Electronic Circuits I
1. Why do we choose q point at the center of the loadline?
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
Compensation techniques: This refers to the use of temperature sensitive
devices such as thermistors diodes. They provide compensating voltages
¤ts to maintain operating point constant.
3. Give the expression for stability factor.
6 >- ,B ,C)]
4. List out the different types of biasing.
Voltage divider bias
Emitter feed back bias
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
• Stabilize the collector current against the temperature variations.
• Make the q point independent of the transistor parameters.