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amaresh92
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i wonder if anyone could tell me ,why does the current gain change as the frequency of ac supply changes?
advanced thanks.
advanced thanks.
what is current and displacement component?what does it mean?cabraham said:Base current consists of conduction & displacement components. At very low frequencies, the conduction component dominates, as the displacement current is very small. As freq increases, the displacement component of base current increases while the conduction component does not. Eventually the base current consists of more displacement than conduction.
So, as freq increases, more base current is needed for a specific value of collector current. The current gain, hfe, decreases as freq increases. The dc/lf value of current gain is denoted "hFE", an "h" with upper case "FE" subscript. The ac/hf current gain is denoted "hfe". Note that the "fe" subscripts are lower case.
At a freq known as the "transition freq", denoted "ft", the current gain is 1. At a freq of ft, to establish 10 mA of collector current requires 10 mA of base current. Above this ft value, the device is not providing current amplification, so ft is the useful bandwidth of the device. At half of ft, hfe = 2, at ft/10 freq, hfe = 10, & so on. at freq low enough, hfs reaches its maximum value of hFE. In other words, hfe < hFE.
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Claude
Think of the displacement current as bypassing the actual base-emitter junction by flowing instead through a parasitic parallel capacitance. This may be a bit oversimplified but for your purposes I think this is the best way to understand it.amaresh92 said:what is current and displacement component?what does it mean?
A current gain transistor is a type of electronic device that is commonly used in circuits to amplify or switch electrical signals. It is made up of three layers of semiconductor material, with each layer having a different level of conductivity. This creates a "sandwich" structure that allows for the control of current flow through the device.
A current gain transistor works by controlling the flow of current from the collector to the emitter, based on the amount of current flowing into the base. When a small current is applied to the base, it causes a larger current to flow from the collector to the emitter, resulting in amplification. This is known as the transistor's current gain.
The current gain of a transistor is an important factor in its performance. It determines how much the output current will be amplified from the input current. A higher current gain allows for greater amplification, making the transistor more efficient and useful in electronic circuits.
The current gain of a transistor can be affected by several factors, including temperature, voltage, and the type of material used in the transistor. In addition, the design and construction of the transistor, such as the thickness and doping level of each layer, can also impact its current gain.
The current gain of a transistor is typically measured using the h-parameter or beta (β) value. This is the ratio of the output current to the input current, and it is usually listed in the transistor's datasheet. The higher the h-parameter or beta value, the greater the current gain of the transistor.