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

onsemi BUH51

Name: BUH51
Brand: onsemi
SKU: BUH51
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUH51

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BUH51.pdf

Description:: TRANS NPN 500V 3A TO-126

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BUH51 from onsemi is an NPN silicon planar power transistor designed for switchmode operation in 50 W halogen electronic transformers, sustaining large inrush currents during startup or short-circuit load conditions. It features V_CEO = 500 V, I_C = 3.0 A continuous, P_D = 50 W at T_C = 25°C, and TO-225 package with base-collector-emitter pinout.

For engineers reviewing the BUH51 datasheet, pinout, applications, or equivalent options, this device is selected for high-voltage, medium-current switching in inductive ballast circuits where robust safe operating area (SOA), low V_CE(sat), and fast turn-off under clamped inductive loads are critical.

Technical Context

The BUH51 employs a state-of-the-art die optimized for halogen transformer applications, featuring high ruggedness against second breakdown and reverse-biased SOA validated under clamped 300 V inductive switching with L = 200 µH. Its forced h_FE remains stable across temperature (6–8 at I_C = 1.0 A, T_J = 125°C) to ensure reliable gate drive margin.

Dynamic saturation voltage (V_CE(dsat)) is characterized at 1.7 V (25°C) and 6.0 V (125°C) under I_C = 1.0 A, IB1 = 0.2 A, confirming low conduction loss during active switching. Turn-off time is specified at 3.5–4.0 µs for resistive loads and 2.3–2.8 µs for inductive loads, supporting efficient high-frequency operation up to ~200 kHz in transformer-driven topologies.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	500 V - Sustains 500 V collector-emitter voltage under switching stress in halogen transformer primary circuits
I_C (continuous)	3.0 A - Supports nominal 50 W output with thermal headroom at T_C = 25°C
P_D @ T_C = 25°C	50 W - Enables compact heatsinking in space-constrained electronic transformer modules
V_CE(sat) @ I_C = 1.0 A	0.3–0.5 V - Minimizes conduction loss and self-heating during on-state
t_off (inductive)	2.3–2.8 µs - Ensures rapid current commutation during transformer reset phase
R_θJC	2.5 °C/W - Allows direct case-to-heatsink thermal path design with predictable junction temperature rise
f_T	23 MHz - Confirms sufficient gain-bandwidth for stable base drive loop response

Pinout & Package

Package: TO-225 (Case 77, Style 3), epoxy molded, UL 94 V-0 rated at 0.125 in thickness, Pb-free compatible.

Pin/Terminal	Circuit Role	Design Meaning
1	Base	Control input requiring low drive current (I_B ≤ 2.0 A continuous) due to high h_FE (8–14 at I_C = 0.8–1.0 A)
2	Collector	High-voltage switching node connected to transformer primary; rated for 800 V V_CBO and 800 V V_CES
3	Emiter	Power return path; tied to ground or low-side switch node in half-bridge configurations

Key Features

Feature	Design Value
High and flat DC current gain (h_FE)	8–14 over I_C = 0.8–2.0 A range enables simplified, low-power base drive circuitry
Robust reverse-biased SOA	Validated at 300 V clamp, 200 µH inductance, ensuring reliability during transformer flyback
Low dynamic saturation voltage	V_CE(dsat) = 1.7 V (25°C) reduces switching loss peak during transition intervals
ESD protection	Machine Model Class C and Human Body Model Class 3B rated for manufacturing handling safety
Thermal performance	R_θJC = 2.5 °C/W supports direct mounting to heatsinks without thermal interface material in many designs

Applications

Halogen Lamp Electronic Transformer	Inductive Load Switching Power Supply
Use Scenario: High-frequency AC-AC conversion for 12 V halogen lamps using resonant or quasi-resonant topology with inductive energy storage. IC Role / Device Role / Timing Role: Main switching transistor in single-ended forward or push-pull configuration, handling primary-side 300 V clamped inductive flyback. Use Value: Sustains repeated inrush currents up to 8 A peak while maintaining safe SOA margins per Figure 23, enabling reliable lamp ignition.	Use Scenario: Medium-power offline SMPS with inductive output filtering and high-voltage primary switching. IC Role / Device Role / Timing Role: Primary-side power switch controlling energy transfer into transformer core; operates in discontinuous or boundary conduction mode. Use Value: Fast t_off (2.3 µs) and low V_CE(sat) reduce switching losses, improving efficiency above 85% at 50 W output.
Short-Circuit Protected Lighting Driver	Industrial Control Relay Replacement
Use Scenario: Constant-power LED or halogen driver with built-in short-circuit foldback protection. IC Role / Device Role / Timing Role: Current-sensing and fault-handling switch that limits peak current during load faults via controlled saturation. Use Value: High I_CM = 8.0 A peak rating and rugged SOA allow temporary overload survival without latch-up or secondary breakdown.	Use Scenario: Solid-state replacement for electromechanical relays in PLC output modules or motor starter logic. IC Role / Device Role / Timing Role: High-voltage DC switching element driving inductive solenoid or contactor coils rated up to 400 V. Use Value: V_CES = 800 V and ESD-rated package enable direct interface with industrial control bus voltages and noisy environments.

Halogen Lamp Electronic Transformer

Inductive Load Switching Power Supply

Use Scenario: High-frequency AC-AC conversion for 12 V halogen lamps using resonant or quasi-resonant topology with inductive energy storage.

IC Role / Device Role / Timing Role: Main switching transistor in single-ended forward or push-pull configuration, handling primary-side 300 V clamped inductive flyback.

Use Value: Sustains repeated inrush currents up to 8 A peak while maintaining safe SOA margins per Figure 23, enabling reliable lamp ignition.

Use Scenario: Medium-power offline SMPS with inductive output filtering and high-voltage primary switching.

IC Role / Device Role / Timing Role: Primary-side power switch controlling energy transfer into transformer core; operates in discontinuous or boundary conduction mode.

Use Value: Fast t_off (2.3 µs) and low V_CE(sat) reduce switching losses, improving efficiency above 85% at 50 W output.

Short-Circuit Protected Lighting Driver

Industrial Control Relay Replacement

Use Scenario: Constant-power LED or halogen driver with built-in short-circuit foldback protection.

IC Role / Device Role / Timing Role: Current-sensing and fault-handling switch that limits peak current during load faults via controlled saturation.

Use Value: High I_CM = 8.0 A peak rating and rugged SOA allow temporary overload survival without latch-up or secondary breakdown.

Use Scenario: Solid-state replacement for electromechanical relays in PLC output modules or motor starter logic.

IC Role / Device Role / Timing Role: High-voltage DC switching element driving inductive solenoid or contactor coils rated up to 400 V.

Use Value: V_CES = 800 V and ESD-rated package enable direct interface with industrial control bus voltages and noisy environments.

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
STMicroelectronics BUL128	V_CEO = 1000 V, I_C = 12 A, R_θJC = 1.5 °C/W - higher voltage/current but larger TO-247 package	Used in >100 W lighting and industrial inverters; not drop-in due to different pinout and thermal footprint	Select when >500 V blocking or >3 A continuous current is required; requires PCB layout change
Infineon BUX87	V_CEO = 450 V, I_C = 10 A, f_T = 15 MHz - lower voltage rating but higher current and slower switching	Common in audio amplifier output stages and linear-regulated supplies; lacks BUH51's clamped SOA validation	Prefer for linear or low-frequency switching where V_CEO margin is acceptable and thermal mass dominates

Compared with BUL128 and BUX87, the BUH51 offers optimal balance of 500 V blocking, 3 A capability, and fast inductive turn-off (2.3 µs) in a compact TO-225 package-making it uniquely suited for cost-sensitive, space-constrained 50 W halogen transformer designs where SOA integrity under transient overload is non-negotiable.

Availability

BUH51 is available at Aetrix Electronics and suitable for halogen electronic transformers, inductive load switching power supplies, and short-circuit protected lighting drivers requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for BUH51 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

onsemi (formerly ON Semiconductor) is a global semiconductor manufacturer specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and IoT applications.

The BUH51 belongs to onsemi's SWITCHMODE™ planar bipolar power transistor product line, engineered specifically for high-reliability, high-voltage switching in lighting ballasts and inductive power conversion systems.

FAQ

What is the maximum continuous collector current rating for the BUH51?

The BUH51 has a maximum continuous collector current (I_C) rating of 3.0 A at T_C = 25°C. This rating assumes proper heatsinking and derates linearly at 0.4 W/°C above 25°C case temperature. The BUH51 also supports 8.0 A peak collector current (I_CM) under pulsed conditions (5 ms, ≤10% duty cycle), making it suitable for inrush current handling in halogen transformer applications.

Does the BUH51 have built-in ESD protection, and what levels are specified?

Yes, the BUH51 is rated for ESD protection per industry standards: Machine Model Class C and Human Body Model Class 3B. These ratings are verified per JEDEC standards and reflect the device's ability to withstand electrostatic discharge during automated handling and PCB assembly-critical for high-yield manufacturing of lighting control modules where the BUH51 is commonly deployed.

What is the safe operating area (SOA) validation basis for the BUH51?

The BUH51's reverse-biased SOA is validated under clamped inductive switching conditions: V_Z = 300 V, L = 200 µH, V_CC = 15 V, with base drive fully removed during turn-off. This test methodology-documented in Figures 23 and 20 of the BUH51 datasheet-ensures the device can sustain simultaneous high voltage and current during transformer flyback without secondary breakdown, a key requirement for halogen electronic transformer reliability.

Can the BUH51 be used in surface-mount designs?

No, the BUH51 is only available in the through-hole TO-225 (Case 77, Style 3) package with three leads (base, collector, emitter). It is not offered in any surface-mount variant. Designers requiring SMT compatibility must select alternative devices such as the onsemi MJD127 (TO-252) or evaluate redesign with adapter hardware, as the BUH51's thermal and electrical performance is tightly coupled to its TO-225 mechanical construction and case-to-heatsink interface.

What is the typical DC current gain (h_FE) of the BUH51 at 1.0 A collector current?

At I_C = 1.0 A, V_CE = 1.0 V, and T_J = 25°C, the BUH51 exhibits a typical DC current gain (h_FE) of 10, with a minimum of 8.0 and maximum of 10 across the production lot. This high and flat h_FE profile-maintained even at elevated temperatures (h_FE ≥ 6.0 at 125°C)-reduces base drive complexity and improves switching consistency in halogen transformer control loops.

BUH51 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: SWITCHMODE™

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

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 3 A

Voltage - Collector Emitter Breakdown (Max):: 500 V

Vce Saturation (Max) @ Ib, Ic:: 500mV @ 200mA, 1A

Current - Collector Cutoff (Max):: 100µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 8 @ 1A, 1V

Power - Max:: 50 W

Frequency - Transition:: 23MHz

Operating Temperature:: -65°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-126

BUH51 FAQ

1.How can I place an order for BUH51 through Aetrix?

Please submit a Request for Quotation (RFQ) for BUH51 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 BUH51 reliable?

The price and inventory of BUH51 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUH51 is usually 5 days.

3.What payment methods are accepted for BUH51?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUH51 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUH51?

BUH51 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUH51 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 BUH51?

For technical support, including BUH51 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUH51 requirements.

6.How does Aetrix verify that BUH51 is sourced from the original manufacturer or authorized distributors?

All BUH51 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 BUH51 meets industry standards.

7.What is the process for return or replacement of BUH51?

All BUH51 units undergo pre-shipment inspection (PSI). If there is an issue with BUH51, 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 BUH51 part is unused and in its original packaging.

Return procedure for BUH51:

1.Submit a request within 90 days.

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

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