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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Bipolar RF Transistors

STMicroelectronics SD1275

Name: SD1275
Brand: STMicroelectronics
SKU: SD1275
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SD1275

Manufacturer:: STMicroelectronics

Category:: Bipolar RF Transistors

Package:: M135

Datasheet:: SD1275.pdf

Description:: RF TRANS NPN 16V M135

Quantity:: RFQ Add To RFQ list

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Inventory:5,930

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Product details

Overview

SD1275 from STMicroelectronics is a 13.6 V, 40 W Class C NPN RF bipolar transistor in M135 stud package, designed for VHF mobile communications at 160 MHz with 9 dB power gain and emitter-ballasted die for load mismatch tolerance. It operates in common-emitter configuration with V_CEO = 16 V, P_DISS = 70 W, and R_TH(j-c) = 1.2 °C/W.

For engineers reviewing the SD1275 datasheet, SD1275 pinout, SD1275 application, or SD1275 equivalent, key selection criteria include VHF power amplification capability, thermal resistance under forced-air or heatsink mounting, ruggedness in mobile radio transmitter final stages, and impedance matching at 160 MHz (Z_IN = 1.0 + j0.4 Ω, Z_CL = 2.3 + j0.1 Ω).

Technical Context

The SD1275 employs an epitaxial silicon planar structure with emitter ballasting to sustain VSWR > 10:1 without failure. Its Class C biasing enables high-efficiency RF amplification in narrowband VHF transmitters, optimized for fixed supply voltage operation at 13.6 V.

Dynamic performance is characterized at f = 160 MHz with P_IN = 5.0 W, delivering ≥40 W output and 9 dB power gain. Static parameters include V_CES = 36 V, I_C = 8.0 A, and h_FE ≥ 20 at V_CE = 5 V / I_C = 250 mA - confirming suitability for driver/final-stage RF amplification.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	16 V - maximum safe collector-emitter voltage under operating bias, defining rail limit for mobile radio PA stage
P_OUT	≥40 W at 160 MHz - usable RF output power into matched 50 Ω load with 5 W drive, enabling 25–30 W ERP in VHF base/mobile radios
G_P	≥9 dB - small-signal-to-large-signal power conversion efficiency, critical for linear gain staging in multi-stage transmitters
R_TH(j-c)	1.2 °C/W - junction-to-case thermal resistance, requiring minimum 0.05 m²·K/W total thermal path (heatsink + interface) for continuous 70 W dissipation
Z_IN @ 160 MHz	1.0 + j0.4 Ω - input impedance magnitude and phase, guiding L-network matching for 50 Ω source
COB	95 pF - output capacitance at 1 MHz/15 V, influencing stability and harmonic content in tuned amplifier designs

Pinout & Package

Package: M135 stud-mount metal package with epoxy-sealed 4-lead configuration (stud collector, two base leads, emitter lead), dimensions per STMicroelectronics mechanical drawing: A = 5.59–5.84 mm, B = 24.89 mm, E = 8.13–8.38 mm, G = 11.43–12.45 mm.

Pin/Terminal	Circuit Role	Design Meaning
1 (Stud)	Collector	Electrically connected to metal case; must be DC-grounded and thermally coupled to heatsink via insulating washer or direct mount
2 & 4	Base	Dual base terminals for low-inductance RF grounding and bias feed; used in parallel to minimize series inductance in Class C drive network
3	Emitter	RF return path and DC emitter connection; requires low-impedance ground plane routing to maintain stability and gain flatness

Key Features

Feature	Design Value
Emitter ballasted die geometry	Enables stable operation under severe load mismatch (VSWR ≥ 10:1), eliminating need for external circulators in mobile radio finals
Class C RF amplification	Optimized for high-efficiency (>65%) narrowband VHF amplification, reducing thermal load vs. Class A/B in battery-powered mobile units
Common-emitter configuration	Provides inverting gain with standard impedance transformation, compatible with conventional π- or T-network output matching
13.6 V nominal supply operation	Matches automotive and marine mobile radio bus voltage, minimizing need for DC-DC regulation in vehicle-mounted transceivers

Applications

VHF Mobile Radio Transmitter Final Stage

Land Mobile Radio Base Station Driver

Use Scenario: High-power VHF FM transmitter in 136–174 MHz band for emergency response vehicles, operating from 13.6 V battery with intermittent duty cycle.

IC Role / Device Role / Timing Role: Final RF power amplifier stage delivering ≥40 W PEP into 50 Ω load, biased Class C for efficiency.

Use Value: Emitter ballasting ensures survivability during antenna detuning or cable fault events without protection circuitry.

Use Scenario: Driver amplifier in 25 W base station exciter, cascaded before a higher-power final stage, requiring stable gain and harmonic control.

IC Role / Device Role / Timing Role: Medium-power RF gain block providing 9 dB gain at 160 MHz with low intermodulation distortion.

Use Value: Matched Z_IN/Z_CL simplifies broadband matching network design across 145–175 MHz band.

VHF Amateur Radio Linear Amplifier

Marine VHF Communications Transceiver

Use Scenario: Home-built 2-meter band linear amplifier for SSB/CW operation, air-cooled with finned aluminum heatsink.

IC Role / Device Role / Timing Role: Single-ended Class C power device delivering clean 40 W output with minimal filtering requirements.

Use Value: Low R_TH(j-c) (1.2 °C/W) enables compact thermal design while maintaining <150 °C junction temperature at full duty.

Use Scenario: Integrated transceiver module in marine VHF radios (156–162 MHz), powered from 12–16 V DC shipboard system.

IC Role / Device Role / Timing Role: Final PA stage operating at nominal 13.6 V, supporting both analog FM and digital DSC modulation envelopes.

Use Value: 16 V V_CEO rating accommodates transient overvoltage spikes common in marine electrical systems.

Availability

SD1275 is available at Aetrix Electronics and suitable for VHF mobile radio transmitter final stages, land mobile radio base station drivers, amateur radio linear amplifiers, and marine VHF transceivers requiring stable component supply despite end-of-life status.

Supply support for SD1275 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 applications.

The SD1275 belongs to ST's legacy RF bipolar transistor product line, engineered specifically for ruggedized VHF power amplification in mobile and portable radio equipment where reliability under mismatch is critical.

FAQ

Is SD1275 still in active production?

No - STMicroelectronics has marked SD1275 as obsolete per its revision history (Rev. 2, May 2004). Aetrix Electronics maintains limited legacy stock with full traceability and offers engineering support for redesign alternatives including ST's newer RF LDMOS portfolio and pin-compatible replacements from NXP and Microsemi.

What thermal interface material is recommended for M135 stud mounting?

For optimal thermal transfer, use a thermally conductive silicone-based grease (e.g., Dow Corning TC-5123) with 0.1–0.2 mm bond line thickness, paired with a mica or ceramic insulator rated ≥2 kV and ≤0.005 °C·in²/W thermal resistance. Mounting torque must not exceed 12 in·lb to avoid die fracture.

Can SD1275 be used in Class AB mode?

Yes - though optimized for Class C, the SD1275 supports Class AB operation with appropriate bias network (e.g., diode-compensated V_BE multiplier). At I_CQ = 200 mA and V_CE = 12 V, it delivers ~25 W P_OUT with improved linearity but reduced efficiency (~45%) and higher thermal load versus Class C.

What is the recommended input matching network for 160 MHz operation?

A single-section L-network is typical: series inductor (≈22 nH) from 50 Ω source to base, shunt capacitor (≈12 pF) from base to ground. Measured Z_IN = 1.0 + j0.4 Ω requires transformation to 50 Ω; simulation with measured COB (95 pF) and package parasitics confirms this topology achieves <1.5:1 VSWR and >8.5 dB gain across 155–165 MHz.

SD1275 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: M135

Packaging:: Box

Product Status:: Obsolete

Transistor Type:: NPN

Voltage - Collector Emitter Breakdown (Max):: 16V

Frequency - Transition:: -

Noise Figure (dB Typ @ f):: -

Gain:: 9dB

Power - Max:: 70W

DC Current Gain (hFE) (Min) @ Ic, Vce:: 20 @ 250mA, 5V

Current - Collector (Ic) (Max):: 8A

Operating Temperature:: 200°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Chassis, Stud Mount

Supplier Device Package:: M135

SD1275 FAQ

1.How can I place an order for SD1275 through Aetrix?

Please submit a Request for Quotation (RFQ) for SD1275 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for SD1275 reliable?

The price and inventory of SD1275 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SD1275 is usually 5 days.

3.What payment methods are accepted for SD1275?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SD1275 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SD1275?

SD1275 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SD1275 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for SD1275?

For technical support, including SD1275 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SD1275 requirements.

6.How does Aetrix verify that SD1275 is sourced from the original manufacturer or authorized distributors?

All SD1275 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SD1275 meets industry standards.

7.What is the process for return or replacement of SD1275?

All SD1275 units undergo pre-shipment inspection (PSI). If there is an issue with SD1275, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The SD1275 part is unused and in its original packaging.

Return procedure for SD1275:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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