BSS138 Detailed explanation of pin function specifications and circuit principle instructions

The BSS138 is a commonly used N-channel MOSFET, manufactured by various semiconductor brands such as Fairchild Semiconductor, ON Semiconductor, and others. The BSS138 typically comes in a SOT-23 package, which is a small surface-mount package with three pins. Below is a detailed explanation of the pin functions and specifications, along with a list of FAQs.

Pin Function Specifications and Circuit Principle of the BSS138

Pinout and Pin Functionality

The BSS138 is available in the SOT-23-3 package, which has 3 pins in total:

Pin Number Pin Name Pin Function Description Pin 1 Gate (G) Gate The Gate pin is the control terminal for the MOSFET. A voltage applied to the gate controls the flow of current between the Drain and Source. Pin 2 Drain (D) Drain The Drain pin is where the current flows out of the MOSFET. It is connected to the load in the circuit. Pin 3 Source (S) Source The Source pin is the entry point for current to the MOSFET. In an N-channel MOSFET, it is typically connected to ground or a negative voltage in the circuit. Functional Details The BSS138 is an N-channel MOSFET, which means it is turned on when a positive voltage (relative to the source) is applied to the Gate. When the Gate voltage exceeds a certain threshold (Vgs(th)), it creates a conductive channel between the Drain and Source, allowing current to flow. The BSS138 is often used for low-power switching applications, such as in digital circuits, power supplies, and signal processing.

Pin Function Overview

Below is a detailed explanation of the functions of all the pins:

Pin 1 (Gate): This is the control terminal. The MOSFET will start conducting when the Gate-to-Source voltage (Vgs) exceeds the threshold voltage (Vgs(th)). The Gate acts like a switch and controls whether the MOSFET is on or off.

Pin 2 (Drain): This is the terminal through which current exits the MOSFET. In a typical circuit, the Drain is connected to the load and supplies current to the circuit when the MOSFET is turned on.

Pin 3 (Source): This is the terminal through which current enters the MOSFET. In a typical circuit, it is connected to the ground or to the negative side of the power supply.

20 FAQ on the BSS138

Q1: What is the BSS138? A1: The BSS138 is an N-channel MOSFET used for low-power switching applications. It has three terminals: Gate, Drain, and Source.

Q2: How do I control the BSS138? A2: The BSS138 is controlled by applying a voltage to the Gate pin. When the Gate voltage exceeds the threshold voltage, the MOSFET turns on, allowing current to flow from Drain to Source.

Q3: What is the threshold voltage of the BSS138? A3: The threshold voltage (Vgs(th)) of the BSS138 is typically between 1.3V and 3V.

Q4: What is the maximum Drain-to-Source voltage (Vds) for the BSS138? A4: The maximum Drain-to-Source voltage for the BSS138 is typically 50V.

Q5: What is the maximum Gate-to-Source voltage (Vgs) for the BSS138? A5: The maximum Gate-to-Source voltage (Vgs) for the BSS138 is typically 20V.

Q6: What is the maximum current rating for the BSS138? A6: The maximum continuous drain current for the BSS138 is typically 220mA at 25°C.

Q7: What is the package type of the BSS138? A7: The BSS138 comes in a SOT-23-3 package, which is a small surface-mount package with three pins.

Q8: Can the BSS138 be used for switching applications? A8: Yes, the BSS138 is commonly used in low-power switching applications, such as in digital circuits and power supplies.

Q9: What are the typical uses of the BSS138? A9: The BSS138 is typically used in signal switching, level shifting, and low-power control circuits.

Q10: Can the BSS138 handle high currents? A10: No, the BSS138 is designed for low-current applications, with a maximum drain current of around 220mA.

Q11: What is the Rds(on) of the BSS138? A11: The typical Rds(on) (on-resistance) of the BSS138 is around 3 ohms when Vgs = 10V.

Q12: What is the Gate capacitance of the BSS138? A12: The Gate capacitance (Cgs) of the BSS138 is typically around 12pF.

Q13: What is the operating temperature range of the BSS138? A13: The operating temperature range of the BSS138 is typically from -55°C to +150°C.

Q14: Can I use the BSS138 in a 5V system? A14: Yes, the BSS138 can be used in a 5V system, as its threshold voltage is well within the 5V range.

Q15: How do I calculate the Gate voltage required to turn on the BSS138? A15: To turn on the BSS138, you need to apply a Gate voltage that exceeds the threshold voltage (Vgs(th)), which is typically 1.3V to 3V.

Q16: Can I use the BSS138 for power supply regulation? A16: Yes, the BSS138 can be used for low-power regulation and switching in power supplies, but it is not suitable for high-power applications.

Q17: Is the BSS138 sensitive to static discharge? A17: Yes, the BSS138 is sensitive to static discharge, and precautions should be taken to avoid damage due to electrostatic discharge (ESD).

Q18: Can the BSS138 be used as a level shifter? A18: Yes, the BSS138 is often used as a level shifter in digital circuits to interface between different voltage levels.

Q19: What should I do if the BSS138 is not turning on? A19: Check the Gate voltage. Ensure it exceeds the threshold voltage (Vgs(th)) to turn on the MOSFET. Also, check the Source voltage relative to the Gate.

Q20: How can I protect the BSS138 from excessive voltage? A20: Use a Gate resistor to limit the Gate current and protect the MOSFET from excessive voltage. Additionally, a zener diode can be used to clamp the Gate voltage if necessary.

Conclusion

The BSS138 is a versatile and widely used N-channel MOSFET, ideal for low-power switching applications. Understanding its pinout, pin functions, and common FAQs can help in designing circuits using this component. If you need more detailed specifications, refer to the datasheet for your particular manufacturer's part number.