A depletion-type MOSFET (metal-oxide-semiconductor field-effect transistor) works by controlling the flow of current between the source and drain terminals using a voltage applied to the gate terminal.
The basic structure of a depletion-type MOSFET consists of a silicon substrate with two heavily doped regions of opposite polarity (called the source and drain) separated by a lightly doped region (called the channel). A layer of oxide insulates the gate electrode, which is placed on top of the channel.
In a depletion-type MOSFET, the channel is already conducting without any voltage applied to the gate, due to the presence of impurities that create a sufficient number of mobile charge carriers (electrons or holes) in the channel. This means that the device is normally on or conducting, and the current can flow freely from the source to the drain.
When a negative voltage is applied to the gate, it repels electrons in the channel, reducing its conductivity and increasing its resistance. As a result, the current flowing between the source and drain is reduced, and the device is turned off.
Conversely, when a positive voltage is applied to the gate, it attracts more electrons to the channel, increasing its conductivity and decreasing its resistance. This allows more current to flow between the source and drain, and the device is turned on.
Overall, the depletion-type MOSFET operates by controlling the resistance of the channel through the voltage applied to the gate, which in turn controls the flow of current between the source and drain terminals.
depletion-type MOSFETs have several uses, including:
Amplification: Depletion-type MOSFETs can be used in amplifier circuits to amplify a small input signal.
Switching: Depletion-type MOSFETs can be used as switches in digital circuits.
Voltage regulation: Depletion-type MOSFETs can be used as voltage regulators in power supply circuits.
Oscillation: Depletion-type MOSFETs can be used in oscillator circuits to generate signals at a specific frequency.
Voltage-controlled resistors: Depletion-type MOSFETs can be used as voltage-controlled resistors in circuits such as filters and equalizers.
Overall, depletion-type MOSFETs can be used in a wide range of electronic circuits, where their properties such as high input impedance, low noise, and low power consumption make them useful components.