RMS meter Peak detector AC/DC converter
AC to DC converter analog circuit is analyzed in this example. Circuit output voltage is shown that is proportional to the peak voltage Vm of the input sinusoid. The circuit is designed using two op amps and two diodes. There are two cascade stages in this circuit. The first phase stage is a half wave rectifier with inverting amplifier gain. The second stage is a lowpass filter in an inverting amplifier topology. The cutoff frequency of this lowpass filter needs to be set sufficiently less than the frequency of the input sinusoid so that this low-pass operational amplifier filter practically completely removes all sinusoidal components in the Fourier series expansion of the half-wave rectified sinusoid. Such removal results in a purely DC or constant component appearing at the output of this circuit. The DC component can represent either the peak value (peak detector case) or RMS value (RMS meter case) with proper choice of the values of the four resistors in this circuit.
This circuit is designed using two op amps and two bipolar junction transistors (BJT). In this video, It is shown that the output voltage of circuit is an exponential conversion of the input voltage scaled by coefficients defined by resistors and also thermal voltage VT. A combination of op amp virtual short, Kirchhoff current law (KCL), Kirchhoff voltage law (KVL) and BJT current-voltage Shockley equation of p-n junction is used to prove that this circuit operates as an exponential amplifier or Antilogarithm converter.
RMS meter Peak detector AC/DC converter
AC to DC converter analog circuit is analyzed in this example. Circuit output voltage is shown that is proportional to the peak voltage Vm of the input sinusoid. The circuit is designed using two op amps and two diodes. There are two cascade stages in this circuit. The first phase stage is a half wave rectifier with inverting amplifier gain. The second stage is a lowpass filter in an inverting amplifier topology. The cutoff frequency of this lowpass filter needs to be set sufficiently less than the frequency of the input sinusoid so that this low-pass operational amplifier filter practically completely removes all sinusoidal components in the Fourier series expansion of the half-wave rectified sinusoid. Such removal results in a purely DC or constant component appearing at the output of this circuit. The DC component can represent either the peak value (peak detector case) or RMS value (RMS meter case) with proper choice of the values of the four resistors in this circuit.
This circuit is designed using two op amps and two bipolar junction transistors (BJT). In this video, It is shown that the output voltage of circuit is an exponential conversion of the input voltage scaled by coefficients defined by resistors and also thermal voltage VT. A combination of op amp virtual short, Kirchhoff current law (KCL), Kirchhoff voltage law (KVL) and BJT current-voltage Shockley equation of p-n junction is used to prove that this circuit operates as an exponential amplifier or Antilogarithm converter.
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