The BS170 is a widely used N-channel enhancement mode MOSFET packaged in a compact, breadboard-friendly TO-92 case. Produced using high-density DMOS technology, it is designed for low-voltage, low-current switching and amplification.
Whether you are a hobbyist looking to trigger a relay with an Arduino or an engineer designing a low-power signal switch, the BS170 is a “must-have” component in your lab.
BS170 Pinout Configuration
When looking at the flat side of the TO-92 package with the leads pointing downwards, the pinout is as follows:
| Pin Number | Terminal Name | Description |
| 1 | Drain (D) | Current enters the MOSFET through this pin. |
| 2 | Gate (G) | The control pin; applied voltage triggers the switch. |
| 3 | Source (S) | Current exits the MOSFET to the ground. |
Technical Specifications
The BS170 is characterized by its high-speed switching and low “on-resistance” (RDS(on)).
- Transistor Polarity: N-Channel
- Max Drain-Source Voltage (VDS): 60V
- Max Continuous Drain Current (ID): 500mA
- Max Pulsed Drain Current (IDM): 1200mA
- Gate-Source Voltage (VGS): ± 20V
- Gate Threshold Voltage (VGS(th)): 0.8V (Min) to 3.0V (Max)
- Static Drain-Source On-Resistance: 1.2$\Omega$ to 5.0$\Omega$
- Total Power Dissipation (PD): 830mW
- Operating Temperature: −55 to +150 °C
Key Features & Benefits
- Logic Level Compatible: With a threshold voltage as low as 0.8V, it can be driven directly by 3.3V and 5V microcontrollers without a buffer.
- High-Speed Switching: Capable of switching in as little as 7ns, making it ideal for high-frequency signal processing.
- High Input Impedance: Draws negligible current from the signal source.
- Rugged and Reliable: Designed to minimize error voltages and handle saturation effectively.
Common Applications
The BS170 is versatile and excels in:
- Microcontroller Interfacing: Driving 5V or 12V relays and LEDs from an Arduino pin.
- Signal Amplification: Boosting weak audio or sensor signals.
- Power MOSFET Drivers: Acting as a small switch to trigger much larger power MOSFETs.
- Fast Switching: Used in digital logic gates and high-speed pulse circuits.
BS170 Equivalent & Substitutes
If you cannot find a BS170, the following components can often be used as direct or near-direct replacements:
- 2N7000: The most common alternative (check pinout, as it is often reversed!).
- 2N7002: The Surface Mount (SMD) version of this MOSFET.
- BS107 / BS108: Similar small-signal N-channel FETs.
Related Tutorials on elxhub
- Master Selection: Need help choosing? See our Ultimate MOSFET Selection Guide.
- Signal Shifting: Learn how to bridge different logic levels in our Logic Level Shifter Tutorial.
- Basics: Understand how MOSFETs differ from BJTs in Transistors – Basics, Types, and Working.
Pro-Tip for elxhub Users
- Always check the Pinout! Many beginners confuse the BS170 with the 2N7000. While they do the same job, their pins are usually mirrored (D-G-S vs S-G-D). Always verify your specific manufacturer’s datasheet before soldering!
Conclusion
The BS170 is an essential tool for any electronics enthusiast. Its ability to act as a robust switch for loads up to 500mA while remaining perfectly compatible with modern logic levels makes it a superior choice over standard BJTs like the BC547 for many switching tasks.
Download the MOSFET Datasheet pdf
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Complete BS170 N-Channel MOSFET datasheet. Learn about its 500mA current rating, TO-92 pinout, logic-level switching, and best equivalents for your projects.