What is stability factor in BJT?

Stability factor (S):

It is the rate of change of collector current (I _C) with respect to the reverse saturation current

saturation current

I_S, the reverse bias saturation current for an ideal p–n diode, is given by (Schubert 2006, 61): are the carrier lifetimes of holes and electrons, respectively. Increase in reverse bias does not allow the majority charge carriers to diffuse across the junction.

https://en.wikipedia.org › wiki › Saturation_current

Saturation current - Wikipedia

of collector junction (I _CO), i.e. S = ∂ I C ∂ I C O ---(1) We know that collector current is given by: I _C = β I _B + (1 + β) I _CO ---(2)

What is stability factor?

Explanation: Stability factor is defined as the rate at which collector current changes when Base to emitter voltage changes, keeping base current constant. It can also be defined as the ratio of change in collector current to change in base current when temperature changes occur.

What is the importance of stability factor?

Significance of Stability Factor

The stability factor indicates change in collector current with respect to change in collector leakage current. If the stability factor is 20, it means that the collector current changes 20 times due to change in collector leakage current.

What is fixed bias in BJT?

Fixed Base Biasing in BJT. In this condition, a single power source is applied to the collector and base of the transistor using only two resistors. Applying KVL to the circuit, Thus, by merely changing the value of the resistor the base current can be adjusted to the desired value.

What is the need of biasing in BJT?

Transistor biasing makes analog and digital operation of a transistor possible. Without transistor biasing, BJT amplifiers fail to deliver the required output across load terminals. The optimum value of transistor bias voltage is equal to two times the required AC output voltage peak.

Bias Stabilization and Stability Factors

What is stabilization and stability factor?

Stability Factor (S):

The extent to which the collector current IC is stabilized with varying ICO is measured by a stability factor S. It is defined as the rate of change of collector current IC with respect to the collector base leakage current ICO, keeping both the current IB and the current gain β constant.

What is the best value of stability factor for a BJT?

The stability factor should be as low as possible so that the collector current doesn't get affected. S=1 is the ideal value. The general expression of stability factor for a CE configuration can be obtained as under.

What are three stability factors?

How many stability factors are there?

Three stability factors are defined as follows, Stability factor S: The above equation can be considered as a standard equation for the derivation of stability factors of other biasing circuits.

What is Q point in a transistor?

The operating point of a device, also known as a bias point, quiescent point or Q-point, is the steady-state DC voltage or current at a specified terminal of an active device such as a transistor with no input signal applied.

What is stability of a transistor?

The stability of a transistor or amplifier circuit is a measure of the likelihood of oscillation when the circuit is energized. However, the conditions that cause oscillation are more stringent than the conditions that make a circuit unstable.

What should be the ideal value of stability factor?

The stability factor should be as low as possible so that the collector current doesn't get affected. S=1 is the ideal value.

Why is the stability of Q Point essential?

The Q point is essential to the overall component and circuit functionality. It ensures that non-linear components like diodes operate at their optimal current and voltage throughout the operating range. This also promotes increased functionality, reliability, and life cycle of your electronic circuits.

What is cut off region in BJT?

Cutoff region

This is the region in which transistor tends to behave as an open switch. The transistor has the effect of its collector and base being opened. The collector, emitter and base currents are all zero in this mode of operation. The following figure shows a transistor working in cutoff region.

What is thermal runaway in BJT?

Thermal runaway

The problem with increasing temperature causing increasing collector current is that more current increase the power dissipated by the transistor which, in turn, increases its temperature. This self-reinforcing cycle is known as thermal run away, which may destroy the transistor.

What are the major factors that affect the stability of a BJT amplifier?

The internal factors are the thermal resistance, the current amplification factor, and the base lead resistance. The external factors are ambient temperature, collector voltage, circuit resistances, and the thermal coupling between the transistor and temperature compensation elements, if any.

Which biasing is best in terms of stability factor?

Voltage Divider Bias

It is most widely used in linear discrete circuits because it provides good bias stability. It is also called universal bias circuit or base bias with one supply.

How does BJT work as an amplifier?

How does a transistor work as an amplifier? A transistor works as an amplifier by taking in a very small weak signal through the base junction and raising the strength of the weak signal. This amplified signal is released through the collector.

What is the types of stability factor?

What is stability in circuits?

A circuit or a group of circuit connected together as a system is said to be stable, if its o/p reaches a fixed value in a finite time. (or) A system is said to be unstable, if its o/p increases with time instead of achieving a fixed value.

What is load line and Q point?

The DC load line is the load line of the DC equivalent circuit, defined by reducing the reactive components to zero (replacing capacitors by open circuits and inductors by short circuits). It is used to determine the correct DC operating point, often called the Q point.

What is meant by slew rate?

Slew rate is defined as the maximum rate of change of an op amps output voltage, and is given in units of volts per microsecond.

What is Q point formula?

Generally, the Q-point of the amplifier is half-way along the load line so the Collector current will be given as half of 9.2mA. Therefore Q = 4.6mA. This DC load line produces a straight line equation whose slope is given as: -1/(RL + Re) and that it crosses the vertical Ic axis at a point equal to Vcc/(RL + Re).

What is the leakage current in transistor?

In bipolar junction transistors, the emitter current is the sum of the collector and base currents. I_e = I_c + I_b. The collector current has two components: minority carriers and majority carriers. The minority current is called the leakage current.