The **BSS84** is a widely used P-Channel enhancement mode vertical Diffusion Metal-Oxide Semiconductor (DMOS) Field Effect Transistor (FET). It is designed primarily for low-voltage, low-current switching applications. --- ### ## 1. Key Specifications and Features The BSS84 is favored for its compact size and low threshold voltage. Below are the typical technical parameters: | Parameter | Symbol | Typical Value | | :--- | :--- | :--- | | **Drain-to-Source Voltage** | $V_{DSS}$ | -50V | | **Continuous Drain Current** | $I_D$ | -130mA to -170mA | | **Gate-Source Threshold Voltage** | $V_{GS(th)}$ | -0.8V to -2.0V | | **Drain-Source On-Resistance** | $R_{DS(on)}$ | ~3.5$\Omega$ to 10$\Omega$ | | **Total Gate Charge** | $Q_g$ | 0.4nC to 1nC | | **Package Type** | SOT-23 | Surface Mount | --- ### ## 2. Pinout Configuration The BSS84 comes in a standard 3-pin **SOT-23** package. 1. **Gate (G):** Controls the flow of current between Drain and Source. 2. **Source (S):** Usually connected to the positive supply in P-channel configurations. 3. **Drain (D):** Connected to the load. --- ### ## 3. Core Characteristics * **Logic-Level Drive:** Because it has a low gate threshold voltage ($V_{GS(th)}$), it can be triggered directly by 3.3V or 5V logic from microcontrollers. * **P-Channel Operation:** This MOSFET conducts when the Gate voltage is lower than the Source voltage. It is commonly used as a "High-Side Switch." * **Fast Switching:** Due to low input capacitance, it can switch states very rapidly. * **Ruggedness:** Most versions include an integrated Zener diode for ESD protection of the gate. --- ### ## 4. Common Applications The BSS84 is not intended for high-power motor control, but rather for signal processing and low-power management: * **Load Switching:** Turning on/off small peripheral devices in battery-powered circuits. * **Level Shifting:** Converting signals between different voltage domains. * **Power Management:** Used in portable electronics to disconnect inactive sub-systems. * **Driver Circuits:** Driving small relays or LEDs. --- ### ## 5. Example Circuit Logic To turn on a load using a BSS84: 1. Connect the **Source** to the positive supply (e.g., +5V). 2. Connect the **Drain** to the positive side of your load. 3. Pull the **Gate** to **Ground (0V)** to turn the switch **ON**. 4. Pull the **Gate** to **High (+5V)** to turn the switch **OFF**. ```python # Conceptual Logic for Microcontroller Control # P-Channel MOSFET (BSS84) Behavior: # Logic LOW (0V) -> MOSFET ON # Logic HIGH (5V) -> MOSFET OFF ```