onsemi BD179

Overview

BD179 from STMicroelectronics is an NPN silicon power transistor in SOT-32 (TO-126) package, designed for general-purpose switching with 3 A continuous collector current, 80 V V_CEO, and low 0.8 V V_CE(sat) at I_C = 1 A / I_B = 0.1 A. It delivers high DC current gain (h_FE ≥ 40 at I_C = 150 mA) and operates up to 150 °C junction temperature, commonly used in linear power supplies and relay drivers.

For engineers reviewing the BD179 datasheet, BD179 pinout, BD179 application, or BD179 equivalent, key selection criteria include saturation voltage under specified drive conditions, safe operating area (SOA) limits at elevated case temperatures, thermal derating behavior, and compatibility with non-inductive resistive load switching circuits per Figure 11.

Technical Context

The BD179 employs Planar technology with "Base Island" layout to achieve high current gain and low saturation voltage simultaneously. Its absolute maximum ratings define a 30 W total dissipation at T_case = 25 °C, with thermal derating above that temperature per Figure 3.

Electrical characteristics are specified at T_case = 25 °C unless noted; pulsed test conditions (e.g., 300 µs, ≤1.5% duty cycle) apply to parameters like V_CEO(sus) and switching time. The device exhibits I_CBO ≤ 0.1 mA at V_CB = 80 V and h_FE = 15 typical at I_C = 1 A.

Key Specifications

Pinout & Package

SOT-32 (TO-126) package: three-terminal through-hole plastic power package with tab-connected collector, standardized mechanical dimensions per page 7 of datasheet (e.g., e = 2.04–2.54 mm pitch, L = 15.3–16 mm length).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BD179, BD180 serves complementary circuit roles rather than substitution, while TIP31C trades higher saturation voltage and variable gain for broader voltage headroom-making BD179 preferable for efficiency-critical linear or switching applications demanding consistent drive characteristics.

Availability

BD179 is available at Aetrix Electronics and suitable for linear power supply regulation, DC motor on/off control, relay driver circuits, and high-current LED dimming requiring stable component supply and long-term industrial availability.

Supply support for BD179 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in automotive, industrial, and power discrete solutions with broad IP and manufacturing scale.

The BD179 belongs to ST's legacy bipolar power transistor family, engineered for cost-effective, thermally robust switching in industrial control and power conversion where reliability under sustained thermal stress is essential.

FAQ

Is BD179 suitable for PWM motor control?

No-BD179 is optimized for linear and low-frequency switching (≤1 kHz), not high-speed PWM. Its resistive-load switching time (Figure 9) exceeds 1 µs for turn-on/turn-off, and SOA limitations restrict safe operation under inductive flyback without snubbers. For PWM, MOSFETs with nanosecond switching and avalanche-rated SOA are recommended.

What is the thermal resistance R_thJC for BD179?

R_thJC is not explicitly specified in the datasheet, but the 30 W P_TOT rating at T_case = 25 °C implies R_thJC ≈ 0.83 °C/W. This value is derived from ΔT = P × R_thJC, where ΔT = 150 °C − 25 °C = 125 °C. Actual thermal performance depends on PCB copper area and mounting pressure to heatsink.

Can BD179 replace BD139 in existing designs?

Yes, with verification: BD179 shares same SOT-32 package and pinout, but offers higher I_C (3 A vs. 1.5 A), higher V_CEO (80 V vs. 80 V), and lower V_CE(sat) (0.8 V vs. 0.5 V typ.). Base drive must be rechecked-BD179's h_FE is lower at high current, requiring increased I_B for full saturation.

Does BD179 have built-in protection features?

No-BD179 is a bare silicon NPN transistor with no integrated protection. External components are required for safe operation: base current limiting resistor, collector snubber network for inductive loads, and heatsink with thermal cutoff if ambient exceeds 60 °C. Safe operating area (Figure 2) must be strictly observed.