How to Select a Low Voltage MOSFET

Introduction

Low voltage MOSFETs are commonly used for load switching, power conversion, battery systems, motor drives and DC-DC converter applications. Device selection requires engineers to balance conduction loss, switching loss, current capability, thermal limits and available board space.

Select the Correct Voltage Rating

The MOSFET voltage rating must exceed the maximum voltage that can occur across the device. This calculation should include input variation, switching spikes and transient conditions. Additional voltage margin may be required in circuits with high parasitic inductance or long PCB traces.

Evaluate RDS(on)

Drain-source on-resistance directly affects conduction loss. Lower RDS(on) can reduce heat generation at high current, but the value changes with gate voltage and junction temperature. Engineers should compare the RDS(on) specified under conditions that match the actual gate-drive circuit.

Compare Gate Charge and Switching Loss

A device with very low RDS(on) may have higher gate charge or capacitance. This can increase switching loss and place greater demand on the gate driver. Higher-frequency circuits generally require careful balancing between conduction performance and switching characteristics.

Review Current, Package and Thermal Limits

The current rating alone does not determine whether a MOSFET is appropriate for the application. Package thermal resistance, PCB copper area, airflow and ambient temperature all affect the device’s allowable operating current. Junction temperature should be calculated under realistic operating conditions.

Product Selection

Toshiba offers 12V to 300V MOSFETs across a range of voltage ratings, package types and electrical characteristics. Review available products and compare selection parameters on the Toshiba 12V to 300V MOSFET product page.