2N5484 JFET DATASHEET PDF

2N datasheet, 2N pdf, 2N data sheet, datasheet, data sheet, pdf, Calogic, N-Channel JFET High Frequency Amplifier. 2N 2N 2N MMBF MMBF MMBF N-Channel RF Amplifier. This device is designed primarily for electronic switching applications. Zero – Gate –Voltage Drain Current. 2N (VDS = 15 Vdc, VGS = 0). 2N IDSS. —. —. mAdc. SMALL–SIGNAL CHARACTERISTICS.

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Static terminal characteristics of two representative JFETs are examined using a PSpice computer analysis of a sophisticated device model.

Although the JFET is a different device from the BJT nevertheless various aspects dataheet device use are similar in general concept if not in precise detail.

The following paragraph is a modest paraphrase of that introducing the note on BJT Biasing. In general all electronic devices are nonlinear, and operating characteristics can change significantly over the range of hfet under which the device operates.

The junction field-effect transistor, for example, has a normal amplifier operating drain voltage range bounded by the VCR range for low voltages and drain-gate junction breakdown for high voltages. It also is bounded by excessive drain current on the one hand ifet cutoff on the other hand. In order to function properly the transistor must be biased properly, i. Our primary concern here however is not to determine what an appropriate operating point is; that determination depends on a particular context of use and even more so involves a degree of judgment.

Rather we consider dafasheet to go about establishing and maintaining a given operating point. Where a specific context is needed for an illustration we assume usually that the transistor is to provide linear voltage amplification for a symmetrical signal, i.

The figure illustrates the essential nature of the JFET topology, actual geometry varies depending on the intended application and fabrication techniques. The JFET is at its heart a nonlinear resistor fabricated from a doped semi-conductor material. To be specific we refer to an N-channel device, meaning the conducting material is an N-type semiconductor. Operation of the complementary P-channel device operation is similar and can be inferred directly from the N-channel discussion.

In the figure the lightly shaded region is the conducting channel. The darker regions at the ends of the channel are relatively heavily doped terminations for the channel to assure good connections to externally accessible terminals. By convention the terminal designations are defined so that carriers electrons for the N-channel device flow from the source and to the drain. For the N-channel device, therefore, a voltage is assumed to be applied so that the drain is positive relative to the source.

The resistance of the channel is a function of its geometry and the electron transport parameters of the doped semiconductor. The device as described thus far is more or less a temperature-sensitive resistor. Suppose now that the channel geometry is changed, e. This is a change of channel geometry, in particular a smaller channel cross-section, which increases the channel resistance, and therefore for a given drain-source voltage less current will flow after the gouging.

Even less current flows with further gouging. We have then a variable resistance, although a mechanically ‘gouged’ the resistor would have a short service life. On the other hand the channel cross-section can be effectively varied without physically removing material. That is, charge carriers can be effectively removed from part of the cross-section electrically reducing the Introductory Electronics Notes Copyright M H Miller: To effectively remove carriers from a region we simply need to shove them out of that region, and the way to shove a charged carrier is with an electric force.

The JFET makes use of the fact that a very strong electric field exists across a PN junction, and that field effectively removes carriers from the junction region. The gate electrode shown in the figure is formed as a PN junction, with the channel forming one side of the junction.

The gate side of the junction is relatively heavily doped so that the junction depletion region extends largely into the channel.

The width of the depletion region increases with increasing reverse-bias, extending further into the channel and further increasing the channel resistance. For small values of drain-source voltage the JFET characteristic is linear, as illustrated by the sketch.

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Increasing the magnitude of the reverse-biased gatesource voltage increases the depletion width and increases the channel resistance. The drain characteristics correspond to a variable resistor, with a voltage-controlled resistance. The conventional JFET icon for an N-channel device also is shown in the figure, and is identified as to type by the gate terminal PN junction arrow. Note that following common convention the drain current is positive in the direction of the current polarity arrow shown for an electron carrier flow from source to drain.

The P-channel device icon would have the gate arrow reversed, and the voltage polarities also would be reversed so that normally the hole carriers flow from source to drain, and the gate junction is reverse-biased. The reason for the emphasis on small values of drain-source voltage in the discussion above arises from the fact that the gate junction extends a significant distance along the channel length as well as across the channel width.

Since the channel is a continuous resistor there is a voltage drop along the length of the channel, and so the gate reverse-bias actually varies along the gate perimeter. The general shape of the depleted region in the earlier illustration is not accidental. It is intended to reflect the increasing junction reverse-bias voltage, and the consequent increasing depletion region width, moving from the source towards the drain.

In addition of course the reverse-bias changes as the drain-source voltage changes, and so there is an influence of the drain-source voltage on the resistance of the channel. In this respect make careful note of the fact that the junction voltage is not the same as the gate-source voltage; it is the channel and not the source terminal that forms one side of the junction.

As already noted because of the voltage variation along the channel the width of the depletion region varies along the channel, being larger at the drain end of the channel. And moreover the depletion region width changes as the drain-source voltage changes. Indeed, as the drain-source voltage increases for an N- channel device the reverse bias across the junction increases and the channel carries less current for a given voltage than it would otherwise.

The drain characteristics viewed over a larger range of drain-source voltage than before appear roughly as shown to the right. As the drain-source voltage increases further a condition known colloquially as pinch-off occurs; this is the condition wherein theoretically the depletion region extends entirely across the channel.

This occurs initially at the drain end of the channel since that is where the depletion width always is widest. When pinch-off occurs there is a junction depletion region between the drain and the source end of the channel. Further increases in drainsource voltage are taken up primarily by depletion-width changes in this junction region, with only second-order effects on overall channel conduction thereafter.

The channel current is to first-order fixed by the conditions when pinch-off occurs; all carriers forming the source-end current are swept across pinch-off junction region by the strong electric field.

This is roughly similar to the carrier injection through the base of a BJT, although the mechanism of carrier injection is different. A still more extended range of variation of the drain characteristics is sketched to the right.

The voltagecontrolled VCR region, i. The constant current pinch-off region to the right is saturation probably all the remarks respecting a conflict with BJT terminology already have been said, repeatedly. The nature of the control process is such that the ability of the channel to carry current is greatest when the control junction has zero bias or slightly positive, but well below the diode ‘knee’ and decreases with increasing reverse bias.

A JFET thus inherently is a device that is ‘full on’ with no control exerted, and is turned off with increasing reverse bias. This is ‘depletion-mode’ operation, so-called after the nature of the physical process through which control is exerted.

The details of the physics underlying the terminal behavior are complex. However it is the terminal behavior and not a quantitative physical explanation for that behavior that is the principal concern here. An exact form of a theoretical expression for a drain characteristic depends on details of both geometry and doping. However various theoretical expressions, despite major differences in mathematical appearance, actually produce very similar numerical characteristics.

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Thus we describe a commonly used working expression, a quadratic first-order approximation for a drain characteristic in the VCR region of operation, which has the advantage of relative simplicity and adequacy for initial design purposes.

This working expression is the quadratic equation: VP is the pinch-off voltage, i. This is notably different from the BJT, where there is a small millivolts collector-emitter voltage for zero collector current, and zero offset can be an advantage in applications where the JFET is used as an analog switch. The theoretical equations are described graphically in the figure following.

The drain current follows the quadratic expression up to its apex i. The quadratic pinch-off characteristic, i. Straightforward calculation shows that the extension of the tangent at the origin to the pinch-off current level intersects that current where VDS equals half the pinch-off voltage, i.

In effect the roles of the source. The left half-plane is included only to display an effect similar to the Early Effect for the BJT, i. The scale is chosen, as stated before, to overemphasize this dependence; the slope of the curves is only of the order of a few kilohms.

Can a JFET Pass More Than Idss?

The common-source characteristics are redrawn below, this time to emphasize a more appropriate range of operation. One notable distinction is that the control parameter datasheer gate-source voltage, and not a base current as for the BJT.

Indeed the gate current of a JFET corresponds to a reverse-biased junction, and therefore is very small. The 2N drain characteristics are re-plotted once again, this time to emphasize the voltage-controlled resistance range.

The solid circles in the figure below mark the intersection of the pinch-off locus with each characteristic i. The actual current at this voltage is 1.

The circles identify the intersection of the pinch-off locus with each characteristic i. Computed drain characteristics covering both the VCR range and saturation are drawn below. JFET Amplifier We start with an examination of a more or less specific circuit to provide a broad background for a consideration of biasing.

Some distinctions from the BJT case are underlined here to ratasheet special attention to them.

InterFET Corp. Page Selector – 2N datasheet

A voltage source in the base loop reverse-biases the gate junction, setting the gate-source voltage to a fixed value VGS 0. Provided the drain source voltage is large enough, and the voltage drop across the drain resistor is not too large, the JFET is in its normal saturated operating mode.

The drain current is in general a function of the gate voltage. If then a small change is made in VGS there is a corresponding change in drain current, and a consequent change in the voltage drop across the drain resistor.

The battery provides each coulomb of charge carried by the drain current around the loop with the ability to do V DD joules of work. Part of this work-doing ability, I D RD joules per coulomb, is expended in the collector resistor. The rate of doing work, i. The power expended in the resistor should be interpreted as a general consumption of energy, for example by a loudspeaker or a small motor.

The transistor provides the current-control capability by acting as a current valve; a change in gate voltage causes a corresponding drain current change. The change in power expended in the drain resistor datasheeg be considerably greater than the power needed to cause the change. Because the gate junction is supposed to be reverse-biased there is only a very small gate current. Dtasheet only a small gate-source voltage change is needed to change drain current significantly. The power that must be provided at the transistor gate to effect a power change in the collector loop is 22n5484 the product of a quite small gate current and a small gate voltage change.

On the other hand not only is the drain current much larger than the gate current but also the battery voltage ordinarily is much larger than the base voltage and can support larger voltage changes. It is convenient to illustrate the solution graphically, particularly so because the transistor volt-ampere relation is nonlinear.