss, reducing thermal stress in sealed TV enclosures. |
Applications
| Color TV Horizontal Deflection | Monitor Flyback Power Switch |
|---|---|
|
Use Scenario: Driving the horizontal deflection yoke and flyback transformer in analog CRT television sets operating at 15.625–15.735 kHz. IC Role / Device Role / Timing Role: Primary high-voltage switching transistor in self-oscillating or IC-synchronized horizontal output stage. Use Value: 1500 V VCES rating handles line-voltage surges and flyback spikes without clamping; 7 µs ts prevents excessive retrace-time distortion. |
Use Scenario: High-voltage switching element in CRT monitor power supplies generating EHT (15–30 kV) and filament/low-voltage rails. IC Role / Device Role / Timing Role: Main energy-transfer switch in quasi-resonant flyback converter topology. Use Value: 2500 VRMS insulation allows direct heatsink grounding, improving EMC and reducing creepage/clearance design overhead. |
| Legacy Broadcast Equipment | Industrial CRT-Based Test Instruments |
|
Use Scenario: Horizontal sweep generation in studio-grade broadcast monitors and waveform analyzers requiring long-term reliability. IC Role / Device Role / Timing Role: Critical timing-critical switch in high-stability deflection circuitry with minimal parameter drift over temperature. Use Value: Tj(max) = 150 °C and Rthj-case = 2.5 °C/W support continuous operation in ventilated but space-constrained rack-mount enclosures. |
Use Scenario: Scan generator in oscilloscopes, spectrum analyzers, and vector displays where CRT brightness and linearity depend on precise deflection timing. IC Role / Device Role / Timing Role: Sustained-duty horizontal output device synchronized to precision timing references. Use Value: Tight fT = 7 MHz and low VBE(sat) = 1.3 V ensure predictable base drive requirements and minimal phase shift in feedback loops. |
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-218 package but non-insulated; Rthj-case = 1 °C/W; Ptot = 125 W; no 2500 VRMS isolation. | Requires insulating hardware for chassis-mounted heatsinks; higher power handling but less mounting flexibility. | Select when thermal budget permits higher dissipation and isolation can be implemented externally. |
| 2SC5027 | VCES = 1500 V, IC = 7 A, ts = 10 µs, TO-3P package; no certified insulation rating. | Compatible in deflection circuits but lacks UL-compliant isolation; requires separate creepage management. | Choose only if legacy board layout accommodates TO-3P footprint and external isolation is already validated. |
Compared with BU508A and 2SC5027, BU508AFI uniquely combines UL-rated insulation, 1500 V blocking, and 7 µs storage time in a single-source, drop-in-replaceable ISOWATT218 form factor - eliminating insulator procurement and qualification overhead in high-reliability CRT manufacturing.
Availability
BU508AFI is available at Aetrix Electronics and suitable for color TV deflection systems, CRT monitor power supplies, broadcast equipment, and industrial test instrumentation requiring stable component supply and long-lifecycle support.
Supply support for BU508AFI 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, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.
BU508AFI belongs to ST's legacy high-voltage power transistor product line, engineered specifically for CRT horizontal deflection and flyback conversion - emphasizing ruggedness, insulation integrity, and switching consistency under repetitive surge conditions.
FAQ
Is BU508AFI still in active production?
BU508AFI is classified as an obsolete part by STMicroelectronics per official documentation, but Aetrix Electronics maintains verified legacy stock with full traceability and extended lifecycle support for ongoing repair and maintenance programs in CRT-based infrastructure.
Can BU508AFI replace BU508A directly on PCB?
No - BU508AFI uses the ISOWATT218 package with insulated leads, whereas BU508A uses the standard TO-218. Mechanical mounting holes and thermal pad layout differ; replacement requires board-level redesign to accommodate insulation clearance and torque specifications (0.8–1 Nm).
What is the maximum safe operating voltage for BU508AFI in continuous DC mode?
The absolute maximum VCES is 1500 V with VBE = 0, but sustained DC operation above 700 V is not recommended. The sustaining voltage VCEO(sus) = 700 V at IC = 100 mA defines the practical upper limit for reliable non-pulsed operation in deflection circuits.
Does BU508AFI require a base resistor in typical horizontal deflection circuits?
Yes - a current-limiting base resistor is mandatory to control IB and ensure saturation at IC = 4.5 A. Typical designs use 1.2–2.2 Ω, 5 W wirewound resistors to deliver ~2 A peak base current while limiting dissipation and preventing secondary breakdown during retrace.
BU508AFI Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- ISOWATT-218-3
- Packaging:
- Tube
- 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:
- 50 W
- Frequency - Transition:
- 7MHz
- Operating Temperature:
- 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- ISOWATT-218FX
BU508AFI FAQ
1.How can I place an order for BU508AFI through Aetrix?
Please submit a Request for Quotation (RFQ) for BU508AFI 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 BU508AFI reliable?
The price and inventory of BU508AFI are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BU508AFI is usually 5 days.
3.What payment methods are accepted for BU508AFI?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BU508AFI transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for BU508AFI?
BU508AFI orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your BU508AFI 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 BU508AFI?
For technical support, including BU508AFI datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BU508AFI requirements.
6.How does Aetrix verify that BU508AFI is sourced from the original manufacturer or authorized distributors?
All BU508AFI 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 BU508AFI meets industry standards.
7.What is the process for return or replacement of BU508AFI?
All BU508AFI units undergo pre-shipment inspection (PSI). If there is an issue with BU508AFI, 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 BU508AFI part is unused and in its original packaging.
Return procedure for BU508AFI:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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