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

onsemi BD678

Name: BD678
Brand: onsemi
SKU: BD678
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD678

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BD678.pdf

Description:: TRANS PNP DARL 60V 4A TO-126

Quantity:: RFQ Add To RFQ list

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Inventory:2,508

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Product details

Overview

BD678 from onsemi is a plastic medium-power silicon PNP Darlington transistor designed for complementary general-purpose amplifier output stages. It features 60 V_CEO, 4.0 A collector current, 40 W power dissipation at T_C = 25 °C, 750 minimum DC current gain (h_FE), and TO-225 package with emitter-base voltage rating of 5.0 V. It is used in linear audio amplifiers and motor drive output stages.

For engineers reviewing the BD678 datasheet, pinout, applications, or equivalent options, key selection considerations include its PNP Darlington topology, 60 V breakdown rating, thermal resistance of 3.13 °C/W, safe operating area limits at elevated case temperatures, and compatibility with complementary NPN devices like BD677/BD677A.

Technical Context

The BD678 operates as a monolithic PNP Darlington pair with integrated base-emitter resistor network absent - requiring external base drive control. Its high h_FE (≥750 at I_C = 1.5 A) enables low base current drive while maintaining saturation voltage ≤2.5 V at I_C = 1.5 A / I_B = 30 mA.

It is thermally rated for junction temperatures from −55 °C to +150 °C and exhibits secondary breakdown-limited SOA at high V_CE, with derating to zero power at T_C = 150 °C per the 0.32 W/°C slope above 25 °C.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	60 Vdc - Maximum collector-emitter voltage before breakdown under open-base conditions; defines upper rail limit in linear amplifier or switching applications.
I_C	4.0 Adc - Continuous collector current rating; sets maximum load-handling capability in output stage designs.
P_D @ T_C = 25 °C	40 W - Total device power dissipation at case temperature 25 °C; requires heatsinking for sustained operation.
h_FE	≥750 - Minimum DC current gain at I_C = 1.5 A, V_CE = 3.0 V; reduces required base drive current in driver circuits.
V_CE(sat)	≤2.5 Vdc - Collector-emitter saturation voltage at I_C = 1.5 A, I_B = 30 mA; determines conduction loss and thermal load in saturated switching.
R_JC	3.13 °C/W - Junction-to-case thermal resistance; directly impacts heatsink sizing for thermal management.

Pinout & Package

BD678 is housed in a TO-225 package (Case 77−09, Style 1), featuring three leads with tab-connected collector (pins 2 and 4), base (pin 3), and emitter (pin 1). The metal tab is electrically connected to the collector.

Pin/Terminal	Circuit Role	Design Meaning
1	Emitter	Main current exit path; referenced to base for biasing; isolated from heatsink when insulated mounting is used.
2, 4	Collector	Common collector node tied to metal tab; must be electrically isolated from chassis unless circuit design permits common-collector grounding.
3	Base	Control input for Darlington pair; requires current-limited drive due to high h_FE and absence of internal base resistor.

Key Features

Feature	Design Value
High DC current gain	h_FE ≥ 750 enables microcontroller-level base drive without additional pre-driver stages.
Monolithic Darlington construction	Single-die integration ensures matched transistor characteristics and stable gain across temperature.
Complementary pairing	Designed to match BD677/BD677A NPN counterparts for push-pull amplifier symmetry and crossover distortion reduction.
Pb-Free and RoHS compliant	Meets environmental compliance requirements for industrial and consumer PCB assembly without lead-free reflow concerns.

Applications

Audio Power Amplifier Output Stage	DC Motor H-Bridge Low-Side Driver
Use Scenario: Final output stage in Class AB linear audio amplifiers delivering up to 20 W into 8 Ω loads. IC Role / Device Role / Timing Role: PNP Darlington output transistor providing high-current sinking capability and low saturation loss during negative half-cycle conduction. Use Value: High h_FE minimizes driver-stage complexity; 60 V rating supports ±25 V rails; TO-225 package allows direct bolt-on heatsinking.	Use Scenario: Low-side switch in brushed DC motor control circuits with PWM frequencies below 20 kHz. IC Role / Device Role / Timing Role: Saturated-switching PNP Darlington controlling motor current return path in half-bridge configurations. Use Value: 4.0 A rating handles peak stall currents; 2.5 V_CE(sat) limits conduction loss; thermal derating curve supports intermittent duty cycling.
Linear Voltage Regulator Pass Element	Relay/LED Load Driver
Use Scenario: Series pass transistor in adjustable linear regulators supplying up to 3 A at ≤50 V differential. IC Role / Device Role / Timing Role: High-gain series regulator element dissipating excess voltage as heat while maintaining precise output regulation. Use Value: 40 W dissipation capacity and 3.13 °C/W R_JC enable stable operation with moderate heatsinks; 150 °C max junction temperature supports industrial ambient conditions.	Use Scenario: High-current interface between microcontroller GPIO and inductive or high-brightness LED loads. IC Role / Device Role / Timing Role: Switching Darlington buffer isolating logic-level signals from 2–4 A load currents. Use Value: Eliminates need for discrete BJT staging; 5.0 V_EB rating protects against reverse-base breakdown during inductive kickback.

Audio Power Amplifier Output Stage

DC Motor H-Bridge Low-Side Driver

Use Scenario: Final output stage in Class AB linear audio amplifiers delivering up to 20 W into 8 Ω loads.

IC Role / Device Role / Timing Role: PNP Darlington output transistor providing high-current sinking capability and low saturation loss during negative half-cycle conduction.

Use Value: High h_FE minimizes driver-stage complexity; 60 V rating supports ±25 V rails; TO-225 package allows direct bolt-on heatsinking.

Use Scenario: Low-side switch in brushed DC motor control circuits with PWM frequencies below 20 kHz.

IC Role / Device Role / Timing Role: Saturated-switching PNP Darlington controlling motor current return path in half-bridge configurations.

Use Value: 4.0 A rating handles peak stall currents; 2.5 V_CE(sat) limits conduction loss; thermal derating curve supports intermittent duty cycling.

Linear Voltage Regulator Pass Element

Relay/LED Load Driver

Use Scenario: Series pass transistor in adjustable linear regulators supplying up to 3 A at ≤50 V differential.

IC Role / Device Role / Timing Role: High-gain series regulator element dissipating excess voltage as heat while maintaining precise output regulation.

Use Value: 40 W dissipation capacity and 3.13 °C/W R_JC enable stable operation with moderate heatsinks; 150 °C max junction temperature supports industrial ambient conditions.

Use Scenario: High-current interface between microcontroller GPIO and inductive or high-brightness LED loads.

IC Role / Device Role / Timing Role: Switching Darlington buffer isolating logic-level signals from 2–4 A load currents.

Use Value: Eliminates need for discrete BJT staging; 5.0 V_EB rating protects against reverse-base breakdown during inductive kickback.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MJE701	Identical V_CEO (60 V), I_C (4.0 A), and h_FE (≥750); same TO-225 package; Pb-Free version designated MJE701G.	No functional difference in amplifier or switching roles; identical safe operating area and thermal characteristics.	Select MJE701 when sourcing from legacy distributor stock or where onsemi BD678G availability is constrained.
BD678AG	Same V_CEO, I_C, and package; differs only in test condition for h_FE (measured at I_C = 2.0 A vs. 1.5 A) and V_CE(sat) (2.8 V vs. 2.5 V).	Slightly higher saturation voltage increases conduction loss at full load; otherwise interchangeable in most linear and switching applications.	Prefer BD678AG only if design specifically targets higher-current h_FE validation points or requires qualification under I_C = 2.0 A test conditions.

Compared with MJE701 and BD678AG, the BD678 offers marginally lower V_CE(sat) at 1.5 A, making it preferable for efficiency-critical linear amplifier outputs, while BD678AG provides verified gain at higher current and MJE701 serves as a cross-manufacturer drop-in alternative with identical electrical and mechanical specs.

Availability

BD678 is available at Aetrix Electronics and suitable for audio power amplifiers, DC motor drivers, linear voltage regulators, and relay/LED load interfaces requiring stable component supply and long-term industrial availability.

Supply support for BD678 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 manufacturer specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and IoT applications.

The BD678 belongs to onsemi's plastic medium-power PNP Darlington transistor family, engineered for complementary output stage use in general-purpose linear amplifiers and robust switching applications demanding high current gain and thermal reliability.

FAQ

What is the maximum collector-emitter voltage rating for BD678?

The BD678 has a maximum collector-emitter voltage (V_CEO) rating of 60 Vdc, specified under open-base conditions with I_C = 50 mA. This rating defines the absolute upper limit for voltage applied between collector and emitter before breakdown occurs, and must not be exceeded in circuit design even under transient conditions. Exceeding this value risks permanent device failure.

Is BD678 pin-compatible with BD678AG?

Yes, BD678 and BD678AG share identical pinout, package (TO-225), and terminal assignments - emitter at pin 1, collector at pins 2 and 4, base at pin 3. They differ only in test conditions for h_FE and V_CE(sat), not physical layout or connection. BD678 can be substituted for BD678AG in existing PCBs without modification, though system-level verification of saturation voltage at target load current is recommended.

What is the thermal resistance junction-to-case for BD678?

The BD678 has a thermal resistance junction-to-case (R_JC) of 3.13 °C/W, measured under standard mounting conditions. This value quantifies how effectively heat transfers from the silicon die to the case surface, directly influencing heatsink selection. For example, at 20 W dissipation, a 62.6 °C temperature rise from junction to case results - requiring sufficient heatsink thermal resistance to maintain T_J ≤ 150 °C.

Does BD678 include an internal base-emitter resistor?

No, the BD678 does not incorporate an internal base-emitter resistor. It is a bare Darlington transistor requiring externally controlled base current. Unlike digital transistors (e.g., MMDT series), BD678 relies on discrete base drive circuitry - such as a current-limiting resistor or dedicated driver IC - to establish proper bias and prevent thermal runaway during conduction.

How does BD678 compare to MJE700 in terms of electrical specifications?

The BD678 and MJE700 are functionally equivalent PNP Darlington transistors with identical V_CEO (60 V), I_C (4.0 A), h_FE (≥750), and TO-225 packaging. Both meet RoHS and Pb-Free requirements. Their electrical parameters align within datasheet tolerances, and they are listed as equivalents in onsemi documentation. No performance or reliability differences are specified between BD678 and MJE700 in published data.

BD678 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

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

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: PNP - Darlington

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

Voltage - Collector Emitter Breakdown (Max):: 60 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

BD678 FAQ

1.How can I place an order for BD678 through Aetrix?

Please submit a Request for Quotation (RFQ) for BD678 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 BD678 reliable?

The price and inventory of BD678 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD678 is usually 5 days.

3.What payment methods are accepted for BD678?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD678 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD678?

BD678 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD678 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 BD678?

For technical support, including BD678 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD678 requirements.

6.How does Aetrix verify that BD678 is sourced from the original manufacturer or authorized distributors?

All BD678 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 BD678 meets industry standards.

7.What is the process for return or replacement of BD678?

All BD678 units undergo pre-shipment inspection (PSI). If there is an issue with BD678, 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 BD678 part is unused and in its original packaging.

Return procedure for BD678:

1.Submit a request within 90 days.

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

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