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

onsemi BD681

Name: BD681
Brand: onsemi
SKU: BD681
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD681

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-225AA, TO-126-3

Datasheet:: BD681.pdf

Description:: TRANS NPN DARL 100V 4A TO-126

Quantity:: RFQ Add To RFQ list

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Inventory:2,022

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Product details

Overview

BD681 from onsemi is a plastic medium-power silicon NPN Darlington transistor rated for 100 V_CEO, 4.0 A collector current, and 40 W total device dissipation at T_C = 25°C, with DC current gain (h_FE) ≥750 at I_C = 1.5 A and V_CE = 3.0 V - used as output devices in complementary general-purpose amplifier applications.

For engineers reviewing the BD681 datasheet, pinout, applications, or equivalent options, key selection criteria include its 100 V_CEO rating, TO-225 package thermal resistance of 3.13°C/W, Darlington configuration enabling high-current switching with low base drive, and RoHS-compliant Pb-free construction.

Technical Context

The BD681 is a monolithic NPN Darlington pair with integrated base-emitter resistor network optimized for linear and switching amplifier output stages. Its structure delivers high h_FE (≥750) and low V_BE(on) (2.5 V) while maintaining safe operating area limits up to 100 V_CE and 4 A_C.

It operates across –55°C to +150°C junction temperature range and features complementary pairing with PNP counterparts BD680/BD680A/BD682. Thermal derating begins above 25°C at 0.32 W/°C, and secondary breakdown limits define its dynamic safe operating area.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	100 Vdc - maximum collector-emitter voltage before breakdown; enables use in high-voltage amplifier rails and motor control outputs.
I_C	4.0 Adc - continuous collector current capability; supports medium-power load driving without external heat sinking at moderate duty cycles.
P_D @ T_C = 25°C	40 W - total device power dissipation limit; requires thermal management when operating near max ratings.
h_FE	≥750 @ I_C = 1.5 A, V_CE = 3.0 V - high DC current gain reduces required base drive current, simplifying driver stage design.
R_JC	3.13 °C/W - junction-to-case thermal resistance; informs heatsink sizing for reliable operation under sustained load.
V_CE(sat)	2.5 Vdc @ I_C = 1.5 A, I_B = 30 mA - saturation voltage determines conduction loss and thermal load in switching applications.

Pinout & Package

BD681 is housed in a TO-225 package (Case 77-09, Style 1), featuring three electrically active terminals and a metal tab connected to the collector. The package provides mechanical robustness and thermal path via the backside tab.

Pin/Terminal	Circuit Role	Design Meaning
1	Emitter	Main emitter terminal of the Darlington pair; referenced to ground or low-side return in common-emitter configurations.
2, 4	Collector	Shared collector connection (pins 2 and 4 are internally tied); connects to high-side load or supply rail; tab is electrically identical.
3	Base	Input control terminal; drives both internal transistors; requires current-limiting resistor in series for proper biasing.

Key Features

Feature	Design Value
High DC current gain (h_FE ≥750)	Reduces base drive requirements by >10× versus single bipolar transistors, easing interface with logic-level controllers.
Monolithic Darlington construction	Ensures matched transistor characteristics and stable gain over temperature without discrete assembly tolerances.
100 V_CEO rating	Supports operation in 80–100 V DC bus systems such as industrial power supplies and audio amplifiers with elevated rail voltages.
Pb-free, RoHS-compliant packaging	Meets global environmental compliance requirements without compromising thermal or electrical performance.

Applications

Audio Power Amplifier Output Stage	DC Motor Driver Output Stage
Use Scenario: Final push-pull output stage in Class AB audio amplifiers delivering 20–50 W into 4–8 Ω loads. IC Role / Device Role / Timing Role: NPN Darlington output transistor providing high-current, low-distortion signal amplification. Use Value: High h_FE minimizes driver complexity; 100 V_CEO accommodates ±45 V rails; TO-225 package allows direct mounting to heatsinks.	Use Scenario: Unidirectional H-bridge half-bridge or linear speed controller for 24–72 V DC brushed motors. IC Role / Device Role / Timing Role: High-current switching element controlling motor current direction and magnitude in analog or PWM-driven topologies. Use Value: 4.0 A I_C and 40 W P_D support continuous 30–40 W motor drive; V_CE(sat) = 2.5 V limits conduction loss at rated current.
Industrial Linear Regulator Pass Element	Relay/Solenoid Driver Interface
Use Scenario: Series pass transistor in adjustable linear regulators powering sensitive analog circuitry from unregulated 30–90 V inputs. IC Role / Device Role / Timing Role: Voltage-controlled current source regulating output voltage via feedback loop. Use Value: High V_CEO withstands input transients; low V_BE(on) ensures stable biasing; SOA curve supports safe linear-mode operation.	Use Scenario: Direct-drive interface between microcontroller GPIO and 24–48 V industrial relays or solenoids drawing ≤3 A. IC Role / Device Role / Timing Role: Switching interface transistor enabling logic-level control of high-voltage/high-current loads. Use Value: 750 h_FE permits direct MCU drive with minimal base resistor; built-in Darlington gain eliminates need for pre-driver stage.

Audio Power Amplifier Output Stage

DC Motor Driver Output Stage

Use Scenario: Final push-pull output stage in Class AB audio amplifiers delivering 20–50 W into 4–8 Ω loads.

IC Role / Device Role / Timing Role: NPN Darlington output transistor providing high-current, low-distortion signal amplification.

Use Value: High h_FE minimizes driver complexity; 100 V_CEO accommodates ±45 V rails; TO-225 package allows direct mounting to heatsinks.

Use Scenario: Unidirectional H-bridge half-bridge or linear speed controller for 24–72 V DC brushed motors.

IC Role / Device Role / Timing Role: High-current switching element controlling motor current direction and magnitude in analog or PWM-driven topologies.

Use Value: 4.0 A I_C and 40 W P_D support continuous 30–40 W motor drive; V_CE(sat) = 2.5 V limits conduction loss at rated current.

Industrial Linear Regulator Pass Element

Relay/Solenoid Driver Interface

Use Scenario: Series pass transistor in adjustable linear regulators powering sensitive analog circuitry from unregulated 30–90 V inputs.

IC Role / Device Role / Timing Role: Voltage-controlled current source regulating output voltage via feedback loop.

Use Value: High V_CEO withstands input transients; low V_BE(on) ensures stable biasing; SOA curve supports safe linear-mode operation.

Use Scenario: Direct-drive interface between microcontroller GPIO and 24–48 V industrial relays or solenoids drawing ≤3 A.

IC Role / Device Role / Timing Role: Switching interface transistor enabling logic-level control of high-voltage/high-current loads.

Use Value: 750 h_FE permits direct MCU drive with minimal base resistor; built-in Darlington gain eliminates need for pre-driver stage.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MJE803	Same V_CEO = 100 V, I_C = 4 A, but h_FE min = 500 (vs. BD681's 750); TO-225 package, identical pinout.	Slightly lower gain may require increased base drive; otherwise interchangeable in linear and switching roles.	Preferred where cost sensitivity outweighs marginal gain advantage; verify base current margin in high-temp operation.
BD681G (same part, alternate marking)	No electrical or mechanical difference; "G" suffix denotes Pb-free version per onsemi ordering convention.	Identical functional behavior and qualification; only distinction is RoHS compliance documentation and marking.	Select BD681G for new designs requiring documented Pb-free compliance; legacy BD681 may be available in limited stock.

Compared with MJE803 and BD681G, the BD681 offers higher guaranteed h_FE for reduced base drive burden, while BD681G provides identical performance with formal RoHS certification - making BD681 optimal for gain-critical linear amplifiers and BD681G preferred for compliant production builds.

Availability

BD681 is available at Aetrix Electronics and suitable for audio power amplifiers, DC motor drivers, industrial linear regulators, and relay/solenoid interfaces requiring stable component supply and long-term industrial availability.

Supply support for BD681 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 management, analog, sensing, and connectivity solutions for automotive, industrial, and cloud infrastructure markets.

The BD681 belongs to onsemi's plastic medium-power Darlington transistor family designed specifically for complementary output-stage applications in general-purpose amplifiers and industrial control systems.

FAQ

What is the maximum collector-emitter voltage rating for BD681?

The BD681 has a maximum collector-emitter voltage (V_CEO) rating of 100 Vdc, verified per onsemi's datasheet under test condition I_C = 50 mA and I_B = 0. This rating defines the upper limit for safe DC operation in amplifier output stages and switching circuits. Exceeding this voltage risks avalanche breakdown and permanent device failure. Always maintain design margin below 100 V in real-world applications with transient suppression.

Is BD681 pin-compatible with BD679G or BD677G?

Yes, BD681 shares the same TO-225 package (Case 77-09, Style 1) and identical pinout (Emitter=Pin1, Collector=Pin2&4, Base=Pin3) with BD679G and BD677G. However, BD681 differs in V_CEO (100 V vs. 80 V and 60 V respectively), so substitution requires verification of voltage headroom in the target circuit. Electrical compatibility is not automatic despite mechanical equivalence.

Does BD681 require a heatsink in normal operation?

BD681 can operate without a heatsink at low duty cycles or ambient temperatures below 40°C when dissipating ≤10 W. However, at full 40 W rating or continuous 4 A conduction, a heatsink is mandatory due to its R_JC of 3.13°C/W and maximum T_J of +150°C. Thermal design must account for case-to-heatsink interface resistance and ambient airflow to prevent thermal runaway.

What is the DC current gain (h_FE) specification for BD681?

The BD681 guarantees h_FE ≥750 when tested at I_C = 1.5 A and V_CE = 3.0 V, per onsemi's Electrical Characteristics table. This high gain is intrinsic to its monolithic Darlington architecture and enables low-base-current drive - critical for interfacing with microcontrollers or op-amp drivers without additional gain stages.

Is BD681 suitable for switching applications?

Yes, BD681 is qualified for both linear and switching use, with specified V_CE(sat) = 2.5 V at I_C = 1.5 A and I_B = 30 mA. Its Darlington structure introduces slower turn-off due to stored charge, limiting practical switching frequency to ≤10 kHz. For higher-frequency PWM, consider adding Baker clamp or base-turnoff assist circuitry to improve response.

BD681 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-225AA, TO-126-3

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN - Darlington

Current - Collector (Ic) (Max):: 4 A

Voltage - Collector Emitter Breakdown (Max):: 100 V

Vce Saturation (Max) @ Ib, Ic:: 2.5V @ 30mA, 1.5A

Current - Collector Cutoff (Max):: 500µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 750 @ 1.5A, 3V

Power - Max:: 40 W

Frequency - Transition:: -

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

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-126

BD681 FAQ

1.How can I place an order for BD681 through Aetrix?

Please submit a Request for Quotation (RFQ) for BD681 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 BD681 reliable?

The price and inventory of BD681 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD681 is usually 5 days.

3.What payment methods are accepted for BD681?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD681 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD681?

BD681 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD681 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 BD681?

For technical support, including BD681 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD681 requirements.

6.How does Aetrix verify that BD681 is sourced from the original manufacturer or authorized distributors?

All BD681 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 BD681 meets industry standards.

7.What is the process for return or replacement of BD681?

All BD681 units undergo pre-shipment inspection (PSI). If there is an issue with BD681, 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 BD681 part is unused and in its original packaging.

Return procedure for BD681:

1.Submit a request within 90 days.

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

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