# Analog electronics (BJT circuit analysis)

• Engineering
In summary, the question asks for the DC voltage at the collector for a circuit with beta = 100 and a large ro value. The equations IB = IE(β+1) and IC = β*IB are used to find the values of IB and IC, which are then used to determine the voltage across the 30kΩ load. The assumptions of VBE = 0.7 volts and the capacitors acting as open circuits for the DC analysis are also mentioned.

## Homework Statement

For beta = 100 and assuming ro is very large, what is the DC voltage at the collector?

IB = IE(β+1)

IC = β*IB

## The Attempt at a Solution

Since IE = 0.5mA, IB = 0.0505 A
Then, IC = 5.05 A (which doesn't feel right)
VC is the same potential across the 30kΩ load?
I tried doing KCL with those currents (to find the current thought the load resistor).
Should I not be analyzing the direct circuit--should I make an equivalent T-model?

## Homework Statement

View attachment 110203
For beta = 100 and assuming ro is very large, what is the DC voltage at the collector?

IB = IE(β+1)

IC = β*IB

## The Attempt at a Solution

Since IE = 0.5mA, IB = 0.0505 A
Then, IC = 5.05 A (which doesn't feel right)
VC is the same potential across the 30kΩ load?
I tried doing KCL with those currents (to find the current thought the load resistor).
Should I not be analyzing the direct circuit--should I make an equivalent T-model?
Your equation should read ## I_E=I_B (\beta+1) ##. Try again. I think you also need to assume ## V_{BE}=.7 \, volts ## (approximately). One hint for you: The capacitors basically block any steady state current trying to go through them so the capacitor is an open circuit for the DC part of the analysis.

Last edited:

## 1. What is a BJT circuit?

A BJT (Bipolar Junction Transistor) circuit is a type of electronic circuit that uses bipolar junction transistors as its main component. It is a three-layer semiconductor device that can amplify and switch electronic signals.

## 2. What is the difference between analog and digital circuits?

Analog circuits use continuous, varying signals to represent data, whereas digital circuits use discrete signals with only two possible states (on or off) to represent data. Analog circuits are better suited for processing and amplifying audio and video signals, while digital circuits are more efficient for processing and storing data.

## 3. How do you analyze a BJT circuit?

To analyze a BJT circuit, you can use Kirchhoff's circuit laws and the BJT's current-voltage characteristics. First, apply Kirchhoff's laws to determine the current and voltage values at different points in the circuit. Then, use the BJT's characteristics (such as the base-emitter voltage and collector current relationship) to calculate the values of the BJT's parameters, such as its current gain and output resistance.

## 4. What is the purpose of BJT amplifiers?

BJT amplifiers are used to increase the strength of an electronic signal. They can amplify both alternating current (AC) and direct current (DC) signals by controlling the amount of current flowing through the device. BJT amplifiers are commonly used in audio and radio frequency (RF) applications.

## 5. What are some common applications of BJT circuits?

BJT circuits have a wide range of applications in electronics, including amplifiers, switches, oscillators, and logic gates. They are commonly used in audio and video equipment, power supplies, and communication systems. BJT circuits are also used in computer processors and other digital devices as a component of logic gates and memory cells.

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