How to Solve Severe Heating of MOSFETs under Low Current

1. Check Conduction Losses Caused by High On-Resistance (Rds(on))

The most common cause of MOSFET heating in low-current scenarios is excessive conduction loss due to a relatively high Rds (on). While MOSFETs are designed to have low resistance when fully conducting, improper selection or insufficient gate drive voltage can prevent them from entering the full-on state, increasing Rds (on).

• Solution: Ensure the MOSFET is correctly selected for the application. Look for devices with lower Rds(on) specifications, especially those optimized for low-current operations. YFW's MOSFET series, such as the YFW1234, are engineered to minimize conduction losses with advanced manufacturing processes, providing excellent low-resistance performance.

2. Verify Adequate Gate Drive Voltage (Vgs)

Inadequate gate voltage can cause the MOSFET to operate in the linear region rather than the saturation region, leading to higher power dissipation. Even small deviations from the recommended Vgs (typically 4.5V to 10V for logic-level MOSFETs) can significantly increase Rds(on).

• Solution: Confirm that the gate drive circuit provides sufficient voltage and clean signals. Use a voltage regulator or buffer to stabilize Vgs and reduce noise interference. For low-power applications, consider logic-level MOSFETs that fully enhance at lower gate voltages, ensuring full conduction with standard microcontroller outputs.

3. Optimize Thermal Management and PCB Layout

Poor thermal design can hinder heat dissipation, even when power losses seem minimal. Small currents may generate cumulative heat if the MOSFET lacks proper thermal pathways.

• Solution:

• Increase the copper area under the MOSFET on the PCB to act as a heat sink.

• Use thermal vias to conduct heat to the inner layers or the backside of the board.

• For critical applications, add an external heat sink or thermal pad, especially if the device operates in high-temperature environments. YFW's MOSFET packages are designed with thermal-efficient leads and pads to facilitate easy heat dissipation.

4. Avoid Parasitic Inductance and Voltage Spikes

Inductive loads or rapid switching can induce voltage spikes (Vds) that increase power dissipation. Even in low-current circuits, parasitic inductance in the layout or load can cause transient overvoltages, leading to additional heating.

• Solution:

• Shorten the traces connecting the MOSFET to the load and power supply to reduce parasitic inductance.

• Use snubber circuits (RC or RCD networks) across the MOSFET to dampen voltage spikes.

• Ensure proper grounding and decoupling capacitance to stabilize the power supply and reduce switching noise.

5. Monitor Load Matching and Duty Cycle

Continuous operation at the edge of the MOSFET's safe operating area, even with low current, can cause gradual heating. High duty cycles without adequate cooling will accumulate heat over time.

• Solution: Calculate the power dissipation using
  

• (gate drive loss) and ensure it stays within the device's thermal specifications (θJA). Derate the current rating if the application involves prolonged operation or limited airflow.

Conclusion

Addressing MOSFET overheating under low-current conditions requires a systematic approach: proper device selection, optimal gate drive, efficient thermal design, and careful circuit layout. By choosing high-quality components like YFW's MOSFETs, which balance low Rds(on) with robust thermal performance, and implementing these solutions, engineers can effectively mitigate heat issues, ensuring reliable and efficient circuit operation. Always refer to the datasheet for specific thermal and electrical parameters, and conduct thermal simulations or prototype testing to validate the design.