onsemi BF423

Overview

BF423 from onsemi is a PNP silicon high-voltage transistor designed for switching and linear amplification in off-line power supplies, relay drivers, and HV bias circuits. It features −250 V_CEO, −250 V_CBO, −5.0 V_EBO, −500 mA continuous collector current, and 830 mW total dissipation at T_A = 25°C in TO-92 package.

For engineers reviewing the BF423 datasheet, pinout, applications, or equivalent options, key selection considerations include its high breakdown voltage capability, DC current gain (h_FE ≥ 50 at I_C = −25 mA), saturation performance (V_CE(sat) ≤ −0.5 V), thermal resistance (R_JA = 150 °C/W), and Pb-free TO-92 packaging.

Technical Context

The BF423 operates as a medium-power PNP bipolar junction transistor optimized for high-voltage switching where robust V_CEO/V_CBO ratings and stable h_FE across temperature (−55°C to +125°C) are required. Its f_T of 60 MHz supports moderate-frequency switching applications.

It exhibits low leakage (I_CBO ≤ −0.01 A, I_EBO ≤ −100 nA), defined saturation behavior (V_BE(sat) ≤ −2.0 V at I_C/I_B = 10), and safe operating area validated up to 1000 V and 1 A with 10 ms pulse width. Thermal design relies on R_JL = 68 °C/W for lead-mounted dissipation.

Key Specifications

Pinout & Package

BF423 is housed in a Pb-free TO-92 package (Case 29, Style 14), with leads bent for ammo-pack mounting. Package dimensions comply with JEDEC TO-226 standards and feature 3.18–4.19 mm body width (C), 4.45–5.20 mm height (A), and 6.35 mm lead length (L).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BF423, BF421ZL1G offers higher voltage margin without layout or drive changes, while MPSA92 trades RoHS compliance and tighter saturation for broader legacy availability-neither is pin-compatible by official documentation, though mechanical fit is identical.

Availability

BF423 is available at Aetrix Electronics and suitable for off-line power supplies, relay drivers, capacitor-charge circuits, and high-voltage bias generators requiring stable component supply and long-term industrial availability.

Supply support for BF423 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 focused on energy-efficient electronics, delivering power management, analog, sensor, and logic solutions for automotive, industrial, cloud, and IoT applications.

The BF423 belongs to onsemi's high-voltage bipolar transistor family, engineered specifically for ruggedized switching and linear bias functions in AC/DC conversion, industrial controls, and instrumentation where reliability under voltage stress is critical.

FAQ

What is the maximum continuous collector current rating for BF423?

The BF423 has a maximum continuous collector current (I_C) rating of −500 mAdc at T_A = 25°C. This rating assumes proper PCB thermal relief (200 mm² of 1 oz copper). Derating is required above 25°C per the 6.6 mW/°C specification. The BF423 must not be operated beyond this limit in sustained DC or high-duty-cycle switching applications without thermal verification.

Is BF423 pin-compatible with BF421?

Yes, BF423 and BF421 share identical TO-92 package (Case 29, Style 14) and pinout: Pin 1 = Emitter, Pin 2 = Collector, Pin 3 = Base. Both devices are mechanically and electrically interchangeable in layout, though BF421 offers −300 V ratings versus −250 V for BF423. The BF423 may be substituted for BF421 only if system voltage stress remains below −250 V.

What is the typical DC current gain (h_FE) of BF423 under standard test conditions?

The BF423 has a minimum h_FE of 50 when tested at I_C = −25 mAdc and V_CE = −20 Vdc at T_A = 25°C. This value is guaranteed across the full operating temperature range (−55°C to +125°C), making BF423 suitable for designs requiring consistent gain stability in varying thermal environments.

Does BF423 meet RoHS and halogen-free requirements?

Yes, BF423 is explicitly marked as Pb-free, halogen-free/BFR-free, and RoHS compliant per onsemi documentation (BF421/D Rev. 5). The "ZL1G" suffix denotes the Pb-free TO-92 package. No exemptions apply, and the device complies fully with EU Directive 2011/65/EU and related regional environmental regulations.

What is the thermal resistance from junction to ambient (R_JA) for BF423?

The BF423 has a specified R_JA of 150 °C/W when mounted on a FR4 board with 200 mm² of 1 oz copper and 5 mm lead length. This value is critical for calculating maximum allowable power dissipation at elevated ambient temperatures. For example, at T_A = 75°C, the BF423 can safely dissipate approximately 500 mW before reaching its 150°C junction limit.