STMicroelectronics SD2931

Overview

SD2931 from STMicroelectronics is a gold-metallized N-channel MOSFET RF power transistor in common-source configuration, rated for 50 V DC large-signal operation up to 230 MHz. It delivers ≥150 W output power with 14 dB power gain and 55–65% drain efficiency at 175 MHz, and features 125 V drain-source breakdown voltage, 20 A continuous drain current, and 0.6 °C/W junction-to-case thermal resistance - used in HF/VHF/UHF broadcast amplifiers and industrial RF heating systems.

For engineers reviewing the SD2931 datasheet, SD2931 pinout, SD2931 application, or SD2931 equivalent, key selection criteria include its 175 MHz small-signal gain flatness, thermal stability under sustained 200 °C junction temperature, gate-source voltage sorting (1.5–4.0 V), and compatibility with 50 Ω impedance-matched RF stages requiring high VSWR tolerance (10:1).

Technical Context

The SD2931 operates as a Class AB RF amplifier in common-source topology with gold-metallized gate and source interconnects for enhanced reliability under thermal cycling. Its dynamic performance is characterized at V_DD = 50 V, I_DQ = 250 mA, and f = 175 MHz, where it achieves 14–15 dB power gain and 55–65% drain efficiency while maintaining stable bias across −20 °C to +80 °C case temperatures.

It exhibits low input/output capacitance (C_iss = 480 pF, C_oss = 190 pF, C_rss = 18 pF at V_DS = 50 V, f = 1 MHz) and a typical input impedance of 1.2 − j2.0 Ω at 175 MHz, enabling direct matching into 50 Ω systems using discrete L-networks or broadband transformers per the documented 175 MHz test circuit.

Key Specifications

Pinout & Package

The SD2931 is housed in the M174 plastic hermetic package (0.500" diameter, flanged metal header), designed for high-power RF applications with low-inductance source grounding and direct case thermal path.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar RF power MOSFET applications.

Compared with MRF158 and BLF177, the SD2931 offers balanced trade-offs: superior thermal resistance versus MRF158 and factory-sorted gate threshold versus BLF177 - making it optimal for production RF amplifiers requiring consistent gain, efficiency, and thermal behavior without post-manufacturing tuning.

Availability

SD2931 is available at Aetrix Electronics and suitable for HF/VHF/UHF broadcast transmitters, industrial RF heating systems, air traffic control radar front-ends, and military HF communications equipment requiring stable component supply and long-lifecycle support.

Supply support for SD2931 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 power management, analog, MEMS, and RF solutions for industrial, automotive, and communications markets.

The SD2931 belongs to ST's legacy RF Power Transistor product line, engineered specifically for high-efficiency, high-reliability HF/VHF/UHF amplification in mission-critical infrastructure where thermal stability and VSWR tolerance are non-negotiable.

FAQ

What is the maximum safe operating frequency for the SD2931?

The SD2931 is characterized and specified for reliable operation up to 230 MHz, with full electrical performance validated at 175 MHz and 30 MHz. Its gain and efficiency roll off above 200 MHz due to intrinsic capacitance limits, and it is not recommended for UHF applications beyond 230 MHz without empirical validation in the target circuit.

Does the SD2931 require external gate protection diodes?

Yes - although the SD2931 has built-in gate oxide protection, STMicroelectronics recommends adding a 10–22 Ω series gate stopper resistor and a pair of back-to-back 18 V Zener diodes (e.g., BZX84-C18) between gate and source to suppress RF-induced gate voltage spikes and prevent catastrophic failure during load mismatch events.

Can the SD2931 be operated in Class C mode?

No - the SD2931 is optimized for Class AB operation with 250 mA quiescent drain current. Its V_GS(Q) sorting, thermal design, and safe operating area (SOA) curves assume linear biasing; Class C operation risks thermal runaway and exceeds SOA limits at high peak currents and low duty cycles.

Is the M174 package RoHS-compliant?

No - the SD2931 M174 package uses lead-based solder and gold-plated metallization, and was manufactured prior to RoHS Directive enforcement. It is classified as an obsolete product and not compliant with current EU RoHS or REACH requirements; suitable only for legacy repair, military sustainment, or exempted industrial applications.