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

STMicroelectronics BUL138FP

Name: BUL138FP
Brand: STMicroelectronics
SKU: BUL138FP
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUL138FP

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-220-3 Full Pack

Datasheet:: BUL138FP.pdf

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

Quantity:: RFQ Add To RFQ list

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Inventory:6,092

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Product details

Overview

BUL138FP from STMicroelectronics is a high-voltage fast-switching NPN power transistor in TO-220FP insulated package, rated for 800 V V_CES, 5 A I_C, and 33 W P_tot at T_c = 25 °C, with fully characterized operation up to 125 °C and 1500 V_RMS insulation withstand voltage - used in electronic ballasts for fluorescent lighting and flyback/forward low-power SMPS.

For engineers reviewing the BUL138FP datasheet, BUL138FP pinout, BUL138FP application, or BUL138FP equivalent, key selection criteria include V_CEO(sus) = 400 V under inductive load, t_s/t_f = 0.7–1.4 µs / 50–100 ns at T_j = 25 °C, h_FE = 8–40 at I_C = 2 A, V_CE(sat) ≤ 1 V at I_C = 5 A, and U.L.-compliant full insulation for heatsink mounting.

Technical Context

The BUL138FP employs Multi Epitaxial Planar technology with Cellular Emitter structure and planar edge termination to achieve high switching speed and robust high-voltage blocking. It is fully characterized at 125 °C and supports safe inductive switching with defined SOA curves and pulsed test conditions (300 µs, 1.5% duty cycle).

Its insulated TO-220FP package provides 1500 V_RMS isolation between all three leads and external heatsink, enabling direct mounting without insulating washers. The device exhibits low dynamic parameter spread and minimal lot-to-lot variation for stable performance in lighting and low-cost SMPS designs.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	800 V - maximum collector-emitter voltage with base open, enabling use in 400 V DC bus applications with safety margin.
I_C	5 A continuous - supports medium-power switching in ballasts and sub-100 W converters without forced cooling.
P_tot	33 W at T_c = 25 °C - defines thermal design envelope when mounted on heatsink with R_thj-case = 3.8 °C/W.
t_s/t_f	0.7–1.4 µs / 50–100 ns - enables >50 kHz switching in flyback topologies with controlled turn-off loss.
V_CE(sat)	≤1 V at I_C = 5 A, I_B = 1 A - minimizes conduction loss and self-heating during saturation.
Visol	1500 V_RMS - allows direct bolt-on heatsink mounting per UL 1557, eliminating insulating hardware.
h_FE	8–40 at I_C = 2 A - determines required base drive current for reliable saturation in hard-switched circuits.

Pinout & Package

Package: TO-220FP (fully insulated, U.L.-compliant), with metal tab electrically isolated from emitter, collector, and base terminals. Mounting hole Ø3.0–3.2 mm centered on tab.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current return path for collector current	Low-inductance connection point; must be routed with short trace to minimize switching oscillation.
2 (Collector)	Main high-voltage current output node	Connected to primary winding of flyback transformer or lamp inverter circuit; handles 800 V transient stress.
3 (Base)	Control input for bipolar conduction	Requires active pull-down (V_BE(off) = –5 V) to ensure fast turn-off; sensitive to Miller capacitance coupling.

Key Features

Feature	Design Value
High-voltage capability	V_CES = 800 V supports 400 V DC link designs with 2× safety margin for surge transients.
Fast switching speed	t_s/t_f ≤ 1.4 µs / 100 ns enables efficient operation at 50–100 kHz in compact lighting ballasts.
Full insulation rating	1500 V_RMS isolation allows direct heatsink mounting without mica washers or silicone pads.
High-temperature characterization	Electrical parameters guaranteed at T_j = 125 °C - ensures reliability in enclosed lamp housings.
Low dynamic parameter spread	Tight distribution of V_CE(sat), h_FE, and t_f across lots reduces need for system-level binning.

Applications

Fluorescent Lamp Electronic Ballast

Flyback Converter for AC-DC Adapters

Use Scenario: Driving resonant LC tank in instant-start fluorescent lamp circuits with 220–240 V AC input rectified to ~320 V DC bus.

IC Role / Device Role / Timing Role: Main switching transistor controlling lamp current via high-frequency (20–60 kHz) hard-switched operation.

Use Value: High V_CES and low t_s/t_f enable reliable zero-voltage switching transitions and reduced EMI in compact form factors.

Use Scenario: Primary-side switch in sub-30 W offline flyback converters powering LED drivers or IoT peripherals.

IC Role / Device Role / Timing Role: Power switch turning on/off primary inductance to transfer energy to secondary side during each cycle.

Use Value: V_CEO(sus) = 400 V under inductive load ensures safe clamping during leakage inductance spikes without snubber overhead.

Forward Converter for Industrial Sensors

Compact DC-DC Isolated Supply

Use Scenario: Single-transistor forward converter supplying 12 V/1 A to industrial temperature or pressure sensors in 24–48 V DC systems.

IC Role / Device Role / Timing Role: Synchronized switch conducting during transformer reset phase, requiring precise base drive timing.

Use Value: Low V_CE(sat) ≤ 1 V at 5 A reduces conduction loss and improves efficiency above 85% at full load.

Use Scenario: Isolated auxiliary supply generating 5 V/0.5 A for microcontroller bias in PLC I/O modules.

IC Role / Device Role / Timing Role: High-side switch in self-oscillating or fixed-frequency forward topology with integrated reset winding.

Use Value: Fully characterized parameters at 125 °C ensure stable startup and regulation across ambient temperatures up to 85 °C.

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
BU508AF	V_CES = 1000 V, I_C = 8 A, R_thj-case = 3.0 °C/W - higher voltage/current but larger die and slower t_f (150 ns).	Used in higher-power (>50 W) ballasts and CRT horizontal deflection; less optimized for compact SMPS.	Select when V_bus exceeds 450 V or peak current > 6 A is required; verify base drive capability for higher h_FE spread.
ST13007	V_CES = 400 V, I_C = 8 A, no insulation rating - lower voltage rating, non-isolated TO-220 package.	Suitable for 115 V AC-input flybacks or low-cost UPS inverters where heatsink isolation is handled externally.	Choose only for cost-sensitive 100–200 W designs with <300 V DC bus; requires insulating hardware and derates V_CEO margin.

Compared with BU508AF and ST13007, the BUL138FP uniquely balances 800 V capability, 1500 V insulation, and sub-microsecond switching for space-constrained fluorescent ballasts and sub-30 W flybacks - offering best-in-class thermal safety and layout simplicity without over-spec'ing voltage or sacrificing speed.

Availability

BUL138FP is available at Aetrix Electronics and suitable for electronic ballasts for fluorescent lighting, flyback and forward single-transistor low-power converters, and industrial sensor power supplies requiring stable component supply and long-term manufacturability.

Supply support for BUL138FP 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 for automotive, industrial, and consumer markets.

The BUL series targets cost-effective, high-reliability power switching in lighting and low-power SMPS - emphasizing voltage ruggedness, thermal stability, and process consistency for high-volume manufacturing environments.

FAQ

Is BUL1308FP still in production?

No - BUL138FP is marked "Obsolete Product(s)" in its official STMicroelectronics datasheet revision (2003). However, Aetrix Electronics maintains legacy inventory and offers extended supply support, including cross-reference assistance and last-time-buy planning for ongoing production programs.

Can BUL138FP replace BU2508DF in a 220 V ballast design?

Not directly - BU2508DF has V_CES = 1500 V and different pinout (collector-tab configuration). BUL138FP's insulated TO-220FP places collector on pin 2, not the tab. Electrical replacement requires PCB layout change and verification of V_CEO(sus) margin under worst-case inductive load conditions.

What is the maximum recommended case temperature for continuous operation?

The absolute maximum junction temperature is 150 °C, and R_thj-case = 3.8 °C/W. For reliable 10+ year operation in sealed fixtures, limit T_c to ≤ 90 °C - corresponding to ≤ 15.8 W dissipation (P_tot × (1 − 90/150)) with appropriate heatsink sizing and airflow.

Does the insulation rating apply to DC or only AC voltage?

The 1500 V_RMS insulation withstand rating is specified for sinusoidal AC per UL 1557. For DC, STMicroelectronics does not publish a derated value; engineering practice applies √2 × 1500 V ≈ 2120 V DC as conservative limit, but actual DC breakdown must be validated per end-equipment safety certification requirements.

BUL138FP Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-220-3 Full Pack

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:: 33 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220FP

BUL138FP FAQ

1.How can I place an order for BUL138FP through Aetrix?

Please submit a Request for Quotation (RFQ) for BUL138FP 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 BUL138FP reliable?

The price and inventory of BUL138FP are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUL138FP is usually 5 days.

3.What payment methods are accepted for BUL138FP?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUL138FP transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUL138FP?

BUL138FP orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUL138FP 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 BUL138FP?

For technical support, including BUL138FP datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUL138FP requirements.

6.How does Aetrix verify that BUL138FP is sourced from the original manufacturer or authorized distributors?

All BUL138FP 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 BUL138FP meets industry standards.

7.What is the process for return or replacement of BUL138FP?

All BUL138FP units undergo pre-shipment inspection (PSI). If there is an issue with BUL138FP, 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 BUL138FP part is unused and in its original packaging.

Return procedure for BUL138FP:

1.Submit a request within 90 days.

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

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