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What does the arrow in bipolar junction transistor symbol represent?
Wiki User
∙ 11y ago
There a two types of bipolar transistors
PNP and NPN .
This refers to the doping elements used in the silicon components of this 3 layer device with base always in the middle.
The arrow is the emitter wire and shows direction of conventional current flow(positive to negative)
NPN transistors (generally used in negative earth circuits) have the arrow pointing away from the base connection
PNP transistors ( generally used in circuits with positive earth) have the arrow pointing towards the base connection.
Wiki User
∙ 11y ago
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What does the circuit symbol below represent?
Switch
What does the symbol u mean in physics?
The symbol 'u' is often used in place of the prefix 'micro-' in math and physics.AnswerThe symbol U is used to represent voltage. In this context, a lower-case 'u' represents an instantaneous AC voltage. In thermodynamics, it is used to represent internal energy.
How do you symbolically represent a conecting wire and a resistance?
The symbol for a wire is simply a line between circuit elements. The symbol for a resistor is a squiggly line. The related link goes directly to a picture of the symbol.
What is the re-model of npn common base transistor?
Thus if we go back to the circuit model for the common emitter transistor, and re-draw it as a small signal model it would look something like Figure 1. Here we have replaced the diode with a linear element (a resistor, called rπ) and we have changed the notation for the currents from IB and IC to ib and ic respectively, to remind us that we are now talking about small signal ac quantities, not large signal ones. The bias currents IB and IC are still flowing through the device (and we will leave it to ELEC 342 to discuss how these are generated and set up) but they do not appear in the small signal model. This model is only used to figure out how the transistor behaves for the ac signal going through it, not have it responds to large DC values. Figure 1: Small signal linear model for the common emitter transistor Figure 1 (3.16.png) Now rπ the equivalent small signal resistance of the base-emitter diode is given simply by the inverse of the conductance of the equivalent diode. Remember, we found rπ===1qkTIB1qkTICββ40IC (1) where we have used the fact that IC=βIB and qkT=40V-1. As we said earlier, typical values for βin a standard bipolar transistor will be around 100. Thus, for a typical collector bias current of IC=1mA, rπ will be about 2.5 kΩ. There is one more item we should consider in putting together our model for the bipolar transistor. We did not get things completely right when we drew the common emitter characteristic curves for the transistor. There is a somewhat subtle effect going on when VCE is increased. Remember, we said that the current coming out of the collector is not effected by how big the drop was in the reverse biased base-collector junction. The collector current just depends on how many electrons are injected into the base by the emitter, and how many of them make it across the base to the base-collector junction. As the base-collector reverse bias is increased (by increasing VCE the depletion width of the base-collector junction increases as well. This has the effect of making the base region somewhat shorter. This means that a few more electrons are able to make it across the base region without recombining and as a result α and hence β increase somewhat. This then means that IC goes up slightly with increasing VCE. The effect is called base width modulation. Let us now include that effect in the common emitter characteristic curves. As you can see in Figure 3, there is now a slope to the IC(VCE) curve, with IC increasing somewhat as VCE increases. The effect has been somewhat exaggerated in Figure 2, and I will now make the slope even bigger so that we may define a new quantity, called the Early Voltage. Figure 2: Common emitter response with base-width modulation effectFigure 2 (3.17b.png) Figure 3: Finding the Early VoltageFigure 3 (3.18b.png) Back in the very beginning of the transistor era, an engineer at Bell Labs, Jim Early, predicted that there would be a slope to the IC curves, and that they would all project back to the same intersection point on the horizontal axis. Having made that prediction, Jim went down into the lab, made the measurement, and confirmed his prediction, thus showing that the theory of transistor behavior was being properly understood. The point of intersection of the VCE axis is known as the Early Voltage. Since the symbol VE, for the emitter voltage was already taken, they had to label the Early Voltage VA instead. (Even though the intersection point in on the negative half of the VCE axis, VA is universally quoted as a positive number.) How can we model the sloping I-V curve? We can do almost the same thing as we did with the solar cell. The horizontal part of the curve is still a current source, and the sloped part is simply a resistor in parallel with it. Here is a graphical explanation in Figure 4. Figure 4: Combining a current course and a resistor in parallelFigure 4 (3.19.png) Usually, the slope is much less than we have shown here, and so for any given value of IC, we can just take the slope of the line as ICVA, and hence the resistance, which is usually called ro is just VAIc. Thus, we add ro to the small signal model for the bipolar transistor. This is shown in Figure 5. In a good quality modern transistor, the Early Voltage, VA will be on the order of 150-250 Volts. So if we let VA=200, and we imagine that we have our transistor biased at 1 mA, then ro==200V1mA200kΩ (2) which is usually much larger than most of the other resistors you will encounter in a typical circuit. In most instances, ro can be ignored with no problem. If you get into high impedance circuits however, as you might find in a instrumentation amplifier, then vbe has to be taken into account. Figure 5: Including ro in the small signal linear modelFigure 5 (3.20.png) Sometimes it is advantageous to use a mutual transconductance model instead of a current gain model for the transistor. If we call the input small signal voltage vbe, then obviously ib==vberπvbeβ40IC (3) But ic=βib=βvbeβ40IC=40ICvbe≡gmvbe (4) Where gm is called the mutual transconductance of the transistor. Notice that β has completely cancelled out in the expression for gm and that gm depends only upon the bias current, IC, flowing through the collector and not on any of the physical properties of the transistor itself! Figure 6: Transconductance small signal linear modelFigure 6 (3.21.png) Finally, there is one last physical consideration we should make concerning the operation of the bipolar transistor. The base-collector junction is reverse biased. We know that if we apply too much reverse bias to a pn junction, it can breakdown through avalanche multiplication. Breakdown in a transistor is somewhat "softer" than for a simple diode, because once a small amount of avalanche multiplication starts, extra holes are generated within the base-collector junction. These holes fall up, into the base, where they act as additional base current, which, in turn, causes IC to increase. This is shown in Figure 7. Figure 7: Ionization at the base-collector junction causes additional base currentFigure 7 (3.22.png) A set of characteristic curves for a transistor going into breakdown is also shown in Figure 8. Figure 8: Bipolar Transistor going into breakdownFigure 8 (3.23b.png) Well, we have learned quite a bit about bipolar transistors in a very short space. Go back over this chapter and see if you can pick out the two or three most important ideas of equations which would make up a set of "facts" that you could stick away in you head someplace. Do this so you will always have them to refer to when the subject of bipolars comes up (In say, a job interview or something!).
What is the symbol used in a formula to represent the rate of energy dissipation in an electric circuit?
"W" for watts, or wattage
On what basis the third terminal of a transistor is given name base?
In the original point contact transistor design, there was a base of semiconductor material at the bottom to which two point contact wires were connected, each point contact wire being very close to the other on the surface of the base. There were three wires, one to each of the point contacts and one to the semiconductor base. The two point contacts were called the collector and emitter, and the base was called - logically, being at the bottom - the base.We tend to show the base as being between the collector and emitter, but in actuality the collector and emitter were added on top of the base.Although all modern bipolar transistors are junction transistors, the standard bipolar transistor symbol is actually a point contact transistor symbol, although the base may be drawn on any side not just the bottom.
What is the schematic symbol for a transistor?
See link below...
How does a npn transistor switch work to switch a load on and off?
let's insert a transistor in place of the switch to show how it can control the flow of electrons through the lamp. Remember that the controlled current through a transistor must go between collector and emitter. Since it is the current through the lamp that we want to control, we must position the collector and emitter of our transistor where the two contacts of the switch were. We must also make sure that the lamp's current will move against the direction of the emitter arrow symbol to ensure that the transistor's junction bias will be correct as in Figure below(b).
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There is no standard symbol for subring
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The symbol that is used to represent a joule is the letter "J". This is a derived unit of energy. It can also be used to represent work, and an amount of heat.
