实际上，使零交叉检测器电路非常容易，并且可以有效地用于保护敏感的电子设备免受电源开关的冲浪。
A zero crossing detector circuit is mainly used for protecting electronic devices from switch ON surges by ensuring that during power switch ON the mains phase always "enters' the circuit at its first zero crossing point.
奇怪的是，除了“ Wikipedia”之外，迄今为止，没有其他顶级在线网站解决了零交叉探测器概念的关键应用，我希望他们在阅读此帖子后会更新其文章。
什么是零交叉检测器？
We all know that our mains AC phase is made up of alternating sinusoidal voltage phases as shown below:
In this alternating AC, the current can be seen alternating across the central zero line and across the top positive and bottom negative peak levels, through a particular phase angle.
这一阶段的角度可以看到上升和下降exponentially, meaning it is doing so in a gradually rising and gradually falling manner.
The alternating cycle in an AC happens 50 times per second for 220V mains and 60 times per second for 120V mains inputs as set by the standard rules. This 50 cycle response is called 50 Hz frequency and the 60 Hz is called 60 Hz frequency for these mains outlets in our homes.
每当我们将设备或电子设备打开到电源时，它会突然进入AC相，如果该入口点恰好处于相位角度的峰值，则可能意味着将最大电流强加于设备上在开关点。
Although, most devices will be ready for this and might be equipped with protection stages using resistors, or NTC or MOV, it is never recommended to subject them to such sudden unpredictable situations.
To tackle such an issue, a zero crossing detector stage is used which ensures that whenever a gadget is switched ON with mains power, the zero crossing circuit waits until the AC phase cycle reaches the zero line, and at this point it switches ON the mains power to the gadget.
How to Design a Zero Crossing Detector
Designing a zero crossing detector is not difficult. We can make it using an opamp, as shown below, however using a opamp for a simple concept as this looks to be an overkill, so we'll also discuss how to implement the same using an ordinary transistor based design:
Opamp zero crossing detector circuit
The figure above show s simple 741 opamp based zero crossing detector circuit which can be used for all applications requiring a zero crossing based execution.
可以看出，741是配置为比较器, wherein its non-inverting pin is connected with ground through a 1N4148 diode, which causes a 0.6V drop potential at this input pin.
The other input pin#2 which is the inverting pin of ther iC is used for the zero crossing detection, and is applied with the preferred AC signal.
As we know that as long as pin#3 potential is lower than pin#2, the output potential at pin#6 will be 0V, and as soon as pin#3 voltage goes above the pin#2, the output voltage will quickly switch to the 12V (supply level).
Therefore within the fed input AC signal during the periods when the phase voltage is well above the zero line, or at least above the 0.6V over the zero line, the opamp output shows a zero potential....but during the periods when the phase is about to enter or cross the zero line, the pin#2 experiences a potential below 0.6V reference as set for pin#3, causing an immediate reversion of the output to 12V.
Thus the output during these points becomes 12v high level, and this sequence goes on triggering each time the phase crosses the zero line of its phase cycle.
The resultant waveform can be seen at the output of the IC which clearly expresses and confirms the zero crossing detection of the IC.
Using a opto-coupler BJT circuit
Although the above discussed opamp zero crossing detector is very efficient, the same can be implemented using an ordinary opto coupler BJT with reasonably good accuracy.
参考上图，可以有效地配置为光耦合器内部的光晶体管形式的BJTsimplest zero crossing detector circuit.
The AC mains is fed to the LED of the opamp via a high value resistor. During its phase cycles as long as the mains voltage is above 2V, the phototransistor stays in the conducting mode and the output response is held at near zero volts, however during times when the phase reaches the zero line of its travel, the LED inside the opto shuts off causing the transistor to also shut off, this response instantly causes a high logic to appear at the indicated output point of the configuration.
Practical Application circuit using zero crossing detection
可以在下面见证使用零交叉检测的实例示例电路，每当电源打开时，除了零交叉点以外的任何其他相位点外，都永远不会在此处切换TRIAC。
This makes sure that the circuit is always kept away from the switch ON current surge, and from its relevant dangers.
在上面的概念中，通过由PNP BJT控制的小信号SCR触发了TRIAC。该PNP BJT配置为执行零交叉传感，以实现TRIAC和相关负载的预期安全切换。
Anytime when power is switched ON, the SCR gets its anode supply from the existing DC trigger source, however its gate voltage is switched ON only at the moment when the input transits through its first zero crossing point.
Once the SCR is triggered at the safe zero crossing point, it fires the triac and the connected load, and in turn becomes latched ensuring a continual gate current for the triac.
This kind of switching at the zero crossing points every time power is switched ON ensures a consistent safe switch-ON for the load eliminating all possible dangers that is normally associated with mains sudden power switch ON.
RF Noise Elimination
Another great application of a zero crossing detector circuit is foreliminating noise in triac switching circuits. Let's take the example of an电子灯光调光电路, we normally find such circuits emitting a lot of RF noise into the atmosphere and also into mains grid causing unnecessary dumping of harmonics.
This happens due to the rapid intersection of the triac conduction across the positive/negative cycles via the zero crossing line...especially around the zero crossing transition where the triac is subjected into a undefined voltage zone causing it to produce rapid current transients which in turn are emitted as RF noise.
如果添加到基于TRIAC的电路中，则零交叉检测器，只有在交流周期完美地越过零线时才允许TRIAC发射，从而消除了这种现象，从而确保了TRIAC的清洁切换，Thererby消除了RF瞬变。
Reference:
您好Swagatamji，我是否需要此电路才能进行SCR开火电路。
can you pleas help to control SKKT 57B16E SCR in back to back model to control AC voltage.
你好，罗希特，对不起，我目前没有SCR控制的调光电路…
Hellow Swagatam, I quite understand the first two zero crossing circuits, but sir, to my understanding, the third circuit ‘practical application circuit might not work, it will conduct at the peak of the line voltage because the base of the PNP BJT is always lower than it’s emitter, and hence is forward biased. Please Sir, if it is a lack of enough understanding on my part, kindly explain how how the zero detection could be accomplished by the PNP BJT.
Hi Afolabi, The base of the PNP is connected with the positive line of the circuit via a few diodes. During the mains peak voltages this line will be at full 12V DC which will keep the PNP switched OFF. The PNP will be able to conduct only during the periods when the peak drops below 1.5V, when the base of the PNP will be able to access the ground negative potential. I hope you got the point.
Let me know if you have any further doubts.
Hi,
Interesting stuff, thanks.
Regarding your “Using a opto-coupler BJT circuit” however, surely it will only work as described during the positive half of the A/C cycle.
在负半周期期间，LED也将关闭，晶体管非传导导致与所示的O/P波形式不同。添加桥梁整流器为LED喂食，需要在草图中显示的每个零交叉处获得脉冲。不？
Cheers,
Brian H.
Uxbridge Ont Canada
我还要质疑第三电路的描述，因为在正半周期中，PNP的基础比发射器低3个二极管，因此能够向SCR触发器设备提供电流。因此，我看不出它如何阻止在正循环中触发的电路。该图缺少PNP发射极上的电容器。没有该电容器，PNP将无法在负半周期期间提供触发电流……但是，尽管它会清除零交叉点，但我看不出任何原因为什么在AC周期的后期部分都不会打开它或负面……。我很乐意与您进一步讨论！
The total diode drop at the base of the PNP will be around 2V, which means as long as the input positive cycle is above 2V across base/emitter, the PNP cannot conduct. Adding a capacitor will mean the PNP keeps conducting permanently due to the holding charge of the capacitor and will make the main purpose useless. The ScR gate current is decided by the 0.33uF value and seems to be quite enough for a SCR triggering. 0.33uF will provide around 15 mA sufficient for the ScR gate.
hello dear sir,God bless you .i always read your site and through site i was able to be almost a few successful in electronics. both zero crossing detectors can not be effective in the negative cycle, My dear friends,i designed a very good circuit that is very effective ,accurate and simple ,and i use this circuit a lot to control triak device and i wanted to share this circuit with you,noble man
Thank you Dear Sedigh,, all the above circuits are supposed to be fed from a bridge rectifier, not from an AC source, and therefore both the cycles will be processed!
I have put a note below all the diagrams for clarifying the issue!
Hi swagatam,
我尝试了第二条电路，并使用了桥梁整流器和MCT2E。如果我尝试180K 0,25W电阻，则电阻的温度似乎还可以。
But If y try 180k 1W resistor it’s very hot (can’t touch the resistor more than 3seconds.)
是正常的吗?
如果我在桥梁整流器之前将43k 1W电阻放在线上，并且它们也很热。
嗨，约翰，这很正常，但是我宁愿与电阻串联添加0.22UF/400V或0.33UF/400V电容器，然后将电阻值降低到10K（4.7K + 4.7K）1/4瓦，并看到效果
Your statement: As we know that as long as pin#3 potential is lower than pin#2, the output potential at pin#6 will be 0V, and as soon as pin#3 voltage goes above the pin#2, the output voltage will quickly switch to the 12V (supply level) is not quite correct. The voltage at pin 2 will fall below the reference voltage applied to pin 3.
我的陈述是正确的，这是一个基本的比较规则……..该输入应该是从桥梁整流器中喂养的
In the second circuit the current limiting resistor (220k in your case) should be wirewound type resistor or something else? Also how to calculate the wattage? Should we aim for lower or higher wattage?
A simple 1/4 watt CFR resistor will do.
Thank you.
Why is it so high resistance? At 230 volts you get 1,04 mA forward current. Is this enough for your optocoupler?
You can try 100k also, the 220k value was selected randomly because I guess even a slightest bit of illumination of the opto LED is enough to drive the transistor ON.
但是我认为，在一种实际情况下，您需要10个MA来打开OptoCoupler中的LED，您只需230伏即可23 KOHM。我走了吗？我没有考虑什么？
LED stat照明即使1 mA坏蛋rent although the illumination will be very dim, barely visible in dark. So the process of illumination is not sudden, rather it follows the intensity of the current from minimum to maximum.
Yes 23k would work but it would dissipate a lot of heat, therefore it will need to be a high watt resistor.