11/21/2023 0 Comments Bjt transistor beta infinite meaning![]() Let’s say if the Ic is 35mA and Ib is 0.15mA, then the required minimum hFE level would be: For example, a transistor may be required to drive a relay of 30ma with a base current of 0.15mA and voltages as low as 1 volts – definitely nothing less than 200 would work here as the hFE. With smaller BJTs, which are supposed to work with very low power inputs, the hFE plays an important role and higher values become imperative. The power transistors to be precise come under the low hFE category and the name itself suggests that the power involved with them is always huge, so lower hFEs might be quite justified here. If we measure the hFEs of a variety of BJTs, we find that as the device becomes bigger in size and capacity, the value of its hFEs starts getting smaller which implies that the devices will be requiring greater base current and voltage for operating their collector loads. The hFE governs the basic amplification property in transistors and therefore this feature becomes particularly important while designing electronic circuits and selecting the devices appropriately. Importance of the hFE Factor in Practical Circuits Generally the AC and DC betas tend to have similar magnitudes at lower levels of I(ceo). Practically, experiments show that the levels of AC current gain β(ac) and DC current gain β(dc) are more or less equal in their magnitudes and therefore become quite interchangeable. This becomes obvious because the collector current is normally the output current for transistors with common-emitter configurations. The datasheets showing transistor specifications typically indicate beta as hFE, where the letter h is derived from an equivalent hybrid circuit, while the subscripts F and E are extracted from forward-current amplification and common-emitter configuration respectively.įor alternating potentials beta AC is expressed as:įormally, beta AC is the factor that decides the common-emitter forward–current amplification of the device. ![]() However, transistors may show considerable difference in their beta levels despite having the same lot and code numbers. An increased beta level corresponds to an increased forward current gain of the device, for example a transistor with a beta of 200 may be capable of producing collector currents 200 times more than the applied base current. ![]() Practically, transistors may exhibit beta levels anywhere between 50 to 400, depending upon their classification. The name itself implies that the Collector terminal is taken as common terminal for both input and output of the transistor.A Bipolar Junction Transistor (BJT) when operated with DC inputs, the levels of its collector current Ic and base current Ib are related by the term _beta (_ β), and expressed as: This configuration is usually used for bias stabilization methods and audio frequency applications. The ratio of change in collector current ($\Delta I_$$Īs the output resistance of CE circuit is less than that of CB circuit. In the CB configuration, the input current is the emitter current I E and the output current is the collector current I C. ![]() The collector voltage V CB is kept constant throughout this. ![]() When the emitter voltage is applied, as it is forward biased, the electrons from the negative terminal repel the emitter electrons and current flows through the emitter and base to the collector to contribute collector current. The common base connection for both NPN and PNP transistors is as shown in the following figure.įor the sake of understanding, let us consider NPN transistor in CB configuration. The name itself implies that the Base terminal is taken as common terminal for both input and output of the transistor. In every configuration, the emitter junction is forward biased and the collector junction is reverse biased. The three types of configurations are Common Base, Common Emitter and Common Collector configurations. Using these 3 terminals the transistor can be connected in a circuit with one terminal common to both input and output in a 3 different possible configurations. A Transistor has 3 terminals, the emitter, the base and the collector. ![]()
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