onsemi BF393G

Overview

BF393G from onsemi is an NPN silicon high-voltage transistor rated for 300 V_CEO, 500 mA continuous collector current, and 1.5 W total device dissipation at T_C = 25°C. It operates across −55°C to +150°C junction temperature and is used in flyback converter switching, relay drivers, and HV signal amplification stages where breakdown voltage and thermal robustness are critical.

For engineers reviewing the BF393G datasheet, pinout, applications, or equivalent options, key selection criteria include verified V_CEO/V_CBO = 300 V, h_FE = 25–40 at I_C = 1–10 mA, f_T = 50 MHz, R_JA = 200°C/W, and TO-92 package compatibility with legacy through-hole layouts.

Technical Context

The BF393G implements a planar epitaxial NPN structure optimized for high-voltage switching with low leakage (I_CBO ≤ 0.1 A at V_CB = 200 V) and stable DC current gain across temperature. Its safe operating area (SOA) is defined up to second breakdown limits under pulsed conditions, supporting reliable operation in inductive load switching.

It features V_BE(sat) ≤ 2.0 V and V_CE(sat) ≤ 2.0 V at I_C/I_B = 10, enabling efficient saturation drive in discrete switch configurations. The f_T = 50 MHz and C_re ≤ 2.0 pF support moderate-frequency switching up to several MHz without excessive capacitive loading.

Key Specifications

Pinout & Package

BF393G is housed in a Pb-free TO-92 package (Case 29-11, Style 1), with standardized lead spacing (2.54 mm pitch), axial lead orientation, and JEDEC-compliant mechanical dimensions including 4.45–5.20 mm height and 2.42–2.66 mm width.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage NPN transistor applications.

Compared with MPSA42 and 2N5551, BF393G offers tighter h_FE range (25–40) and guaranteed 300 V rating - simplifying base drive design and eliminating need for voltage derating in 230 VAC environments.

Availability

BF393G is available at Aetrix Electronics and suitable for relay driver circuits, flyback converter switches, and high-voltage sensor interfaces requiring stable component supply across industrial, energy metering, and appliance OEM programs.

Supply support for BF393G 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, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The BF393G belongs to onsemi's high-voltage bipolar transistor product line, designed specifically for robust switching and amplification in mains-referenced equipment where reliability under sustained HV stress is essential.

FAQ

What is the maximum collector-emitter voltage rating for BF393G?

The BF393G has a guaranteed minimum V_(BR)CEO of 300 Vdc at I_C = 1.0 mAdc and I_B = 0. This rating is validated per onsemi's test conditions and defines the absolute upper limit for safe DC operation between collector and emitter terminals. Exceeding this voltage risks irreversible avalanche breakdown. The BF393G must be applied with appropriate voltage derating margins in real-world circuits with transients or ringing.

Does BF393G support Pb-free soldering processes?

Yes, BF393G is explicitly marked as Pb-free in its ordering code (suffix "G") and conforms to RoHS Directive 2011/65/EU. It supports standard lead-free reflow profiles up to 260°C peak temperature, as documented in onsemi's Soldering and Mounting Techniques Reference Manual (SOLDERRM/D). The TO-92 package is qualified for both wave and reflow soldering without lead finish degradation.

What is the typical DC current gain (hFE) of BF393G at 10 mA collector current?

The BF393G exhibits h_FE = 25–40 at I_C = 10 mAdc and V_CE = 10 Vdc, per its official electrical characteristics table. This range is tighter than many general-purpose HV transistors, reducing base drive design uncertainty. At 1 mA, h_FE remains within the same band, confirming stable gain behavior across its rated operating region - a key advantage of the BF393G in precision biasing applications.

Can BF393G replace BF393 in existing designs?

Yes, BF393G is a direct drop-in replacement for BF393, sharing identical TO-92 package dimensions, pinout (Emitter-Base-Collector), and electrical specifications. The "G" suffix denotes Pb-free construction only; all parametric performance, thermal ratings, and safe operating area curves remain unchanged. No PCB or schematic modifications are required when upgrading from BF393 to BF393G.

What thermal resistance values apply to BF393G in TO-92 package?

The BF393G has R_JA = 200°C/W (junction-to-ambient, free-air) and R_JC = 83.3°C/W (junction-to-case). These values assume standard JEDEC test conditions: 1 in² 2-oz copper pad, no airflow. In practice, R_JA improves significantly with added copper area or forced convection. For example, doubling the copper area typically reduces R_JA by ~25%, directly extending safe continuous current capability of the BF393G.