DC Analysis of BJT Amplifier Circuits
By using my common emitter amplifier circuit shown in Figure 1.5, this use helps the equivalent circuits in analyzing other circuits. DC analysis within a common emitter amplifier circuit also begins by determining the deviation values of the electrical current and then the coupling and overflow capacitors, the load resistor and the signal source for the production of a DC circuit are applied by applying a theory called Thevenin and the Kirchoff voltage law.
The analysis of the coin (AC) of the common emitter circuit begins with knowledge of capacitive reactance (XC) as it is still very low when starting the signal frequency process. By taking into account that the XC is equal to the number zero, if it is, then the process of reducing the circuit from one circuit to another must be equivalent to the current that produces frequencies that requires replacing the three capacitors also in the circuit with effective shorts. Then the analysis process continues by replacing and change the current source of the current in the ground. From an AC analysis perspective, the DC voltage source has an internal resistance of zero ohms
Fixed bias
This form of bias is also called base bias or fixed resistance bias. This model is used as a single power source for example (battery) for both the collector and the transistor base, although other separate batteries can also be used
Advantages
The operating point can be changed anywhere in the active area easily with only the basic resistor (Rb).
Needs a very small number of ingredients
Disadvantages
The combined current does not remain constant, whether at temperature or at the voltage of the power source. For this reason, the BST operating point is is unstable
Changes in Vbe will change IB and thus cause IE to change.
Emitter-Bias
When a separate source or so-called (dual power source) is available, the bias circuit is most effective, and it provides zero voltage at the transmitter or collector. The Vee symbol is used for the negative width of the forward emitter intersection bias by Re, and the VCC is also used for the positive display of the inverse junction bias. Only two resistors are required for the common combining phase and four resistors for the co-emitter (2 for the co-emitter phase and 4 for the co-emitter)
Disadvantages
This model can only be used with a split (dual) power supply.
Voltage
The voltage divider consists of R1 and R2. The voltage is deflected across R2 forward by the emitter junction. Through the correct selection of resistors R1 and R2, the transistor operating point can be made independent of β. In this circuit, the voltage divider carries the fixed base voltage independent of the base current, but the divider current must be greater than the base current. Even with a fixed base voltage, the collector current varies with temperature (for example), so an emitter resistor is added to stabilize the Q point, you can also achieve more stable current levels without the value having a major impact on it
Advantages
- only one dc supply is necessary. Reverse the previous circuits.
- The operating point is independent of the difference β.
- Operating point stability versus temperature shift
Disadvantages
- If RE is large, Vcc height is necessary. Because this increases the cost.
- Since the value of β is constant, this relationship can be achieved by either keeping the RE fairly large, or by making R1 || R2 is too low
Feedback
Feedback is the process by which a portion of the output signal, be it voltage or current, is used as an input. If this part of the feedback is opposite to the value or phase or meaning (“against phase”) then the comments are said to be Negative Feedback, or degenerative feedback
Advantages
• Circuit stabilizes the operating point against variations in temperature and β
• Circuit stabilizes the operating point (as a fraction of Vcc) against variations in Vcc
Disadvantages
• Significant changes in β The operating point has changed significantly. It should be chosen fairly accurately (approximately 25%), but β variance between parts is often greater.
conclusion
In BJT the current pass depends on the two types of charge carriers (electrons and holes). Transistors are more important than diodes for their many uses in electronic circuits, from signal amplification to designing digital logic and memory circuits. The transistor is a very small volume and has many uses that exceed the size of stages.
It is one of the greatest discoveries that have passed through the history of mankind. The transistor consists of a semiconductor crystal containing three regions and is the following pattern (NPN) or (PNP) and one of the ends of these areas is called (E-emitter). This party contains a greater proportion of jealousy from impurities and the other party is called (C - Collector). This party contains a percentage of impurities as well, but it is less than the emitter and the third and last party is called (B - Base) which is a very thin slice of not more than ten thickness
Microns that contain the lowest percentage of impurities depends the basic principle in the transisto The voltage between the two parties to control the difference in the current through the third party
The transistor has uses which are the amplifier, switch, and resistance to change in voltage regulating circuits, From Application of bipolar junction transistor High speed digital logic and Amplifiers and Temperature sensors and Logarithmic converters
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