Latching power switch strip micro USB

USB-Controlled Load Switch with MOSFET

🔧 Project Purpose

This project implements a simple MOSFET-controlled switching system powered via a USB connector. It allows the user to manually control the power delivery to a load (such as an LED or other small device). The circuit includes an indicator LED showing the load status and incorporates protection and filtering components for safe and stable operation.

🔌 Key Features and Components

1. USB Power Input and Filtering

• Connector: USB (labeled as INPUT)

• Fuse (F1, 0466003.NRHF): Protects the circuit against overcurrent conditions.

• R5 (200 Ω): Series resistor on the D+ line, possibly for identification or protection.

• L1 (80 Ω): Small inductor for power line noise filtering.

• C1 (100 µF): Bulk capacitor to filter voltage fluctuations on the VCC rail.

2. Control Switch

• SWITCH (XKB5858-Z-E-75): Manual pushbutton used to control the MOSFET gate.

• D1 (1N4148WS): Diode for protecting the gate circuit from voltage spikes.

• R3, R4, R22: Resistors forming voltage dividers and pull-down configurations:

  • R3: 100 Ω in series with the gate

  • R4: 1 MΩ pull-down resistor

  • R22: 100 kΩ for gate voltage control

3. Load Switching via MOSFET

• Q2 (AOD4184A): N-channel MOSFET acting as a switch for the load.

• LOAD connector: Allows connecting an external load device.

• C2 (10 µF): Decoupling capacitor for the load.

• OUT LED + R1 (1 kΩ): Visual indicator (green LED) showing when the load is active (MOSFET is conducting).

⚙️ How It Works

1. Power Supply: USB provides voltage to the system.

2. Protection and Filtering: Fuse, inductor, and capacitor ensure clean and safe power delivery.

3. Switch Control: User presses the pushbutton switch to alter the MOSFET gate voltage.

4. MOSFET Operation: When the gate receives sufficient voltage, the MOSFET turns on, connecting the load to ground and allowing current to flow.

5. Status Indicator: The green LED lights up to indicate the load is powered.

🔐 Protection and Safety Features

• Fuse: Guards against overcurrent damage.

• Diode: Protects the MOSFET’s gate from voltage transients.

• Inductor & Capacitors: Filter out power supply noise and stabilize the system.

• Pull-down Resistors: Prevent the MOSFET gate from floating and turning on unintentionally.

✅ Possible Applications

• Simple USB-powered load controller

• Manual switch for LEDs or small DC devices

• Projects needing load control without microcontrollers

• Educational circuits for learning about MOSFETs and power switching