“What is a field effect transistor? Field effect transistor (Field Effect TRANSISTOR abbreviation (FET)) is referred to as a field effect transistor. There are two main types: junction FET (JFET) and metal-oxide semiconductor FET (metal-oxide semiconductor FET, referred to as MOS-FET). What are the basic parameters of FET?

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What is a field effect transistor? Field effect transistor (Field Effect Transistor abbreviation (FET)) is referred to as a field effect transistor. There are two main types: junction FET (JFET) and metal-oxide semiconductor FET (metal-oxide semiconductor FET, referred to as MOS-FET). What are the basic parameters of FET?

(1) Basic parameters of FET

① The pinch-off voltage UP is also called the cut-off gate voltage UGS (OFF), which can reduce the drain-source output current of the depletion junction FET or depletion insulated gate FET when the source is grounded. The required gate-source voltage UGS when it is as small as zero.

②Turn-on voltage UT, also called valve voltage, is the minimum gate-source voltage UGS that enables the drain and source to start conducting when the drain-source voltage UDS of the enhanced insulated gate FET is a certain value.

③Saturated drain current IDSS is the drain current of the depletion FET under zero bias (that is, the gate-source voltage UGS is zero) and the drain-source voltage UDS is greater than the pinch-off voltage Up.

④Breakdown voltage BUDS and BUGS

a. Drain-source breakdown voltage BUDS. Also known as the drain-source withstand voltage value, when the drain-source voltage UDS of the FET increases to a certain value, the drain current ID suddenly increases and the maximum drain-source voltage is not controlled by the gate voltage.

b. Gate-source breakdown voltage BUGS. It is the maximum voltage that can be tolerated between the gate and source of the FET.

⑤ Dissipated power PD Also called drain dissipation power, this value is approximately equal to the product of drain-source voltage UDS and drain current ID.

⑥ The leakage current IGSS is the reverse current generated when the gate-channel junction of the FET is reverse biased.

⑦ The DC input resistance RGS, also known as the gate-source insulation resistance, is the resistance value of the FET gate-channel under the action of the reverse bias voltage, which is approximately equal to the ratio of the gate-source voltage UGS to the gate current.

⑧Drain-source dynamic resistance RDS is the ratio of the variation of the drain-source voltage UDS to the variation of the drain current ID, generally more than a few thousand ohms.

⑨ The low-frequency transconductance gm is also called the amplification characteristic, which is the control ability of the gate voltage UG to the drain current ID, which is similar to the current amplification factor β value of the triode.

⑩ Interpole capacitance is the stray capacitance formed by the distributed capacitance between the poles of the FET. The capacitance of the gate-source capacitance (input capacitance) CGS and the gate-drain capacitance cGD is 1~3pF, and the capacitance of the drain-source capacitance CDS is 0.1~1pF.

The main parameters of the field effect tube

1. Turn-on voltage UT (MOSFET)

Usually, the corresponding gate-source voltage when the conductive channel is just formed and the drain current ID appears is called the turn-on voltage, which is represented by UGS(th) or UT.

The turn-on voltage UT is a parameter of the MOS enhancement mode transistor. When the gate-source voltage UGS is less than the absolute value of the turn-on voltage, the FET cannot be turned on.

2. Pinch-off voltage UP (JFET)

When UDS is a fixed value (such as 10V) and ID is equal to a small current (such as 50mA), the voltage applied between the gate and the source is the pinch-off voltage. When UGS=UP, the drain current is zero.

3. Saturation drain current IDSS (JFET)

The saturation drain current IDSS is the drain current when the FET is pre-pinch-off under the condition of UGS = 0. The maximum current that the IDSS type field effect transistor can output.

4. DC input resistance RGS

The DC input resistance RGS is the DC resistance between the gate and the source when the drain-source short circuit is applied, and the gate-source voltage is applied.

Junction field effect transistor: RGS “107ΩMOS tube: RGS” 109 ~ 1015Ω.

5. Transconductance Gm

The ratio of the micro-variable of drain current to the micro-variable of gate-source voltage, namely gm=△ID/△UGS. It is a parameter that measures the ability of the FET gate-source voltage to control the drain current. gm is equivalent to the hFE of the triode.

6. Maximum drain power dissipation

The maximum drain power consumption PD=UDSID, which is equivalent to the PCM of the triode.