onsemi BF393

Overview

BF393 from onsemi is an NPN silicon high-voltage transistor designed for switching and amplification in off-line power supplies, relay drivers, and horizontal deflection circuits. It supports V_CEO = 300 V, I_C = 500 mA, P_D = 625 mW at T_A = 25°C, and f_T = 50 MHz, operating across −55°C to +150°C junction temperature range.

For engineers reviewing the BF393 datasheet, pinout, applications, or equivalent options, key selection criteria include high-voltage blocking capability, DC current gain (h_FE = 25–40), saturation voltage performance (V_CE(sat) ≤ 2.0 V), thermal resistance (R_JA = 200°C/W), and TO-92 package compatibility with legacy through-hole layouts.

Technical Context

The BF393 operates as a general-purpose NPN bipolar junction transistor optimized for high-voltage switching where robust breakdown margins are required. Its V_CEO and V_CBO ratings both reach 300 Vdc, enabling use in flyback snubber networks and line-voltage interface stages without external clamping.

It delivers h_FE ≥ 25 at I_C = 1.0 mA and ≥ 40 at I_C = 10 mA under V_CE = 10 Vdc bias, with V_CE(sat) ≤ 2.0 V at I_C/I_B = 10, supporting reliable turn-on in low-duty-cycle pulse applications such as CRT horizontal output drivers.

Key Specifications

Pinout & Package

Package: TO-92 (Case 29-11, Style 1), Pb-free, through-hole compatible. Dimensions per ANSI Y14.5M-1982; lead pitch 2.54 mm, body height 4.45–5.20 mm.

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, the BF393 offers the most consistent 300 V blocking capability among TO-92 NPN transistors, making it preferred for mains-connected snubbers and deflection circuits where voltage margin is non-negotiable.

Availability

BF393 is available at Aetrix Electronics and suitable for switch-mode power supply snubbers, relay drivers, CRT horizontal deflection stages, and high-voltage signal amplifiers requiring stable component supply and long-term industrial availability.

Supply support for BF393 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 delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The BF393 belongs to onsemi's legacy high-voltage bipolar transistor product line, engineered specifically for reliability-critical analog switching in off-line power conversion and display electronics.

FAQ

What is the maximum collector-emitter voltage rating for the BF393?

The BF393 has a guaranteed minimum V_(BR)CEO of 300 Vdc at I_C = 1.0 mA and I_B = 0. This rating is validated per JEDEC test conditions and applies across the full −55°C to +150°C junction temperature range. The BF393 must not be operated beyond this limit in continuous or repetitive pulse conditions without external clamping.

Is the BF393 available in a lead-free package?

Yes, the BF393ZL1G variant is explicitly marked as Pb-free and complies with RoHS Directive 2011/65/EU. Its TO-92 package uses matte tin plating on leads and meets J-STD-020 moisture sensitivity level 1 (MSL-1), allowing unlimited floor life at ≤30°C/60% RH.

What is the DC current gain (h_FE) range of the BF393 at typical operating conditions?

The BF393 exhibits h_FE ≥ 25 at I_C = 1.0 mA and V_CE = 10 Vdc, and h_FE ≥ 40 at I_C = 10 mA under the same V_CE. These values are specified at T_A = 25°C and represent minimum guaranteed performance; actual units may exceed these values but must be verified per application.

Can the BF393 replace the MPSA42 in existing designs?

The BF393 and MPSA42 share identical TO-92 packaging, pinout, V_CEO, I_C, and R_JA specifications. However, the BF393 has a narrower h_FE range (25–40 vs. 25–75), so designs relying on high-end h_FE for marginal base drive may require validation. The BF393 remains a functional alternative where consistent gain behavior is preferred.

What thermal derating applies to the BF393 at elevated ambient temperatures?

At T_A > 25°C, the BF393's total device dissipation must be linearly derated by 5.0 mW/°C. For example, at T_A = 75°C, maximum allowable P_D = 625 mW − (50°C × 5.0 mW/°C) = 375 mW. This derating ensures junction temperature remains within −55°C to +150°C limits under steady-state conduction.