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

STMicroelectronics STR1550

Name: STR1550
Brand: STMicroelectronics
SKU: STR1550
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: STR1550

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-236-3, SC-59, SOT-23-3

Datasheet:: STR1550.pdf

Description:: TRANS NPN 500V 0.5A SOT-23

Quantity:: RFQ Add To RFQ list

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Inventory:11,066

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Product details

Overview

STR1550 from STMicroelectronics is a high-voltage fast-switching NPN power transistor in SOT-23 package, rated for V_CEO = 500 V, I_C = 0.5 A, and P_TOT = 500 mW at T_A = 25 °C. It features excellent hFE linearity up to 50 mA and is optimized for LED driving circuits requiring robust breakdown margin and low saturation voltage.

For engineers reviewing the STR1550 datasheet, STR1550 pinout, STR1550 application, or STR1550 equivalent, key selection criteria include verified V_CEO/V_CBO = 500 V rating, hFE ≥ 100 at I_C = 50 mA, V_CE(sat) ≤ 0.3 V under switching conditions, and SOT-23 thermal resistance of 250 °C/W.

Technical Context

This transistor uses diffused collector planar technology with base island structure and planar edge termination to achieve fast switching while preserving wide RBSOA. Its design supports stable operation across -55 °C to 100 °C junction temperature range with pulsed current capability up to 1 A (t_p < 5 ms).

The device delivers consistent V_BE(on) = 0.9 V at I_C = 50 mA and V_CE = 10 V, and maintains hFE ≥ 100 from I_C = 1 mA to 50 mA-enabling predictable current gain in linear and switching modes without gain collapse.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	500 V - Enables direct interface with 400 V DC bus or rectified AC lines without external snubbing.
I_C	0.5 A continuous - Supports medium-current LED strings or relay drivers in compact SOT-23 footprint.
V_CE(sat)	0.3 V at I_C = 50 mA, I_B = 6 mA - Minimizes conduction loss and self-heating during on-state operation.
hFE	100–300 at I_C = 50 mA - Ensures reliable base drive margin and stable current amplification in analog/digital control loops.
R_thJA	250 °C/W - Requires PCB copper area ≥1 cm² for safe thermal management at full power dissipation.
T_J(max)	150 °C - Allows operation in industrial ambient environments up to 85 °C with appropriate derating.

Pinout & Package

SOT-23 plastic surface-mount package with standard 3-pin configuration: emitter (E), base (B), collector (C) arranged as pin 2, pin 1, and pin 3 respectively. Dimensions comply with ECOPACK environmental specifications.

Pin/Terminal	Circuit Role	Design Meaning
1 (B)	Base	Control input terminal; requires I_B ≥ 6 mA to saturate at I_C = 50 mA per datasheet test condition.
2 (E)	Emitter	Current return path; internally connected to substrate; must be referenced to system ground or common rail.
3 (C)	Collector	High-side switching node; rated for 500 V blocking; connects to load anode or positive supply rail.

Key Features

Feature	Design Value
High-voltage blocking	V_CBO = V_CEO = 500 V - Eliminates need for series-connected transistors in HV LED driver topologies.
Fast-switching architecture	Base island + planar edge termination - Reduces storage time and improves turn-off speed vs. conventional planar NPNs.
hFE linearity	Stable gain ≥100 up to I_C = 50 mA - Enables accurate current regulation in analog dimming circuits.
Thermal robustness	T_stg = –65 to 150 °C - Supports reflow soldering and operation in extended-temperature industrial enclosures.

Applications

LED Constant-Current Driver

AC/DC Secondary-Side Switch

Use Scenario: Driving 1–3 high-brightness white LEDs from 12–48 V DC supply with analog dimming control.

IC Role / Device Role / Timing Role: NPN power switch regulating LED current via base-controlled saturation.

Use Value: V_CE(sat) ≤ 0.3 V minimizes power loss and thermal rise in space-constrained lighting modules.

Use Scenario: Isolated feedback switch in flyback converter secondary-side synchronous rectification or optocoupler biasing.

IC Role / Device Role / Timing Role: High-voltage NPN switch interfacing with TL431 reference and optocoupler LED.

Use Value: 500 V V_CEO withstands reflected primary-side transients without clamping components.

Industrial Relay Driver

High-Voltage Signal Switch

Use Scenario: Driving 24 V/48 V coil relays in PLC output modules with microcontroller GPIO control.

IC Role / Device Role / Timing Role: Medium-current NPN buffer amplifying logic-level signals to relay coil current.

Use Value: hFE ≥ 100 at I_C = 50 mA ensures single-stage drive without Darlington configuration.

Use Scenario: Multiplexing 100–400 V DC control signals in test equipment or HV sensor interfaces.

IC Role / Device Role / Timing Role: High-breakdown discrete switch enabling signal routing under elevated potential.

Use Value: Verified V_BREBO = 12 V and V_BRCBO = 500 V support safe gate/base biasing in floating domains.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MMBT5551	V_CEO = 160 V, I_C = 0.6 A, hFE = 80–250 - Lower voltage rating, higher current capability.	Not suitable for >200 V DC bus applications; limited to low-to-medium voltage LED or relay drivers.	Select when operating voltage ≤160 V and higher I_C margin is required over voltage headroom.
BCP56-10	V_CEO = 80 V, I_C = 1 A, SOT-223 package - Lower voltage, higher current, larger thermal mass.	Requires board space for SOT-223; unsuitable for 400 V line-referenced circuits.	Prefer for high-current, low-voltage switching where PCB area allows and thermal performance is critical.

Compared with MMBT5551 and BCP56-10, STR1550 uniquely balances 500 V blocking, SOT-23 compactness, and hFE linearity-making it optimal for space-constrained, high-voltage LED and industrial control designs where voltage margin cannot be compromised.

Availability

STR1550 is available at Aetrix Electronics and suitable for LED constant-current drivers, industrial relay interfaces, and high-voltage signal switching applications requiring stable component supply and long-term manufacturability.

Supply support for STR1550 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 microcontrollers, power transistors, sensors, and analog ICs for industrial, automotive, and consumer markets.

STR1550 belongs to ST's high-voltage bipolar transistor product line, engineered specifically for robust switching in LED lighting, power supply feedback, and industrial control systems operating up to 500 V.

FAQ

What is the maximum continuous collector current for STR1550?

The absolute maximum continuous collector current (I_C) is 0.5 A at T_A = 25 °C. Derating is required above 25 °C ambient: R_thJA = 250 °C/W implies ~2 mA/°C reduction beyond 25 °C. At 85 °C ambient, max I_C drops to approximately 0.35 A to maintain T_J ≤ 150 °C.

Can STR1550 replace a MOSFET in high-voltage switching applications?

STR1550 can replace low-speed, medium-current MOSFETs only where gate drive simplicity and cost outweigh efficiency needs. Unlike MOSFETs, it requires sustained base current (e.g., 6 mA for 50 mA I_C) and exhibits V_CE(sat) > 0.2 V-making it less efficient than modern HV MOSFETs above 100 kHz. Best suited for <100 kHz switching or linear regulation.

Is STR1550 RoHS-compliant and halogen-free?

Yes. STR1550 is manufactured in ST's ECOPACK®-compliant SOT-23 package, meeting RoHS Directive 2011/65/EU and halogen-free requirements per IEC 61249-2-21. Full compliance documentation is available in ST's ECOPACK® database and DS8710 revision history.

What is the recommended PCB footprint for STR1550?

The recommended SOT-23 footprint matches ST's mechanical drawing 8162275_footprint_REV3: pad length 0.6 mm, pad width 0.5 mm, pitch 0.95 mm, and 1 cm² copper pour beneath the package for thermal relief. Minimum solder mask dam of 0.05 mm between pads is advised to prevent bridging during reflow.

STR1550 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-236-3, SC-59, SOT-23-3

Packaging:: Tape & Reel (TR)

Product Status:: Active

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 500 mA

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

Vce Saturation (Max) @ Ib, Ic:: 300mV @ 6mA, 50mA

Current - Collector Cutoff (Max):: 10µA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 100 @ 50mA, 10V

Power - Max:: 500 mW

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23

STR1550 FAQ

1.How can I place an order for STR1550 through Aetrix?

Please submit a Request for Quotation (RFQ) for STR1550 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 STR1550 reliable?

The price and inventory of STR1550 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for STR1550 is usually 5 days.

3.What payment methods are accepted for STR1550?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for STR1550 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for STR1550?

STR1550 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your STR1550 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 STR1550?

For technical support, including STR1550 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your STR1550 requirements.

6.How does Aetrix verify that STR1550 is sourced from the original manufacturer or authorized distributors?

All STR1550 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 STR1550 meets industry standards.

7.What is the process for return or replacement of STR1550?

All STR1550 units undergo pre-shipment inspection (PSI). If there is an issue with STR1550, 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 STR1550 part is unused and in its original packaging.

Return procedure for STR1550:

1.Submit a request within 90 days.

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

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