Circuit Diagram 13-Triode Amplifier Circuit Diagram

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Circuit Diagram 13-Triode Amplifier Circuit Diagram [Copy link]

The transistor amplifier circuit includes the transistor single-stage amplifier circuit, the transistor double-stage amplifier circuit, and the negative feedback transistor amplifier circuit. Being familiar with the composition and function of these amplifier circuits and mastering their working principles is the basis for reading the whole machine circuit diagram.

1. Reading the transistor single-stage amplifier circuit diagram

The transistor single-stage amplifier circuit is the most widely used unit circuit in electronic circuits. There are three types of transistor single-stage amplifier circuits: common base amplifier, common emitter amplifier, and common collector amplifier. The easiest way to distinguish these three amplifiers is to check the AC ground pin of the amplifier tube, and then you can confirm the type of amplifier. For example, if the emitter of the amplifier tube is AC grounded, then the amplifier is a common emitter amplifier. 1. Common emitter amplifier The common emitter amplifier is the most widely used amplifier. The so-called common emitter amplifier is an amplifier whose signal input and signal output are completed by the emitter stage. The figure below is a typical common emitter amplifier. In this amplifier, VT is the amplifier tube, C1 is the input signal coupling capacitor, C2 is the output signal coupling capacitor, R1, R2 and VT base DC bias resistor, R3 is the collector load resistor of VT, VCC is the power supply voltage, Ui is the input signal, and U0 is the output signal. 1) DC bias After the supply voltage VCC is divided by R1 and R2, it is added to the base of VT to provide a DC bias voltage for the base. The current flowing through R1 is divided into two paths to the ground: one path to the ground through R2, and the other path to the ground through the emitter junction of VT. 34)]2) Signal amplification process

The input signal Ui is coupled to the base of VT through C1, so that the base current of VT changes with the change of Ui, causing the collector current of VT to change accordingly, and the amount of change is a certain multiple of the base current. The collector current produces a voltage drop at both ends of R3 that changes accordingly, and VCC minus this voltage drop is the collector voltage of VT. Therefore, this voltage is opposite to the input signal voltage in phase, that is, the amplifier is an inverting amplifier.

From the above analysis, it can be seen that the common emitter amplifier not only has the function of current amplification, but also has the function of voltage amplification.

2. Common Collector Amplifier

The common collector amplifier is also a widely used amplifier. The figure below shows a typical common collector amplifier. In this amplifier, BT is the amplifier tube, C1 is the input signal coupling capacitor, C2 is the output signal coupling capacitor, R1 is the DC bias resistor of the VT base, R2 is the emitter resistor of VT, VCC is the power supply voltage, Ui is the input signal, and U0 is the output signal.

As we have introduced before, which type of amplifier is the one that is AC grounded? However, in the figure above, the collector of VT is not grounded. How can it be a common collector amplifier? This is because the internal resistance of VCC is small, and large-capacity filter capacitors are connected to both ends of the power supply, so the power supply is equivalent to a short circuit in the AC state. Therefore, the collector of VT is grounded through the power supply VCC and its filter capacitor.

1) DC bias

The power supply voltage VCC is added to the base of VT through the current limiting R1 to provide a DC bias voltage for the base. The loop of the base current is: VCC-R1-VT's emitter junction-R2-ground.

2) Signal amplification

The input signal is coupled to the base of VT through C1, so that the base current of VT changes with the input signal, causing the emitter current of VT to change accordingly, and the amount of change is the amplification factor +1. The emitter current produces a voltage drop at both ends of R2, which is coupled by C2 to obtain an AC output signal. This signal has the same phase as the input signal, so the amplifier is also called an emitter follower amplifier, or emitter follower for short.

From the above analysis, we can know that the input signal of the common collector amplifier is input from the base and emitter of the amplifier, and the output signal is taken from the emitter. The amplifier only has the current amplification function, not the voltage amplification function.

Since the common collector amplifier has the advantages of high input impedance and low output impedance, in the multi-stage amplifier circuit, the common collector amplifier is usually used to isolate the front and rear amplifiers, and it is used to buffer and amplify the signal to prevent the front and rear amplifiers from affecting each other. Because the common collector amplifier has the current amplification function, not only the series voltage regulator uses this type of amplifier, but also the final amplifier of some multi-stage amplifier circuits uses this type of amplifier. 3. Common base amplifier34)]The application of common base amplifier is much less than the previous two amplifiers. The figure below is a typical common base amplifier.

In this amplifier, VT is the amplifier tube, C1 is the input signal coupling capacitor, C2 is the output signal coupling capacitor, C3 is the base AC grounding capacitor, R1, R2 are the DC bias resistors of the VT base, R3 is the collector load resistor of VT, R4 is the emitter resistor of VT, VCC is the supply voltage, Ui is the input signal, and Uo is the output signal.

1) DC bias

The power supply voltage VCC is divided by R1 and R2 and then added to the base of VT to provide a DC bias voltage for the base. The current flowing through R1 is divided into two paths to the ground: one path is through R2 to the ground, and the other path is through the emitter junction of VT, R4 to the ground.

2) Signal amplification

The input signal is coupled to the emitter of VT through C1, so that the emitter current of VT changes with the input signal, causing the collector current of VT to change accordingly. The collector current produces a voltage drop at both ends of R3, and VCC minus the voltage drop is the collector voltage of VT. Because the collector voltage changes synchronously with the input signal voltage, the phase is the same. The input signal is coupled by C2 to obtain an AC output signal.

The common base amplifier has the advantage of good high-frequency characteristics, but it also has the disadvantages of small input impedance and large output impedance. Therefore, this amplifier is mainly used in high-frequency signal amplification circuits.

Two-stage transistor amplifier circuit diagram

The two-stage transistor amplifier circuit is an amplifier circuit composed of two transistors. This type of circuit is also the most common amplifier circuit. According to the different coupling methods of the front and rear amplifiers, there are four types of two-stage amplifiers: resistor-capacitor coupling, direct coupling, transformer coupling, and photoelectric coupler coupling.

1. Resistor-capacitor coupling method

The resistor-capacitor coupling method is that the input end of the rear amplifier is connected to the output end of the front amplifier through a capacitor. The resistor-capacitor coupling amplifier circuit has the advantages of no mutual influence between the DC operating points of the two-stage amplifiers, high amplification factor, and small signal transmission loss, but it also has the disadvantages of not being able to amplify DC signals, the structure is relatively loaded, and it is not easy to integrate.

The figure below shows a typical two-stage resistor-capacitor coupling amplifier circuit. VT1 and VT2 in the circuit are amplifier tubes, C1~C3 are low-frequency signal coupling capacitors, Ui is the input signal, and Uo is the output signal.

1) DC bias

R1 and R2 are the base bias resistors of the amplifier tube VT1, which provide bias voltage for its base; R4 and R5 are the base bias resistors of the amplifier tube VT2, which provide bias voltage for its base. 2) Signal amplification The input signal Ui is coupled to the base of the amplifier tube VT1 through C1, and after inverting amplification, it is coupled to the base of VT2 through C2, and inverted amplified again by VT2, and coupled through C3 to obtain the AC output signal Uo.

2. Direct coupling method

The direct coupling method is that the input end of the post-stage amplifier is directly connected to the output end of the pre-stage amplifier. The direct coupling amplifier circuit has a high amplification factor, can amplify DC signals, and is conducive to circuit integration, but the DC operating points between amplifiers affect each other, and it is easy to have abnormal phenomena such as zero drift.

The figure below shows a typical direct coupling two-stage amplifier circuit. VT1 and VT2 in this circuit are amplifier tubes, Ui is the input signal, and Uo is the output signal. R1 and R2 are the base bias resistors of the amplifier tube VT1, providing bias voltage for its base; R3 is not only the collector load resistor of VT1, but also the base bias resistor of VT2, providing bias voltage for its base. 3. Transformer coupling method The transformer coupling method is that the input end of the rear amplifier is connected to the output end of the front amplifier through a transformer. Transformer coupling amplifier circuits are mainly used in situations where cold or hot ground isolation or driving current needs to be increased. The figure below shows a typical color TV line excitation circuit. VT1 in this circuit is the line excitation tube, VT2 is the line output tube, Ui is the line excitation signal, R is the power supply current limiting resistor of the line excitation circuit, C is the filter capacitor, and T2 is the line output transformer.The row excitation signal Ui passes through the base of VT1, is inverted and amplified by VT1, and then transformed into an excitation signal with lower voltage but larger current by the row excitation transformer T1, driving the row output tube VT2 to work in the switching state.

4. Photocoupler coupling method

The photocoupler coupling method is that the input end of the post-amplifier is connected to the output end of the pre-amplifier through a photocoupler. The photocoupler coupling amplifier circuit is mainly used in occasions where cold and hot ground isolation is required.

The figure below shows a typical switching power supply voltage regulation control circuit. The error sampling method of the switching power supply adopts a direct sampling method, that is, the power supply samples the DC voltage measured on the cold ground, and then controls the conduction time of the switch tube through the width adjustment tube on the hot ground side to achieve voltage regulation control.

When the B+ voltage increases, the increased B+ voltage not only increases the voltage provided to the 1-pin of IC through R1, but also increases the voltage sampled by R2, RP, and R3. This voltage is added to the base of VT1. Since the emitter of VT1 is provided with a reference voltage by the voltage regulator tube VZ, VT1 is turned on and strengthened due to the increase of the base input voltage. Its collector current increases, making the light-emitting diode in the IC emitter more luminous. The corresponding photosensitive transistor is turned on and strengthened due to the light enhancement, making the width-adjusting tube VT2 turn on and strengthen, the switch tube VT1 conduction time is shortened, the energy stored in the switch transformer T decreases, and the B+ voltage drops to the normal value. On the contrary, the control process is the opposite. In this way, through the coupling of the IC, the error sampling and amplification signal at the cold ground end is transmitted to the width-adjusting circuit at the hot ground end, thereby controlling the conduction time of the switch tube and realizing voltage stabilization control.

III. Negative feedback transistor amplifier circuit diagram 1. Feedback circuit and structure

The process of sending part of the output (voltage or current) of the amplifier back to the input is feedback, and the circuit that transmits the feedback is the feedback circuit. The typical feedback circuit structure is shown in the figure below.

If the phase of the feedback quantity is the same as that of the input quantity, the feedback that increases the amplification factor is called positive feedback; if the phase of the feedback quantity is opposite to that of the input quantity, the feedback that reduces the amplification factor is called negative feedback. Since positive feedback is used to generate oscillation in the circuit and negative feedback is used to improve the working performance of the amplifier circuit, the amplifier circuit mainly uses negative feedback.

2. Classification of negative feedback circuits

The negative feedback circuits used by the amplifier include parallel current negative feedback, parallel voltage negative feedback, series current negative feedback, and series voltage negative feedback. If the negative feedback quantity is proportional to the output voltage, it can stabilize the output voltage and increase the output resistance, which is called current negative feedback. The feedback quantity of series negative feedback is connected in series to the input loop, and the feedback quantity of parallel negative feedback is connected in parallel to the input loop. Series negative feedback can increase the input impedance, while parallel negative feedback can reduce the input impedance and output impedance.

In addition, according to the nature of the feedback signal, it can be divided into three types of negative feedback circuits: AC negative feedback, DC negative feedback and AC/DC. As the name implies, if the feedback signal has only AC components, it belongs to AC negative feedback. If the feedback signal has only DC components, it belongs to DC negative feedback; if the feedback signal has not only AC components but also DC components, it belongs to AC and DC negative feedback.

3. Single-stage current series negative feedback amplifier

The single-stage current negative feedback amplifier is an amplifier with a wide range of applications. The figure below shows a typical single-stage current series negative feedback amplifier. The core components of this amplifier are the amplifier tube VT and the negative feedback resistor R3. The output current of the amplifier generates a voltage drop Uf across R3, which reduces the amplification factor by increasing the emitter potential of VT, so the circuit belongs to negative feedback control. After the output signal Uo is short-circuited to the ground to make Uo 0, the feedback voltage Uf still exists, indicating that the circuit belongs to the current negative feedback circuit. At the same time, since Uf is connected in series with the input signal Ui and then added to the emitter junction of VT, the circuit belongs to the series negative feedback circuit. Because Uf contains not only DC components but also AC components, the circuit belongs to the AC and DC negative feedback circuit.

4. Single-stage voltage parallel negative feedback amplifier

The single-stage voltage parallel negative feedback amplifier is also a widely used amplifier. The figure below shows a typical single-stage voltage parallel negative feedback amplifier. The core components of this amplifier are the amplifier tube VT and the negative feedback resistor R2.

The output voltage of the amplifier provides feedback voltage Uf to the base of VT through R2. Since VT is an inverting amplifier, the polarity of Uf is opposite to that of Ui, which reduces the voltage input to the base, so it belongs to negative feedback control. When the output voltage Uo is short-circuited to the ground and Uo is 0, the negative feedback voltage Uf disappears, indicating that the circuit belongs to a voltage negative feedback circuit. Since Uf is connected in parallel with the input signal Ui and then added to the base of VT, the circuit belongs to a parallel negative feedback circuit.

5. Two-stage voltage series negative feedback amplifier

The two-stage voltage series negative feedback amplifier is also a widely used amplifier. As shown in the figure below, it is a typical two-stage voltage series negative feedback amplifier. The core components of the amplifier are amplifier tubes VT1 and VT2, negative feedback resistor R6, and negative feedback capacitor C3.

The output voltage of the collector of amplifier VT2 provides feedback voltage Uf for the emitter of VT1 through C3 and R6, which reduces the conduction voltage on the emitter junction of VT1, so it belongs to negative feedback control. After the output signal Uo is short-circuited to the ground to make Uo 0, the negative feedback voltage Uf disappears, indicating that the circuit belongs to a voltage negative feedback circuit. Since the negative feedback voltage Uf is connected in series with the input signal Ui, the circuit belongs to a series negative feedback circuit. And because the negative feedback circuit uses coupling capacitor C3, the circuit belongs to an AC negative feedback circuit.