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

STMicroelectronics SD1405

Name: SD1405
Brand: STMicroelectronics
SKU: SD1405
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SD1405

Manufacturer:: STMicroelectronics

Category:: Bipolar RF Transistors

Package:: M174

Datasheet:: SD1405.pdf

Description:: RF TRANS NPN 18V M174

Quantity:: RFQ Add To RFQ list

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Inventory:7,923

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Product details

Overview

SD1405 from STMicroelectronics is a 12.5 V, 75 W RF power NPN transistor in common-emitter configuration, designed for HF SSB communications at 30 MHz with 13 dB gain and −32 dBc IMD. It features gold metallization, infinite VSWR tolerance under rated conditions, and operates up to +200 °C junction temperature.

For engineers reviewing the SD1405 datasheet, SD1405 pinout, SD1405 application, or SD1405 equivalent, key selection criteria include its 18 V V_CEO, 270 W P_DISS, 0.65 °C/W R_th(j-c), 350 pF C_OB, and Class C bias suitability for linear HF amplification stages.

Technical Context

The SD1405 is a silicon epitaxial planar NPN device optimized for HF (30 MHz) single-sideband amplification in Class C operation. Its diffused emitter resistors enable robust VSWR resilience, while gold metallization ensures stable high-frequency interconnect reliability at elevated junction temperatures.

It delivers 75 W P_OUT min. with 13 dB power gain and −32 dBc third-order intermodulation distortion under 12.5 V V_CE, 100 mA I_CQ bias - confirming design intent for high-efficiency, linearity-critical HF transmitter final stages.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	18 V - Maximum safe collector-emitter voltage under operating bias, defining DC supply headroom for HF amplifier rails.
P_OUT min.	75 W - Minimum RF output power at 30 MHz, enabling full-power SSB transmission in amateur and marine HF bands.
G_P	13 dB - Small-signal power gain, sufficient to drive final stage without excessive driver-stage complexity.
IMD	−32 dBc - Third-order intermodulation distortion level, meeting linearity requirements for multi-tone SSB voice fidelity.
R_th(j-c)	0.65 °C/W - Junction-to-case thermal resistance, enabling effective heatsinking for continuous 270 W dissipation capability.
C_OB	350 pF - Output capacitance at 12 V V_CB, directly impacting matching network design and bandwidth limitation at 30 MHz.

Pinout & Package

M174 hermetically sealed metal-ceramic package with flange-mounting; 4-terminal configuration: two source terminals (pins 2 and 4), drain (pin 1), gate (pin 3).

Pin/Terminal	Circuit Role	Design Meaning
1	Drain	High-current RF output node - connected to collector in NPN topology; requires low-inductance RF grounding via flange.
2	Source	Emitter terminal - used for DC bias return and RF emitter degeneration; shared with pin 4 for parallel current handling.
3	Gate	Base terminal - RF input node; requires impedance-matched drive and DC bias network for Class C operation.
4	Source	Second emitter terminal - electrically identical to pin 2; enables dual-path emitter routing for thermal and current distribution.

Key Features

Feature	Design Value
Infinite VSWR tolerance	Diffused emitter resistors prevent thermal runaway during antenna mismatch - critical for field-deployed HF transceivers.
Gold metallization	Ensures long-term bond-wire integrity and low-contact-resistance at >150 °C case temperatures.
Class C optimized bias	100 mA I_CQ quiescent current enables high-efficiency RF amplification with minimal DC power draw.
+200 °C T_j max	Supports sustained operation in convection-cooled or thermally constrained HF amplifier enclosures.

Applications

Amateur Radio HF Transmitter Final Stage

Marine SSB Communications Amplifier

Use Scenario: 30 MHz HF SSB voice transmission in portable or mobile amateur radio rigs with variable antenna VSWR.

IC Role / Device Role / Timing Role: RF power amplifier transistor in common-emitter Class C configuration driving 50 Ω load.

Use Value: 75 W output with −32 dBc IMD preserves voice intelligibility across multi-tone SSB signals under real-world antenna mismatches.

Use Scenario: Shipboard long-range HF voice communication using narrowband SSB modulation over saltwater paths.

IC Role / Device Role / Timing Role: Final-stage RF power device delivering regulated 75 W PEP into maritime antenna systems.

Use Value: Infinite VSWR tolerance prevents failure during dynamic antenna detuning caused by vessel motion or seawater coupling effects.

Shortwave Broadcast Auxiliary Amplifier

HF Military Tactical Radio Transmitter

Use Scenario: Low-duty-cycle HF broadcast repeater stage requiring high peak power and thermal resilience.

IC Role / Device Role / Timing Role: Linear RF power transistor biased for PEP-limited Class C operation at 30 MHz.

Use Value: 0.65 °C/W R_th(j-c) and +200 °C T_j rating allow reliable intermittent operation without forced-air cooling.

Use Scenario: Manpack or vehicle-mounted HF tactical radio operating in extreme ambient temperatures (−40 to +70 °C).

IC Role / Device Role / Timing Role: High-reliability RF power amplifier core with gold-metallized interconnects for mission-critical transmission.

Use Value: Gold metallization and hermetic M174 package ensure stable RF performance and corrosion resistance in humid, dusty, or saline environments.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MRF454	Higher V_CEO (35 V), lower P_OUT (50 W), TO-220 package, no infinite VSWR design	Suitable for fixed-tuned 27–30 MHz amplifiers with stable loads; lacks VSWR resilience for mobile antennas	Select when supply voltage exceeds 18 V and thermal management allows plastic packaging.
BLW33	Same V_CEO (18 V), lower gain (10 dB), higher IMD (−28 dBc), ceramic-metal package	Acceptable for non-critical HF links where spectral purity is relaxed; less robust under mismatch	Choose only if legacy board layout mandates identical footprint and lower cost outweighs linearity loss.

Compared with MRF454 and BLW33, the SD1405 uniquely combines infinite VSWR tolerance, 75 W output, and gold-metallized reliability - making it irreplaceable for field-deployed HF transmitters demanding simultaneous efficiency, linearity, and fault resilience.

Availability

SD1405 is available at Aetrix Electronics and suitable for amateur radio transmitters, marine SSB amplifiers, shortwave broadcast repeaters, and military HF tactical radios requiring stable component supply across extended production lifecycles.

Supply support for SD1405 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 SD1405 belongs to ST's legacy HF RF power transistor family, engineered specifically for ruggedized, high-linearity HF SSB amplification in environments where antenna mismatch and thermal stress are unavoidable.

FAQ

Is SD1405 still in active production?

No - SD1405 is marked "Obsolete Product(s)" in the official ST datasheet. Aetrix Electronics maintains limited legacy stock with full traceability and offers engineering support for redesign alternatives where required.

What is the correct bias configuration for SD1405 in Class C operation?

The SD1405 is specified for Class C with V_CE = 12.5 V and I_CQ = 100 mA. Base bias must be set via resistor-divider or active circuit to achieve this quiescent current while maintaining stable thermal operating point on the M174 flange.

Can SD1405 be used at frequencies above 30 MHz?

No - electrical specifications are guaranteed only at 30 MHz. Gain drops sharply above 30 MHz (typ. <8 dB at 50 MHz), and IMD degrades beyond specification; it is not characterized or recommended for VHF or UHF use.

Why does SD1405 have two source pins (2 and 4)?

Pins 2 and 4 are internally connected emitter terminals. This dual-terminal layout reduces emitter lead inductance and improves current sharing, enhancing thermal distribution and RF stability in high-power HF operation.

SD1405 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: M174

Packaging:: Box

Product Status:: Obsolete

Transistor Type:: NPN

Voltage - Collector Emitter Breakdown (Max):: 18V

Frequency - Transition:: -

Noise Figure (dB Typ @ f):: -

Gain:: 13dB

Power - Max:: 270W

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

Current - Collector (Ic) (Max):: 20A

Operating Temperature:: 200°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: M174

SD1405 FAQ

1.How can I place an order for SD1405 through Aetrix?

Please submit a Request for Quotation (RFQ) for SD1405 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 SD1405 reliable?

The price and inventory of SD1405 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SD1405 is usually 5 days.

3.What payment methods are accepted for SD1405?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SD1405 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SD1405?

SD1405 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SD1405 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 SD1405?

For technical support, including SD1405 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SD1405 requirements.

6.How does Aetrix verify that SD1405 is sourced from the original manufacturer or authorized distributors?

All SD1405 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 SD1405 meets industry standards.

7.What is the process for return or replacement of SD1405?

All SD1405 units undergo pre-shipment inspection (PSI). If there is an issue with SD1405, 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 SD1405 part is unused and in its original packaging.

Return procedure for SD1405:

1.Submit a request within 90 days.

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

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