TRANSISTOR CONFIGURATION – Common emitter Configuration, Common emitter Configuration, Common Collector Configuration

TRANSISTOR CONFIGURATION

A Transistor is a device with three Terminals. However, it needs “4” Terminals to connect to a circuit. two input Terminals and two output Terminals, Respectively. So, the input and output Circuits share one of the Terminals. The typical Terminal is Grounded.

TYPES OF TRANSISTOR CONFIGURATION

Three types of TRANSISTOR CONFIGURATION is available

1) COMMON BASE CONFIGURATION (CB CONFIGURATION)

2) Common emitter Configuration (CE Configuration)

3) Common Collector Configuration (CC Configuration)

1. COMMON BASE CONFIGURATION

In common base Configuration circuit is shown in figure. Here base is Grounded and it is used as the common Terminal for both input and output.

It is also called as grounded base configuration. Emitter is used as a input Terminal where as Collector is the output Terminal.

CB Input Characteristics

The Characteristic curve between input voltage and input current when the output voltage is constant is what is meant by this term. When Determining input Characteristics, the emitter current IE is Increased from zero by Increasing VEB while the Collector base voltage VCB is kept constant at zero. For higher fixed values of VCB, this is repeated.

A curve is drawn between emitter current and emitter base voltage at constant Collector base voltage is shown in figure 2.11. When VCB is zero EB Junctions is forward biased. So it behaves as a diode so that emitter current increases rapidly.

CB Output Characteristics

In cases where input current is constant, it is the characteristic curve between output voltage and output current. The emitter current IE is held constant at zero to determine output characteristics, and the collector current Ic is increased from zero by increasing VCB. For higher fixed values of IE, this is repeated. As can be seen from the characteristic, Ic is independent of VCB for constant values of IE, and the curves are parallel to the axis of VCB. The majority carriers, or electrons from the emitter region, are injected into the base region because the emitter base junction is forward biassed.

In CB configuration a variation of the base-collector voltage results in a variation of the quasi- neutral width in the base. The gradient of the minority-carrier density in the base therefore changes, yielding an increased collector current as the collector-base current is increased. This effect is referred to as the Early effect.

2. Common emitter Configuration

Circuit in a typical emitter configuration is depicted in the figure. In this case, the emitter is grounded and serves as the terminal that is shared by the input and output. The grounded emitter configuration is another name for it. Collector is the output terminal, whereas base is used as an input terminal.

CE Input Characteristics

When output voltage is constant, it is described as the characteristic curve between input voltages and input current. Base current IB is increased from zero by increasing VBE, while collector base voltage VCB is kept constant at zero to determine input characteristics. For higher fixed values of VCE, this is repeated.

A curve is drawn between base current and base emitter voltage at constant collector base voltage is shown in figure2.14. Here the base width decreases. So curve moves right as VCE increases.

CE Output Characteristics

In cases where input current is constant, it is the characteristic curve between output voltage and output current. In order to determine output characteristics, the collector current Ic is raised from zero by increasing VCE while the base current IB is maintained at zero. For higher fixed values of IB, this is repeated.

From the characteristic it is seen that for a constant value of IB, Ic is independent of VCB and the curves are parallel to the axis of VCE.

The output characteristic has 3 basic regions:

Active region –defined by the biasing arrangements.

Saturation region– region of the Characteristics to the left of VCB = 0V.

Cutoff region – region where the Collector current is 0A

3. Common Collector Configuration

Circuit is depicted in figure in common collector configuration. In this instance, the collector is grounded and serves as the terminal that connects input and output. The grounded collector configuration is another name for it. While emitter is the output terminal, base is used as an input terminal.

CC Input Characteristics

The characteristic curve between input voltage and input current when the output voltage is constant is what is meant by this term.

To determine input characteristics, the emitter base voltage VEB is kept constant at zero and base current IB is increased from zero by increasing VBC. This is repeated for higher fixed values of VCE.A curve is drawn between base current and base emitter voltage at constant collector base voltage is shown in figure2.17.

CC Output Characteristics

In cases where input current is constant, it is the Characteristic curve between output voltage and output current. In order to determine output Characteristics, the emitter current IE is Increased from zero by Increasing VEC while the base current IB is kept constant at zero. For higher fixed values of IB, this is repeated.

From the Characteristic it is seen that for a constant value of IB, IE is independent of VEB and the curves are parallel to the axis of VEC.

A comparison of CB, CE and CC Configurations