What are the characteristics of MOSFET?

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2023-03-31 14:48:48 1120

Parasitic Capacitance and Temperature Characteristics of MOSFET

Capacitance of MOSFET

In the structure of the power MOSFET, as shown in Figure 1, there is a parasitic capacity.

In terms of the structure of the power MOSFET, as shown in Figure 1, there is a parasitic capacitance. The G (gate) terminal of the MOSFET is insulated from other electrodes by an oxide film, and a PN junction is formed between the DS (drain, source) to form a built-in diode structure. Cgs, Cgd capacity is determined by the capacitance of the oxide film, and Cds is determined by the junction capacity of the built-in diode.

Figure 1: Capacitance Model for MOSFETs

Generally speaking, the three types of Ciss/Coss/Crss in Table 1 are recorded in the MOSFET specification.

Table 1 Capacitance characteristics of MOSFET
Mark	Formula	Meaning
Ciss	Cgs+Cgd	Input capacity
Coss	Cds+Cgd	Output capacity
Crss	Cgd	Feedback capacity

As shown in Fig. 2, the capacitance characteristics depend on the voltage VDS between DS (drain and source). The larger the VDS, the smaller the capacity value.

Figure 2: Capacity - VDS dependency

Temperature characteristics

The actual measurement examples are shown in Figures (1) ~ (3)

There is little difference in the temperature dependence of the capacity characteristics.

Figure 3: Capacitance Temperature Characteristics

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About MOSFET switching and its temperature characteristics

About MOSFET switching time

After the gate voltage is ON/OFF, the MOSFET is ON/OFF. This delay time is the switching time. The switching time is as shown in Table 1. Generally speaking, td(on)/tr/td(off)/tf are recorded in the specification.

Slkor determines the typ. value of the specification based on the measured value of the circuit in Figure 2.　

Table 1: SW Characteristics of MOSFETs
Mark	Content
td(on)	Turn on delay time (VGS 10%→VDS 90%)
tr	Rise Time (VDS 90%→VDS 10%)
td(off)	OFF delay time (VGS 90%→VDS 10%)
tf	fall time (VDS 10%→VDS 90%)
ton	opening time (td(on) + tr)
toff	OFF time (td(off) + tf)

Temperature characteristics

The measured examples are shown in Figure 3(1)~(4).

The switching time increases slightly as the temperature rises, but it increases by about 10% when the temperature rises to 100°C, and there is almost no temperature dependence of the switching characteristics.

Figure 3: Switching Temperature Characteristics

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Regarding VGS(th) of MOSFET (threshold value)

About VGS(th) of MOSFET

When the MOSFET is turned on, the voltage required between GS (gate, source) is called VGS(th) (threshold value).

That is, when the voltage above the limit value is input, the MOSFET is turned on.

So how much A current can the MOSFET pass through when it is in the on state? For each component, it is recorded in the electrical characteristics column of the specification sheet.

Table 1 is an example of the electrical characteristics column of the specification. In this case, when the input VDS=10V, the gate threshold voltage ID(th) required to pass 1mA current through ID is 1.0V to 2.5V.

Table 1: Electrical Characteristics Column of Specifications

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ID-VGS characteristics and temperature characteristics

Figures 1 and 2 show the actual measurement examples of ID-VGS characteristics and threshold temperature characteristics.

As shown in Figure 1, in order to pass most of the current, a relatively large gate voltage is required.

The models listed in Table 1 have a limit value of 2.5V or less in the specifications, but they are 4V driven products.

When using, please input the gate voltage to make it turn on sufficiently.

As shown in Figure 2, the limit value decreases with temperature.

By observing the threshold voltage change, the channel temperature of the element can be calculated.

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What are the characteristics of MOSFET?

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