Transistor input and output characteristic curve

Transistor characteristic curve Source: 21ic Sorting keywords:transistor characteristic curve

The relationship between the voltage and current of the transistor is called the characteristic curve of the transistor, also called the Volt-ampere characteristic curve. It can not only reflect the quality and characteristics of transistors, but also can be used to quantitatively estimate the parameters of transistors, is an important basis for the analysis and design of transistor circuit.

There are different characteristic curves for different connection modes of transistors. The most widely used is the common emitter circuit, the basic test circuit Z0118, the common emitter characteristic curve can be plotted by the stroke method, can also be directly displayed by the transistor characteristic diagram.

First, the input characteristic curve

In the case of transistor co-emitter connection, when the voltage ube between the collector and the emitter is maintained at different values,

A cluster relationship curve between Ube and IB, called the common emitter input characteristic curve, is shown in Z0119. The mathematical expression for the input characteristic curve is:

Ib=f (UBE) | UBE = constant GS0120

This cluster curve can be seen from figure Z0119, with the following features:

(1) a curve of UBE = 0 is similar to the forward characteristic of a diode. This is because UCE = 0 o'clock, the collector is shorted to the emitter, equivalent to two diodes in parallel, so that the IB's relationship with the UCE becomes the Volt-ampere characteristic of two parallel diodes.

(2) When the UCE is gradually increased from zero, the input characteristic curve shifts to the right, and when the value of UCE increases to a larger size (such as uce>1v), the curves are almost coincident. This is because when the UCE increases gradually from 0, the width of the junction increases and the base width is correspondingly reduced, so that the number of injected carriers in the substrate is reduced and the compound decreases, thus the IB decreases. If you keep IB as the fixed value, you must increase the ube, so the curve right shift. When the UCE is large (such as UCE >1V), the junction of the reverse voltage, can be injected into the base area of the majority of the unbalanced carrier is pulled to the collector, so that the UCE increased, IB also no longer significantly reduced, so that the formation of the curve almost coincident phenomenon.

(3) Like diodes, transistors also have a threshold voltage vγ, usually silicon tube is about 0.5~0.6v, germanium tube is about 0.1~0.2v.

Second, the output characteristic curve

The output characteristic curve is shown in Z0120. Test circuit Z0117.

The mathematical expression of the output characteristic curve is:

As can be seen from the figure, the output characteristic curve can be divided into three regions:

(1) Cutoff area: refers to the area below the characteristic curve of the ib=0. In this area, the transistor's transmit junction and the collector junction are in the reverse bias state, the transistor loses the amplification function, the collector only has the tiny penetrating current ICEO.

(2) Saturation zone: refers to the green area. In this area, the output characteristic curve clusters that correspond to the different IB values are almost coincident. In other words, when the UCE is small, the IC increases, but the IC does not increase, that is, IB loses control of the IC. This condition, called the saturation of the transistor. At saturation time, the transistor's transmitting and collecting junctions are in a positive bias state. The voltage between the transistor collector and the emitter is called the set one-shot saturation pressure drop, expressed in uces. UCEs is very small, usually small and medium power silicon tube uces<0.5v; the voltage between the transistor base and the emitter is called the base one-shot saturation pressure drop, to uces, the uces of the silicon tube is 0. Around 8V.

The OA line is called the Critical saturation line (the right edge line of the green area), and each point on this curve should be

| uce| = | ube|. It is the line of sharp corners of each characteristic curve. In the critical saturation of the transistor, the collector current is called the critical collector Current, expressed in ICS, the base current is called the critical base current, expressed in IBS. In this case, the relationship between ICS and IBS is still established.

(3) Amplification area: Above the cutoff area, the area between the saturation zone and the breakdown area is the amplification area. In this region, the characteristic curve is approximate to a cluster of parallel equidistant horizontal lines, the IC change amount and the IB's variable basically maintain linear relation, namely Δic=βδib, and Δic >>δib, that is, in this region, transistor has the current amplification function. In addition, the collector voltage on the collector current control function is also very weak, when Uce>1 V, even if the increase uce,ic almost no longer, at this time, if the IB is unchanged, then the transistor can be regarded as a constant current source.

In the amplification area, the transistor's transmit junction is in the forward bias, and the collector junction is in reverse bias state.

Transistor input and output characteristic curve