onsemi BD679

Overview

BD679 from onsemi is a plastic medium-power silicon NPN Darlington transistor in TO-225 package, rated for 80 V_CEO, 4.0 A collector current, and 40 W power dissipation at T_C = 25°C. It delivers high DC current gain (h_FE ≥ 750 at I_C = 1.5 A), low V_CE(sat) ≤ 2.5 V, and operates across –55°C to +150°C junction temperature - used as output stage in audio amplifiers and motor drivers.

For engineers reviewing the BD679 datasheet, pinout, applications, or equivalent options, key selection criteria include its 80 V breakdown rating, Darlington topology enabling high-current switching with low base drive, thermal resistance of 3.13°C/W, and Pb-free TO-225 packaging compliant with RoHS.

Technical Context

The BD679 integrates two monolithic NPN transistors in Darlington configuration, providing cascaded current amplification where the emitter of the first stage drives the base of the second. Its design supports linear and switching operation with guaranteed h_FE ≥ 750 at I_C = 1.5 A and V_CE = 3.0 V, and V_BE(on) = 2.5 V under same conditions.

It features complementary pairing with PNP counterparts BD676/676A/678/678A/680/680A/682, and shares electrical equivalence with MJE802. Thermal derating begins above 25°C at 0.32 W/°C, and safe operating area is bounded by bonding wire limits, secondary breakdown, and thermal constraints.

Key Specifications

Pinout & Package

BD679 is housed in TO-225 package (Case 77-09, Style 1), with metal tab electrically connected to collector. Package dimensions: 10.6–11.1 mm D × 7.4–7.8 mm E × 14.5–16.63 mm L; lead pitch 2.54 mm; Pb-free "G" suffix denotes RoHS compliance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJE802 and BD679AG, the BD679 provides identical core Darlington functionality and TO-225 mechanical fit, but differs in test condition emphasis (1.5 A vs. 2.0 A) and manufacturer branding - all three support drop-in use in amplifier output, relay, and motor control circuits.

Availability

BD679 is available at Aetrix Electronics and suitable for audio amplifier output stages, DC motor drivers, and relay interface circuits requiring stable component supply and long-term industrial availability.

Supply support for BD679 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 IoT applications.

The BD679 belongs to onsemi's plastic medium-power Darlington transistor family, engineered for reliable high-current amplification and switching in cost-sensitive industrial and consumer systems where thermal robustness and gain consistency are critical.

FAQ

What is the maximum collector-emitter voltage rating for BD679?

The BD679 has a maximum collector-emitter voltage (V_CEO) rating of 80 Vdc, verified under test condition I_C = 50 mA and I_B = 0. This rating defines the absolute upper limit for voltage applied between collector and emitter before breakdown occurs. Operating BD679 above this voltage risks irreversible damage, even momentarily. Designers must maintain at least 20% margin below 80 V in practical circuits to accommodate transients and tolerances.

Is BD679 pin-compatible with BD679AG?

Yes, BD679 and BD679AG share identical TO-225 package (Case 77-09, Style 1), pinout (Emitter=1, Collector=2&4, Base=3), and mechanical footprint. The "A" suffix denotes tighter test conditions for h_FE and V_CE(sat) at I_C = 2.0 A rather than 1.5 A, but both variants are electrically and physically interchangeable in PCB layouts. BD679AG is not discontinued and remains a valid alternative for BD679 in new designs.

What is the thermal resistance junction-to-case for BD679?

The BD679 has a thermal resistance junction-to-case (R_JC) of 3.13°C/W, measured under standard test conditions. This value quantifies how effectively heat transfers from the silicon die to the metal tab, which is electrically connected to pins 2 and 4 (collector). When mounted to a heatsink with proper thermal interface material, this R_JC enables accurate junction temperature estimation using T_J = T_C + (P_D × 3.13), where T_C is case temperature.

Does BD679 require a heatsink in typical operation?

Yes, BD679 requires a heatsink for any sustained power dissipation above ~5 W. With a maximum P_D of 40 W at T_C = 25°C and R_JC = 3.13°C/W, junction temperature rises rapidly without thermal management. For example, at 10 W dissipation and 25°C ambient, even with modest heatsink R_CA = 10°C/W, T_J exceeds 100°C. The BD679 datasheet mandates heatsinking for reliability in all applications exceeding brief pulse operation.

What is the DC current gain (h_FE) specification for BD679?

The BD679 guarantees a minimum DC current gain (h_FE) of 750 when tested at I_C = 1.5 A and V_CE = 3.0 V, per onsemi's official datasheet. This high gain is intrinsic to its monolithic Darlington structure and enables efficient base drive - for instance, only ~2 mA base current is needed to sustain 1.5 A collector current. Actual h_FE may exceed 1000 at lower currents but must be designed to worst-case 750 for robustness.