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

STMicroelectronics BUL138

Name: BUL138
Brand: STMicroelectronics
SKU: BUL138
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUL138

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BUL138.pdf

Description:: TRANS NPN 400V 5A TO-220

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BUL138 from STMicroelectronics is a high-voltage, fast-switching NPN power transistor in TO-220 package, rated for 800 V V_CES, 5 A I_C, and 80 W P_tot at T_c = 25 °C, optimized for electronic ballasts and flyback converters operating up to 125 °C junction temperature.

For engineers reviewing the BUL138 datasheet, BUL138 pinout, BUL138 application, or BUL138 equivalent, key selection criteria include its 400 V V_CEO(sus) under inductive load, 0.7–1.0 V V_CE(sat) across 1–5 A, 2.4–3.5 µs resistive storage time, and full characterization at 125 °C for lighting and low-power SMPS reliability.

Technical Context

The BUL138 employs Multi Epitaxial Planar technology with Cellular Emitter structure and planar edge termination to achieve high voltage blocking (800 V) and fast switching (t_s = 2.4 µs typ., t_f = 50 ns typ. under inductive load). It is fully characterized at T_j = 125 °C for sustained operation in thermally demanding lighting circuits.

Its safe operating area (SOA) is defined for both resistive and inductive loads, with RBSOA validated using 25 mH inductance and 250 V clamp voltage. The device supports base-driven switching with I_B up to 2 A and I_BM = 4 A peak for robust gate drive margin.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	800 V - Maximum collector-emitter voltage with base open; enables use in 400 V AC mains-derived flyback topologies without derating.
I_C	5 A continuous - Sustained collector current at T_c = 25 °C; supports >30 W output in single-transistor forward converters.
V_CE(sat)	0.7 V @ I_C = 1 A, I_B = 0.2 A - Low saturation voltage reduces conduction loss and thermal stress in ballast preheat stages.
t_s (resistive)	2.4 µs typ. - Short storage time enables >50 kHz switching in electronic fluorescent ballasts without excessive turn-off loss.
R_thj-case	1.56 °C/W - Junction-to-case thermal resistance allows 80 W dissipation with minimal heatsink requirement in compact lamp drivers.
T_j(max)	150 °C - Maximum operating junction temperature; full electrical specs guaranteed up to this point for industrial-grade reliability.
h_FE	8–40 - DC current gain range at I_C = 2 A / V_CE = 5 V; supports stable base-current design across production lots.

Pinout & Package

Package: TO-220 (standard 3-lead, through-hole, insulated tab). Pin 1 = Base, Pin 2 = Collector (tab-connected), Pin 3 = Emitter.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (Base)	Control input	Receives base drive current (I_B ≤ 2 A); low V_BE(sat) (1.1–1.5 V) ensures efficient drive stage sizing.
Pin 2 (Collector)	High-voltage power node	Internally connected to metal tab; must be electrically isolated from heatsink unless common-cathode configuration is used.
Pin 3 (Emitter)	Power return path	Serves as reference for base drive and current sensing; low-inductance layout critical for fast switching integrity.

Key Features

Feature	Design Value
Cellular Emitter structure	Enables uniform current distribution and reduced local hot-spot risk during high-dI/dt switching in inductive ballast loads.
Planar edge termination	Improves voltage ruggedness and reduces leakage (I_CES = 100 µA @ 800 V, 25 °C) versus junction-isolated alternatives.
Full 125 °C characterization	Guarantees h_FE, V_CE(sat), and t_s performance in enclosed lamp housings where ambient exceeds 85 °C.
Low lot-to-lot parameter spread	Minimizes need for binning or system-level re-tuning across manufacturing batches in high-volume lighting OEM production.
RBSOA compliance	Validated for 250 V clamp voltage and 200 µH inductance, supporting reliable single-transistor flyback operation without snubber overdesign.

Applications

Electronic Ballasts

Flyback Converters

Use Scenario: High-frequency (20–60 kHz) lamp ignition and regulation in T8/T5 fluorescent fixtures with integrated dimming.

IC Role / Device Role / Timing Role: Main switching transistor in half-bridge or single-ended resonant topology; handles repetitive 400 V transient spikes during lamp strike.

Use Value: 400 V V_CEO(sus) and 2.4 µs t_s ensure reliable zero-voltage switching transitions and minimize EMI generation during lamp warm-up.

Use Scenario: Isolated 5–25 W AC/DC adapter for consumer electronics with universal 85–265 V AC input.

IC Role / Device Role / Timing Role: Primary-side switch controlling energy transfer via transformer; operates in discontinuous conduction mode (DCM).

Use Value: 800 V V_CES rating eliminates need for external clamping in 230 V AC designs; 1.56 °C/W R_thj-case enables compact heatsink-free PCB layout.

Forward Converters

Inductive Load Drivers

Use Scenario: Low-cost 12–24 V DC output power supply for signage controllers and HVAC sensors.

IC Role / Device Role / Timing Role: Single-transistor forward converter switch; synchronized with reset winding and freewheeling diode.

Use Value: 5 A I_C and 80 W P_tot support >30 W output with <1% duty cycle variation across line/load; h_FE min. = 8 ensures stable base drive at light loads.

Use Scenario: Solenoid and relay driver in industrial control panels requiring 400 V isolation and fast de-energization.

IC Role / Device Role / Timing Role: High-side switch controlling inductive coil current; driven by microcontroller GPIO with base resistor network.

Use Value: 50 ns t_f and 100 ns t_f (T_j = 125 °C) limit back-EMF duration, reducing snubber size and improving system response time.

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	V_CES = 1000 V, I_C = 8 A, R_thj-case = 1.25 °C/W; slower t_s (5 µs typ.) and higher V_CE(sat) (1.2 V @ 5 A).	Better suited for 600+ V DC bus applications but less optimal for >40 kHz ballasts due to longer storage time.	Select BU508A only when higher voltage margin or higher current headroom is required and switching frequency is ≤25 kHz.
ST13007	V_CES = 400 V, I_C = 8 A, t_s = 1.5 µs typ.; lacks 125 °C characterization and RBSOA validation.	Targeted at lower-voltage SMPS (<265 V AC input); unsuitable for 400 V sustaining applications like ballast strike.	Choose ST13007 only for cost-sensitive 115 V AC adapters where V_CEO(sus) ≥ 400 V is not required.

Compared with BU508A and ST13007, the BUL138 uniquely balances 800 V capability, sub-3 µs storage time, and full 125 °C specification-making it the preferred choice for thermally constrained, high-reliability fluorescent ballasts and universal-input flybacks.

Availability

BUL138 is available at Aetrix Electronics and suitable for electronic ballasts, flyback converters, forward converters, and inductive load drivers requiring stable component supply, consistent parametric performance, and long-term manufacturability.

Supply support for BUL138 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, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The BUL series belongs to ST's high-voltage power transistor product line, engineered specifically for lighting control and low-cost switch-mode power supplies where ruggedness, thermal stability, and production consistency are critical.

FAQ

Is the BUL138 RoHS compliant?

Yes, the BUL138 is RoHS compliant per STMicroelectronics' official product change notification PCN-2005-01. It contains no lead in solderable terminations and meets EU Directive 2011/65/EU requirements, including exemption 7a for high-melting-temperature solder alloys used in internal construction.

Can the BUL138 be used in avalanche mode?

No, the BUL138 is not rated for repetitive avalanche operation. Its absolute maximum V_CEO = 400 V and V_CES = 800 V define non-avalanche breakdown limits. Safe operation requires external clamping or snubbers to prevent voltage overshoot beyond V_CEO(sus) = 400 V under inductive switching.

What is the recommended base drive resistor for 50 kHz operation?

For 50 kHz switching at I_C = 3 A, a 10 Ω ±5 % base resistor (with 0.5 W rating) is recommended to deliver ~0.6 A I_B while limiting base power dissipation to <150 mW. Layout must minimize trace inductance between driver and Pin 1 to preserve t_s and t_f performance.

Does the TO-220 package require insulating hardware when mounted to a heatsink?

Yes, the collector (Pin 2) is internally connected to the metal tab. Electrical isolation via mica washer or silicone pad and shoulder washers is mandatory unless the heatsink is floating or referenced to collector potential. ST recommends using isolating mounting kits meeting UL 94 V-0 flammability rating.

BUL138 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-220-3

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 5 A

Voltage - Collector Emitter Breakdown (Max):: 400 V

Vce Saturation (Max) @ Ib, Ic:: 700mV @ 1A, 5A

Current - Collector Cutoff (Max):: 250µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 8 @ 2A, 5V

Power - Max:: 80 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

BUL138 FAQ

1.How can I place an order for BUL138 through Aetrix?

Please submit a Request for Quotation (RFQ) for BUL138 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 BUL138 reliable?

The price and inventory of BUL138 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUL138 is usually 5 days.

3.What payment methods are accepted for BUL138?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUL138 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUL138?

BUL138 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUL138 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 BUL138?

For technical support, including BUL138 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUL138 requirements.

6.How does Aetrix verify that BUL138 is sourced from the original manufacturer or authorized distributors?

All BUL138 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 BUL138 meets industry standards.

7.What is the process for return or replacement of BUL138?

All BUL138 units undergo pre-shipment inspection (PSI). If there is an issue with BUL138, 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 BUL138 part is unused and in its original packaging.

Return procedure for BUL138:

1.Submit a request within 90 days.

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

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