BS170 N-Channel MOSFET Transistor (TO-92) – Support Documentation
The BS170 is a popular small-signal N-channel enhancement-mode MOSFET housed in a TO-92 package. It’s widely used in low-voltage, low-current switching applications and is ideal for general-purpose use in prototyping, educational projects, and lightweight embedded systems.
Key Features
- Maximum Drain-Source Voltage: 60V
- Maximum Continuous Drain Current: 500mA
- Maximum Power Dissipation: 830mW
- Gate Threshold Voltage: 0.8V to 3.0V
- Low Input Capacitance: 60pF typical
- Fast Switching Speed
- Package: TO-92 (Through-hole)
Pinout (TO-92 Package)
Viewed from flat side, pins downward:
| Pin | Name | Description |
|---|---|---|
| 1 | Drain (D) | Load side of the MOSFET |
| 2 | Gate (G) | Controls the MOSFET (logic input) |
| 3 | Source (S) | Connected to ground in typical switching configurations |
Electrical Characteristics
| Parameter | Symbol | Value | Unit | Condition |
|---|---|---|---|---|
| Drain-Source Voltage | VDS | 60 | V | — |
| Gate-Source Voltage | VGS | ±20 | V | — |
| Continuous Drain Current | ID | 0.5 | A | TA = 25°C |
| On-Resistance | RDS(on) | 5 | Ω | VGS = 10V, ID = 200mA |
| Gate Threshold Voltage | VGS(th) | 0.8 – 3.0 | V | ID = 1mA |
| Input Capacitance | Ciss | 60 | pF | VDS = 10V, VGS = 0V |
Applications
- Low-power switching
- Logic-level interfacing
- LED and relay control
- PWM motor control (low current)
- DIY and prototyping electronics
Usage Guidelines
- Drive the Gate with at least 5V for full saturation.
- Include a 100Ω resistor in series with the Gate to prevent oscillations.
- Add a 10kΩ pull-down resistor on the Gate to ensure it stays off when floating.
- Always observe correct polarity and handling precautions for static-sensitive components.
Package Dimensions (TO-92)
| Dimension | Value | Unit |
|---|---|---|
| Body Width | 4.5 | mm |
| Body Height | 5.0 | mm |
| Lead Pitch | 2.54 | mm |
Frequently Asked Questions
- Can I use BS170 directly from a microcontroller pin?
- Yes, provided your load current is under 500mA and you’re supplying 5V or higher to the Gate.
- What is the maximum load I can switch?
- 500mA continuously. For higher loads, use a power MOSFET like IRF540 or IRLZ44N.
- Does it need a heatsink?
- Not usually. But if you’re drawing near its current limit continuously, ensure good ventilation or add a small clip-on heatsink.