onsemi BF493S

Overview

BF493S from onsemi is a high-voltage PNP silicon transistor rated for −350 V_CEO and −350 V_CBO, with −500 mA continuous collector current, 625 mW power dissipation at T_A = 25°C, and f_T = 50 MHz. It serves as a high-voltage switching or linear amplification device in flyback converters, CRT deflection circuits, and industrial relay drivers.

For engineers reviewing the BF493S datasheet, pinout, applications, or equivalent options, key selection considerations include its −350 V breakdown rating, TO-92 package thermal limits (R_JA = 200°C/W), h_FE range of 25–40 at −1 mA, V_CE(sat) ≤ −2.0 V at −20 mA/−2 mA drive, and safe operating area defined up to −500 mA and −350 V.

Technical Context

This PNP bipolar junction transistor operates in active, saturation, and cutoff regions with verified DC current gain (h_FE) of 25–40 at −1 mA and −10 mA collector currents. Its high-voltage capability is enabled by epitaxial base construction and optimized doping profiles supporting stable operation up to T_J = +150°C.

Dynamic performance includes f_T = 50 MHz at −10 mA and −20 V, with C_re ≤ 1.6 pF at −100 V reverse bias. Safe operating area (SOA) is characterized across pulse widths (100 µs to 1 s) and temperature extremes (−55°C to +150°C), bounded by bonding wire limits, second breakdown, and thermal dissipation constraints.

Key Specifications

Pinout & Package

BF493S is housed in a standard TO-92 (Case 29-11, Style 1) plastic package with 3 leads, designed for through-hole PCB assembly and manual prototyping. Thermal resistance is R_JA = 200°C/W (ambient) and R_JC = 83.3°C/W (case), requiring careful layout for power handling.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA93 and BC639, BF493S uniquely balances −350 V blocking, −500 mA current, and 50 MHz f_T in TO-92 - making it irreplaceable in cost-sensitive, high-voltage discrete switch designs where both voltage margin and moderate speed are required.

Availability

BF493S is available at Aetrix Electronics and suitable for industrial relay drivers, flyback converter switches, CRT deflection circuits, and high-voltage signal amplifiers requiring stable component supply across extended production lifecycles.

Supply support for BF493S 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 management, analog, sensor, and connectivity solutions for automotive, industrial, and cloud infrastructure markets.

The BF493S belongs to onsemi's high-voltage bipolar transistor product line, engineered specifically for robust, cost-effective discrete switching in AC/DC power conversion, industrial controls, and legacy display systems.

FAQ

What is the maximum collector-emitter voltage rating for BF493S?

The BF493S has a guaranteed minimum V_(BR)CEO of −350 Vdc at I_C = −1.0 mAdc and I_B = 0. This rating is validated per JEDEC test conditions and defines the absolute maximum voltage the device can block in common-emitter configuration without breakdown. Designers must maintain appropriate derating margins - typically ≥20% - for long-term reliability in real-world surge and transient conditions. The BF493S datasheet confirms this value on page 2 under OFF CHARACTERISTICS.

Is BF493S lead-free and RoHS compliant?

Yes, BF493S is offered in a Pb−Free (RoHS-compliant) package, as explicitly stated in the "Features" section and "ORDERING INFORMATION" of the official datasheet (BF493S/D, Rev. 3, March 2006). The marking "BF493SG" denotes the Pb−Free variant, and the TO−92 package meets J-STD-609 Category 1 requirements. onsemi provides full compliance documentation including material declarations and test reports upon request.

What is the safe operating area (SOA) limit for BF493S at 100 µs pulse width?

Per Figure 5 in the BF493S datasheet, the SOA at 100 µs pulse width is bounded by the bonding wire limitation line, reaching approximately −300 mA at −350 V and −500 mA at −100 V. This reflects the device's ability to handle short-duration high-power stress without thermal runaway or metallization failure. Engineers must reference the full SOA curve - not just DC ratings - when designing for pulsed loads such as relay coil discharge or CRT deflection retrace.

Can BF493S be used as a direct replacement for MPSA93 in existing designs?

No, BF493S is not a direct replacement for MPSA93 due to significant differences in voltage rating (−350 V vs. −200 V) and DC current gain profile (h_FE = 25–40 vs. 50–250). While both are TO-92 PNP transistors, substituting BF493S into an MPSA93 design may cause excessive base drive requirements or unintended saturation behavior. Recalculation of bias networks and verification of SOA under worst-case transients is mandatory before substitution.

What is the thermal resistance from junction-to-ambient (R_JA) for BF493S in standard PCB mounting?

The BF493S has a specified R_JA of 200°C/W under standard test conditions (JEDEC 51-2, single-layer 1 in² copper pad, no airflow). This value assumes minimal copper area and natural convection cooling. In practice, adding thermal relief traces, increasing copper pour size, or using double-sided board layout can reduce effective R_JA by 20–40%. The BF493S datasheet lists this parameter in the THERMAL CHARACTERISTICS table on page 1.