STMicroelectronics SD1728

Overview

SD1728 from STMicroelectronics is a 50V epitaxial silicon NPN planar RF power transistor in M177 hermetic package, designed for HF SSB amplification at 13.56 MHz with 200W output power, 15 dB gain, and 56% efficiency under Class C operation at V_CC = 44 V. It features gold metallization, emitter ballasting for ruggedness, and common-emitter configuration for industrial RF heating and amateur radio transmitters.

For engineers reviewing the SD1728 datasheet, SD1728 pinout, SD1728 application, or SD1728 equivalent, key selection criteria include its 55 V V_CEO, 40 A I_C, 0.4 °C/W R_thJC, 250–360 pF C_OB, and suitability for fixed-frequency HF linear/Class C amplifier stages requiring high thermal reliability and stable gain at 13.56 MHz.

Technical Context

The SD1728 operates as a common-emitter NPN RF power amplifier with gold-metallized emitter and base terminals, optimized for fixed-frequency HF applications at 13.56 MHz. Its epitaxial silicon structure supports 200 W P_OUT with 15 dB small-signal power gain and 56% collector efficiency in Class C mode at V_CC = 44 V.

Emitter ballasting improves current sharing and thermal stability under pulsed or continuous RF drive. The device's 0.4 °C/W junction-to-case thermal resistance and 200 °C maximum junction temperature enable high-power dissipation (330 W) in forced-air or heatsink-mounted configurations without derating below 25 °C case temperature.

Key Specifications

Pinout & Package

The SD1728 is housed in an epoxy-sealed M177 hermetic metal package (Ø0.550", 4-lead, flanged), with copper-tungsten base for low thermal resistance and gold-plated leads for corrosion resistance and wire-bond compatibility.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MRF176 and BLF178, the SD1728 delivers superior thermal robustness at 13.56 MHz via emitter ballasting and hermetic packaging, while offering higher efficiency than MRF176 and better narrowband gain flatness than BLF178 in fixed-frequency HF SSB and induction heating roles.

Availability

SD1728 is available at Aetrix Electronics and suitable for RF induction heating systems, amateur radio transmitters, HF plasma generators, and ISM-band 13.56 MHz power modules requiring stable component supply and long-lifecycle support.

Supply support for SD1728 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, designing and manufacturing analog, digital, and mixed-signal ICs for industrial, automotive, and power applications.

The SD1728 belongs to ST's high-voltage RF bipolar transistor product line, engineered specifically for rugged, high-efficiency HF power amplification in industrial and communications infrastructure where thermal stability and fixed-frequency performance are critical.

FAQ

What is the recommended bias configuration for SD1728 in SSB linear operation?

The SD1728 is typically biased in Class AB for SSB applications using fixed base bias with emitter degeneration resistors. Recommended conditions: V_CC = 44 V, I_CQ = 1.5–2.5 A, V_CE ≈ 30 V. Emitter ballasting allows stable quiescent current without thermal runaway, and h_FE ranking (C–F) must be selected per gain consistency requirements.

Can SD1728 be used at frequencies other than 13.56 MHz?

Yes - the SD1728 operates up to ~30 MHz, but its published 200 W P_OUT and 15 dB G_P are validated only at 13.56 MHz. At 27 MHz, output drops to ~120 W with reduced efficiency (~45%). Performance above 30 MHz is not characterized; use only within documented dynamic specifications.

Is the M177 package RoHS-compliant?

Yes - the SD1728 uses ST's ECOPACK®-compliant M177 package with lead-free second-level interconnect, certified per JEDEC JESD97. The inner box label indicates compliance level, and soldering profiles follow ST's specified reflow guidelines for hermetic packages.

How does emitter ballasting improve reliability in SD1728?

Emitter ballasting introduces distributed series resistance across parallel emitter fingers, equalizing current density during RF peaks and preventing localized hot spots. This mitigates thermal runaway under mismatched loads or transient overdrive, extending MTTF by >3× versus non-ballasted equivalents in continuous-duty HF amplifiers.