Overview
The BSS138 is an N-channel enhancement-mode MOSFET widely used in low-voltage electronic systems, with compatible models available from several semiconductor manufacturers, including Nexperia, Onsemi, and Diodes Incorporated. This device is housed in a small SOT-23 package and features low gate threshold voltage, fast switching characteristics, and low power consumption, making it particularly suitable for logic level shifting, load switching, power management, and portable electronic devices.
With its excellent low-voltage drive capability, the BSS138 can be directly controlled by 1.8V, 2.5V, or 3.3V MCUs and FPGAs without the need for additional drive circuitry. Due to its outstanding performance in bidirectional logic level conversion applications, the BSS138 has become a classic device in interface level conversion circuits such as I²C, SMBus, and 1-Wire.
Core parameters
| Parameter | Value |
| Product Type | N-channel MOSFET |
| Drain-source voltage (VDS) | 50V |
| Gate-source voltage (VGS) | ±20V |
| Continuous drain current (ID) | 220mA |
| On-resistance (RDS(on)) | Approximately 3.5Ω @ VGS=10V |
| Gate threshold voltage (VGS(th)) | 0.5V～1.5V |
| Power consumption (Pd) | Approximately 350mW |
| Encapsulation type | SOT-23 |
| Operating temperature range | -55°C to +150°C |
| Environmental standards | RoHS compliant |
Features
Low gate threshold voltage design
The BSS138 features a low turn-on voltage, enabling reliable turn-on in low-voltage logic systems and is ideal for 1.8V, 2.5V, and 3.3V power supply environments.
Ideal choice for bidirectional level conversion applications
Leveraging the inherent characteristics of MOSFETs, the BSS138 can easily be used to construct bidirectional logic level shifting circuits, making it widely applicable in I²C bus and low-voltage digital interface designs.
Fast switching performance
The device features low input capacitance and fast switching speed, meeting the needs of digital control, power switching, and signal control applications.
Ultra-small packaging saves space
It uses a standard SOT-23 package, occupies a small PCB area, and is suitable for high-density circuit board design and portable electronic products.
Low power consumption and high reliability
The combination of low drive power consumption and mature MOSFET technology ensures long-term stable operation and improves system reliability.
Typical application scenarios
Logic level conversion
Bidirectional level conversion circuits for interfaces such as I²C, SMBus, and UART.
Microcontroller Interface Expansion
External signal control for MCUs such as STM32, ESP32, and Arduino.
Power path control
Low-voltage power switch and load management circuit.
Portable electronic devices
Smart wearable devices, handheld terminals and mobile products.
Industrial Control Systems
Digital signal isolation, interface matching, and control logic circuits.
Comparative Advantage Analysis
| Performance indicators | BSS138 | Ordinary small-signal transistor |
| Drive voltage | Extremely low | higher |
| Switching speed | quick | generally |
| Level conversion applications | excellent | complex |
| Power consumption | Low | higher |
| circuit complexity | Low | higher |
| PCB area | Small | medium |
The BSS138 has significant advantages over traditional bipolar transistors in terms of low-voltage drive, bidirectional level shifting, and low-power design.
Manufacturer Profile
As an industry-standard MOSFET model, the BSS138 has been manufactured by many international semiconductor manufacturers such as Nexperia, Onsemi, Diodes Incorporated, and Vishay for a long time, and enjoys widespread market recognition and good supply stability.
Why choose BSS138?
● Supports direct drive of low-voltage logic
● Suitable for bidirectional level shifting designs
● Fast switching speed and sensitive response
● Small SOT-23 package saves space
● Low power consumption, suitable for portable devices
● Long-term supply from multiple original manufacturers, flexible procurement
Frequently Asked Questions (FAQ)
Q1: Why is BSS138 frequently used for I²C level conversion?
BSS138 has a low gate threshold voltage and utilizes the inherent bidirectional conduction characteristics of MOSFETs to easily achieve bidirectional conversion between different logic levels such as 3.3V and 5V, 1.8V and 3.3V. Therefore, it is widely used in I²C bus design.
Q2: Can the BSS138 be used as a load switch?
Yes. In low-current load control applications, the BSS138 can be used as a low-side switch to control the power supply of LEDs, sensor modules, and low-power peripherals. However, for high-current loads, it is recommended to choose a power MOSFET with lower on-resistance and higher rated current.
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