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What percentage of the total current in a transistor flows through the collector?
Wiki User
∙ 14y ago
The total current in a transistor is the emitter current, which is the sum of the collector current and the base current. The ratio of collector current over base current, in linear mode, is beta-DC, or hFe. However, in order for linear mode to be true, the ratings of the transistor must not be exceeded, and the collector current must not be limited by the circuit. Note also that hFe is temperature dependent, and is expressed in the data sheet as a minimum, not an absolute value - it can vary from transistor to transistor.
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∙ 14y ago
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Working of npn transistor?
N-p-n transistor is made by sandwiching thin layer of p-type semiconductor between two layers of n-type semiconductor. It has three terminals, Emitter, Base and collector. The npn transistor has two supplies, one is connected through the emitter base and one through the collector base. The supply is connected such that emitter-base are forward biased and collector base are reverse biased. It means , Base has to be more positive than the emitter and in turn, the collector must be more positive than the base. The current flow in this type of transistor is carried through movement of electrons. Emitter emits electrons which are pulled my the base as it is more positive. these end up in the collector as it is yet more positive. In this way, current flows in the transistor. Transistor can be used as an amplifier, a switch etc.
What does resistor means?
A transistor has three leads, called the base, the collector, and the emitter. The voltage of the base (in relation to the ground) determines whether and how much current flows from the collector to the emitter. An NPN transistor can be off, meaning that there is no (or very little) voltage from the base; partly on, meaning that there is some voltage from the base; or saturated, meaning that it is receiving full voltage from the base. A saturated transistor allows the current to flow from the collector to the emitter unopposed; a partly on transistor provides some resistance; and a transistor that is off provides full resistance. A PNP transistor is similar to an NPN transistor except it performs the opposite function: when it is saturated, the current is fully resisted; when there is no voltage from the base, the current is not at all resisted; and when it is partly on there is some resistance. In sum, a transistor controls the flow between the collector and the emitter based upon the voltage of the base. this is carbage. a transistor is basicaly two diodes back to back base being common TO BOTH DIODES because of inpurity doping on purpose at the depletion region the transistor will control the current flow on the other diode. Once it reaches saturation both diodes conduct therefore current can flow in BOTH DIRECTIONS ACROSS IT.
What are the bias conditions of the base-emitter and base-collector junction for a transistor to operate as an amplifier?
Normally the Emitter lead should be connected to a negative source, the collector to a positive source, and the base to a positive source. the condition is that the collector V should be the highest positive Voltage through the transistor for it to work properly.Now the thing to remember is that if a small amount of current flows through the base then large current will be transferred from the emitter to the collector. therefore it is recommended that the base has a potentiometer to allow you to variate the current to make sure you have the most efficient bias. Another Key thing that you should know is that the best voltage to bias a transistor at is directly between the forward break over voltage and saturation if you dont know these terms then look them up. otherwise those are the conditions for current magnification of a transistor
Is BJT is a current control device or voltage control device?
transistor is a current controlled device. as the current flows through the base of the transistor , it works like a close switch.
Explain the operation npn transistor when used as amplifier.. and explain the basic operation of NPN when used as switch?
The NPN transistor when used as an amplifier is operating in linear mode, and, when operating as a switch, in saturated mode.In the following discussion, base currrent means base-emitter current, while the base is more positive than the emitter, and collector current means collector-emitter current, while the collector is more positive than the emitter. There is base-collector current, but we are going to ignore it for now - besides, we are going to discuss class A, common emitter, configuration.The PNP transistor is very similar. Everything is backwards, including Vcc, which is now -Vcc, or appropriate reconfiguration. The rules are the same - just backward.In switched or saturated mode, the ratio of base to collector current is far greater than beta-dc, or hFe, so the transistor is operating way out of its linear mode. We call that saturated mode, and the transistor is essentially either fully on or fully off, and therefore operating as an on-off switch.The rest of this discussion will focus on linear or amplilfier mode.If the ratio of base to collector current is less than beta-dc, or hFe and, if both base and collector voltage are greater than cutoff voltage, then the transistor is operating in linear mode. Well, sort of, for best linear mode, we look at the data sheet, or make empirical observations, and we pick the base and collector currents that are centered between the base knee and the collector knee, i.e. "in the middle of" the linear region.In this mode, a very small base current can control a much larger collector current, and, most importantly, a very small change in base current can create a much larger change in collector current.In the theoretical case, for example, where the emitter is grounded and where hFe is 100, then 1 mA of base current translates to 100 mA of collector current, and 2 mA of base current translates to 200 mA of collector current. Problem is, that hFe varies amongst even so called identical transistors, and hFe varies as a function of temperature as well.So, in the practical case, an emitter resistor is added to stabilize the transistor and place limits on the need for hFe of a particular value. Done properly, this will yield predictable gain for various transistors and for various temperatures.Now, lets look at how gain works in the practical sense. The base voltage is also a known delta above emitter voltage. Yes, temperature will affect this, but proper design can make this a negligable factor. The emitter current times the emitter voltage results in a known voltage. By Norton's current law, the base current and the collector current add up to be the emitter current, but by hFe, the base current is very much smaller than collector current, meaning that the really important part is that collector and emitter current are the same for all practical purposes.So, now add a collector resistor. Ignoring base current, the collector/emitter circuit is a series circuit, and Norton's current law, reinterpreted for series circuits, says the two resistors have the same current. Think about what that means; if the current in both resistors is the same, then the ratio of the voltage across the two resistors is proportional to their value. The gain of the amplifier is collector resistor divided by emitter resistor. That is critical knowledge. Again, base current enters into the equation but, if hFe is high enough, it does not matter.All that is left, then, is to bias the base. You want to pick a base voltage (current) that places the collector current in the center (or in an appropriate point) of the linear region. Choose a nominal hFe, divide by collector current, and you get an approximation of what base current bias should be. Choose a resistor divider to match, keeping in mind that the two resistors (base to Vcc and base to Gnd) in parallel will reflect your effective input impedance.Review everything, particularly your power levels. To calculate the power through the collector/emitter junction subtract collector resistor voltage from emitter resistor voltage from Vcc, and you get collector/emitter voltage. Multiply that by collector current, and you get power dissipated by the transistor in nomial bias condition.Play with the values until you have what you want. You could even set this up in a spreadsheet.Last, but not least, there is a base bias voltage. If you are going to amplify something, you need to maintain that nominal bias voltage. Connect a series capacitor between the base and the input point and you will be able to operate from an AC signal that is zero referenced. Just pick the RC time constant appropropriate for your application.Similarly, there is a collector bias, so, if you want an AC output zero referenced, use a series capacitor also in between the collector and the ouput.This is an AC coupled, inverting amplifier. There are DC coupled non-inverting versions, but they are more complicated, requiring more than one transistor, and this answer does not address them. Good luck!
Why is the base current in transistor very small?
Because a transistor's collector current is proportionally limited by its base current, it can be used as a sort of current-controlled switch. A relatively small flow of electrons sent through the base of the transistor has the ability to exert control over a much larger flow of electrons through the collector.
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).
Relation between current gain and collector current?
That's referred to as, `hfe` in transistor parlance. Essentially, since a transistor is a current operated device, the gain means that for every milliamp in at the base, the gain (times X) will be amplified through the junction of the collector/emitter. For instance, take a transistor with a gain of 30. One milliamp in at the base will allow the transistor to pass 30 milliamps through the collector/emitter junction. Of course, there will also be a resultant voltage drop of 1.2 volts over all. -.6 volts for the base and -.6 volts through the collector/emitter junction. Remember, you're working with a current controlled device, and not a voltage controlled device like an op-amp.
What happens when collector and base of a transistor are short?
this transistor is common emitter configurated transistor nd if emmiter nd collector both terminals are reversed bias then no current will be flowing through th terminal...
Why base current is very small?
Small is relative term, current gain of the transistor decides how small base current would be than collector current. Most of the emitter current of electrons diffuses through the thin base into the collector. Moreover, modulating the small base current produces a larger change in collector current.Small is relative term, current gain of the transistor decides how small base current would be than collector current. Most of the emitter current of electrons diffuses through the thin base into the collector. Moreover, modulating the small base current produces a larger change in collector current.Small is relative term, current gain of the transistor decides how small base current would be than collector current. Most of the emitter current of electrons diffuses through the thin base into the collector. Moreover, modulating the small base current produces a larger change in collector current.
What is the working of a transistor?
For proper working of a transistor,the voltage at the base region must be more positive than that of the emitter region.The voltage at the collector region, in turn, must be more positive than that of the base region.when voltage is applied to transistor, the emitter supplies electron,which is pulled by the base from the emitter as it is more positive than the emitter.This movement of electrons from emitter to collector creates as flow of electricity through the transistor.The current passes from the emitter to the collector through the base.Thus, adjustment of voltage in the base region modifies the flow of the current in the transistor by changing the number of electron in the base region. In this way, small changes in the base voltage can cause large changes in the current flowing out of the collector. We have three transistor element, a.)Emitter b.)Base c.)Collector
Why is the base lightly doped in a tranistor?
Since the base in an n-p-n transistor is kept very thin, very few electrons get to recombine with holes and escape out of base, most of the electrons are injected from emitter into the collector. As a result, Base-current is very small. Whereas the Collector-current is almost equal to the Emitter-current.
Working of npn transistor?
N-p-n transistor is made by sandwiching thin layer of p-type semiconductor between two layers of n-type semiconductor. It has three terminals, Emitter, Base and collector. The npn transistor has two supplies, one is connected through the emitter base and one through the collector base. The supply is connected such that emitter-base are forward biased and collector base are reverse biased. It means , Base has to be more positive than the emitter and in turn, the collector must be more positive than the base. The current flow in this type of transistor is carried through movement of electrons. Emitter emits electrons which are pulled my the base as it is more positive. these end up in the collector as it is yet more positive. In this way, current flows in the transistor. Transistor can be used as an amplifier, a switch etc.
Did someone ask the question can you use a transistor as a diode there is a device called a transistor diode connect base to either c or e forgot which to make a zero bias diode?
You can use a transistor as a diode if you connect the base to the collector. Any forward current through the base-emitter junction would cause a corresponding increase in the available current through the collector-emitter junction. Since the base-emitter and collector-emitter junctions are in parallel, this would effectively be a diode, but a true diode would be a better solution if diode functionality is what seek. A: There are actually two diodes, per se, inside a transistor. The base to emitter diode will suffice. By tying the collector to the base it will in effect be two diodes in parallel.
How do NPN transistors work?
on or off
How the current flow through npn?
A; The base must be positive with respect to the emitter this condition will allow collector current to flow from collector to emitter. If the transistor manage to get saturated the current can flow in both direction. as a switch
What are the 3 electrodes of transistor?
Three legs on a transistor are represented by these letters E Emitter =you connect your input depending on type of your transisitor neg or pos B Base = you connect control input again depends on type C collector = here comes your amplified output there are 2 types of transistors PNP and NPN there is no current flow from emitter to collector when ther is no control input at the base. a very small opposite current to the emitter polarity make current flow multiplied by the amplification factor of each transistor. if you use a sound frequency input at the base you have amplified sound output at collector if you just use dc you have amplified dc current output. some transistors leak current to kill that unwanted flow through collector use a small resister from emitter to base.
