Transistor what is beta

The beta of transistor is the amplification factor between the base current and the collector current. We can measure Beta of a transistor current gain using a voltage-current converter and current-voltage converter.

These manuals have a minimum or approximate values of the real values. This means that we do not know the real beta of a specific transistor. Keep in mind that two transistors with the same name e. The circuit below allows us to obtain the value of beta, for a specific transistor. This circuit comprises a voltage to current converter, on the left side of the transistor and a current to voltage converter, on the right side see the circuit diagram.

When designing any transistor circuit, it is necessary to ensure there is sufficient gain to enable the circuit to operate correctly. Gain levels can be very high for many small signal devices, with current gains up to not uncommon, but for power transistors, gains are very much lower and can sometimes be in the region of only 25 - 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:. At low current: This occurs when the bipolar transistor is running at very low current levels as a result of leakage mechanisms being seen and affecting the overall transistor current.

This results from a high level injection occurring. Normally the bipolar transistor is biassed to operate in its linear region for analogue signals and it can be assumed that the current gain is constant.

Accordingly, for good linear operation, the transistor should be operated well within its operating range and not running into the rails or drawing excessive current for the particular semiconductor device. Frequency: The frequency of operation will have a marked effect on the value of current gain.