Characteristics transistor

1) Convention on the currents:

They are considered positive if entering in the transistor.

 

2) Transistor in active zone of operation:

It is come true polarizing the splice directly base-emettitore so as to to reduce the barrier of it upgrades them, in a pnp will be therefore of the gaps that they will diffuse in the base while the free electron number that they diffuse in the emettitore is much inferior in how much has come true a drugged base less of the emettitore, the current that slides in this last one is therefore , comes moreover defined the emettitore rendering . Analogous it comes defined the rendering of base and the rendering of collector .

Being the polarized splice collector-emettitore inversely, the barrier of upgrades is elevated them and being crossed in reduction, the current of spread in the emettitore will be much high one, has , adding it to_{the C0} due to the inverse polarization has the quindi is equal to the relationship between the variation of the current of collector regarding the interdiction and the variation of the current of emettitore regarding the same interdiction, typical values are 0,90 < to < 0,995.

The previous expression of_{the C} is valid for the active region of operation of the transistor, while the generalized expression is that, in short only expresses the fact that to the current in the splice pn between collector and base sum a fraction to of the current that circulates in the emettitore.

 

3) constructive Technologies of the discreet transistor:

to) Realization of the transistor for increase:

A single crystal from a silicon fusion is extracted of which it comes changed the concentration of the impurità during the draft operation.

b) Realization of the transistor for alloy:

2 littles ball of trivalente Indian rest on the two faces of a semiconductor, raise the temperature until catching up the fusion of the Indian, dopodichè in the cooling it crystallize realizing two drugged regions "p".

c) Realization of the transistor for spread (to glide down):

They come used of the masks and the gaseous emissions of impurità that go to affect the semiconductor.

 

4) Early Effect:

Polarizing inversely J_C one region of emptying is created that extends mostly in the drugged base being this less of the collector, the effects that achieve some are:

to)       the probability of recombination in the base diminishes therefore increases to

b)       the spread current increases with the degree of the concentration and since the base is reduced, such gradient increases and with it also_and

c)       for inverse polarizations high, the base can become of amplitude null electrical worker "reach-through".

 

5) Logon to common base:

The base to mass therefore in a pnp is had for having J_and polarizes to you directly must have Va positive _BE while for having one polarizedJ _C inversely I must have V_{a CB} negativa. Dalla deduces that in the escape characteristic, the escape is_{the C} while V_CB and I_and are the income largenesses, it is preferred of the two to take_and like parameter in how much_{the C} @ _And and they are obtained of the straight horizontals in the active region that extends in the quadrant characterized from_and> 0 and V0_CB < the region of saturation in which increases of current with V are had bruschithe almost constant _CB are obtained for_and> 0 0 andV_CB > that is directlypolarized J _C while the interdiction region is had for_and< 0 and the splices are obtained inversely polarizing both.

As far as the income characteristic, it is the same one of the directly polarized diode valve unless to growing of V_{the CB} for Early effect it increases_and and therefore the curves are gotten thicker.

 

6) characteristic Equation of the logon to common emettitore:

is had, of the rest therefore replacing dove is had is the current of inverse saturation with open base (…_B= 0) while is the factor of amplification in current for large marks them of the logon to common emettitore (…observes that_{the CE0} =_{the CB0} where CE = Common Emitter and

CB = Collector Base). It comes moreover defined the gain of current in continuous and the gain in current for small marks them . One observes that the curves that compose the characteristic of escape with_{the C} to varying of V_{the CE} and the I_B as parameter is not horizontal as one is had instead for the common base in how much small variation of to determines one great variation of b .

 

7) Zones of saturation for the common emettitore:

_{The CE} is obtained polarizing both directly the splices thereforeV is much small and since the emettitore is to mass, the independently from the value of_{the B} .

 

8) Zone of interdiction for the common emettitore:

The interdiction conditions are the same ones of the common base that is , but in this case if the open base lets and therefore_{the B} = 0 does not have the interdiction in how much depends gives to and _{the C0} can be arrivedto having 10_C=, the problem is resolved inserting one V_BE @ -0.1V for transistor to GE and V_BE @ 0V for transistor to. It is observed that in interdiction conditions _{the CB0} inthe collector splice slide one who does not coincide with_{the C0} for following the two reasons:

to)       to growing of V_{the CE} one increases the dimension of the emptied layer and verification the effect avalanche

b)       there are currents that cross the splice on the surface of the transistor and not in the body

moreover_{the CB0} are much variable one from transistor transistor also of the same model.

 

9) Curve of transfer_C- V_BE for the common emettitore:

For V_BE ® -¥ is had that_{the C}®_{the CB0} and the transistor is interdetto, for V_BE = 0 has_{the C} =_{the CES}, catches up the tension then of primes V_g when_{the C} is worth of_{the C Sat} and sin when the tension of saturation V is not caught up_s the transistor is in the active region, for the silicon V _sis had @ 0,8V.

 

10) Equations of Ebers-Moll and relative model:

The general equation of the transistor can be written in the shape where "N" stà for way

of normal operation, if we imagine to exchange the roles of the two splices has also where "the" stà for operation invert and vige the relation moreover V_C represents the tension between finishes them of collector and an inner point to the base, it is had that it differs from V_{the CE} for the presence of a of the value of approximately 100W which extrinsic the difficulties that the bearers meet to exit from finishes them of base being wide and tightened it. Such resistance does not appear in the model of Ebers-Moll constituted from two diode valves in contropunta everyone with a generator of current controlled in parallel, they is null single if to = to_N = 0 that is if the width of the base is greater of the length of spread and therefore all the charges they are recombined in the base, is this the situation that is had if two real diode valves in contropunta are put, in the which case has sure not come true a transistor.

From the two equations of Ebers-Moll they can be estrinsecare V_and and V_C and therefore and therefore obtains the expression of the current of escape of the transistor from which _CE -¥® is looked atthat V while the relationship is constant and is worth b .

 

11) Values limit for the inverse tensions:

Independently from the characteristics of dissipation of the transistor, maximum inverse tension V_CB that can be applied between collector and base is limited from the two following phenomena:

Multiplication headlong

The accelerated charges produce for collision new bearers therefore increase to, if the configuration is to common base_{the C}=to_and it is had that the tension for which_{the C}®¥ is much high one, must instead in fact be had®a ¥, in the common emettitore being enough that a®1 in order to make to diverge_{the C} therefore for an inferior tension, a feature to negative resistance in how much for small is had but_{The C} the current that slides in the base is small therefore the circuit is like a common base, to growing of_{the C} it increases but the dissipation of the resistance of base and the circuit it returns to behave itself like a common emettitore.

Reach-Through

To growing of the inverse tension the dimension of the base is reduced therefore increases the gradient of the concentration of the minority bearers and therefore the current until also exceeding the admitted maximum limits from the device grows.

The tension to which the phenomenon verification is not only depended on the configuration but on physics of the device.

 

12) Fototransistore:

Turning out current is an evolution of the fotodiodo in how much concurs of having one greater, it can be realized with a transistor in which the collector splice is discovered, and leaving the base opened, or it can be sended one current on the base and possession therefore a double control, in such case has in fact .