3sk41 Datasheet -

The 3SK41 is a high-performance N-channel dual-gate MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) primarily used in radio frequency (RF) applications. While some older records may misidentify it as a relay, it is most recognized in amateur radio and signal processing for its fast switching and low noise characteristics. Key Technical Specifications

The following specifications are common for the 3SK41 dual-gate MOSFET: Type: N-channel dual-gate MOS field-effect transistor. Package: Typically found in a CAN-4 (metal can) package.

Primary Application: RF amplifiers, balanced mixers, and signal converters in communication equipment. Key Features:

Dual-Gate Construction: Allows for improved AGC (Automatic Gain Control) characteristics and lower cross-modulation. Low Noise: Optimized for high-frequency sensitivity.

Fast Switching: Suitable for high-speed power management and signal switching. Common Applications

RF Amplifiers: Often used in receiver front-ends to improve sensitivity and selectivity.

Balanced Mixers: Employed in radio stages to reduce internal noise and prevent front-end overload.

Control Circuits: Used for general-purpose signal conversion and switching in alarms and security systems. Datasheet Resources

You can access the full technical PDF files through these sources: 3sk41 datasheet

Alldatasheet: Provides various versions of the PDF datasheet from multiple manufacturers.

Veswin: Contains detailed information on pinouts, circuit diagrams, and equivalent components.

Jotrin: Offers factory information and application notes for brands like NEC, Hitachi, and Motorola. 3SK41 - NEC/HITACHI/MOTOROLA - Jotrin

The 3SK41 is a legacy N-channel dual-gate MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) primarily designed for high-frequency applications, such as VHF (Very High Frequency) amplifiers and mixers in radio and television tuners. Core Specifications

While specific values can vary slightly by manufacturer (historically produced by companies like Hitachi or NEC), the standard parameters for the 3SK41 include: Type: N-Channel Depletion Mode Dual-Gate MOSFET. Drain-Source Voltage ( VDScap V sub cap D cap S end-sub ): Max 20V. Drain Current ( IDcap I sub cap D ): Max 25mA. Power Dissipation ( Ptotcap P sub t o t end-sub ): Approximately 200mW to 300mW. Forward Transfer Admittance ( ): Typically 10 to 15 mS (millisiemens) at 1kHz. Input Capacitance ( Cisscap C sub i s s end-sub ): Low, typically around 5.0pF to 6.0pF.

Package: Often found in a 4-pin TO-72 metal can or similar small plastic packages. Functional Roles

The "dual-gate" design is the defining feature of the 3SK41, allowing it to excel in two specific areas:

Automatic Gain Control (AGC): By applying a control voltage to the second gate (Gate 2), you can vary the gain of the signal passing through the first gate (Gate 1). This is essential for stabilizing radio reception under varying signal strengths. The 3SK41 is a high-performance N-channel dual-gate MOSFET

Mixing: In superheterodyne receivers, the dual-gate structure allows one gate to receive the RF (Radio Frequency) signal and the other to receive the LO (Local Oscillator) signal, mixing them with high isolation and low noise. Key Performance Features

High Power Gain: It provides significant amplification in the VHF band (up to 200–300 MHz).

Low Noise Figure: Designed to minimize the "hiss" or thermal noise added to weak signals, making it ideal for the front-end stages of receivers.

Low Feedback Capacitance: The dual-gate construction reduces the internal capacitance between the drain and the input gate, which improves stability and prevents unwanted oscillations at high frequencies. Typical Pinout (TO-72 Style)

When looking at the bottom of a TO-72 metal package (with the tab as a reference): Source (often connected to the case) Drain Gate 2 Gate 1 Modern Availability

The 3SK41 is largely considered an obsolete or "vintage" component. It is rarely used in new designs today, as it has been replaced by more modern surface-mount devices (SMD) like the BF998 or high-speed Gallium Arsenide (GaAs) FETs. However, it remains highly sought after by hobbyists for repairing vintage ham radios, scanners, and TV tuners.

While a standard essay on a datasheet might sound dry, the "3sk41" is actually a fascinating subject because it sits at the precise intersection of consumer history and electronic obsolescence. The 3SK41 is not a modern microprocessor; it is a N-channel dual-gate MOSFET, a component that was once the beating heart of the VHF and UHF tuners in analog television sets.

Here is an essay exploring the significance of this humble component. Interpreting the 3SK41 datasheet — practical guide for

Interpreting the 3SK41 datasheet — practical guide for engineers and hobbyists

Summary: the 3SK41 is an N‑channel dual‑gate MOSFET (small RF/low‑power device in a CAN/TO‑style metal can) used historically in VHF/UHF tuner and RF front‑end circuits. Below I break down what a datasheet for this part usually contains, explain the key specs, show how they affect circuit behavior, give practical tips for selection, testing, PCB layout and replacement/cross‑reference, and include simple application examples.

Part 2: Absolute Maximum Ratings (Ta = 25°C)

Before designing any circuit, you must respect the limits listed below. Exceeding these values will destroy the MOSFET, as it is extremely static-sensitive.

| Parameter | Symbol | Rating | Unit | | :--- | :--- | :--- | :--- | | Drain-Source Voltage | VDS | 20 | V | | Gate 1 to Source Voltage | VG1S | ±15 | V | | Gate 2 to Source Voltage | VG2S | ±15 | V | | Drain Current | ID | 30 | mA | | Total Power Dissipation (Ta=25°C) | Ptot | 200 | mW | | Channel Temperature | Tch | 125 | °C | | Storage Temperature | Tstg | -40 to +125 | °C |

⚠️ Critical Warning: The input impedance of the 3SK41 is extremely high (in the megohm range). This makes it susceptible to damage from electrostatic discharge (ESD). Always use grounded soldering irons and anti-static wrist straps when handling.

Testing and measurement tips

1. Concept Overview

This feature utilizes the high-speed switching characteristics and voltage handling of the 3SK41 to create a Soft-Start Mechanism for AC induction motors or high-intensity lighting systems (such as industrial halogen lamps).

Instead of applying full voltage instantly (which causes high inrush current and mechanical stress), this feature gradually ramps up the voltage delivered to the load using Pulse Width Modulation (PWM).

Part 3: Pinout and Physical Configuration

One of the most common reasons for downloading a 3sk41 datasheet is to identify the pin configuration. The 3SK41 is typically packaged in a TO-72 metal can (4-pin) or a SIP (Single In-line Package) plastic case.

Part 5: Application Circuits from the Datasheet

Historical datasheets provided two classic topologies: VHF Amplifier and AGC-controlled IF Amplifier.

2. Technical Implementation

The circuit uses the 3SK41 as the primary power-switching element.