Опубликовано 2013-05-03 14:06:12 автором MRS
operational amplifier - this sort of thing , which can be used in different ways to change the analog signal ( amplify, attenuate , invert , etc.). On the concept denoted as follows He left two entrances, which are designated : + ( direct , does not change the polarity of the voltage ) and - ( inverse changes the polarity of the voltage ) . Input resistance is very large, ideally equal to infinity in reality - hundreds of megohms , so in the current inputs are not techet.Operatsionny amplifier measures the voltage at the input , but it is affected minimally . Right - exit . At the operational amplifier has two power inputs , but usually they are not displayed on the chart The output voltage depends on switching circuit OS , but can not be greater than the supply voltage. In the simplest case, you can apply a voltage directly to the inputs of the OS , and in this case, the output voltage will be calculated according to the formula :
U out = (U inp1 -U inp2 ) * K, here
U inp1- the voltage at the non-inverting input ,
U inp2- the inverting input voltage ,
U out- the output voltage ,
K- gain without feedback. Let us model the option to include the OS without feedback in Proteus and see what will be the output. scheme As we can see in the diagram , the supply voltage op amp 10V input on the line , we serve 5B on inverse - 3B. At the output we should be ( 5-3 ) * K , K - very large number, such as 10 6 , and we have a total of 9 volts. This is due to the fact that the output voltage may not be greater than the supply voltage. Increase the voltage up to 1000 volts at the output we get 999V . Such inclusion OS is almost never used because you can not adjust the gain op amp , it is always maximized. Operational amplifier operates as he seeks to make the output voltage so that the voltage at the inverting input and forward were equal (their difference is zero ). used for this purpose including feedback op amp . Here's how: the voltage output through a resistor divider is input . The non-inverting amplifier
Gain is calculated by the formula:
K = 1 + (R2/R1)As we remember, the OS operating principle is to make the output voltage such that the input voltage difference is zero. Here we are on the line input is 5V , and inverted through a resistor divider half of the output voltage. DU remains nothing how to raise the output voltage twice relative to the direct input. With this integration , you can multiply the voltage op amp to a number greater than 1. But where it can come in handy ? For example, we need to measure the current . To do this, take a small shunt resistance of 0.01 ohm, the voltage drop across it at a current of 2 A is U = I * R, U = 2 * 0.01 = 0.02 . Amplified by the OS 100 times , it will be 2B, and fed to an ADC of the microcontroller.
Gain is calculated by the formula:
K = - (R2/R1)Direct entry to us to put on the ground, the OS will try to do so and at the inverse input was zero. For this he needs to lower the output voltage is below zero, and that you see in the diagram .
Output voltage equal to the voltage on the direct input , but you may ask why this is necessary because you can just throw a straight wire . Imagine the situation: there is a resistive divider and to the outlet you need to connect a light bulb . But the light bulb has its own resistance, and it will affect our resistive delitel.Chtoby remove this influence bufferiziruetsya output operational amplifier inputs , then he has a very high resistance and influence he will be on the lowest resistive divider and the output current can provide dozens or even hundreds miliamper , which is enough for the bulb.
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