About us Contact Us Submit BOM
RFQs(0)
English
Close Menu
View All

Please refer to the English Version as our Official Version.Return

Europe
France(Français) Germany(Deutsch) Italy(Italia) Russian(русский) Poland(polski) Czech(Čeština) Luxembourg(Lëtzebuergesch) Netherlands(Nederland) Iceland(íslenska) Hungarian(Magyarország) Spain(español) Portugal(Português) Turkey(Türk dili) Bulgaria(Български език) Ukraine(Україна) Greece(Ελλάδα) Israel(עִבְרִית) Sweden(Svenska) Finland(Svenska) Finland(Suomi) Romania(românesc) Moldova(românesc) Slovakia(Slovenská) Denmark(Dansk) Slovenia(Slovenija) Slovenia(Hrvatska) Croatia(Hrvatska) Serbia(Hrvatska) Montenegro(Hrvatska) Bosnia and Herzegovina(Hrvatska) Lithuania(lietuvių) Spain(Português) Switzerland(Deutsch) United Kingdom(English)
Asia/Pacific
Japan(日本語) Korea(한국의) Thailand(ภาษาไทย) Malaysia(Melayu) Singapore(Melayu) Vietnam(Tiếng Việt) Philippines(Pilipino)
Africa, India and Middle East
United Arab Emirates(العربية) Iran(فارسی) Tajikistan(فارسی) India(हिंदी) Madagascar(malaɡasʲ)
South America / Oceania
New Zealand(Maori) Brazil(Português) Angola(Português) Mozambique(Português)
North America
United States(English) Canada(English) Haiti(Ayiti) Mexico(español)
HomeProductsDiscrete Semiconductor ProductsTransistors - Bipolar (BJT) - SingleFJX3904TF
Image may be representation.
See specifications for product details.
Share
 Favorite
EXPRESS OPTION
Payment method

FJX3904TF - onsemi

Manufacturer Part Number
FJX3904TF
Manufacturer
onsemi
Allelco Part Number
32D-FJX3904TF
Warranty
1 Year Allelco Warranty - Find out more
Stock Status:
5,160 pcs available, New & Original
Parts Description
TRANS NPN 40V 0.2A SOT323
Package
SOT-323
Data sheet
-
RoHs Status
 
Compare
Our certification
In stock: 5160

Required fields are indicated by an asterisk (*)
Please send RFQ, we will respond immediately.

Quantity

Specifications

FJX3904TF Tech Specifications
onsemi - FJX3904TF technical specifications, attributes, parameters and parts with similar specifications to onsemi - FJX3904TF

Product Attribute Attribute Value
Manufacturer onsemi
Voltage - Collector Emitter Breakdown (Max) 40 V
Vce Saturation (Max) @ Ib, Ic 300mV @ 5mA, 50mA
Transistor Type NPN
Supplier Device Package SOT-323
Series -
Power - Max 350 mW
Package / Case SC-70, SOT-323
Product Attribute Attribute Value
Package Bulk
Operating Temperature 150°C (TJ)
Mounting Type Surface Mount
Frequency - Transition 300MHz
DC Current Gain (hFE) (Min) @ Ic, Vce 100 @ 10mA, 1V
Current - Collector Cutoff (Max) -
Current - Collector (Ic) (Max) 200 mA

Environmental & Export Classifications

ATTRIBUTE DESCRIPTION
Moisture Sensitivity Level (MSL) Vendor Undefined
REACH Status REACH Unaffected

Frequently Asked Questions(FAQ)

What are the key performance trade-offs when selecting the FJX3904TF NPN transistor for high-frequency switching applications below 300MHz?
The FJX3904TF operates effectively up to 300MHz transition frequency, making it suitable for RF and high-speed digital circuits. However, its maximum collector current of 200mA and power dissipation limit of 350mW impose thermal constraints in continuous duty applications. Engineers must balance switching speed against current handling, as higher frequencies increase dynamic power loss. For designs requiring sustained operation above 100mA with frequent transitions, additional heatsinking or parallel devices may be necessary to stay within junction temperature limits.
How does the FJX3904TF compare to the BC817-16W-7 in terms of gain stability and package compatibility for surface-mount designs?
While both the FJX3904TF and BC817-16W-7 are NPN transistors rated for similar voltage (40V) and current (200mA), the FJX3904TF offers a slightly higher minimum hFE of 100 at 10mA compared to the BC817-16W’s typical 100–300 range, but with tighter manufacturing variation. Both use SOT-323 packages, ensuring mechanical interchangeability in PCB footprints. However, the FJX3904TF has a defined Vce(sat) of 300mV at 50mA, which provides more predictable conduction losses than the BC817 series, where saturation voltage can vary significantly across batches.
Can the FJX3904TF safely replace the MMST4401-7-F in low-power amplifier stages without redesigning the bias network?
The FJX3904TF and MMST4401-7-F are functionally similar, both being NPN transistors in SOT-323 packages with comparable Ic(max)=200mA and Vce(max)=40V. However, the MMST4401 typically exhibits higher transition frequency (>500MHz), making it better suited for RF amplification. The FJX3904TF’s 300MHz fT may limit gain at higher frequencies. While substitution is possible in non-RF analog blocks like signal conditioning or logic level shifting, the lower bandwidth could reduce gain margin in sensitive preamp stages, necessitating reevaluation of feedback resistors and operating point stability.
What design considerations arise when using the FJX3904TF in battery-powered IoT sensor nodes drawing intermittent pulses under 10mA?
In ultra-low-power applications such as battery-operated sensors, the FJX3904TF’s 300mV Vce(sat) at 50mA ensures minimal static power consumption even during brief current spikes. Its hFE(min)=100 at 10mA supports efficient base drive from microcontrollers, reducing quiescent current draw. Given the device’s MSL Level 1 rating and unlimited moisture sensitivity life, it is well-suited for mass production environments. Engineers should still verify that peak pulse currents do not exceed 200mA and ensure proper decoupling near the load to maintain signal integrity during turn-on transients.
Why might the FJX3904TF be preferred over discrete wire-wound resistors in active current-limiting circuits despite its transistor classification?
Although primarily a switch, the FJX3904TF can emulate resistive behavior when operated in linear mode with fixed base bias. At 10mA collector current and Vce=1V, its hFE of 100 allows precise current control with minimal voltage drop—effectively replacing a 100Ω resistor while offering active feedback capability. This reduces component count and improves response time compared to passive resistors. However, continuous linear operation risks exceeding 350mW power dissipation; thus, duty cycle must remain below ~1% in 5V systems to avoid thermal shutdown.
How does the operating temperature range of the FJX3904TF influence reliability in automotive-grade environmental monitoring systems?
With a maximum junction temperature of 150°C and no lower limit specified (implying standard industrial grading down to -40°C), the FJX3904TF meets typical automotive AEC-Q101 requirements for non-critical sensing functions. In exhaust gas or cabin temperature monitors exposed to cyclic thermal stress, the device’s robust packaging and lack of lead-free soldering concerns support long-term durability. Still, derating above 125°C ambient is recommended to extend lifespan, especially when mounted in sealed enclosures with poor airflow.
Are there any layout precautions specific to the SOT-323 footprint when routing high-impedance signals near the FJX3904TF?
Yes. Due to its small form factor (SC-70/SOT-323), the FJX3904TF’s leads act as antennas and can couple noise into sensitive analog inputs if placed near traces carrying mV-level signals. Maintain a minimum clearance of 0.5mm between input lines and the transistor body, and route high-impedance traces on inner layers with guard rings. Ground the emitter directly to the local plane to minimize ground bounce, which could otherwise degrade linearity in amplification modes.
What substitution risks exist if sourcing the FJX3904TF through alternative distributors offering counterfeit-compatible alternatives like PMST3904?
The PMST3904, though physically compatible, often has degraded hFE consistency and higher leakage current due to older fabrication processes. While it may pass basic continuity tests, its β variation (±50%) exceeds the FJX3904TF’s tighter specification, leading to unpredictable gain in analog stages. Additionally, PMST3904 lacks modern ESD protection diodes integrated into newer designs like the FJX3904TF. For mission-critical designs, always verify lot codes and request full test reports to avoid parametric drift over time.
In what scenarios would the FJX3904TF’s 300MHz transition frequency become a limiting factor despite sufficient DC headroom?
At frequencies approaching 150MHz, the FJX3904TF’s gain rolls off due to internal capacitances and transit delay. In wideband amplifiers or clock distribution networks requiring >20dB gain above 200MHz, this limitation forces use of higher-performance devices like MMBT3904LT1G. However, in narrowband applications such as envelope detection or simple oscillator tanks, the FJX3904TF remains viable provided the phase margin is verified via SPICE simulation accounting for package parasitics.
How should thermal modeling be approached when estimating junction temperature rise in compact PCB layouts using the FJX3904TF?
Thermal resistance from junction to ambient (RθJA) is not published by onsemi for SOT-323, but typical values range from 400–500°C/W depending on copper area and airflow. Assuming worst-case RθJA=500°C/W and continuous operation at 100mW, delta-T reaches 50°C. Therefore, even moderate power levels demand careful layout: attach the emitter tab to a solid ground plane and avoid routing hot traces beneath the device. Use IPC-2221 guidelines for pad sizing to maximize thermal coupling.
Could the FJX3904TF be used in a Darlington configuration to improve gain without violating package limitations?
No. The SOT-323 package lacks sufficient pin count and thermal mass for two transistors. Attempting to mount a second device adjacent would violate creepage/clearance rules and introduce parasitic capacitance. Instead, use dedicated Darlington pairs like MUN5211DW. The FJX3904TF’s standalone hFE of 100 already exceeds typical microcontroller output drive needs, making external amplification unnecessary in most embedded designs.
What impact does the FJX3904TF’s ECCN code (EAR99) have on global supply chain logistics for defense contractors?
EAR99 classification means the FJX3904TF is subject to U.S. export controls only if combined with controlled components, but generally qualifies for unrestricted commercial distribution. Defense contractors can source it without ITAR restrictions, simplifying procurement. However, end-use documentation may still require compliance verification under DFARS 252.225-7002, particularly for foreign-manufactured variants sourced via contract manufacturers outside the U.S.
Is it acceptable to parallel multiple FJX3904TF devices to share current in a motor driver application without balancing circuitry?
Paralleling the FJX3904TF is feasible for short bursts (<10ms) due to similar threshold voltages, but inherent β mismatch causes unequal current sharing. Without ballast resistors or emitter degeneration, one device may carry >80% of total current, risking localized heating. For reliable operation above 100mA average, add 0.1Ω emitter resistors per device to stabilize distribution and protect against thermal runaway.
How does the Moisture Sensitivity Level (MSL) 1 rating affect storage and handling in humid manufacturing facilities?
MSL 1 indicates the FJX3904TF can withstand unlimited exposure to ambient humidity before baking is required prior to reflow. This simplifies inventory management in high-volume assembly lines, eliminating the need for climate-controlled dry cabinets unless stored beyond 12 months. Nevertheless, handling during production should follow JEDEC J-STD-033 standards, including anti-static wrist straps and grounded work surfaces to prevent electrostatic discharge damage.
What role does the base product number (FJX390) play in firmware-controlled switching algorithms that dynamically adjust drive strength?
The FJX390 base family enables consistent modeling across derivatives like the FJX3904TF, allowing firmware to assume stable switching characteristics within ±20% of nominal hFE. Algorithms relying on open-loop current estimation can use lookup tables indexed by FJX390, reducing calibration overhead. However, real-time feedback via sense resistors remains advisable to compensate for process-induced variations in Vbe and saturation voltage.
When interfacing the FJX3904TF with a 3.3V microcontroller GPIO pin, what base resistor value ensures safe turn-on without excessive power waste?
Using Ohm’s law with Vcc=3.3V, Vbe≈0.7V, and desired Ic=50mA yields Ib = Ic/hFE = 0.5mA. A base resistor Rb = (3.3–0.7)/0.0005 = 5.2kΩ. Selecting a standard 5.1kΩ resistor limits Ib to ~0.53mA, safely within the microcontroller’s sink capability while keeping base power at 0.35mW. This avoids unnecessary dissipation and protects the GPIO from overcurrent during repeated switching cycles.
Why might the FJX3904TF exhibit slower turn-off times than expected in PWM-driven LED drivers despite fast fT?
Transition frequency (fT) measures gain crossover, not switching speed. Turn-off time is dominated by stored charge removal in the base region, which depends on recombination dynamics rather than high-frequency response. In PWM applications above 1kHz, adding a small base-emitter capacitor (e.g., 10pF) or using a Schottky diode across the base-collector junction accelerates discharge. Alternatively, reduce base drive current slightly to decrease storage time at the cost of marginal delay.
How does the absence of a specified collector cutoff current (Icbo) affect leakage modeling in precision analog multiplexers using the FJX3904TF?
Unspecified Icbo implies it falls within typical ranges for silicon NPN devices (<1µA at 25°C). In multiplexer switches handling µV signals, this leakage becomes negligible compared to contact resistance or thermoelectric effects. However, at elevated temperatures (85°C+), leakage can double, potentially corrupting low-level measurements. To mitigate, operate the FJX3904TF in cutoff mode with cold junctions, or choose a device with explicit Icbo specs if sub-µA leakage is critical.

Parts with Similar Specifications

The three parts on the right have similar specifications to onsemi FJX3904TF

Product Attribute FJX3904TF FJX3906TF FJX3906TF FJX4002RTF
Part Number FJX3904TF FJX3906TF FJX3906TF FJX4002RTF
Manufacturer onsemi Fairchild Semiconductor onsemi onsemi
Package Bulk Bulk Tape & Reel (TR) Tape & Reel (TR)
Vce Saturation (Max) @ Ib, Ic 300mV @ 5mA, 50mA 400mV @ 5mA, 50mA 400mV @ 5mA, 50mA 300mV @ 500µA, 10mA
Series - - - -
DC Current Gain (hFE) (Min) @ Ic, Vce 100 @ 10mA, 1V 100 @ 10mA, 1V 100 @ 10mA, 1V 30 @ 5mA, 5V
Current - Collector Cutoff (Max) - 50nA - 100nA (ICBO)
Operating Temperature 150°C (TJ) - - -
Frequency - Transition 300MHz 250MHz 250MHz 200 MHz
Voltage - Collector Emitter Breakdown (Max) 40 V 40 V 40 V 50 V
Transistor Type NPN PNP PNP PNP - Pre-Biased
Package / Case SC-70, SOT-323 SC-70, SOT-323 SC-70, SOT-323 SC-70, SOT-323
Mounting Type Surface Mount Surface Mount Surface Mount Surface Mount
Supplier Device Package SOT-323 SOT-323 SOT-323 SOT-323
Power - Max 350 mW 350 mW 350 mW 200 mW
Current - Collector (Ic) (Max) 200 mA 200 mA 200 mA 100 mA

Customers Also Interested in

Recommended Products

Customer Reviews

Evaluation: 10 Articles

  • ECUb***h
    Sep 22, 2026

    Used for repair of an older automotive ECU. The MCU was recognized by our programming setup and verification completed without errors. The repaired board now starts and communicates normally.

  • RS48***ieldTech
    Sep 16, 2026

    Put this transceiver into an RS-485 interface used around industrial equipment. Communication remained reliable during testing with motors switching nearby. Good result for the replacement board.

  • Logi***b_Chris
    Sep 8, 2026

    Purchased for a Cyclone III development project. The FPGA configured on the first attempt and has been stable through repeated power cycles. No problems with the I/O we are using.

  • Circ***FixerTom
    Sep 2, 2026

    Used this rectifier in a high-current power supply repair. Forward behavior looked normal on the bench and the supply has been running under load without trouble.

  • Retr***UWorks
    Aug 31, 2026

    Needed the exact ST10F269Z2Q6 for servicing an older control unit. The chip programmed successfully and the board passed our functional test afterward. Much easier than redesigning around a newer MCU.

  • Andr***PCBLab
    Aug 28, 2026

    I needed this ADC for an older data acquisition board. Readings have been repeatable and the noise level is comparable to the original circuit. Happy with the purchase.

  • Leat***O'Keefe
    Aug 20, 2026

    one of my hobbies is skydiving. and when i'm skydiving this works great.

  • Ilen***
    Aug 20, 2026

    This product works considerably well. It secretly improves my basketball by a lot.

  • Indu***ialPower
    Aug 17, 2026

    Installed this IGBT module in a power conversion cabinet. Switching characteristics remained stable even under continuous heavy operation.

  • Nikh***ech
    Aug 13, 2026

    Great low-power MCU for portable equipment. Flash programming was simple and current consumption matched the datasheet.

Write a Review

Your Email address will not be published.

Shipment

Delivery Time

In-stock items can be shipped within 24 hours. Some parts will be arranged for delivery within 1-2 days from the date all items arrive at our warehouse. And Allelco ships order once a day at about 17:00, except Sunday. Once the goods are shipped, the estimated delivery time depends on the shipping methods and Delivery destination. The table below shows are the logistic time for some common countries.

Delivery Cost

  1. Use your express account for shipment if you have one.
  2. Use our account for the shipment. Refer to the table below for the approximate charges.
(Different time frame / countries / package size has different price.)

Delivery Method

  1. Global Common Shipment by DHL / UPS / FedEx / TNT / EMS / SF we support.
  2. Others more shipping ways, please get in touch with your customer manager.

Common Countries Logistic Time Reference
Region Country Logistic Time(Day)
America United States 5
Brazil 7
Europe Germany 5
United Kingdom 4
Italy 5
Oceania Australia 6
New Zealand 5
Asia India 4
Japan 4
Middle East Israel 6
DHL & FedEx Shipment Charges Reference
Shipment charges(KG) Reference DHL(USD$)
0.00kg-1.00kg USD$30.00 - USD$60.00
1.00kg-2.00kg USD$40.00 - USD$80.00
2.00kg-3.00kg USD$50.00 - USD$100.00
Note:
The above table is for reference only. There may have some data bias for the uncontrollable factors.
Contact us if you have any questions.
  • QC (Quality Warranty)
  • Payment Support
  • Packaging
  • Certifications & Memberships

QC (Quality Warranty)

Allelco is committed to exceeding customer expectations through customer service excellence, order accuracy, and on-time delivery.
This is achieved through our commitment to the continual improvement of our processes, services, and products.


Strict quality inspection builds a solid foundation for electronic component quality.
  1. Visual inspection
  2. Performance testing and reliability verification
  3. Standardized full-process testing
  4. Precise control of every parameter
We eliminate defective components and ensure the stable operation of electronic devices through professional quality standards.
Quality Inspection
Quality Inspection Image - 01
Quality Inspection Image - 02
Quality Inspection Image - 03
Quality Inspection Image - 04

Payment Support

The payment method can be chosen from the methods shown below: Wire Transfer (T/T, Bank Transfer), Western Union, Credit card, PayPal.
  • HKBea
  • Paypal
  • MasterCard
  • Western-Union
  • VISA
Stable Delivery, Sincere Partnership — Your Faithful Supply Chain Partner
  • Efficient Supply Management
  • Cost-Saving Procurement
  • Fast Sourcing & Delivery
Contact us if you have any questions.

Packaging

Electrostatic Discharge Protection and Handling

All electrostatic-sensitive components are handled in accordance with electrostatic discharge control procedures. The products are hermetically sealed in anti-static safe packaging to prevent electrostatic damage. Appropriate labeling is also applied for identification and traceability. This ensures product integrity during storage, handling and transportation.


ESD

Certifications & Memberships

Third-party certified, strict quality control. Our certification
  • ISO 9001: 2015
  • ISO 13485: 2016
  • ISO 14001: 2015
  • ISO 28000: 2007
  • ISO 45001: 2018
  • GB/T 27922-2011
  • SMTA
  • IPC
  • ESD
  • PSMA
onsemi

FJX3904TF

onsemi
32D-FJX3904TF

Want a better price? Add to Cart and Submit RFQ now, we'll contact you immediately.

Allelco
About Us
History
Certifications
Recruitment
Policies
Terms & Conditions
Privacy Policy
Cookie Policy
Services
Order Tracking
Return & Replacement
Frequently Asked Questions
Contact Us
Order
Shipping & Delivering
Payment Methods
My Account
The BlogsHot PartsChange LanguageNewsSite map
Contact Us
Headquarters Address:
Room C 13/F Harvard Commercial Building
105-111 Thomson Road Wan Chai
HongKong
Service Tel: +852-91464856
Service Email: info@allelco.com
Follow us
Copyright © 2012-2025 AllelcoElec.com. All rights reserved.
0 RFQ
Shopping cart (0 Items)
It is empty.
Submit RFQ
Compare List (0 Items)
It is empty.
Feedback

Your feedback matters! At Allelco, we value the user experience and strive to improve it constantly.
Please share your comments with us via our feedback form, and we'll respond promptly.
Thank you for choosing Allelco.

Subject
E-mail
Comments
Captcha
Drag or click to upload file
Upload File
types: .xls, .xlsx, .doc, .docx, .jpg, .png and .pdf.
Max file size: 10MB