Another advantage of applying a voltage follower is that the op amp input impedance is increased, so that the capacity of the input capacitance can be greatly reduced, which provides a prerequisite guarantee for the application of high-quality capacitors.Īnother question, what about isolation? Because the op amp input impedance of the voltage follower is very large, it can be approximated as an open circuit. At this time, a voltage follower is needed to buffer from it. If the input impedance of the subsequent stage is relatively small, part of the signal will be lost in the output resistance of the previous stage. Since the output impedance of the voltage amplifier is generally relatively high, usually in the range of several kiloohms to tens of kiloohms. After adding a voltage follower, the waveform loaded on the input of the voltage follower will basically not change, and the input-output stage voltage ratio is very close to unity. For example, if a sinusoidal voltage waveform with a peak value of 10V, the sinusoidal peak value loaded to the latter stage may only be 8V. Otherwise, if the previous-stage input impedance is large, and the latter stage is small, the signal will definitely be distorted. In this way, the magnification or other performance of the previous stage can be kept unchanged. Within the design requirement, no matter how the circuit connected to the subsequent stage changes, the output voltage is constant and does not change. Here is a question, how to understand the buffering effect? Is the voltage of the former having a small impact on the back circuit? No, it is equivalent to a constant voltage source. 2.2 Buffer Amplifier & Isolation Amplifier Because the op amp input impedance is large and the output impedance is small, voltage follower can reduce the impact on the signal and improve the load capacity. It can be composed of transistors or operational amplifiers (best). The "follow" in the follower means that the voltage remains unchanged before and after, and the output waveform is almost not lost. When the op amp gain is approximately 1, that is, the magnification is approximately 1. Ⅱ Voltage Follower Characteristics 2.1 Op Amp Impedance Matching If the current output is not enough, which may affect the signal output by the single-chip microcomputer, in this way, the voltage follower comes in handy. One LED does not require much current, so there is generally no big problem, however, when multiple LEDs need to light, current may definitely not large enough. It improves the load capacity to a considerable extent, while ensuring that the waveform and amplitude of the signal remain unchanged.įor example, a single-chip microcomputer outputs a PWM signal to control LED lights. When a weaker signal is used to drive a relatively high current, voltage follower is often added in the middle, so that it can make weak signal stronger. Op amp voltage follower is actually a simple circuit structure which play a role in impedance matching. It should be noted that voltage follower is a special case of negative feedback amplifier (voltage series). Within the rated output current range, the feedback voltage is equal to the output voltage, the output voltage is in phase with the input voltage, and the output voltage is slightly smaller than the input voltage. Because the gain of the op amp is extremely high, the input impedance of the op amp follower tends to be infinite, and the output impedance tends to zero. The op amp follower sacrifices the voltage amplification factor in exchange for the performance of increasing the input impedance and reducing the output impedance.
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