Amplifiers of power

1) Classes of operation of the power amplifiers:

A the angle of circulation of the current in the cargo is of 360° independently from the amplitude of the income

B the angle of circulation of the current in the cargo is of 180° independently from the amplitude of the income

AB the angle of circulation of the current in the cargo is comprised between 180° and 360° in function of the amplitude of it marks them of income

C the angle of circulation of the current in the cargo is smaller of 180° independently from the amplitude of the income

It is observed that salting with the alphabet it increases the efficiency h while diminishes the gain in power, in particular passing from the class To to the B class it is reduced of 6 dB that is demonstrated simply observing through Fourier that the amplitude peak peak of the 1ª harmonic is exactly equal to the amplitude of the semiwave.

 

2) Rendering of emettitore:

where P₂ is the supplied useful power to the cargo while P_CC is the power distributed from the generator, it is observed that it comes neglected the income power that is possible mostly in vlf where the powers in game are elevated.

 

3) PAE:

Stà for Power Added Efficiency where h it is the emettitore rendering that we have seen increases passing from To to the B while G is the gain in power which it diminishes passing from To to the B therefore after all the PAE will introduce a maximum allotted in class AB and the choice of a various amplifier is looked at that to increasing of the gain (..mediante) the maximum of the PAE is moved more and more towards the B. class Is a parameter a lot used in vhf where the escape powers are low and therefore the income power is not negligible.

 

4) P_out1dB(CP):

The escape power does not have a linear course regarding the income power, but from a sure point in then it introduces a concavity turned towards the bottom, comes therefore considered power of the maximum escape the power for which a difference of 1 dB between the intentional power in escape and power is had that really is had. CP stà for Compression Point.

 

5) Distortion:

The transcaratteristica of an active device in kind is not a straight one but a more complex curve that pu² to be approximated through the developments in series of Taylor in the shape, arresting to us for semplicità to 2° the order and replacing the expression of the tension of income obtains that is beyond to the fundamental member with the same pulsation of marks them of income has also a second harmonica to double frequency and one continuous member which alters the polarization that therefore goes opportunely compensated. The values of the B coefficients_n can be calculated setting up an equal number of equations characterized from such momentsw t to simplify the trigonometrical terms.

It comes defined harmonic distortion of n-esima the relationship while is defined distortion total and concurs to write the power total yielded to the cargo in the shape:

One technical a lot used is the manipulation of the harmonicas that consists in making as an example to see to every harmonica a various cargo by means of a filter.

 

6) Amplifier of power in class To:

Reference to a configuration to characterized common base from a npn is made whose base is to mass and it marks them of income is applied to the emettitore through a having condenser the scope to separate the previous stage from negative tension â?"V_EE that polarizes the splice directly base-emettitore, on the collector comes instead applied the tension of feeding through the cargo resistance R_L. The conversion rendering is where the power of income in how much infinitesimal one regarding P _CC has been neglected to the denominator while is the supplied useful power to the cargo, is the dissipated power in continuous on the cargo and is the dissipated medium power on the collector that turns out to be maximum in absence of marks them of income, replacing is had that can be improved diminishing P_R through a transformer whose head physician finds itself between the feeding and the collector while to the heads of the secondary one there is the cargo, in such case has itself: .

In truth the rendering turns out inferior to 50% is for the losses due to the transformer is because it is necessary to avoid on the characteristic the saturation and interdiction zones.

 

7) Push-pull Amplifier:

It comes realized by means of two transistors npn feeds to you from the same one marks them of income through a taken transformer to centers them pure mail to mass like the emettitori of the transistors while the collectors are to the opposite heads of the head physician of a taken transformer to center connected them to the tension of feeding and having the cargo on the secondary one.

The presence of the transformer of escape fed to the two ends from the collectors of the transistors makes that the harmonicas of elidano equal order from they generated.

In continuous the bases of the pure transistors they are to mass like the emettitore therefore draft of an amplifier in B class which it introduces distortions of cross-over due to the fact that the transistors begin to only lead after that the income tension has caught up v_g . The distortion of cross-over can be reduced making to work the Push-pull in class AB feeding the taken one centers them of the transformer of income through a connected resistivo partitore to the feeding tension as also the emettitori must be connected to mass not directly but through resistenza of stabilization termica. a rendering of emettitore it is where is the supplied useful power to the cargo while is the power distributed from the local p0wer source therefore replacing has while assuming where R_L^' is the cargo resistance seen from the head physician it has that the power dissipated on the collector is from which famous that if it marks them of income is null and therefore V_M= 0 also the power dissipated on the collector is null while the value of V_M for which P_C the derivative of P _C regarding V is maximum is obtained equalingto zero_M , in its correspondence has while the maximum of the supplied useful power to the cargo is had for V_M = V_CC and is worth , replacing obtains the relation therefore the power that crosses the transistor is 0,4 times the power that is supplied to the cargo, follows some that smaller transistors regarding the class can be used To.

 

8) Single-ended Amplifier in B class and its evolution:

A transformer of escape in B class therefore as it is had for the Push-pull configuration is enough voluminoso and expensive, if it can some avoid I use it through a Single-ended logon, in short the two transistors come puttinges in the configuration to totem therefore as it had for the Cascode but the brace is fed between V_CC and â?"V_CC so that the common point finds for symmetry to 0v, putting the cargo between this point and mass are had that in it continuum flow does not slide. The advanced transistor amplifies the positive semiwave that exiting on the emettitore does not come invert while the inferior transistor amplifies the negative semiwave but exiting of collector it renders it positive therefore in order to avoid that the amplifier is behaved from rectifier is necessary sfasare the incomes that it obtains using a wrapped transformer of income with two secondary ones in opposite way, they feeds every transistor between base and emettitore in such a way the transistor up also being a common collector is behaved like a common emettitore not inverting. To the introduced circuit the following improvements are moreover applicable:

to) Modification for the polarization and the thermal stabilization of the Single-ended amplifier in B class:

The customary outline with the two resistances is adopted that form the partitore of base and the resistance on the emettitore that carries out the thermal stabilization, for the calculation of the job point you notice the absence of the resistance R_C and that being i transistor equalT ₁ andT ₂, to the heads of every block a potential difference is had them of V_CC / 2.

b) Modification for the operation of the Single-ended amplifier in B class with one single battery:

A condenser is used place to mount of the cargo, it loads itself when the transistor up leads and discharge when it is interdetto and it leads that one under, the dimensioning of the condenser is function of the maximum period of the sinusoidi presents in income, and customarily it is gone around on the hundreds of mF.

c) Modification for the operation of the Single-ended amplifier in B class without the income transformer:

The scope of the income transformer was to supply two marks them equal but in controfase to the two bases of the transistors, an analogous function can be carried out from an amplifier parafase, with the single shrewdness to load the two escapes with a cargo much high one, in order to make that every transistor final is constituted from a Darlington brace stabilized thermally through a resistance R₃ on the emettitore, moreover through condenser C₂ it makes so that it marks them comes in such a way applied between the base and the emettitore of the transistorT ₁ obtaining that even if the configuration he is a common collector, the gain the same one of the common emettitore is not inverting that is but. It is observed that the driver parafase _CC are fed toV / 2 through one resistance that acts as also from feedback reducing the distortion.

d) Modification for the reduction of the ripple in the Single-ended amplifier in B class:

Alimentary possible E' the driver to V_CC instead that to V_CC / 2 to pact but to insert a filter low-pass filter that cuts via the ripple in the feeding that goes to the income stage, in fact such ripple could harmfully be amplified, the same one ripple comes but sended to the final transistors in how much otherwise in the resistance of the filter a lot of the feeding power would be dissipated uselessly.

 

9) Amplifier to complementary symmetry :

It can be obviated to the two generation marks them in opposition of phase (through transformer or preamplifier parafase) sending the income on the bases of a npn and of pnp having emettitori in common from which it comes captured the escape through a condenser avoiding therefore I use it of 2ª the battery. The two transistors are mount to you to common collector, however a gain in power until to 100 times advanced can be obtained making that the two stages are behaved like emettitori common not inverting that is obtained dynamically applying marks them between the base and the emettitori by means of one ability C. In the operating outline an endowed preamplifier of polarization and thermal stabilization is had moreover while in order to make to work the transistors in class AB and to compensate the variations of V_be with the temperature, between the bases there are 2 diode valves and one resistance.

 

10) Amplifier to nearly complementary symmetry :

The greater problem of the complementary symmetry is that the two stages introduce various resistances of income and cannot be rendered infinite in how much is almost impossible to realize a Darlington pnp with characteristics similar to a Darlington npn, then the complementary symmetry like driver is used to low power that has the task to supply to the stage single-ended which the cargo is connected the unchanged positive semiwave and the negative invert so that enduring in single-ended an ulterior reversal, it is introduced on the cargo like negative semiwave. For the corrected operation it is necessary in particular that the driver it sees always the same cargo independently from which brace of transistors leads, imposing that the currents that reach the cargo from the two jams is equal obtains the condition that the transistors of the single-ended must be to high gain while imposing that the tensions on the bases of the complementary symmetry are equal, the condition is obtained that these two transistor must be equal.