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| circuit_design:4_opamp_basic_circuits_ii [2023/09/13 08:54] – mexleadmin | circuit_design:4_opamp_basic_circuits_ii [2023/09/19 22:16] (aktuell) – mexleadmin |
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| ====== 4. Basic Circuits II ====== | ====== 4 Basic Circuits II ====== |
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| <callout> | <callout> |
| === Introductory Example=== | === Introductory Example=== |
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| In various applications, currents must be measured. In an electric motor, for example, the torque is caused by the current flowing through the motor. A motor control and also a simple overcurrent shutdown are based on the knowledge of the current. For further processing, a voltage must be generated from the current. The simplest current-to-voltage converter is the ohmic resistor. A sufficiently large voltage as required by a microcontroller, for example, cannot be achieved with this. So not only the current has to be converted, but also the generated potential difference has to be amplified. | In various applications, currents must be measured. In an electric motor, for example, the torque is caused by the current flowing through the motor. A motor control and a simple overcurrent shutdown are based on the knowledge of the current. For further processing, a voltage must be generated from the current. The simplest current-to-voltage converter is the ohmic resistor. A sufficiently large voltage as required by a microcontroller, for example, cannot be achieved with this. So not only does the current have to be converted, but also the generated potential difference has to be amplified. |
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| One such current sense amplifier is the [[http://www.ti.com/lit/ds/symlink/ina240.pdf|INA 240]] device. This is installed as shown below. In the simulation, a real current source feeds the electrotechnical image of a DC motor on the left (in the example: inductance with $L_{\rm L}=10~\rm mH$ and internal resistance $R_{\rm L}=1~\Omega$). The current flowing from the motor is conducted through a measuring resistor ($R_{~\rm M}=0.01~\Omega$) which is noticeably smaller than the internal resistance of the motor. Thus, most of the power acts in the motor and the current is only marginally affected by the sense resistor. The simulation above shows the inner workings of the current measuring amplifier. | One such current sense amplifier is the [[http://www.ti.com/lit/ds/symlink/ina240.pdf|INA 240]] device. This is installed as shown below. In the simulation, a real current source feeds the electrotechnical image of a DC motor on the left (in the example: inductance with $L_{\rm L}=10~\rm mH$ and internal resistance $R_{\rm L}=1~\Omega$). The current flowing from the motor is conducted through a measuring resistor ($R_{~\rm M}=0.01~\Omega$) which is noticeably smaller than the internal resistance of the motor. Thus, most of the power acts in the motor and the current is only marginally affected by the sense resistor. The simulation above shows the inner workings of the current measuring amplifier. |
| ===== Programmable Gain Amplifier ===== | ===== Programmable Gain Amplifier ===== |
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| Often in applications an analog signal is too small to process (e.g. to digitalize it afterward). | Often in applications an analog signal is too small to process (e.g. to digitalize it afterward). \\ |
| To amplify it an OpAmp can be used. However, for a wide input range, it might be beneficial to have an adjustable scale. | To amplify it an OpAmp can be used. However, for a wide input range, it might be beneficial to have an adjustable scale. |
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| This can be done with a simple non-inverting amplifier combined with a resistor network as seen in the next simulation. | This can be done with a simple non-inverting amplifier combined with a resistor network as seen in the next simulation. \\ |
| In this case, a so-called **single-ended** input is used. This means the input voltage is always referred to the ground. | In this case, a so-called **single-ended** input is used. This means the input voltage is always referred to the ground. |
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| </WRAP> | </WRAP> |
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| When the signal is not referred to the ground, the following circuit based on an instrumentation amplifier can be used. | \\ \\ |
| | When the signal is not referred to the ground, the following circuit based on an instrumentation amplifier can be used. \\ |
| | In this case, the input signal is **differential**. Referred to the ground the input signal (here the difference of $5 ~\rm mV$) can have an offset voltage with regard to the ground. \\ |
| | An example of this setup is the [[https://www.ti.com/lit/ds/symlink/ina351.pdf|INA 351]]. |
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| </WRAP> | </WRAP> |
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