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MOSFET Selection Guide —-A PRACTICAL HANDBOOK FOR ENGINEERS

MOSFET Selection Guide —-A PRACTICAL HANDBOOK FOR ENGINEERS

May 22, 2026
  • MOSFET Selection Parameters
  • Core selection priority: Breakdown Voltage, Drain Current, On-resistance, Gate Charge, Threshold Voltage, Package & Thermal Resistance
  • 1. Absolute Maximum Ratings
  • 1.VDSS: Drain-source breakdown voltageReserve 1.5~2x margin over actual operating voltage to avoid breakdown.
  • 2.ID: Continuous drain currentDerate to 50%~70% under high temperature; take 1.5~2x rated value for safety.
  • 3.IDM: Peak pulsed drain currentSustain surge current from inductive loads and instant startup.
  • 4.VGS: Gate-source voltageCommon range: ±20V; logic-level MOSFET: ±12V.
  • 5.PD: Maximum power dissipationActual working power shall not exceed 80% of rated power.
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  • 2. Static Characteristic Parameters
  • 1.RDS(on): Drain-source on-resistanceLower value brings less conduction loss and heat generation.
  • 2.VGS(th): Gate threshold voltageStandard type: 2~4V; Logic type: 1~2.5V for direct MCU driving.
  • 3. Dynamic Characteristic Parameters
  • 1.Qg: Total gate chargeSmaller value achieves faster switching speed and lower drive loss.
  • 2.Ciss/Cgs/Cgd: Input & parasitic capacitanceCritical index for high-frequency circuit design.
  • 3.tr/tf: Rise & fall timeShorter time reduces switching loss.

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  • 4. Thermal Parameters
  • 1.Tj: Junction operating temperatureNormal range: -55℃ ~ 150℃.
  • 2.RθJC/RθJA: Thermal resistanceSmaller thermal resistance means better heat dissipation.
  • 5. Package & Channel Type
  • Small power: SOT-23, SOT-223
  • Medium power: TO-220, TO-252
  • High power: TO-247, SOT-227
  • N-channel: Widely used for low-side switching
  • P-channel: Applied to high-side power control
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  • 5-step Selection Guide
  • 1.Confirm VDSS with sufficient voltage margin
  • 2.Determine ID according to actual load current
  • 3.Select low RDS(on) to minimize heating
  • 4.Match driving voltage with threshold voltage
  • 5.Verify gate charge, package and heat dissipation
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