Is this what the 0 detection is like?

captzs

Is this what the 0 detection is like? [Copy link]

 

I often see posts about 0 detection, but I don't know what function they want to achieve. Some even cite foreign papers, which are very complicated and difficult to understand. I simulated the attached circuit, but I don't know if it has the same function as theirs?

The small triangle wave on the 0 axis when the negative sine wave ( green in the figure ) overshoots is the exact position where the sine wave crosses 0 , which is indicated by the U rectangular wave detected by the comparator . The amplitude of the sine wave cannot be too small, so that the overshoot of the sine wave is sharp and the position is accurate.

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hungchou

When using bridge rectifier, there is a diode conduction voltage drop, and there is a voltage difference between the signal source and GND.

There is a problem with detecting when the diode is not conducting

It is recommended to use OP rectifier circuit

maychang

This simulation result is correct.

However, as the original poster said, the amplitude of the sine wave cannot be too small. Only when the amplitude of the sine wave is large enough, the rectangular pulse output by the comparator will be narrow enough.

captzs

maychang published on 2019-8-11 10:43 This simulation result is correct. However, as the original poster said, the amplitude of the sine wave cannot be too small. The amplitude of the sine wave is large enough, and the rectangular pulse output by the comparator is narrow enough...

@maychang: I don't have a very clear understanding of the concept of zero-crossing detection. I need to understand it and then improve the circuit. Because I see that their circuit is very complicated, I wonder if I think it's too simple.

captzs

Over 0 detection files.

zero_crosser_1mS_Pulse.pdf (100.17 KB, downloads: 18)

2019-8-11 11:17 上传

点击文件名下载附件

zero_crosser_1mS_Pulse.pdf (100.17 KB, downloads: 18)

2019-8-11 11:17 上传

点击文件名下载附件

maychang

captzs posted on 2019-8-11 10:52 maychang posted on 2019-8-11 10:43 The simulation result is correct. However, as the original poster said, the amplitude of the sine wave cannot be too small. The amplitude of the sine wave...

The circuit in the first post is simple enough, but it also has the disadvantage of a large pulse width. Most of those complex circuits are designed around a lower sinusoidal voltage and require a very narrow zero-crossing pulse.

In fact, as long as the AC voltage of the first circuit is reduced to tens of volts, the zero-crossing pulse width can be greatly reduced.

qwqwqw2088

Zero crossing is commonly used in thyristor control circuits

The simulation on the first floor is AC5V

If you use the AC100--240V in the document given on the 5th floor, the circuit provided in the document can be

qwqwqw2088

Here is a multisim simulation, you can refer to

captzs

Overshoot and crossover distortion of the steamed bun wave.

After the sine wave half cycle ends, the junction capacitance of the diode will discharge the stored energy during the delay time, and the generated forward voltage causes the steamed wave voltage to overshoot onto the 0 axis.

The peak value of the steamed bun wave is less than the two diode voltage drops D V of the sine wave , resulting in a delay of t =T/4-t=2 p Vp/4SR-2 p ( Vp- D V)/4SR . Substituting the slope SR=2 p fVp into the crossover distortion, we can get the overshoot time length 2 t = D V/2fVp . It can be seen that the larger the amplitude Vp of the sine wave and the smaller 2 t , the smaller the width of the rectangular wave generated by it, and the 0 point always remains in the middle of 2 t .

captzs

Assume sine wave f=50Hz , Vp=14V , D V=1.2V , then the width of the rectangular wave 2t = D V /2fVp=1.2/2*50*14=857us , simulation 824us

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