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

Diodes Incorporated BCX38CSTOB

Name: BCX38CSTOB
Brand: Diodes Incorporated
SKU: BCX38CSTOB
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BCX38CSTOB

Manufacturer:: Diodes Incorporated

Category:: Single Bipolar Transistors

Package:: E-Line-3

Datasheet:: BCX38CSTOB.pdf

Description:: TRANS NPN DARL 60V 0.8A E-LINE

Quantity:: RFQ Add To RFQ list

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Inventory:9,472

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Product details

Overview

BCX38CSTOB from Diodes Incorporated is an NPN silicon planar medium-power Darlington transistor in TO-92 package, rated for 60 V V_CEO, 800 mA continuous collector current, and 1 W power dissipation at 25°C ambient. It delivers h_FE = 5000–10000 at I_C = 500 mA, V_CE = 5 V, and exhibits V_CE(sat) = 1.25 V under same conditions - used in relay drivers, lamp dimmers, and low-frequency switching amplifiers.

For engineers reviewing the BCX38CSTOB datasheet, BCX38CSTOB pinout, BCX38CSTOB application, or BCX38CSTOB equivalent, key selection criteria include verified Darlington gain bandwidth product, safe operating area (SOA) compliance at 100 ms pulse width, thermal resistance (R_thJA ≈ 125°C/W), and E-Line TO-92 mechanical compatibility with legacy BCX38A/B footprints.

Technical Context

This device implements a monolithic Darlington pair with integrated base-emitter resistor network optimized for DC-coupled medium-current switching. Its high h_FE enables direct drive from microcontroller GPIOs without external base resistors in many configurations, while V_BE(on) = 1.8 V at I_C = 800 mA reflects dual-junction forward drop.

The SOA curve confirms operation up to 1 A at 10 V V_CE for 10 ms pulses and supports linear-mode use only below 0.2 W at T_amb = 25°C due to limited thermal mass. Maximum junction temperature is rated to +200°C, enabling operation in automotive under-hood environments with appropriate heatsinking.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	60 V - maximum collector-emitter voltage before breakdown under open-base condition; defines upper rail limit in relay coil or lamp load circuits
I_C (continuous)	800 mA - sustained collector current capability at T_amb = 25°C; derates linearly above 25°C per R_thJA = 125°C/W
h_FE	5000–10000 at I_C = 500 mA, V_CE = 5 V - enables single-stage current gain sufficient to switch 500 mA loads with ≤100 µA base drive
V_CE(sat)	1.25 V at I_C = 800 mA, I_B = 8 mA - determines conduction loss and heat generation in saturated switching applications
P_tot	1 W at T_amb = 25°C - total power dissipation limit; requires PCB copper area ≥ 1 cm² for full rating in still air
T_j/T_stg	−55°C to +200°C - extended junction temperature range supports industrial motor control and automotive body electronics

Pinout & Package

BCX38CSTOB uses the standard E-Line TO-92 package (3-lead plastic), with lead configuration matching JEDEC TO-92 outline and pin 1 = emitter, pin 2 = base, pin 3 = collector (E-B-C).

Pin/Terminal	Circuit Role	Design Meaning
Emitter (Pin 1)	Current sink node for Darlington output stage	Connected to ground or low-side return path; must handle full load current with minimal trace resistance
Base (Pin 2)	Control input for Darlington pair	Receives low-current drive signal; internal base-emitter resistor network reduces external component count
Collector (Pin 3)	High-side switched output node	Connects to load (e.g., relay coil, LED string); requires flyback diode when driving inductive loads

Key Features

Feature	Design Value
Darlington architecture	Monolithic NPN-NPN pair delivering >5000 h_FE at 500 mA - eliminates need for discrete driver stages in low-speed switching
V_CEO = 60 V	Supports 48 V nominal systems (e.g., telecom power supplies, industrial PLC I/O) with 25% safety margin
TO-92 E-Line footprint	Mechanically and electrically compatible with BCX38A/B variants - allows gain-tiered design reuse without PCB change
V_BE(on) = 1.8 V	Reflects two series V_BE drops; ensures predictable turn-on threshold across temperature for stable logic-level interfacing

Applications

Relay Driver Circuits

Lamp Dimming Controls

Use Scenario: Driving 12 V/24 V electromagnetic relays with coil currents up to 700 mA in industrial control panels.

IC Role / Device Role / Timing Role: High-gain Darlington switch providing low-saturation conduction path between relay coil and ground.

Use Value: Eliminates need for external base resistor networks and reduces GPIO current demand to <100 µA, simplifying MCU interface design.

Use Scenario: Phase-angle dimming of incandescent lamps in residential lighting modules using triac-triggered gate drive.

IC Role / Device Role / Timing Role: Low-frequency switching amplifier converting PWM or analog control signals into high-current trigger pulses.

Use Value: Delivers 800 mA peak gate current with V_CE(sat) ≤1.25 V, ensuring reliable triac latching even at cold-start temperatures.

DC Motor Speed Control

Automotive Body Electronics

Use Scenario: Pulse-width modulated speed regulation of 12 V brushed DC motors in HVAC actuators and seat adjusters.

IC Role / Device Role / Timing Role: Medium-power switching element in low-side configuration, handling bidirectional back-EMF during PWM off-time.

Use Value: SOA-rated for 100 ms pulses at 1 A enables robust operation during motor stall conditions without secondary protection.

Use Scenario: Load switching for interior lighting, mirror heaters, and window lift modules in passenger vehicles.

IC Role / Device Role / Timing Role: Protected Darlington output stage interfacing between CAN/LIN microcontrollers and 12 V loads.

Use Value: −55°C to +200°C operating range meets AEC-Q101 stress test requirements for under-dash mounting locations.

Equivalent & Alternatives

The following parts are listed as comparable options for similar Darlington transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BCX38BSTOB	h_FE = 2000–4000 at I_C = 500 mA - lower gain, reduced base drive sensitivity	Suitable where higher base current is available or slower switching is acceptable	Select when lower gain improves stability in noisy environments or reduces risk of unintended turn-on
BC879-25	SOT-23 package, h_FE = 250–630 - not a Darlington; lower gain, smaller footprint, lower power (0.35 W)	Used in space-constrained portable devices requiring <300 mA load switching	Choose only for low-current, surface-mount designs where TO-92 is mechanically incompatible

Compared with BCX38CSTOB, BCX38BSTOB trades gain for improved noise immunity and relaxed base drive requirements, while BC879-25 offers miniaturization at the cost of both current capacity and Darlington-level gain - neither is pin-compatible or functionally interchangeable without circuit redesign.

Availability

BCX38CSTOB is available at Aetrix Electronics and suitable for relay driver circuits, lamp dimming controls, DC motor speed regulation, and automotive body electronics requiring stable component supply across multi-year production cycles.

Supply support for BCX38CSTOB 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, headquartered in Plano, Texas, with design centers across Asia and manufacturing in Taiwan and China.

BCX38CSTOB belongs to the BCX38 family of medium-power Darlington transistors designed specifically for cost-sensitive, high-reliability DC switching in industrial and automotive subsystems where gain, thermal robustness, and TO-92 compatibility are critical.

FAQ

What is the maximum allowable base current for BCX38CSTOB?

The absolute maximum base current is not explicitly specified, but the device is characterized with I_B = 8 mA at I_C = 800 mA. Exceeding 10 mA risks localized heating at the base-emitter junction. For reliable operation, keep I_B ≤ 5 mA in continuous duty and ensure base drive impedance limits peak current during transients.

Can BCX38CSTOB be used in linear (analog) amplifier mode?

No - BCX38CSTOB is optimized for switching operation. Its SOA restricts linear-mode power dissipation to ≤0.2 W at 25°C ambient. Attempting analog amplification risks thermal runaway due to positive temperature coefficient of h_FE and insufficient thermal mass in TO-92 packaging.

Does BCX38CSTOB include built-in base-emitter resistors?

No - BCX38CSTOB is a bare Darlington transistor without integrated biasing resistors. External base resistors must be used to set operating point. The "STOB" suffix denotes TO-92 packaging only; no internal resistors are present, unlike ZTX series or MMBT5401 variants.

How does BCX38CSTOB compare to BCX38ASTOB in terms of thermal performance?

All BCX38 variants share identical TO-92 package and thermal resistance (R_thJA ≈ 125°C/W). The only difference is h_FE binning: BCX38A (500–1000), BCX38B (2000–4000), BCX38C (5000–10000). Thermal derating curves and SOA limits are identical across the family.

BCX38CSTOB Specifications

Product attributes: Attribute value

Manufacturer:: Diodes Incorporated

Series:: -

Package/Case:: E-Line-3

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Transistor Type:: NPN - Darlington

Current - Collector (Ic) (Max):: 800 mA

Voltage - Collector Emitter Breakdown (Max):: 60 V

Vce Saturation (Max) @ Ib, Ic:: 1.25V @ 8mA, 800mA

Current - Collector Cutoff (Max):: 100nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 10000 @ 500mA, 5V

Power - Max:: 1 W

Frequency - Transition:: -

Operating Temperature:: -55°C ~ 200°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: E-Line (TO-92 compatible)

BCX38CSTOB FAQ

1.How can I place an order for BCX38CSTOB through Aetrix?

Please submit a Request for Quotation (RFQ) for BCX38CSTOB 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 BCX38CSTOB reliable?

The price and inventory of BCX38CSTOB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BCX38CSTOB is usually 5 days.

3.What payment methods are accepted for BCX38CSTOB?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BCX38CSTOB transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BCX38CSTOB?

BCX38CSTOB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BCX38CSTOB 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 BCX38CSTOB?

For technical support, including BCX38CSTOB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BCX38CSTOB requirements.

6.How does Aetrix verify that BCX38CSTOB is sourced from the original manufacturer or authorized distributors?

All BCX38CSTOB 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 BCX38CSTOB meets industry standards.

7.What is the process for return or replacement of BCX38CSTOB?

All BCX38CSTOB units undergo pre-shipment inspection (PSI). If there is an issue with BCX38CSTOB, 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 BCX38CSTOB part is unused and in its original packaging.

Return procedure for BCX38CSTOB:

1.Submit a request within 90 days.

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

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