How to choose a MOSFET?

There are two types of MOSFETs, N-channel and P-channel. In power systems, MOSFETs can be considered as electrical switches. The switch of an N-channel MOSFET conducts when a positive voltage is added between the gate and the source. While conducting, current can flow through the switch from the drain to the source. There is an internal resistance between the drain and the source called the on-resistance RDS(ON).

 

MOSFET as a basic component of the electrical system, Guanhua Weiye tell you how to make the right choice according to the parameters?

I. Channel Selection

The first step in selecting the correct device for your design is to determine whether to use an N-channel or P-channel MOSFET. in power applications, a MOSFET is grounded and the load is connected to the trunk voltage when the MOSFET forms a low-voltage side switch. N-channel MOSFETs should be used in low voltage side switching due to the consideration of the voltage required to turn off or turn on the device. High voltage side switching should be used when the MOSFET is connected to the bus and load ground connection.

 

II. Selecting Voltage and Current

The higher the rated voltage, the higher the cost of the device. According to practical experience, the rated voltage should be greater than the trunk voltage or bus voltage. Only then can it provide sufficient protection against MOSFET failure. When selecting a MOSFET, the maximum voltage from drain to source needs to be determined.

In continuous conduction mode, the MOSFET is in a steady state, when current passes continuously through the device. Pulse spikes are when there are large surges (or peak currents) flowing through the device. Once the maximum current is determined under these conditions, just select the device that can withstand the maximum current.

 

Third, conduction loss

Because the on-resistance varies with temperature, the power loss will vary proportionally. For portable design, the use of lower voltage is more common, while for industrial design, higher voltage can be used.

 

System Thermal Requirements

Regarding system cooling requirements, Crown Worldwide reminds you that there are two different scenarios that must be considered, the worst case and the real situation. Use the worst-case calculation because this result provides a larger margin of safety and can guarantee that the system will not fail.

The MOSFET is gradually replacing the triode in integrated circuits because of its low power consumption, stable performance, and radiation resistance. But it is still very delicate, and although most of them already have built-in protection diodes, they can be damaged if care is not taken. Therefore, it is best to need to be careful in the application as well.