WAHT'S THE MOSFET parameters

WAHT'S THE MOSFET parameters

1.VGS(th) (turn-on voltage) 

When the applied gate control voltage VGS exceeds VGS(th), the surface inversion layers of the drain and source regions form a connected channel.

In applications, the gate voltage when the ID is equal to 1 mA under the drain short-circuit condition is often referred to as the turn-on voltage. This parameter generally decreases with increasing junction temperature.

The conduction condition of the MOS DIODE

The switching conditions of the MOS DIODE:

N-channel: when Vg>Vs, when Vgs>Vgs(th) is turned on;

P channel: conduction when Vg< Vs, Vgs< Vgs(th) conduction.

MOS DIODE conduction condition: |Vgs| > |Vgs(th)|

2. VGS (maximum gate-source voltage)

The maximum voltage that the gate can withstand. The gate is the weakest part of the MOS DIODE. When designing, it must be noted that the voltage applied to the gate cannot exceed this maximum voltage.

3. RDS(on) (drain-source resistance)

The maximum impedance between the drain and source when it is turned on, which determines the power consumption when the MOSFET is turned on. This value should be as small as possible, because once the resistance value is too large, the power consumption will increase.

After the MOS transistor is turned on, there is an on-resistance, so the current will consume energy on this resistance. This part of the energy consumed is called the conduction loss. Selecting a MOS DIODE with a small on-resistance will reduce the conduction loss.

The on-resistance of the current low-power MOS transistors is generally around tens of milliohms, and there are also several milliohms.

4. ID (conduction current)

The maximum drain-source current. It refers to the maximum current allowed to pass between the drain and source when the MOSFET is working normally. The working current of the FET should not exceed ID.

In general practical applications as a switch, it is necessary to consider the power consumption of the end load to determine whether the ID will be exceeded.

5. VDSS (drain-source breakdown voltage)

The drain-source breakdown voltage refers to the maximum drain-source voltage that the MOSFET DIODE can withstand when the gate-source voltage VGS is 0.

After the breakdown, the ID will increase dramatically.

This is a limit parameter, and the working voltage applied to the FET must be less than V(BR)DSS.

6. gfs (transconductance)

Refers to the ratio of the change in drain output current to the change in gate-source voltage,

It is an important parameter to characterize the amplification ability of MOS DIODE, and it is a measure of the control ability of gate-source voltage to drain current.

If it is too small, the turn-off speed of the MOS DIODE will be reduced, if it is too large, the turn-off speed will be too fast, and the EMI characteristics will be poor.