ECE

ELECTRONIC CIRCUITS PART-1

1. Why do we choose Q point at the center of the load-line?

The operating point of a transistor is kept fixed usually at the center of the active region in order that the input signal is well amplified. If the point is fixed in the saturation region or the cut off region the positive and negative half cycle gets clipped off respectively.

2. Name the two techniques used in the stability of the q point .explain.

Stabilization technique: This refers to the use of resistive biasing circuit which allows IB to vary so as to keep IC relatively constant with variations in Ico and VBE.Compensation techniques: This refers to the use of temperature sensitive devices such as thermistors diodes. They provide compensating voltages &currents to maintain operating point constant.

3. Give the expression for stability factor.

        

4. List out the different types of biasing.

Voltage divider bias, Base bias,Emitter feed back bias and collector feedback bias

5. What do you meant by thermal runway?

Due to the self heating at the collector junction, the collector current rises.This causes damage to the device. This phenomenon is called thermal runway.

6. Why is the transistor called a current controlled device?

The output characteristics of the transistor depend on the input current. So the transistor is called a current controlled device.

7. Define current amplification factor?

It is defined as the ratio of change in output current to the change in input current at constant other side voltage.

8. What are the requirements for biasing circuits?

· The Q point must be taken at the Centre of the active region of the output characteristics.
· Stabilize the collector current against the temperature variations.
· Make the q point independent of the transistor parameters.
· When the transistor is replaced, it must be of same type.


9. When does a transistor act as a switch?

The transistor acts as a switch when it is operated at either cutoff region or saturation region.

10. What is biasing?

To use the transistor in any application it is necessary to provide sufficient voltage and current to operate the transistor. This is called biasing.

11. What is operating point?

For the proper operation of the transistor a fixed level of current and voltages are required. This values of currents and voltages defined at a point at which the transistor operate is called operating point.

12. What is stability factor?

Stability factor is defined as the rate of change of collector current with respect to the rate of change of reverse saturation current.

13. What is d.c load line?

The d.c load line is defined as a line on the output characteristics of the transistor which gives the value of Ic & Vce corresponding to zero signal condition.

14. What are the advantages of fixed bias circuit? 

This is simple circuit which uses a few components. The operating point can be fixed any where on the Center of the active region

15. Explain about the various regions in a transistor?

The three regions are active region saturation region cutoff region.

16. Explain about the characteristics of a transistor?

Input characteristics: it is drawn between input voltage & input current while keeping output voltage as constant.
Output characteristics: It is drawn between the output voltage &output current while keeping input current as constant.

17. What is the necessary of the coupling capacitor?

It is used to block the DC signal to the transistor amplifier. It allows a c &blocks the d c.

18. What is reverse saturation current?

The current due to the minority carriers is called the reverse saturation current.

19. Why is the operating point selected at the Centre of the active region?

The operating point is selected at the Centre of the active region to get to perfect amplification. Moreover there is no distortion.

20. What are the basic rules of an operating amplifier?

The operating point should be fixed on the load line. The upper end of the load line lies on the saturation region &lower end lies on the cutoff region.

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