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Module 7 Part 2

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💫 Short Summary

The video segment covers the analysis of Bipolar Junction Transistors (BJT) as amplifiers, switches, and constant current sources, emphasizing mastering BJT circuit analysis. It discusses gain in amplifiers, using transistors as switches, and controlling loads with transistors. The importance of stability in circuits, selecting resistor values, and calculating load voltages for LED circuits is also highlighted. The speaker provides practical examples and exercises for further learning, concluding with a recap of key concepts and a thank you message.

✨ Highlights
📊 Transcript
Analysis of Bipolar Junction Transistors (BJT) as amplifiers, switches, and constant current sources.
BJT circuit analysis is crucial for current and future courses.
Three steps for BJT circuit analysis include determining conduction through the base-emitter junction, testing for active mode, and saturation mode.
Viewers are provided with an exercise to analyze a transistor circuit with specific parameters and values of input voltage.
The segment encourages viewers to complete the exercise and verify their answers.
Transition of a transistor from cut off to active mode.
When VN is zero, the transistor is cut off with no collector current.
As input voltage increases, the transistor transitions to the active mode, amplifying the input signal at the output.
The output voltage varies between 5 and 0.2 as the input ranges from 0.7 to 1.18.
The transistor operates in the active region between 0.7 and 1.18 volts, providing power amplification capabilities.
The concept of gain in amplifiers is explained, showing how an amplifier magnifies the time-varying component of the input signal at the output.
Negative gain is discussed, where the output decreases as the input increases.
Smaller values of R2 or B result in larger gains in practical amplifiers.
The segment demonstrates how a transistor can act as an amplifier to amplify small signals.
The video also covers how a BJT can be used as a switch, outlining the characteristics of an ideal switch and how to control current flow through a load.
Using a silicon transistor as a switch in electronic circuits.
Explains selecting a suitable RB value to turn on the load using a one volt signal.
Calculation involves determining IB, load current, and ensuring the transistor is in active mode.
Goal is to efficiently control the load using the transistor as a switch.
Showcases practical applications of transistor operation in electronic circuits.
Calculation of the minimum value of IB to put a transistor on the verge of saturation is discussed.
Value of RB to achieve the saturation point is determined.
A factor of safety in engineering suggests choosing a resistor value slightly lower than the calculated 750 ohms, like 680 ohms.
This practical approach accounts for potential variations in transistor characteristics.
Ensures load current stability even if transistor characteristics change slightly.
Importance of BJT in active mode for circuit stability.
Beta, temperature, and device replacement affect constant current source stability.
Beta variations are main source of instability, impacting sensitivity to temperature changes.
RB tolerance and resistor variations also play a role in circuit stability.
Introduction of stable constant current source with an emitter resistor.
Emitter resistor minimizes dependence on beta, the main source of instability in the circuit.
The modification results in a more stable load current by ensuring the transistor remains in active mode and VCE never drops below VC ESAT.
Circuit stability is dependent on maintaining stable values for VBE active and RE.
Explanation of LED bulb circuit components and voltages involved.
Discussion on current flow through LEDs and importance of resistor value for proper functioning.
Methods for adjusting current, including precision resistors or variable resistors.
Calculation of maximum number of LED bulbs a circuit can drive while maintaining 300mA current.
Emphasis on computing maximum allowable load voltage for driving LED bulbs.
Determining the maximum allowable load voltage for driving LEDs in a circuit.
Calculations involve subtracting voltage drops across components to find the maximum voltage.
Maximum allowable load voltage is 45.5 volts, supporting up to 13 LEDs at 3.3 volts each.
Powering 14 LEDs with the same voltage may result in dimly lit or non-functioning LEDs due to insufficient voltage per LED.
Practice exercises provided for further learning.
The video segment concludes with a brief explanation of the key concepts discussed.
Emphasizes the importance of understanding the content on bjts.
Expresses confidence in the viewers' comprehension.
The lecture wraps up with a thank you message.
Signals the end of the particular session.