The heating issue of your MOSFET is typically caused by circuit design problems, excessively high driving frequency, inadequate heat dissipation design, or improper MOSFET selection. Heating can lead to increased power loss in the power transistor, affecting the performance of the MOSFET. Therefore, attention should be paid to heat dissipation design, selection of appropriate heat sinks, and choosing MOSFETs with low on-state resistance to reduce heating issues.

Recently, VBsemi has often heard colleagues say:

"Why is my MOSFET heating up when the current is not large?"

The heating problem of MOSFET is a common issue in its application. Today, VBsemi will briefly explain the heating problem of MOSFET and how to deal with such situations.

Let's first understand the basic situation of MOS heating.

There are several important parameters in MOSFET: on-state resistance RDS(ON), gate/drive voltage VGS, and drain-source current ID flowing through the switch.

Among them, the on-state resistance RDS(ON) is related to the gate (or drive) voltage VGS and the current flowing through the switch.

Under sufficient gate drive, RDS(ON) is a relatively static parameter. MOSFET is prone to generate heat under continuous conduction, leading to heating. The slowly rising junction temperature causes RDS(ON) to gradually increase, and the power loss of the power transistor also increases, leading to the heating and overheating of the MOSFET.

In summary, the heating of MOSFET can be roughly divided into the following factors:

1. Circuit design issues

MOSFET works mainly in a linear state, not in a switch state. If the conduction time of MOSFET is too long, it will lead to heating.

2. Excessively high MOSFET driving frequency, which is proportional to the conduction loss. Therefore, when heating occurs, check if the frequency selection is too high. In addition, pursuing a smaller volume may also lead to a higher frequency and increased loss on the MOSFET.

3. Inadequate heat dissipation design will result in excessive drain-source conduction current ID. However, even if ID is smaller than the maximum current, severe heating may still occur. Therefore, sufficient auxiliary heat sinks are needed to help MOSFET dissipate heat effectively.

4. Proper MOSFET selection is crucial. As mentioned earlier, the key parameter RDS(ON) is the main cause of heating. Therefore, choosing MOSFETs with low on-state resistance is essential. However, it should be noted that the lower the internal resistance, the larger the cgs and cgd capacitances, so MOSFETs with suitable internal resistance should be selected for specific applications.

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