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

onsemi BC373

Name: BC373
Brand: onsemi
SKU: BC373
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BC373

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-226-3, TO-92-3 Long Body

Datasheet:: BC373.pdf

Description:: TRANS NPN DARL 80V 1A TO92

Quantity:: RFQ Add To RFQ list

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Inventory:5,632

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Product details

Overview

BC373 from onsemi is an NPN silicon Darlington transistor in TO-92 package, rated for 80 V_CEO, 1.0 A continuous collector current, and 1.5 W power dissipation at T_A = 25°C. It delivers high DC current gain (h_FE = 8–160 at I_C = 100 mA), low saturation voltage (V_CE(sat) ≤ 1.1 V), and operates across −55°C to +150°C junction temperature - used in relay drivers, lamp dimmers, and industrial control interface stages.

For engineers reviewing the BC373 datasheet, pinout, applications, or equivalent options, key selection criteria include its 80 V breakdown rating, Darlington configuration enabling high-current switching with low base drive, thermal resistance (R_JA = 200°C/W), and Pb-free TO-92 packaging compliance.

Technical Context

The BC373 integrates two cascaded NPN transistors in a monolithic Darlington pair, delivering high current gain without external biasing components. Its structure supports high-voltage switching up to 80 V_CEO while maintaining low V_BE(sat) (1.4–2.0 V) and V_CE(sat) (≤1.1 V) under I_C/I_B = 100 conditions.

Designed for linear and saturated-mode operation, it features f_T = 100–200 MHz bandwidth, Cob = 10–25 pF output capacitance, and NF = 2.0 dB noise figure at 1 kHz - suitable for medium-speed switching and analog amplification where gain stability and thermal robustness are prioritized over RF performance.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	80 V - Maximum safe collector-emitter voltage before avalanche breakdown; defines upper limit for load-side voltage swing in switching applications.
I_C (continuous)	1.0 A - Continuous collector current handling capacity; determines maximum load current in relay or solenoid driver designs.
P_D @ 25°C	1.5 W - Total power dissipation capability at ambient; requires heatsinking or derating above 25°C (12 mW/°C).
h_FE	8–160 - DC current gain range at I_C = 100 mA; enables microcontroller-level base drive (e.g., 1 mA base → 100 mA collector).
V_CE(sat)	≤1.1 V - Saturation voltage at I_C = 250 mA, I_B = 0.25 mA; minimizes conduction loss and self-heating in on-state operation.
f_T	100–200 MHz - Current-gain bandwidth product; supports switching frequencies up to ~10 MHz with adequate gain margin.
R_JA	200°C/W - Junction-to-ambient thermal resistance; dictates required PCB copper area or heatsink for thermal management.

Pinout & Package

BC373 is housed in a standard TO-92 (Case 29-11) plastic package with axial leads, compatible with through-hole assembly and manual prototyping. The package measures 4.45–5.20 mm (A) × 4.32–5.33 mm (B) × 3.18–4.19 mm (C), with lead pitch of 2.54 mm (P).

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Emitter terminal of Darlington pair	Common emitter node; connects to ground or low-side return path; carries full load current.
2 (Base)	Input control terminal	Drives both internal transistors; requires ~0.25 mA for full saturation at 250 mA collector load.
3 (Collector)	Output current terminal	Connects to load and supply rail; withstands up to 80 V when off; sinks full switched current.

Key Features

Feature	Design Value
High-voltage Darlington architecture	Monolithic NPN-NPN pair enabling 80 V blocking and >100× current gain without external components.
Pb-free TO-92 packaging	RoHS-compliant construction (BC373ZL1G variant); supports lead-free reflow and hand-soldering per J-STD-020.
Wide operating temperature	−55°C to +150°C junction range; validated for industrial and automotive under-hood environments.
Low saturation voltage	V_CE(sat) ≤ 1.1 V ensures <1.1 W conduction loss at 1 A, reducing thermal stress in compact layouts.
Controlled dynamic parameters	Cob = 10–25 pF and f_T = 100–200 MHz allow predictable turn-on/turn-off timing in 1–10 MHz switching circuits.

Applications

Relay Driver Circuits	Lamp Dimming Controls
Use Scenario: Driving 12–24 V electromagnetic relays with coil currents up to 800 mA in PLC I/O modules. IC Role / Device Role / Timing Role: High-gain switch amplifying microcontroller GPIO signals to energize relay coils. Use Value: Eliminates need for discrete base resistors or secondary transistors due to integrated Darlington gain and 80 V V_CEO.	Use Scenario: Phase-angle dimming of incandescent lamps in residential lighting controllers. IC Role / Device Role / Timing Role: Main switching element in TRIAC gate drive or direct AC load switching stage. Use Value: Withstands 80 V peak line transients and delivers 1 A surge current during zero-crossing transitions.
Industrial Motor Starters	Power Supply Enable Switches
Use Scenario: Controlling small DC motors (e.g., 24 V, 500 mA) in factory automation actuators. IC Role / Device Role / Timing Role: Low-side switch interfacing between logic-level controller and motor winding. Use Value: 1.5 W power rating and R_JA = 200°C/W support continuous duty without forced cooling.	Use Scenario: Enabling/disabling auxiliary rails (e.g., 5 V, 12 V) in multi-output AC/DC power supplies. IC Role / Device Role / Timing Role: High-side or low-side enable switch controlled by supervisor IC or microcontroller. Use Value: V_BE(sat) ≤ 2.0 V ensures reliable turn-on even with marginal base drive from 3.3 V logic.

Relay Driver Circuits

Lamp Dimming Controls

Use Scenario: Driving 12–24 V electromagnetic relays with coil currents up to 800 mA in PLC I/O modules.

IC Role / Device Role / Timing Role: High-gain switch amplifying microcontroller GPIO signals to energize relay coils.

Use Value: Eliminates need for discrete base resistors or secondary transistors due to integrated Darlington gain and 80 V V_CEO.

Use Scenario: Phase-angle dimming of incandescent lamps in residential lighting controllers.

IC Role / Device Role / Timing Role: Main switching element in TRIAC gate drive or direct AC load switching stage.

Use Value: Withstands 80 V peak line transients and delivers 1 A surge current during zero-crossing transitions.

Industrial Motor Starters

Power Supply Enable Switches

Use Scenario: Controlling small DC motors (e.g., 24 V, 500 mA) in factory automation actuators.

IC Role / Device Role / Timing Role: Low-side switch interfacing between logic-level controller and motor winding.

Use Value: 1.5 W power rating and R_JA = 200°C/W support continuous duty without forced cooling.

Use Scenario: Enabling/disabling auxiliary rails (e.g., 5 V, 12 V) in multi-output AC/DC power supplies.

IC Role / Device Role / Timing Role: High-side or low-side enable switch controlled by supervisor IC or microcontroller.

Use Value: V_BE(sat) ≤ 2.0 V ensures reliable turn-on even with marginal base drive from 3.3 V logic.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BC372	Higher V_CEO (100 V) but identical package, pinout, and gain range; lower I_C rating (1.0 A same) and same P_D.	Preferred where higher voltage margin is needed (e.g., 48 V industrial buses), otherwise functionally interchangeable.	Select BC372 only if system transient voltages exceed 80 V; BC373 remains optimal for cost-sensitive 24–36 V designs.
MJD127	TO-220 package, 100 V_CEO, 8 A I_C, higher P_D (15 W); not pin-compatible; requires PCB layout change.	Suitable for higher-power loads (>1 A) where TO-92 thermal limits are exceeded.	Choose MJD127 only when BC373's 1.5 W dissipation is insufficient and board space allows TO-220 mounting.

Compared with BC372, BC373 trades 20 V breakdown margin for identical footprint and cost; versus MJD127, it offers TO-92 compatibility and lower drive requirements but cannot scale to >1 A continuous loads without thermal derating.

Availability

BC373 is available at Aetrix Electronics and suitable for relay drivers, lamp dimmers, industrial motor starters, and power supply enable switches requiring stable component supply across extended production lifecycles.

Supply support for BC373 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The BC373 belongs to onsemi's legacy bipolar transistor family designed for robust, cost-effective high-voltage switching in industrial controls, appliance interfaces, and power management subsystems.

FAQ

What is the maximum collector-emitter voltage rating for BC373?

The BC373 has a maximum collector-emitter voltage (V_CEO) rating of 80 Vdc. This value is specified under test condition I_C = 100 µA with base open, and represents the highest voltage the device can block in the off state without entering avalanche breakdown. Exceeding 80 V risks irreversible damage. The BC373ZL1G variant maintains this same rating.

Does BC373 require an external base resistor for microcontroller driving?

Yes - BC373 requires an external base resistor to limit base current and ensure proper saturation. At I_C = 250 mA and I_B = 0.25 mA, a typical 10 kΩ resistor is used with 3.3 V or 5 V GPIO. The BC373 datasheet specifies V_BE(sat) = 1.4–2.0 V, so resistor value must account for that drop to avoid overdriving the base.

Is BC373 pin-compatible with BC372?

Yes - BC373 is fully pin-compatible with BC372: both use TO-92 package with identical pin 1 (emitter), pin 2 (base), pin 3 (collector) assignment and mechanical dimensions. The only functional difference is V_CEO (80 V vs. 100 V); all other electrical characteristics, including h_FE, V_CE(sat), and thermal specs, are aligned per datasheet.

What is the thermal resistance junction-to-ambient for BC373?

The BC373 has a thermal resistance junction-to-ambient (R_JA) of 200°C/W when mounted on a standard FR-4 PCB with minimal copper. This value assumes no heatsink and natural convection; actual R_JA improves with added copper pour or airflow. Derating begins above 25°C ambient at 12 mW/°C.

Can BC373 be used in linear amplifier configurations?

BC373 can operate in linear mode but is optimized for switching. Its f_T = 100–200 MHz and NF = 2.0 dB at 1 kHz support low-frequency analog amplification, yet h_FE variation across I_C (see Figure 1) and thermal drift limit precision. For dedicated amplifiers, onsemi's BC548 or MMBT3904 are better suited; BC373 is recommended for saturated-switch applications.

BC373 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-226-3, TO-92-3 Long Body

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN - Darlington

Current - Collector (Ic) (Max):: 1 A

Voltage - Collector Emitter Breakdown (Max):: 80 V

Vce Saturation (Max) @ Ib, Ic:: 1.1V @ 250µA, 250mA

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

DC Current Gain (hFE) (Min) @ Ic, Vce:: 10000 @ 100mA, 5V

Power - Max:: 625 mW

Frequency - Transition:: 200MHz

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

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92 (TO-226)

BC373 FAQ

1.How can I place an order for BC373 through Aetrix?

Please submit a Request for Quotation (RFQ) for BC373 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 BC373 reliable?

The price and inventory of BC373 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC373 is usually 5 days.

3.What payment methods are accepted for BC373?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC373 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BC373?

BC373 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BC373 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 BC373?

For technical support, including BC373 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC373 requirements.

6.How does Aetrix verify that BC373 is sourced from the original manufacturer or authorized distributors?

All BC373 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 BC373 meets industry standards.

7.What is the process for return or replacement of BC373?

All BC373 units undergo pre-shipment inspection (PSI). If there is an issue with BC373, 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 BC373 part is unused and in its original packaging.

Return procedure for BC373:

1.Submit a request within 90 days.

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

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