release time:2022-03-03Author source:SlkorBrowse:1102
High-frequency triodes are generally used in high-frequency broadband low-noise amplifiers such as VHF, UHF, CATV, wireless remote control, and radio frequency modules. Most of these applications are used in low voltage, small signal, small current, and low noise conditions. watts, collector current up to 500 mA.
Its selection principles in the use process are as follows:
(1) When the ambient temperature of the triode is higher than 30℃, the power dissipation Pcm should be derated by 60-80%.
(2) The triode should be kept away from the heating element as far as possible to ensure that the triode can work stably and normally.
(3) Among the parameters of the triode, there are some parameters that are easily affected by temperature, such as iceo, ubeo and β values. Where iceo and ubeo change with temperature are as follows:
①For every 6℃ increase in temperature, the iceo of the silicon tube will double;
②Every time the temperature increases by 10℃, the iceo of the germanium tube will double;
③The variation of silicon tube ubeo with temperature is about 1·7mv/℃.
(4) If it is used in the case of low voltage of 3V and 5V, the breakdown voltage should not be too large. If the breakdown voltage is too large (higher than 15V), its linearity at low voltage is not good, but it will affect the use.
(5) When the input signal is weak, it is recommended to use the 2SC3356 with a smaller insertion gain in the primary amplifier, and the BFQ591 or 2SC3357 with a larger gain for the secondary amplifier.
(6) The characteristic frequency fT of the selected high-frequency triode should be six to eight times (at least 3 times or more) the actual frequency of use, in order to reduce the insertion noise and increase the gain during use.
(7) For triodes used in high frequency or microwave circuits, in order to reduce parasitic effects, the lead wires should be as short as possible, and it is best to use surface mount packages.
(9) In order to prevent the secondary breakdown of the power transistor, the load with excessive reactance components should be avoided as much as possible.
(10) Under the premise that the amplification parameters required by the whole machine can be met, a transistor with appropriate insertion gain and DC amplification factor hfe is selected to prevent self-excitation. Generally, the primary amplification requires a small insertion gain, and its DC amplification factor hfe should be selected to be larger, and the secondary amplification requires a larger insertion gain, and its DC amplification factor hfe should not be too large.
(11) When the high-frequency triode is connected to the circuit, the base should be connected first. Do not open the base circuit while the collector and emitter have voltage.
(12) There are many types of high-frequency triodes, so the type of triode should be determined according to the requirements of the specific circuit, and then selected according to the main parameters of the triode.
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