They turn ON by applying positive gate-source voltage for N channel & by negative gate-source voltage for P channel Enhancement MOSFET. The Enhancement type MOSFET do not normally conduct when gate-source voltage is at zero. They switch OFF by applying positive or negative gate-source voltage for P channel or N channel MOSFET respectively.
The Depletion type MOSFET is normally ON at zero gate-source voltage. It is a voltage controlled current device. MOSFET or Metal-oxide Semiconductor FET is another field effect transistor whose gate is completely isolated from the current carrying channel that is why it is also known as IGFET (insulated Gate FET).
The main advantage of this Sziklai pair is that it switch on with 0.7v while the total gain remains the same as in Darlington pair. The Sziklai transistor is made from combining two NPN & PNP transistors in Darlington pair formation. the total gain of Darlington transistor is the product of gains of individual BJT & the voltage drop is twice at base-emitter. It can be made from NPN or PNP transistors by connecting it in this configuration. It is a special type of transistor made by connecting the emitter of one BJT with the base of another BJT to increase the current gain & sensitivity. The voltage at the gate terminal switches the PUT on & off when it crosses its cutoff level. PUT or programmable UJT is a four PN layer device just like the thyristors but it operate like UJT if programmed with two external resistors. The P channel JFET switches off by maintaining positive gate to source voltage. A P channel JFET is made up of P-type channel made between Drain & Source while the gate is made of N-type material.
This symbol represents a P-channel JFET (denoted by arrow pointing outwards). The N channel JFET has N-type channel between Source & drain while the gate is made of P-Type material. The voltage increase or decrease the depletion region controlling the current flow. the current flow is controlled by the voltage at its gate terminal. JFET or junction field effect transistors are unipolar transistors because the current flow is due to single carrier type.
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