MOSFET Overview and how to check mosfet using digital multimeter

A MOSFET, or Metal-Oxide-Semiconductor Field-Effect Transistor, is a crucial component in electronic circuits for amplification and switching applications.

• Types of MOSFETs:
  • N-Channel and P-Channel: MOSFETs come in two main types based on the majority charge carriers in the channel – N-Channel and P-Channel.
• Three Terminal Device:
  • A MOSFET has three terminals: Gate (G), Source (S), and Drain (D).
• Operation Principle:
  • The MOSFET operates on the principle of an electric field controlling the conductivity of a channel between the source and drain.
• Subtypes:
  • Enhancement Mode: Requires a positive voltage at the gate to turn it on.
  • Depletion Mode: Normally conducts and requires a negative voltage at the gate to turn it off.
• Applications:
  • MOSFETs are used in amplifiers, digital circuits, voltage regulators, power supplies, and switching circuits.
• Advantages:
  • High input impedance.
  • Low power consumption.
  • Fast switching speed.
  • Compact size.
• MOSFET Symbols:
  • In circuit diagrams, N-Channel and P-Channel MOSFETs are represented by different symbols.
• Classes:
  • Bulk MOSFET: The traditional type with a bulk semiconductor material.
  • SOI (Silicon on Insulator): Utilizes a thin layer of silicon on an insulating substrate.
• High-Side and Low-Side Switching:
  • MOSFETs can be used for high-side or low-side switching depending on the application.
• Gate Drive Requirements:
  • Proper gate drive voltage and current are crucial for MOSFET operation.

Checking a MOSFET Using a Digital Multimeter

1. Set Multimeter to Diode Test Mode:
   • Turn on your multimeter and set it to the diode test mode. This mode is often represented by a diode symbol on the multimeter.
2. Identify MOSFET Pins:
   • Identify the three pins of the MOSFET: gate (G), drain (D), and source (S). Refer to the datasheet for your specific MOSFET to confirm pin configurations.
3. Check Gate-Source Diode:
   • Place the multimeter’s positive lead on the MOSFET’s gate (G) and the negative lead on the source (S). Note the reading.
   • Reverse the leads (positive on source, negative on gate) and note the reading.
   • If one direction shows a low resistance (near 0 ohms) and the other shows a high resistance (infinite or OL), the gate-source diode is likely intact.
4. Check Drain-Source Diode:
   • Place the positive lead on the MOSFET’s drain (D) and the negative lead on the source (S). Note the reading.
   • Reverse the leads and note the reading.
   • Similar to gate-source, if one direction shows low resistance and the other shows high resistance, the drain-source diode is likely intact.
5. Check Gate-Drain Resistance:
   • Measure the resistance between the gate (G) and drain (D) with the multimeter. It should read as an open circuit (infinite resistance).
6. Check Gate-Source Voltage:
   • Apply a small voltage (usually around 5V) between the gate (G) and source (S). This should be done with the MOSFET removed from the circuit. Monitor for any change in the drain-source resistance.