STMicroelectronics SD1274

Overview

SD1274 from STMicroelectronics is a 13.6 V, 30 W Class C NPN RF bipolar power transistor in M135 stud package, designed for VHF mobile communications at 160 MHz with 10 dB gain and emitter-ballasted die for load mismatch tolerance.

For engineers reviewing the SD1274 datasheet, SD1274 pinout, SD1274 application, or SD1274 equivalent, key selection criteria include VCEO = 16 V, POUT ≥ 30 W @ 160 MHz, RTH(j-c) = 1.2 °C/W, COB = 95 pF, and common-emitter configuration for high-efficiency VHF amplifier stages.

Technical Context

The SD1274 operates in Class C bias for high-efficiency RF amplification in VHF mobile transmitters, using epitaxial silicon planar construction with emitter ballasting to sustain VSWR > 10:1 without failure. Its 16 V VCEO rating and 8 A IC limit define safe operating area under pulsed RF conditions.

Designed for fixed-tuned 160 MHz operation, it delivers 30 W output with 3 W drive and 13.6 V supply, leveraging low junction-to-case thermal resistance (1.2 °C/W) and optimized ZIN/ZCL impedance matching (1.0 + j0.4 Ω / 2.3 + j0.1 Ω at 175 MHz) for broadband VHF band use.

Key Specifications

Pinout & Package

M135 is a 4-terminal stud-mount metal package with insulated base flange, rated for high-power RF operation. Thermal path is direct from die to case via copper stud; terminals are isolated from case except Collector (Terminal 1).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MRF454 and BLW60, the SD1274 uniquely combines 16 V VCEO, 30 W output, emitter ballasting, and 1.2 °C/W thermal resistance in a cost-effective stud-mount package-making it optimal for commercial VHF mobile radios where reliability under real-world antenna mismatch is essential.

Availability

SD1274 is available at Aetrix Electronics and suitable for land-mobile radio transmitters, VHF airband communication systems, and marine band transceivers requiring stable component supply across extended production cycles.

Supply support for SD1274 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, designing and manufacturing analog, power, and RF components for industrial, automotive, and communications markets.

The SD1274 belongs to ST's legacy RF power transistor product line, engineered specifically for ruggedized VHF mobile radio amplifiers where thermal resilience and load mismatch tolerance are non-negotiable.

FAQ

Is the SD1274 RoHS compliant?

No. The SD1274 was released in 2004 and manufactured prior to RoHS Directive 2011/65/EU compliance requirements. It contains leaded solder and Pb-in-glass seals consistent with pre-RoHS industrial RF transistor standards. STMicroelectronics discontinued RoHS conversion for this part due to obsolescence status.

What is the recommended heatsink mounting torque for the M135 package?

The M135 stud requires 12–15 in·lb (1.36–1.70 N·m) mounting torque onto a flat, unpainted aluminum heatsink with thermal compound. Over-torquing distorts the copper stud and degrades thermal contact; under-torquing increases RTH(j-sink) beyond 2.5 °C/W. Mounting hardware must use #8-32 UNC-2A thread specification per Figure 8.

Can the SD1274 be operated in Class AB mode?

Yes, but not recommended. While static hFE and VCEO allow Class AB biasing, the emitter ballasting and thermal design are optimized for Class C switching operation. Operating in Class AB reduces efficiency below 50%, increases junction temperature beyond safe limits at full POUT, and voids the guaranteed 30 W output specification.

Does the SD1274 require external base bias stabilization?

No. The integrated emitter ballasting provides inherent current stabilization across temperature and device variation. External emitter degeneration resistors or feedback networks are unnecessary for standard Class C operation. However, RF chokes and DC blocking capacitors must follow ST's recommended layout in Figure 1 to prevent parasitic oscillation.