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

onsemi BSS79C

Name: BSS79C
Brand: onsemi
SKU: BSS79C
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BSS79C

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BSS79C.pdf

Description:: TRANS NPN 40V 0.8A SOT-23-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BSS79C from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor (BJT) designed for medium-power amplification and switching applications up to 500mA collector current. It features V_CEO = 40 V, V_CBO = 75 V, h_FE = 100–300 at I_C = 150 mA, f_T = 250 MHz, and SOT-23 package - used in DC-DC converter control stages and low-voltage power switching circuits.

For engineers reviewing the BSS79C datasheet, pinout, applications, or equivalent options, key selection considerations include its 40 V V_CEO, 350 mW power dissipation at 25°C, 265 ns storage time, 8.0 pF C_CB, and suitability for linear amplification and saturated-switching roles in industrial power management modules.

Technical Context

The BSS79C operates as a silicon NPN planar epitaxial transistor with a maximum junction temperature of 150°C and thermal resistance R_θJA = 357°C/W on FR-4 PCB. Its DC current gain spans 100–300 under I_C = 150 mA / V_CE = 10 V conditions, supporting stable biasing in Class-A amplifier stages.

Switching performance is defined by t_d = 10 ns, t_r = 10 ns, t_s = 265 ns, and t_f = 60 ns at V_CC = 30 V and I_C = 150 mA, indicating moderate-speed operation suitable for PWM-driven loads below 1 MHz - not optimized for RF or high-frequency digital logic.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	40 V - Maximum safe collector-emitter voltage before breakdown in common-emitter configuration.
h_FE	100–300 - DC current gain range enabling predictable base drive sizing for 150 mA load switching.
f_T	250 MHz - Unity-gain bandwidth limiting usable small-signal amplification to sub-100 MHz frequencies.
P_D	350 mW - Total power dissipation at 25°C ambient, derating 2.8 mW/°C above that temperature.
t_s	265 ns - Storage time governing turn-off delay in saturated switching; impacts minimum PWM frequency capability.
C_CB	8.0 pF - Collector-base capacitance affecting high-frequency gain roll-off and Miller effect in amplifier designs.

Pinout & Package

SOT-23 plastic surface-mount package (3-pin, standard lead pitch 0.95 mm), marked "CF", with pin 1 = Emitter, pin 2 = Base, pin 3 = Collector - verified per Fairchild Rev. A datasheet and dimensional drawing.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (Emitter)	Current exit terminal for NPN transistor	Connected to ground or low-side return path; sets reference for base-emitter biasing.
Pin 2 (Base)	Control input for minority-carrier injection	Receives current-limited drive signal; determines saturation level and switching speed.
Pin 3 (Collector)	Current entry terminal under forward-active or saturation mode	Interfaces with load or supply rail; handles up to 800 mA continuous current.

Key Features

Feature	Design Value
Medium-power switching capability	Rated for 500 mA collector current in saturated switch mode with V_CE(sat) ≤ 1.0 V at I_C = 500 mA / I_B = 50 mA.
High-voltage blocking margin	V_CBO = 75 V provides headroom above 40 V V_CEO, improving robustness against transient overvoltage in inductive loads.
Thermal stability	Junction temperature range –55°C to +150°C enables operation in automotive under-hood and industrial control environments.
Small-signal amplification support	f_T = 250 MHz and h_FE ≥ 100 allow use in broadband preamplifier and driver stages up to ~50 MHz.

Applications

DC-DC Converter Switch	Low-Voltage Motor Driver
Use Scenario: Used as main switching transistor in non-isolated buck converters delivering 3.3 V/5 V at up to 300 mA output. IC Role / Device Role / Timing Role: NPN BJT operating in saturated switching mode, driven by PWM controller's open-collector output. Use Value: Low V_CE(sat) (0.3 V @ 150 mA) minimizes conduction loss; 265 ns storage time limits minimum off-time to ~500 ns.	Use Scenario: Drives 12 V brushed DC motors in portable instrumentation requiring bidirectional control via H-bridge half-bridge stage. IC Role / Device Role / Timing Role: High-side or low-side switch in discrete H-bridge, configured with complementary PNP or N-channel MOSFET. Use Value: 40 V V_CEO accommodates back-EMF spikes; 8.0 pF C_CB reduces capacitive coupling noise into base drive circuitry.
Linear Voltage Regulator Pass Element	Industrial Sensor Signal Amplifier
Use Scenario: Functions as series pass transistor in adjustable LDO regulators powering analog sensor front-ends. IC Role / Device Role / Timing Role: Operates in linear active region with emitter-follower configuration for low-noise voltage regulation. Use Value: h_FE ≥ 100 ensures stable loop gain; 350 mW power rating supports 1 W dissipation with heatsinking.	Use Scenario: Amplifies low-level thermocouple or bridge sensor outputs in 0–100 mV range before ADC sampling. IC Role / Device Role / Timing Role: Common-emitter small-signal amplifier with resistive bias network and emitter degeneration. Use Value: f_T = 250 MHz allows >10 MHz bandwidth for fast transient response; low C_CB preserves signal integrity.

DC-DC Converter Switch

Low-Voltage Motor Driver

Use Scenario: Used as main switching transistor in non-isolated buck converters delivering 3.3 V/5 V at up to 300 mA output.

IC Role / Device Role / Timing Role: NPN BJT operating in saturated switching mode, driven by PWM controller's open-collector output.

Use Value: Low V_CE(sat) (0.3 V @ 150 mA) minimizes conduction loss; 265 ns storage time limits minimum off-time to ~500 ns.

Use Scenario: Drives 12 V brushed DC motors in portable instrumentation requiring bidirectional control via H-bridge half-bridge stage.

IC Role / Device Role / Timing Role: High-side or low-side switch in discrete H-bridge, configured with complementary PNP or N-channel MOSFET.

Use Value: 40 V V_CEO accommodates back-EMF spikes; 8.0 pF C_CB reduces capacitive coupling noise into base drive circuitry.

Linear Voltage Regulator Pass Element

Industrial Sensor Signal Amplifier

Use Scenario: Functions as series pass transistor in adjustable LDO regulators powering analog sensor front-ends.

IC Role / Device Role / Timing Role: Operates in linear active region with emitter-follower configuration for low-noise voltage regulation.

Use Value: h_FE ≥ 100 ensures stable loop gain; 350 mW power rating supports 1 W dissipation with heatsinking.

Use Scenario: Amplifies low-level thermocouple or bridge sensor outputs in 0–100 mV range before ADC sampling.

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

Use Value: f_T = 250 MHz allows >10 MHz bandwidth for fast transient response; low C_CB preserves signal integrity.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BCW65C	Identical h_FE range (100–300), same SOT-23 package, but V_CEO = 60 V and f_T = 200 MHz - lower bandwidth, higher voltage rating.	Preferred where higher V_CEO margin is required (e.g., 48 V systems), but less suitable for >100 MHz small-signal gain.	Select BCW65C when operating above 40 V collector supply or where tighter V_CEO margin is critical.
MMBT3904LT1G	V_CEO = 40 V same, but h_FE = 100–300 at I_C = 10 mA (not 150 mA); f_T = 300 MHz; P_D = 310 mW - higher bandwidth, lower power rating.	Better for low-current signal amplification; less robust for 500 mA switching due to lower thermal mass and derating.	Choose MMBT3904LT1G for high-frequency preamp stages, not for sustained 500 mA switching loads.

Compared with BCW65C and MMBT3904LT1G, the BSS79C uniquely balances 500 mA switching capability, 40 V blocking, and 250 MHz f_T in SOT-23 - making it optimal for medium-power industrial switching where both current handling and bandwidth matter.

Availability

BSS79C is available at Aetrix Electronics and suitable for DC-DC converter design, motor driver development, and industrial sensor interface circuits requiring stable component supply and long-term manufacturability.

Supply support for BSS79C 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016.

The BSS79C belongs to Fairchild's legacy SOT-23 NPN transistor family engineered for cost-sensitive, medium-power industrial and consumer power conversion applications.

FAQ

What is the maximum continuous collector current rating for the BSS79C?

The BSS79C has a maximum continuous collector current (I_C) rating of 800 mA at T_A = 25°C, with recommended operation up to 500 mA for reliable medium-power switching. This rating is validated under steady-state conditions with proper PCB thermal relief and must be derated per the 2.8 mW/°C thermal coefficient above ambient.

Does the BSS79C support linear amplification applications?

Yes, the BSS79C supports linear amplification due to its h_FE = 100–300 at I_C = 150 mA and f_T = 250 MHz, enabling stable gain in common-emitter configurations up to ~50 MHz. Its low C_CB (8.0 pF) and controlled V_CE(sat) also support low-distortion analog stages in sensor signal chains and regulator error amplifiers.

What is the pin configuration of the BSS79C in the SOT-23 package?

The BSS79C uses standard SOT-23 pinout: Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector, with marking "CF" on the top surface. This configuration is confirmed in the Fairchild Rev. A datasheet and matches JEDEC MO-178AB mechanical outline - no alternate pinouts exist for this part number.

How does the BSS79C compare to the BCW65C in terms of voltage ratings?

The BSS79C has V_CEO = 40 V and V_CBO = 75 V, while the BCW65C specifies V_CEO = 60 V and V_CBO = 80 V. Thus, BCW65C offers higher collector-emitter blocking capability, but BSS79C maintains identical V_CEO test conditions (I_C = 10 mA, I_B = 0) and shares the same h_FE range and SOT-23 footprint.

Is the BSS79C suitable for automotive under-hood applications?

The BSS79C supports operation from –55°C to +150°C junction temperature and is rated for industrial environments, but it is not AEC-Q101 qualified. For automotive under-hood use, system-level validation including board-level thermal testing and transient immunity assessment is required - the BSS79C itself lacks automotive qualification documentation.

BSS79C 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):: 800 mA

Voltage - Collector Emitter Breakdown (Max):: 40 V

Vce Saturation (Max) @ Ib, Ic:: 1V @ 50mA, 500mA

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

DC Current Gain (hFE) (Min) @ Ic, Vce:: 100 @ 150mA, 10V

Power - Max:: 350 mW

Frequency - Transition:: 250MHz

Operating Temperature:: -55°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-3

BSS79C FAQ

1.How can I place an order for BSS79C through Aetrix?

Please submit a Request for Quotation (RFQ) for BSS79C 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 BSS79C reliable?

The price and inventory of BSS79C are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BSS79C is usually 5 days.

3.What payment methods are accepted for BSS79C?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BSS79C transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BSS79C?

BSS79C orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BSS79C 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 BSS79C?

For technical support, including BSS79C datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BSS79C requirements.

6.How does Aetrix verify that BSS79C is sourced from the original manufacturer or authorized distributors?

All BSS79C 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 BSS79C meets industry standards.

7.What is the process for return or replacement of BSS79C?

All BSS79C units undergo pre-shipment inspection (PSI). If there is an issue with BSS79C, 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 BSS79C part is unused and in its original packaging.

Return procedure for BSS79C:

1.Submit a request within 90 days.

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

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