How do MOSFETs work?

1, MOSFET introduction

FieldEffect Transistor abbreviation (FET)) title MOSFET. by a small number of carriers to participate in heat conduction, also known as multi-pole transistor. It belongs to voltage mastering type semi-superconductor mechanism. There are being output resistance is high (10^8 ~ 10^9Ω), low noise, low power consumption, static range, easy to integrate, no second breakdown phenomenon, the insurance task of the sea wide and other advantages, has now changed the bipolar transistor and power junction transistor of the strong collaborators.

 

2, MOSFET characteristics

1, MOSFET is a voltage control device, it through the VGS (gate source voltage) control ID (drain DC);

2, MOSFET's output DC pole is small, so the output resistance is large.

3, it is the application of a small number of carriers to conduct heat, so he has a better measure of stability;

4, it consists of the reduction path of the electrical reduction coefficient is smaller than the triode consists of the reduction path of the reduction coefficient;

5, MOSFET anti-irradiation ability;

6, due to the absence of a faulty activity of the oligon dispersion caused by scattered particles of noise, so the noise is low.

 

3、MOSFET task principle

MOSFET's operating principle in one sentence, is "drain - source between the ID flowing through the channel for the gate and the channel between the pn junction formed by the reverse bias of the gate voltage master ID", to be precise, ID flows through the width of the path, that is, the channel cross-sectional area, is the change in the reverse bias of the pn junction, which produces a depletion layer The reason for the extended variation control. In the non-saturated sea of VGS=0, since the expansion of the transition layer is not very large, according to the addition of the magnetic field of VDS between the drain-source, some electrons in the source sea are pulled away by the drain, i.e., there is a DC ID activity from the drain to the source. The moderate layer enlarged from the gate to the drain makes a whole body of the channel form a blocking type, ID full. Call this form a pinch-off. Symbolizing the transition layer to the channel of a whole obstruction, rather than DC power is cut off.

 

Because there is no free movement of electrons and holes in the transition layer, it has almost insulating properties in the ideal form, and it is difficult for the general current to flow. But then the electric field between the drain - source, in fact, the two transition layer contact drain and gate pole near the lower part, because the drift electric field pulls the high-speed electrons through the transition layer. The intensity of the drift field is almost constant producing the fullness of the ID scene.

 

The circuit uses a combination of an enhanced P-channel MOSFET and an enhanced N-channel MOSFET. When the input is low, the P-channel MOSFET conducts and the output is connected to the positive terminal of the power supply. When the input is high, the N-channel MOSFET conducts and the output is connected to the power supply ground. In this circuit, the P-channel MOSFET and the N-channel MOSFET always operate in opposite states, with their phase inputs and outputs reversed.