MOS tube parameters

MOS diode parameters

1, VGS(th) (turn-on voltage)

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

In application, the gate voltage with ID equal to 1 mA under the condition of short drain connection is often called the turn-on voltage. This parameter generally decreases with the increase of junction temperature.

On-condition of MOS transistor

Switching conditions of MOS diode:

N-channel: Turn on when VG > VS, and when VGS > VGS (th);

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

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

2. VGS (maximum gate-source voltage)

The maximum voltage that the grid can bear, the grid is the weakest part of the MOS diode, so it should be noted when designing that the voltage loaded on the grid cannot exceed this maximum voltage.

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

The maximum impedance between drain and source when conducting determines the power consumption of MOSFET when conducting. 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, which is called on loss. Select MOS diode with small on-resistance to reduce on-loss

At present, the on-resistance of low-power MOS diodes is generally around tens of milliohms, and there are also several milliohms.

4. ID (conduction current)

Maximum drain-source current. Refers to the maximum current allowed to pass between the drain and the source when the field effect transistor works normally. The working current of FET should not exceed ID.

In general, practical application as a switch needs to consider the power consumption of the end load and judge whether it will exceed ID.

5. VDSS (drain-source breakdown voltage)

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

After 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 variation of drain output current to the variation of gate-source voltage.

It is an important parameter to characterize the amplification ability of MOS transistor, 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 MOS diode will decrease; if it is too large, it will lead to too fast turn-off speed and poor EMI characteristics.