What is transistor beta

The part of the circuit which controls the emitter current is a current-voltage converter and supplies the emitter current of the transistor. The base of the transistor is 0 V. The emitter current is set with the input voltage of the voltage-current converter and the resulting current base current is obtained by measuring the output voltage of the current-voltage converter.

Name required. E-mail required. We can find out the two magnitudes of IC at the place where the two intersections of I B and the vertical axis intersect by drawing a horizontal line across the vertical axis and by evaluating the resulting values of I C. However, remember that these values could be vary across BJTs, even if they are from the same batch or lot. Typically, the similarity in the values of the two betas depends on how small the specification of I CEO is for the particular transistor.

Smaller I CEO will present higher similarity and vice versa. Since the preference is to have the least I CEO value for a BJT, the similarity dependence of the two betas turns out to be a genuine and acceptable occurrence. If we had the characteristic appearing as shown in Fig. This proves that the values of the ac and dc betas will be identical if the characteristic of the BJT appear like in the Fig.

In the following analysis, we will be ignoring the ac or dc subscripts for the betas just to keep the symbols simple and clean. We have already discussed regarding alpha in one of our earlier posts. Let's now see how we can create a relationship between the alpha and beta by applying the fundamental principles learned so far. The above results is as indicated in Fig. Beta becomes a crucial parameter as it allows us to identify a direct relationship between the magnitudes of currents across the input and output stages for a common-emitter configuration.

Normally current gain specifications for transistors normally have a very wide tolerance, and therefore circuits need to be able to accommodate this. However the minimum transistor gain must be sufficient to support the correct operation. Although it is not strictly exact, the equation below is more than accurate enough for all practical calculations. This transistor gain equation is the one that is seen in most instances.

More in-depth transistor gain equations and theory. Transistor H fe , h fe are often seen quoted as the current gain. This can lead to some confusion. The reason for using h fe is that it refers to way of measuring the input and output parameters of a transistor. Z parameters are one of the basic parameters used when treating a circuit as a black box. However as a transistor exhibits a low input impedance and a high output impedance a form of parameter known as h or hybrid parameters are used.

The notations for the two figures are slightly different. Similarly for hfe. H fe with a capital H is used for the DC gain, where as the AC or small signal gain is denoted by h fe with a small letter h. There are several points which are of interest when judging the level of current gain that a transistor has:.