Basic Amplifier Circuits

1 - amplifier

1.1 - great concept khuyeh circuit.

Amplifying circuit is used in most electronic devices, such as audio-frequency amplifier circuit in cassete, amplifiers, amplify the signal in the color television video, etc. ..

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There are three types of amplifier circuits are :

• Amplified voltage : As we make a circuit when the signal amplitude is small, it will output a signal with amplitude several times larger.
• The current amplifier circuit : 
  A circuit as we take a weak signal intensity in the output that will be a signal to the electric current many times stronger.
• Amplifier circuits of production : As we take a circuit when the signal is weak capacity of the output signal obtained has a lot of times more powerful, in fact amplifying circuit capacity of a combination of both amplifier circuits voltage and a current amplifier.

1.2 - Modes of operation of amplifier circuits.

The operation mode of the amplifier circuit is dependent on the polarization mode transistors, depending on the intended use amplification circuit is polarized to KD mode A, mode B, AB or mode mode C

a) amplifier circuit in mode A.As the amplifier circuit to obtain the signal completely brittle with the input signal.

A amplifying circuit amplifying mode both sales cycle input signal

* To Transistor operation mode A, so we must bias voltage U CE ~ 60% ÷ 70% Vcc .

* Mode amplifier circuit A is used in the intermediate circuit as high-frequency amplifier, intermediate frequency amplifiers, preamps, etc. ..

b) amplifying mode Mach B.

Amplifier circuit is the circuit mode B only amplify a signal half-cycle, if semi-amplifier NPN transistor we use the term positive if amplified sound we used to sell any PNP transistor, amplifier circuit in mode B without bias.

Amplifier circuit in mode B only amplify one part cycle of the input signal.

* B mode amplifier circuits are often used in the circuit of push-pull amplifier as the frequency of sound, the frame of the TV, in the capacity of push-pull circuit, it uses two NPN and PNP light problems series, each lamp will 
gain a sales cycle of the signal, two lights in the push-pull amplifier circuit to have the same specifications:

* Amplifier circuit capacity of a combination of both A and B mode.

Amplifier circuit can amplify the production: Q1 amplified mode A, Q2 and Q3 amplified mode B, Q2 amplify 
the positive semi-cycle, Q3 sales cycles for amplification of sound.

c) amplifying circuit in AB mode.
mode amplifier circuit AB amplifier circuit is similar in mode B, but has improved so that the voltage U BE stomach Wholesale 0.6 V, the circuit also amplified half cycle of signal distortion and fix the intersection of B mode amplifier circuit, this circuit is also used in the production of push-pull circuit.

d) amplifying circuit in mode C
is the amplification circuit voltage U BE assigned range for the purpose only get back the output signal is a top of the input signal, this circuit is often used in the detector signal: For example, sync pulse separation circuit television in color.

Application mode amplifier circuit C in pulse synchronous separation circuit color TV.

2 - Types of questions Transistor

2.1 - Transistor General E-style questions.

Circuits getting very common type E E game or play directly into the mass of bone mass to break through into the 
AC signal into the pole B and C taken on the pole, the circuit diagram as follows:

Voltage amplifier circuit problems generally E type, positive signals into B and C taken on pole

Rg : resistance is ghanh, RDT : A bias resistor, RPA : A resistive voltage division.

Characteristics of general E amplifier circuit.

• E amplifier circuit is generally such that bias voltage U CE 60% ÷ 70% Vcc .
• The amplitude of the received signal is greater than the signal amplitude at several times, so the voltage amplifier circuit.
• Output currents greater than the input signal, but not significantly.
• Reverse-phase output signal with the input signal: because when the input voltage increases => the line I BEincreases => the line I CE
  increases => drop the Rg increases => the result is a decrease C pin voltage, and vice versa when the input voltage reduces the voltage increased foot C => so the output voltage with reverse-phase input signal.
• E-style circuit common questions on the application of most electronic devices.

2.2 - Transistor type C common problems.

Suffering from type C circuit common C leg connected to the mass or solar power (Note: on the positive aspects of the AC 
source is equivalent to mass), positive signals are put into B and remove the poles E, primary circuit map as follows:

Suffering from type C circuit common, positive signals into B and remove the poles E

Characteristics of common C amplifier circuit.

• Positive signals into B and remove the poles E
• The amplitude of the signal with the input signal amplitude: Since each tank is always worth around 0.6 V voltage so as to increase how much foot B foot C shall also increased this much => so the signal amplitude out by the input signal amplitude.
• Output in phase with the input signal: Since the voltage to increase => the output voltage increases, and voltage to reduce the output voltage decreases.
• The intensity of the stronger signal strength of signals at various times: Because the input signal amplitude is increased => line I BE increases => the line I CE was also increased β line I BE because I CE = β.I BE assume the gain transistors have β = 50 times when the line I BE increased 1mA => line I CE will increase 50mA, current I CE is the line of the output signal, so the output signal intensity electric current many times stronger than the input signal.
• On the application circuit in circuit gain more night (damper), before the split signal to multiple branches, one damper circuit used to amplify the signal stronger. In addition, the application circuit is also very much in the circuit voltage source (we will learn in the next section)

2.3 - Transistor type B common problems.

• Suffering from type B circuit common signal pins into E and C taken on foot, leg B are released through the mass gathering.
• Type B Mach common problems are rarely used in practice.

Type B amplifier circuit common, the voltage amplifier and amplifying the current.

3 - The cascade model

3.1 - cascade through the capacitor.* Circuitry cascade through the capacitor

Amplifier circuit from - two floors are amplified through capacitors coupled together.

• The above is the first amplifier circuit diagram from the radio cassette, amplifier circuits of two-storey type E suffer general, the floor signal via the coupling capacitor, it uses the capacitor C1, C3, C5 to converge floor connected to an AC signal to pass through and prevent voltage dc, the capacitors C2 and C4 can work out the AC component from E down leg mass, filter capacitor C6 is the source. 
  
• Advantages of the circuit is simple, easy to fit so many circuits used in electronic devices, the downside is not exploited the full capability of the transistor amplifier so that the gain is not large.
• Above is the audio-frequency amplifier circuit, so the stacking together of a common capacitor values ​​from 10μF 1μF ÷.
• In the high frequency amplifier circuit, the capacitor value connected with a small layer of a few nano-Fara.

3.2 - cascade through the transformer.* intermediate frequency circuit diagram languages ​​used in Radio cascade transformer

The voice of Radio Frequency floor using cascade transformer.

• Above the high frequency radio circuit diagram using the cascade transformer, the output signal of this layer are coupled through a transformer to go into the rear floor.
• Advantages of the circuit is to coordinate the resistance between the layers so that the optimal exploitation of the gain, more primary winding transformer may play parallel resonant capacitor to the amplifier circuit at a frequency fixed.
• Cons: if the circuit operates in the wide band frequency will cause distortion, making the circuit complex and take up valuable space.

3.3 - direct cascade.

* Direct cascade type commonly used in the production circuit audio-frequency amplifiers.

Amplifier circuit of the island of light frequency is phase Q1 coupled directly with the two lights of Q2 and Q3.

4 - Method of testing an amplifier floor

4.1 - In the amplifier circuit (mode A) how the polarization is right.

Amplifier circuit is properly polarized.

• Amplifier circuit (mode A) is the correct polarity is a circuit U BE ~ 0.6 V; U CE ~ 60% ÷ 70% Vcc
  
• When the circuit is polarized right shows, the output signal has maximum amplitude and signal distortion.

4.2 - amplifier circuit (mode A) is polarized in the wrong.

Amplifier circuit is polarized wrong voltage U CE is too low.

Amplifier circuit is polarized wrong voltage U CE is too high.

• When the circuit is polarized in the wrong (ie U CE is too low or too high), we find that the distorted signal format, the gain of the circuit is reduced.
• This phenomenon will cause distortion in the sound being shy or blocked in the audio-frequency amplifier circuit.

Method of testing an amplifier floor.

• An amplifier floor if we check that U CE too low or too high on his stomach wholesale sources with the source => amplify the story that matters.
• If U CE is too low there could be short-CE (broken Transistor), or off Rg.
• If U CE high ~ Vcc may be broken or damaged Transistor RDT.
• A good amplifier floor common: 
  U BE ~ 0.6 V; U CE ~ 60% ÷ 70% Vcc