The main four parameters of the crystal triode

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The main four parameters of the crystal triode






The parameters of the transistor can be divided into DC parameters, AC parameters, limit parameters, and characteristic frequencies. The parameters of the transistor are an important basis for the use and selection of the three-stage tube. For this reason, understanding the parameters of the transistor can avoid damage to the tube caused by improper selection or use.


1, DC parameters


Collector - base reverse current I (CBO). When the emitter is open and a specified reverse voltage is applied between the collector and the base, the leakage current in the collector junction is called I(CBO). The smaller the value, the better the thermal stability of the transistor. Generally, the small power tube is about 10OA, and the silicon tube is smaller. The collector-one emitter reverse current I (CBO) is also referred to as the penetration current. It refers to the leakage current of the collector when a predetermined reverse voltage is applied between the collector and the emitter when the base is open. The smaller the value, the better. Silicon tubes are generally small, below about 1 μA. If the test finds that this value is large, the tube is not easy to use.



2, the limit parameters


Collector Maximum Allowable Current I(CM) When the beta value of the transistor drops to half of the maximum value, the collector current of the tube is called the maximum allowable current of the collector. When the collector current Ic of the tube exceeds a certain value, it will cause a change in some parameters of the transistor, most notably the decrease in the value of β. Therefore, in practical applications, Ic is smaller than the maximum allowable dissipated power P (CM) of the I (CM °) collector. When the transistor is operated, the collector junction is heated due to the dissipation of a certain power of the collector. When the temperature is too high, the temperature is too high. This will cause a change in the parameters and even burn the transistor. To this end, it is stipulated that the power of the collector of the transistor is increased so as not to burn the collector, which becomes the maximum power dissipation of the collector. In order to increase the P (CM) value, a heat sink can be added to the high-power tube. The larger the heat sink, the more the P (CM) value is increased. Collector emitter reverse breakdown voltage BU (CEO) The maximum voltage allowed between the collector and the emitter when the base is open. In practical applications, the voltage applied between the collector and the emitter must be less than BU (CEO), otherwise the transistor will be damaged.


3, current amplification factor


The DC amplification factor β" is expressed by h (FE). It refers to the ratio of the common emitter circuit, the collector output DC I (B) and the base input DC when there is no AC signal. That is: β = I (c /I(B)β is an important parameter to measure the current amplification ability of the transistor. However, for the same transistor, there are different β at different collector currents. The AC amplification factor β can also be used for h(FE). This parameter refers to the ratio of the change amount of the collector current ΔAIc to the change amount of the base current ΔI(B) in the common emitter circuit when the AC signal is input. That is, β=ΔIc/ The two parameters above △I(B) indicate the amplification ability of the transistor for DC current and the amplification of AC current. However, since the two parameters are approximately equal, ie β≈β, they are generally not used in actual use. According to the production process, even if the tubes of the same batch are produced, the β value is different. For convenience and convenience, the manufacturer sometimes marks the corpus value on the crystal triode for the user to select.


4, characteristic frequency


The higher the frequency, the more severe the β decline. The characteristic frequency light of a transistor is the frequency value when the value drops to 1. That is to say, the transistor operating at this frequency has lost the amplification capability, that is, f(T) is the limiting frequency in the use of the transistor. Therefore, when the transistor is selected, the characteristic frequency of the general tube is at least the frequency of the circuit. More than 3 times higher. But the higher the f(T) is, the better. If it is chosen too high, it will cause the circuit to oscillate.



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read ()  •  May 11, 2019  •  Edit


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