# What is early effect in bjt

## Transistor characteristic curves

Bipolar transistors have the current quantities I.E., I.C., I.B. and the voltage quantities UCE, UBE, UC (CB). The relationships between the individual currents and voltages would result in a total of 30 characteristic curves. If a bipolar transistor is used as an amplifier or switch, 4 characteristic curves are sufficient. The relationship between the relevant values ​​is shown in a four-quadrant characteristic field. Depending on the basic circuit, these characteristic fields look different. The descriptions of these characteristic curves relate to the basic circuit shown here.
The dashed lines in the characteristic fields show the relationship between the individual currents and voltages.

### Input characteristic field IB. = f (UBE)

The input variables of the emitter circuit are the base current I.B. and the base-emitter voltage UBE. The relationship between these two values ​​represents the forward characteristic of the pn layer between base and emitter. This is one of the two diode paths in the transistor. The characteristic curve applies to a specific collector-emitter voltage U in each caseCE.

The increase at a certain point in the characteristic is called the differential input resistance rBE.
The resistance rBE changes when the voltage UCE is not constant and relates to a specific operating point.

### Output characteristic field IC. = f (UCE)

The output variables of the emitter circuit are the collector current I.C. and the collector-emitter voltage UCE. The relationship between these two values ​​is given for different base currents I.B. specified.
Each characteristic curve applies to a different base current I.B..

The increase at a certain point in the characteristic is called the differential output resistance rCE.
The resistance rCE changes when the current I.B. is not constant and relates to a specific operating point.

### Current control characteristic field IC. = f (IB.)

The current control characteristic results from the relationship between the collector current I.C. and the base current I.B.. The current control characteristic is also referred to as the transfer characteristic.
The characteristic curve applies to a specific collector-emitter voltage U in each caseCE. The characteristic of the curve is initially almost linear and then curves a little towards the end.
The direct current gain Β and the differential current gain β can be read from the steepness of the characteristic curve. The steeper the characteristic, the greater the current gain. If the characteristic curve is strongly curved, the gain is not constant. This creates distortions at the output of an amplifier circuit.

The direct current amplification factor Β results directly from the collector current I.C. and the base current I.B., at a certain collector-emitter voltage.

The alternating current amplification factor β results from the change in the collector current ΔI.C. and the base current change ΔI.B. at a certain collector-emitter voltage UCE.

### Reaction characteristic field UB. = f (UCE)

The reaction from the output (voltage UCE) to the input (voltage UBE) is shown in the feedback curve field.
A change in the collector-emitter voltage UCE leads to a change in the base-emitter voltage U.BE. This reaction should be kept as small as possible. This is not possible through circuit engineering measures. Only the transistor manufacturer has an influence.
The reaction characteristic relates to a specific base current I.B..

The measure for the reaction is the differential reaction factor D for a certain base current. The reaction factor D changes when the base current I.B. is not constant and relates to a specific operating point.

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