Field-effect transistors and their principle of operation

FET's are referred to as such semiconductor devices, the principle of which is based on modulation of the resistance of the transverse electric field of a semiconductor material.

A Distinctive feature of devices of this type is that field effect transistors have a high voltage gain and high input resistance.

These devices in creating the electric current participate only carriers of the same type of charge (electrons).

There are field-effect transistors of two types:

- having the structure of the TIR, i.e. the metal, then a dielectric, then the semiconductor (TIR);

- have a control p-n junction.

Part of the simple field effect transistor includes a plate made of semiconductor material having only one p-n junction in the center and nevidiamaia contacts at the edges.

The Electrode of such a device, in which conducting channels are charge carriers, is called the source, and the electrode on which the electrode out of the channel – drain.

Sometimes it happens that such a powerful key device come with failure. Therefore, during the repair of any electronic equipment is often necessary to check the field-effect transistor.

This requires desoldering device, since an electronic circuit to verify it will fail. And then, following some of the instructions, proceed to checkout.

Field-effect transistors have two modes-dynamic and key.

The Key mode of operation of the transistor – one in which the transistor is located in two States – in the fully open or fully closed. But it is an intermediate state when the component is opened partially missing.

In the ideal case, when the transistor is "open", i.e. located in the so-called saturation mode, the resistance between terminals "drain" and "source" tends to zero.

The Power losses in the open state is represented by the product of voltage (equal to zero) the magnitude of the current. Consequently, the power dissipation is zero.

In the cutoff mode, i.e., when the transistor is locked, the resistance between the "drain/source"-conclusions tends to infinity. Lose power when the closed state is the product of the voltage across a current value of zero. Accordingly, the power loss = 0.

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It Turns out that in key mode, the power loss of the transistors is zero.

In practice, when you open the transistor, naturally, some resistance "sink/source" will be present. When closed, transistor on these findings, the current of small magnitude is still leaking. Consequently, in static mode, the power loss in the transistor is minimal.

A dynamic, if the transistor is closed or open, its linear boost region operating point where the current passing through the transistor, conventionally, is half of the drain current. But the voltage "sink/source" are likely to achieve half the maximum value. Consequently, dynamic mode transistor provides the allocation of huge power losses, which reduces to nothing the remarkable properties key mode.

But, in turn, prolonged exposure of the transistor in the dynamic mode is much smaller than the duration of stay in the mode of statics. With the result that the efficiency of the cascade transistor, which operates in key mode, very high and may be from ninety three to ninety eight percent.

Field-effect transistors that operate in the above mode, have a wide application in power Converter installations, the sources of pulsed power supply to output stages of certain transmitters, etc.