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

onsemi BCX70K

Name: BCX70K
Brand: onsemi
SKU: BCX70K
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BCX70K

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BCX70K.pdf

Description:: TRANS NPN 45V 0.2A SOT-23-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BCX70K from ON Semiconductor is an NPN epitaxial silicon general-purpose transistor in SOT-23 package, rated for 45 V V_CEO, 200 mA I_C, and 350 mW P_C; used in low-power switching and amplification circuits such as LED drivers and signal buffering in consumer electronics.

For engineers reviewing the BCX70K datasheet, pinout, applications, or equivalent options, key selection criteria include DC current gain (h_FE = 100–630), saturation voltage (V_CE(sat) ≤ 0.55 V at 50 mA), noise figure (6 dB), f_T = 125 MHz, and SOT-23 thermal and layout compatibility.

Technical Context

The BCX70K operates as a discrete NPN bipolar junction transistor with epitaxial base construction, enabling stable h_FE across collector currents from 10 µA to 50 mA and V_CE up to 5 V. Its low Cob (4.5 pF) and 125 MHz f_T support medium-frequency small-signal amplification.

Designed for general-purpose linear and switching use, it features V_BE(sat) of 0.6–1.05 V and t_ON/t_OFF of 150 ns / 800 ns under defined test conditions, making it suitable for digital logic interfacing and pulse applications where moderate speed and gain consistency are required.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	45 V - Maximum safe collector-emitter voltage before breakdown; defines upper rail limit in switching designs.
I_C	200 mA - Continuous collector current rating; sets maximum load drive capability in active mode.
P_C	350 mW - Power dissipation limit at T_A = 25°C; constrains thermal design in SOT-23 footprint.
h_FE	100–630 - DC current gain range across operating points; enables predictable biasing in amplifier and switch stages.
f_T	125 MHz - Current gain bandwidth product; supports small-signal amplification up to ~100 MHz with usable gain.
V_CE(sat)	0.35–0.55 V - Low saturation voltage at I_C = 10–50 mA; minimizes conduction loss in saturated-switch applications.
NF	6 dB - Noise figure at 1 kHz with 2 kΩ source; indicates suitability for low-noise preamplifier stages.

Pinout & Package

SOT-23 plastic surface-mount package with gull-wing leads; compact 2.9 mm × 1.3 mm footprint and 1.0 mm height; thermally optimized for PCB pad exposure.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Control electrode	Accepts forward-biased current to enable conduction between Collector and Emitter; requires series resistor for current limiting in digital drive.
2 (Emitter)	Current return path	Common reference node for bias network; connected to ground or low-side return in most switching configurations.
3 (Collector)	Output current terminal	Delivers switched or amplified current to load; routed to V_CC or pull-up in common-emitter topology.

Key Features

Feature	Design Value
Epitaxial base structure	Ensures consistent h_FE and low leakage (I_CES ≤ 20 nA) across temperature and process variation.
Low V_CE(sat)	Reduces power loss and self-heating during saturation, improving efficiency in battery-powered switch circuits.
125 MHz f_T	Enables reliable operation in audio preamps, oscillator buffers, and medium-speed digital interface circuits.
6 dB noise figure	Supports clean signal amplification in sensor front-ends and low-level analog signal chains without added noise degradation.
SOT-23 footprint	Provides high-density placement compatibility with standard pick-and-place equipment and reflow profiles.

Applications

LED Driver Circuit	Logic-Level Translator
Use Scenario: Driving 20 mA indicator LEDs from 3.3 V or 5 V microcontroller GPIO pins. IC Role / Device Role / Timing Role: NPN switch configured in common-emitter mode, turning LED on/off via base current control. Use Value: Low V_CE(sat) (≤ 0.55 V) ensures >90% LED forward voltage utilization; h_FE ≥ 100 guarantees full saturation with ≤ 0.5 mA base drive.	Use Scenario: Interfacing 3.3 V logic outputs to 5 V TTL inputs in mixed-voltage systems. IC Role / Device Role / Timing Role: Level-shifting transistor in open-collector configuration with pull-up to 5 V rail. Use Value: Fast t_ON/t_OFF (150 ns / 800 ns) supports >1 MHz data rates; low Cob (4.5 pF) prevents signal distortion at transition edges.
Audio Pre-amplifier Stage	Signal Buffer for Sensor Outputs
Use Scenario: Amplifying weak microphone or piezo sensor signals prior to ADC sampling. IC Role / Device Role / Timing Role: Common-emitter small-signal amplifier with emitter degeneration and DC bias network. Use Value: 6 dB noise figure and 125 MHz f_T preserve SNR and bandwidth up to 20 kHz; h_FE stability enables repeatable gain calibration.	Use Scenario: Isolating and driving high-impedance analog sensor outputs (e.g., thermistor dividers) into ADC input stages. IC Role / Device Role / Timing Role: Unity-gain emitter-follower buffer providing low-output-impedance drive. Use Value: High h_FE (up to 630) ensures minimal loading of source; low V_BE(on) (0.55–0.75 V) maintains accuracy over temperature.

LED Driver Circuit

Logic-Level Translator

Use Scenario: Driving 20 mA indicator LEDs from 3.3 V or 5 V microcontroller GPIO pins.

IC Role / Device Role / Timing Role: NPN switch configured in common-emitter mode, turning LED on/off via base current control.

Use Value: Low V_CE(sat) (≤ 0.55 V) ensures >90% LED forward voltage utilization; h_FE ≥ 100 guarantees full saturation with ≤ 0.5 mA base drive.

Use Scenario: Interfacing 3.3 V logic outputs to 5 V TTL inputs in mixed-voltage systems.

IC Role / Device Role / Timing Role: Level-shifting transistor in open-collector configuration with pull-up to 5 V rail.

Use Value: Fast t_ON/t_OFF (150 ns / 800 ns) supports >1 MHz data rates; low Cob (4.5 pF) prevents signal distortion at transition edges.

Audio Pre-amplifier Stage

Signal Buffer for Sensor Outputs

Use Scenario: Amplifying weak microphone or piezo sensor signals prior to ADC sampling.

IC Role / Device Role / Timing Role: Common-emitter small-signal amplifier with emitter degeneration and DC bias network.

Use Value: 6 dB noise figure and 125 MHz f_T preserve SNR and bandwidth up to 20 kHz; h_FE stability enables repeatable gain calibration.

Use Scenario: Isolating and driving high-impedance analog sensor outputs (e.g., thermistor dividers) into ADC input stages.

IC Role / Device Role / Timing Role: Unity-gain emitter-follower buffer providing low-output-impedance drive.

Use Value: High h_FE (up to 630) ensures minimal loading of source; low V_BE(on) (0.55–0.75 V) maintains accuracy over temperature.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN general-purpose transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BC847B	Higher h_FE min (200 vs. 100), same V_CEO/I_C, identical SOT-23 package	Better suited for low-base-drive amplification; less margin for saturation at high I_C	Select BC847B when higher gain consistency is needed; verify V_CE(sat) at target I_C.
MMBT3904	Same absolute ratings, slightly lower f_T (300 MHz typical but not guaranteed), broader h_FE spread (100–400)	More widely available; acceptable for non-critical switching where gain tolerance is relaxed	Choose MMBT3904 for cost-sensitive volume production where 125 MHz f_T is not required.

Compared with BCX70K, BC847B offers tighter h_FE control for precision biasing, while MMBT3904 provides broader supply-chain availability at the expense of guaranteed high-frequency performance - both require validation of V_CE(sat) and thermal behavior in the final layout.

Availability

BCX70K is available at Aetrix Electronics and suitable for LED driver circuits, logic-level translation, audio pre-amplifiers, and sensor buffering requiring stable component supply and SOT-23 footprint compatibility.

Supply support for BCX70K 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

ON Semiconductor is a global semiconductor manufacturer specializing in energy-efficient power and signal management solutions, with roots in Fairchild Semiconductor's legacy discrete portfolio.

The BCX70K belongs to ON Semiconductor's general-purpose bipolar transistor product line, designed for cost-effective, reliable switching and amplification in consumer, computing, and industrial electronics.

FAQ

What is the maximum collector-emitter voltage rating for BCX70K?

The BCX70K has a maximum collector-emitter voltage (V_CEO) rating of 45 V at T_A = 25°C. This value is confirmed in the Absolute Maximum Ratings table and applies under continuous DC operation. Exceeding this voltage risks avalanche breakdown and permanent device failure. Derating is recommended above 25°C ambient per the datasheet thermal curves.

Does BCX70K have a specified noise figure, and under what conditions?

Yes, the BCX70K has a specified noise figure of 6 dB, measured at V_CE = 5 V, I_C = 0.2 mA, R_S = 2 kΩ, and f = 1 kHz. This parameter is documented in the Electrical Characteristics table and reflects its suitability for low-noise small-signal amplification tasks such as sensor front-end stages.

What is the pin configuration of BCX70K in the SOT-23 package?

The BCX70K uses standard SOT-23 pinout: Pin 1 is Base, Pin 2 is Emitter, and Pin 3 is Collector. This configuration is explicitly shown in the "Package Dimensions" diagram and marked as "AK" on the device top side. It matches JEDEC TO-236AB mechanical outline and is compatible with automated assembly tooling.

Can BCX70K be used in switching applications above 1 MHz?

The BCX70K has a current gain bandwidth product (f_T) of 125 MHz, but its practical switching speed is limited by t_ON = 150 ns and t_OFF = 800 ns. While small-signal amplification remains viable near 100 MHz, reliable digital switching is recommended below 500 kHz to ensure full saturation and avoid excessive switching losses due to minority carrier storage delay.

Is BCX70K RoHS compliant and halogen-free?

Yes, BCX70K is RoHS compliant and halogen-free, consistent with ON Semiconductor's corporate compliance policy and the environmental specifications published for Fairchild-integrated products. The device meets EU Directive 2011/65/EU and IEC 61249-2-21:2013 requirements, with material declarations available upon request through Aetrix Electronics' compliance portal.

BCX70K Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

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

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 200 mA

Voltage - Collector Emitter Breakdown (Max):: 45 V

Vce Saturation (Max) @ Ib, Ic:: 550mV @ 1.25mA, 50mA

Current - Collector Cutoff (Max):: 20nA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 380 @ 2mA, 5V

Power - Max:: 350 mW

Frequency - Transition:: 125MHz

Operating Temperature:: -

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-3

BCX70K FAQ

1.How can I place an order for BCX70K through Aetrix?

Please submit a Request for Quotation (RFQ) for BCX70K 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 BCX70K reliable?

The price and inventory of BCX70K are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BCX70K is usually 5 days.

3.What payment methods are accepted for BCX70K?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BCX70K transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BCX70K?

BCX70K orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BCX70K 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 BCX70K?

For technical support, including BCX70K datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BCX70K requirements.

6.How does Aetrix verify that BCX70K is sourced from the original manufacturer or authorized distributors?

All BCX70K 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 BCX70K meets industry standards.

7.What is the process for return or replacement of BCX70K?

All BCX70K units undergo pre-shipment inspection (PSI). If there is an issue with BCX70K, 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 BCX70K part is unused and in its original packaging.

Return procedure for BCX70K:

1.Submit a request within 90 days.

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

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