2N7000 vs BS170

The 2N7000 and BS170 are both N-channel enhancement mode MOSFETs, but they have some differences:
Electrical Characteristics
Drain-Source Voltage (Vdss): Both have a maximum drain-source voltage of 60V.
Drain Current (Id): The BS170 has a higher maximum continuous drain current of 500mA compared to the 2N7000's 200mA. The BS170 also has a higher pulsed drain current of 1200mA.
Gate Threshold Voltage (Vgs(th)): The BS170 has a lower maximum gate threshold voltage of 3V, making it easier to drive with logic-level signals compared to the 2N7000.
On-Resistance (Rds(on)): The BS170 has a typical on-resistance of 1.2 ohms, which is lower than the 2N7000's 6.5 ohms.
Packaging
2N7000: Commonly available in TO-92 and SOT-23 packages.
BS170: Available in TO-92 and SOT-23 packages.
Applications
2N7000: Suitable for low-power switching applications, such as driving small loads like LEDs and small motors.
BS170: Ideal for slightly higher current applications, such as driving relays, small lamps, and motors. It is also suitable for high-speed switching due to its fast turn-on and turn-off times.
Conclusion
The BS170 is often used as a replacement for the 2N7000 due to its higher current rating and lower on-resistance. However, the choice between the two depends on the specific requirements of the application, such as the maximum current and voltage levels, and the available gate drive voltage.