The voltage follower, as the name suggests, is that the output voltage is the same as the input voltage, that is, the voltage amplification of the voltage follower is always less than and close to 1. No voltage magnification? ? What are his characteristics and functions?
The salient feature of voltage followers is that the input impedance is high and the output impedance is low. Generally speaking, it is easy to achieve an input impedance of several megaohms. The output impedance is low, usually to a few ohms or even lower.
In the circuit, the voltage follower is generally used as buffer level and isolation level. Because the output impedance of the voltage amplifier is generally relatively high, usually in the range of several thousand ohms to tens of thousands of ohms, if the input impedance of the latter stage is relatively small, then a considerable part of the signal will be lost in the output resistance of the preceding stage. At this time, a voltage follower is needed to buffer from it. Play the role of inheritance. Another advantage of using a voltage follower is that it increases the input impedance. In this way, the capacity of the input capacitor can be greatly reduced, which provides a prerequisite for the application of high-quality capacitors.
Another function of the voltage follower is isolation. In the HI-FI circuit, the controversy about negative feedback has been for a long time. In fact, if there is really no negative feedback, I believe that most of the amplifier circuits cannot work well. of. However, due to the introduction of a large-loop negative feedback circuit, the back electromotive force of the speaker will pass through the feedback circuit and be superimposed on the input signal. As a result, the sound quality is blurred and the intelligibility is reduced. Therefore, some power amplifiers use a circuit without large-loop negative feedback at the final stage, trying to eliminate the disadvantages of large-loop negative feedback by disconnecting the negative feedback loop. However, because the operating current of the final stage of the amplifier varies greatly, its distortion is difficult to guarantee.
Here, the role of the voltage follower just reaches the application. Putting the circuit between the front stage and the power amplifier can cut off the interference effect of the back electromotive force of the speaker on the front stage, so that the clarity of the sound quality is greatly improved.
The following small circuits are specific applications using transistors and field effect transistors. Experiment with them, and you may get unexpected gains.
LCD (short for Liquid Crystal Display) liquid crystal display. The LCD structure is to place a liquid crystal cell between two parallel glass substrates. The lower substrate glass is equipped with TFT (Thin Film Transistor), and the upper substrate glass is equipped with a color filter. The liquid crystal molecules are controlled by the signal and voltage changes on the TFT. Rotate the direction, so as to control whether the polarized light of each pixel point is emitted or not to achieve the purpose of display. LCD has replaced CRT as the mainstream, and the price has dropped a lot, and it has become fully popular.
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LCD features:
(1) Low-voltage micro power consumption
(2) The appearance is small and exquisite, the thickness is only 6.5~8mm
(3) Passive display type (no glare, no irritation to human eyes, and no eye fatigue)
(4) The amount of display information is large (because the pixels can be made small)
(5) Easy to colorize (reproduce very accurately on the chromatogram)
(6) No electromagnetic radiation (safe for the human body, conducive to information confidentiality)
(7) Long life (this kind of device has almost no deterioration problem, so the life is extremely long, but the life of the LCD backlight is limited, but the backlight part can be replaced)
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