Does anyone know what circuit this is and what function it has?

QiuLJie

Does anyone know what circuit this is and what function it has? [Copy link]

 

It feels like peak detection, but it doesn't... What kind of circuit is this and what function can it achieve?

maychang

Not peak detection.

The two operational amplifiers form a full-wave precision rectifier circuit. Its output end (the left end of R9) is the absolute value of the input signal, and after the R9C9R8C8 secondary filtering, the output is the average value of the absolute value of the input signal.

埋土书生

The front op amp forms a full-wave precision rectifier, the upper op amp is negative half cycle and the lower op amp is positive half cycle. The back RC low-pass filter should be the peak value of the signal.

maychang

Maidu Shusheng published on 2020-4-10 19:01 The front op amp forms a full-wave precision rectifier, the upper op amp is negative half cycle and the lower op amp is positive half cycle. , the back RC low-pass filter, the output should be the peak value of the signal

"After the RC low-pass filter, the signal should be at its peak value."

How can a low-pass filter produce a peak? It is obviously the average value. To be more precise, it is the average absolute value.

QiuLJie

Thank you so much everyone!!

hungchou

請問一下，D5功用為何？

maychang

hungchou 发表于 2020-4-11 08:11 請問一下，D5功用為何？

D5 and D2 have the same function, which is to prevent the op amp from entering deep saturation even in the half cycle when it is not working.

hungchou

maychang published on 2020-4-11 11:00 D5 and D2 have the same function, which is to ensure that the op amp will not enter deep saturation even in the half cycle when it is not working.

D5那一個好像還是會到達輸入腳的值？

瞭解了，只是避免飽和

D2那邊頂多-0.6V，D5這邊則是輸入再減0.6V。

topwon

Tried it with simulation software

maychang

topwon posted on 2020-4-13 13:34 Tried it with simulation software

What is the frequency of the input signal during simulation?

In addition, the input signal is bipolar, how can the op amp use a single power supply?

topwon

maychang posted on 2020-4-13 14:04 What is the frequency of the input signal during simulation? In addition, the input signal is bipolar, how can the op amp use a single power supply?

50Hz, and 500Hz have also been tried, with little difference.

I have also tried positive and negative power supplies, and it doesn't seem to have any effect.

topwon

This is a single 5V power supply 500Hz

topwon

This is a positive and negative 5V dual power supply 500Hz

maychang

topwon posted on 2020-4-13 14:13 This is a positive and negative 5V dual power supply 500Hz

Then, the step size of your simulation on the 9th floor may be too large. Can you try to make the step size smaller (for example, to one tenth)?

PowerAnts

The left leg of R9 has a high impedance to the ground. It needs to be connected to a resistor much smaller than the input impedance of the filter so that the output can approach the average value.

PowerAnts

Average value precision rectifier

topwon

Correction, zoom in and see, there is still a difference.

Dual power supply 500Hz

Dual power supply 50Hz

Single power supply 500Hz

PowerAnts

If there is high impedance to ground in the middle, then isn't it dual to the half-wave rectifier inductor filter?

maychang

PowerAnts posted on 2020-4-13 14:28 The left foot of R9 has a high impedance to ground. It needs to be connected to a resistor much smaller than the input impedance of the filter so that the output can approach the average value

That makes sense! That's what happened.

captzs

This is the distortion caused by the intersection of precision rectified steamed bun waves, it is inevitable. Take a look at Teacher Chen’s experiment.