Basic amplifying circuit

1 - amplifier circuit
1.1 - The concept of khuyeh college circuit.
Amplifier circuit is used in most electronic devices, such as audio-frequency amplifying circuit in cassete, amplifiers, amplify the signal in color television video, etc. ...
There are three types of amplifier circuits are:

• Amplified voltage: As the circuit when we put a small amplitude signal at the output we will get a signal amplitude greater than several times.
• The current amplifier circuit:
  As we put a circuit when the signal is weak in intensity, it will output a signal to the electric current many times stronger.
• Amplifier circuit of production: The circuit as we take a weak signal capacity of the output signal is obtained with the more powerful of times, the capacity of the amplifier circuit is a combination of both amplifier circuits voltage and a current amplifier.

1.2 - The operating mode of the amplifier circuit.
The operating mode of the amplifier circuit is dependent on the polarization mode transistors, depending on intended use that circuit to amplify the KD polarization mode A, mode B, or AB mode mode C
a) Amplifier circuit in mode A.
As the amplifier circuit to obtain signals entirely brittle with the input signal.

A mode amplifier circuits amplify both sides of the input signal cycle

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

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

b) amplifying mode Mach B.

Amplifying circuit is a circuit mode B only amplify half cycle of the signal, if any positive gain sales we use NPN transistor, if the sale of any sound amplification I use PNP transistor, amplifier circuit in mode B no bias.

Amplifier circuit in mode B only a semi-cycle amplification 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, we use two NPN and PNP get lights series, each lamp will
a semi-cycle amplification of the signal, two lamps in push-pull amplifier circuit must have the same specifications:

* The circuit amplifying the combination of both A and B modes.

Amplifier circuits amplify the production are: Q1 gain in mode A, Q2 and Q3 in mode B amplifiers, amplifier Q2
the positive semi cycle, Q3 sales cycles amplify the sound.

c) Circuit amplified in AB mode.
Amplifier circuit mode AB amplifier circuit is similar in mode B, but has improved so that the voltage U BE prone wholesale 0.6 V, the circuit also amplify the signal a half cycle and overcome the distortion amplifier circuit intersection of B mode, this circuit is also used in the capacity of push-pull circuit.

d) amplifying circuit in mode C
Amplifying circuit is a 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: the example pulse splitting circuit in color television sets.

Amplifier circuit applications in C mode pulse synchronous separation circuit color TV.

2 - The default type of Transistor
2.1 - Transistor General E-style questions.
Circuits getting very common type E E game play directly into the mass or the mass gathering to break down components
AC signal into the polar B and C taken on pole, circuit diagram as follows:

Voltage amplifier circuit type E suffer general, 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 bias voltage U CE so that approximately 60% ÷ 70% Vcc.
• The amplitude of the received signal is greater than the signal amplitude at various times, thus amplifying circuit voltage.
• Current output is greater than the input signal, but not significantly.
• Reverse-phase output signal to input signal: because when the input voltage increases => the line I BE increase => the I CE
  up => increased pressure drop on Rg => resulting voltage pin C decrease, and vice versa when the input voltage decreases, the voltage increased foot C => so reverse-phase output voltage with input signal .
• E-style circuit common questions on the application of most electronic devices.

2.2 - Transistor common C-style problems.

Suffering from common C-style circuit with stand C source connected to ground or positive (Note: AC on the positive aspects
source is equivalent to mass), maximum signal is included in B and E taken on pole, circuit diagram as follows:

Suffering from type C circuit common, positive signals into B and took out the pole E

Characteristics of common C amplifier circuit.

• Positive signals into B and took out the pole E
• Signal amplitude by the input signal amplitude: Because each tank is always worth about 0.6 V so that when the voltage increases how much leg B C shall be increased much leg => so the signal amplitude out by the input signal amplitude.
• Output in phase with the input signal: Since the input voltage increases => the output voltage is increased, the voltage to reduce the output voltage decreases.
• The intensity of the stronger signal of the signal intensity at various times: Since the input signal with increasing amplitude => line I BE increases => the CE I β was also increased by the BE because I CE I = BE β.I assume Transistor amplification coefficient β = 50 times, when I line up BE 1mA => 50mA current I will increase CE, I CE is the line of the output signal, so the output signal amperage is many times stronger than the input signal.
• Circuit is used extensively in the amplifier circuit at night (damper), before the split signals to multiple branches, one damper circuit used to amplify the signal stronger. In addition, the circuit also numerous applications in the power circuit voltage (we will explore in the next section)

2.3 - Transistor type B common problems.

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

Type B amplifier circuit common voltage amplifier and power amplifier on the line.

3 - The cascade model
3.1 - cascade through the capacitor.
* Circuitry cascade through capacitor

Amplifier circuit from - there are two floors amplification coupled together through the capacitor.

• Above is a schematic amplified from the cassette radio, amplifier circuit consists of two layers of type E suffer general, the signal levels coupled through capacitor, the capacitor is used C1, C3, C5 capacitor connected to an AC signal levels to pass through and prevent the DC voltage, the capacitor C2 and C4 can work out the AC component from E to vacuum
  mass, power filter capacitor C6.
• Advantages of the circuit is simple, easy to install so many circuits used in electronic devices, the disadvantage is not fully exploit the capabilities of the transistor amplifier so that the gain is not large.
• Above is the audio-frequency amplifier circuit, thus stacking the capacitors used are of value capacitors from 1μF 10μF ÷.
• In the high frequency amplifying circuit, the capacitor value connected with a small layer of a few nano-FARA.

3.2 - cascade through the transformer.
* Circuitry sound intermediate frequency transformer used in Radio cascade

The voice of Radio Frequency floor using transformer cascade.

• Above is a schematic intermediate frequency transformer using Radio cascade, the output signal of this layer is 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, further primary winding transformer can play along with the resonant capacitor to the amplifier circuit at a frequency fixed.
• Cons: if the circuit operates in the wide band frequency will cause distortion, circuit fabrication complexity and take up valuable space.

3.3 - Pairing floor directly.

* Type the direct cascade is used in the amplifier circuit capacity of frequency.

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

4 - Method of testing a cascade amplifier
4.1 - In the amplifier circuit (mode A) How does the polarity is correct.

Amplifier circuits are correctly polarized.

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

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

Amplifying circuit is polarized wrong, the voltage U CE is too low.

Amplifying circuit is polarized wrong, the 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.

The method of inspecting an amplified floor.

• A floor amplified if we check that U CE is too low or too high compared to sources with bow wholesale source => the floor amplify the problem.
• If U CE is too low there could be short-CE (broken Transistor), or off Rg.
• If U ~ Vcc CE too high, they may break or damage Transistor RDT.
• A good story amplify common:
  U BE ~ 0.6 V; U CE ~ 60% ÷ 70% Vcc