Analysis of Common Issues in MOSFET Applications

As a core switching component in electronic circuits, MOSFETs are widely used in fields such as switching power supplies, motor drives, and power amplifiers. Problems in their application often present chain reactions, requiring full-process control from the source of design to system protection.

Inappropriate Selection of Components

Inappropriate component selection is the primary cause of MOSFET failures. When the voltage, current, or frequency parameters of the device do not match the actual requirements, it will directly cause the operating point to shift, manifested as an abnormal increase in on-resistance or a decrease in switching speed. To solve this problem, it is necessary to strictly screen models based on key indicators such as load power, ambient temperature, and switching frequency, combined with the maximum ratings and thermal resistance parameters in the data sheet, so as to avoid cost waste or insufficient performance caused by parameter redundancy.

Defects in Gate Drive Design

Defects in gate drive design can significantly affect the switching characteristics of MOSFETs. Insufficient drive voltage will lead to incomplete conduction, while weak drive capability will prolong the switching time, both of which will increase losses. In practical applications, a dedicated driver IC should be used to provide sufficient transient current, and a series gate resistor should be used to control the switching speed, so as to balance EMI suppression and switching loss. For high-side drives in bridge topologies, a bootstrap circuit is required to achieve floating drive.

On-State Loss and Switching Loss

On-state loss and switching loss are the main sources of MOSFET heating. On-state loss is determined by on-resistance, so devices with low on-resistance should be prioritized. Switching loss is positively correlated with switching frequency; in high-frequency applications, SiC or GaN wide-bandgap devices can be considered, as their switching speed is 3-5 times faster than traditional silicon-based devices. It should be noted that excessively pursuing switching speed may increase dv/dt, which in turn exacerbates EMI issues.

Insufficient Thermal Design

Inadequate thermal design directly causes junction temperature to exceed the safe range, leading to device parameter drift or even permanent damage. Effective thermal solutions include: reserving a copper foil heat dissipation area of over 20 square millimeters during PCB layout, using TO-252 packages with heat sinks, and adding heat sinks or forced air cooling when necessary. Thermal resistance calculations must cover the complete path from junction to ambient, ensuring that junction temperature does not exceed 150°C under extreme operating conditions.

Avalanche Breakdown

Voltage spikes generated when inductive loads are turned off are the main cause of avalanche breakdown. Inductive components such as motors or transformers generate hundreds of volts of back EMF at the moment the switch is turned off, exceeding the rated drain-source voltage. Protection measures include: paralleling an RC snubber circuit in the power loop, selecting MOSFETs with avalanche energy ratings, or connecting a TVS diode in series for voltage clamping.

High-Frequency Switching Operation

EMI interference generated by high-frequency switching operations can affect the normal operation of surrounding circuits. Control strategies include: limiting dv/dt to within 50V/ns by adjusting the gate resistor, paralleling a 100pF capacitor between the gate and source to suppress oscillation, and using shielding for key signal lines. PCB design should avoid forming loop areas exceeding 1 square centimeter, and power ground and signal ground should adopt single-point grounding.

Lack of Protection Mechanisms

The lack of protection mechanisms exposes MOSFETs to risks under abnormal operating conditions. A complete protection system should include: overcurrent protection, overtemperature protection, undervoltage lockout, etc. Driver ICs with integrated protection functions can simplify design, while software should include fault response mechanisms to turn off the drive signal when abnormalities are detected.

In practical applications, it is recommended to verify key waveforms using simulation tools in the early stage of design, with a focus on voltage spikes at switching nodes and gate oscillation. Establish a standardized component selection process, incorporate parameters such as on-resistance, gate charge, and EAS into the evaluation system, and verify long-term reliability through high-low temperature cycle tests.

To address the 7 core issues in MOSFET applications, in addition to optimizing the design scheme, selecting devices with inherent performance advantages is a more efficient approach. Hekotai's MOSFET series, through hardware-level feature enhancement, reduces the probability of failure from the source, providing engineers with dual guarantees of simplified design and improved reliability.

Company Introduction

Heketai, founded in 1992, is a high-tech and specialized enterprise integrating R&D, design, production and sales of professional components. It focuses on providing cost-effective component supply and customization services to meet the R&D needs of enterprises.

Product supply categories: covering semiconductor packaging materials, passive components such as resistors/capacitors/inductors; as well as MOSFET, TVS, Schottky, voltage regulators, fast recovery, bridge rectifiers, diodes, triodes, power devices, power management ICs and others, providing one-stop procurement for R&D and production needs.

Two intelligent manufacturing centers: South China and Southwest manufacturing centers (Huizhou 75,000㎡ + Nanchong 35,000㎡) are equipped with more than 3,000 advanced equipment and testing instruments; in 2024, 3 new semiconductor material subsidiaries were added to control production capacity and delivery efficiency from the source.

Providing packaging and testing OEM services: supporting sample customization and small-batch trial production, combined with more than 100 patented technologies and ISO9001, IATF16949 certification systems, so that "quality first" runs through every link from R&D to delivery.

Heketai always takes "customer first, innovation-driven" as its core, providing stable and reliable components for enterprises.

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