Zero crossing detector

• Apr 20, 2006

• #1

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sjjm

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zero crossing detector comparator

Hello
Im looking for a working circuit for a zero crossing detector employing a 741 op amp. If possible a zero crossing detector which can produce pulses at only the positive or negative-going zero crossings.

 

• Apr 20, 2006

• #2

safwatonline

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zero crossing detector using op amp

i think schmitt trigger can be used ,

 

• Apr 20, 2006

• #3

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Miguel Gaspar

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zero crossing comparator

Look up for a window comparator. But you must use comparators.

 

• Apr 20, 2006

• #4

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SkyHigh

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op amp zero crossing detector

Zero crossing detector is a simple circuit using 741.
Make 741 an open-loop comparator.
Connect Vcc to the positive rail, and Vee to negative rail.
Connect V(-) to ground.
Connect V(+) as input to incoming signal.
Now you have a simple zero crossing comparator.

I don't know why such a simple circuit can crack the heads all the forumers who replied before me.

 

• Apr 21, 2006

• #5

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shaz

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zero crossing detector

refer this circuit in this link

 

• Apr 29, 2006

• #6

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eng_wael ashraf

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comparator zero crossing detector

i can help u
if u want this circuit u can send ur mail to my email
eng_wam2020@yahoo.com

 

• May 1, 2006

• #7

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Miguel Gaspar

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zero crossing detection

Yes You can do it with op-amps if your requeriments of frequency are slow up to 10kHz, but are better for lower frequencies.

If you need upper frequencies and/ or more current, voltage comparators are better.

 

• May 2, 2006

• #8

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jassi

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comparator zero crossing

look for it on this site only i saw it few days back

 

• Jul 26, 2006

• #9

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MrEd

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mains zero crossing detector

Just some experince. I made a dimmer a while back and if you do the zero crossing on the secondary side of a transformer you will most probably get a "scew" detection depending on the transformer. It can also vary depending on your load of the transformer. So for high precision detection you should do it on the mains side and opto couple it or something like that.

Eddie

 

• Jul 26, 2006

• #10

T

tronix

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741 zero cross detector

SkyHigh said:

Zero crossing detector is a simple circuit using 741.
Make 741 an open-loop comparator.
Connect Vcc to the positive rail, and Vee to negative rail.
Connect V(-) to ground.
Connect V(+) as input to incoming signal.
Now you have a simple zero crossing comparator.

I don't know why such a simple circuit can fix the heads all the forumers who replied before me.

Click to expand...

makes complete sense , whats the problem guys?

 

• Jul 26, 2006

• #11

Enlightenment

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zero crossing detector using op-amp

Here is a schematic that I found on the net. I've done it in the past using similar concepts using different parts.

 

• Jul 26, 2006

• #12

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dfullmer

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zero crossing detector op amp

Another possible.

Just my 2 cents....

dfullmer

 

• Jul 26, 2006

• #13

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MrEd

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zero-crossing comparator

Those schematics will work but leaves quite a big zero pulse, Around 2V over the LED makes it be off during that time. You will need a delay in your software that pushes your action point closer to the real zero point, if you trig just before the zero cross you will have trouble and the light will flicker - That is if it is a mains dimmer you want to make... Maybe you are making a machine to prove that emptiness exist...

Also, the resistors could get a bit hot if you drive the LED's directly via mains. If there is an optocoupler with a LED that switches at 1mA or less it should work ok but if you run 20mA through the LED the resistor will cook and you will need some kind of ventilation solution.

If you have an isolated scope you can build all the controls on the mains side and do the optocoupling just before data coming. Sounds good in theory but trust me, it will be a pain - for real - to work with.

Only work with LED's now...and batteries...

Eddie

 

• Jul 27, 2006

• #14

Enlightenment

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zero crossing detector using opamp

If "sjjm" is driving a processor, then it really doesn't matter the width of the pulse, because you can subtract out the average of the width of the pulse to determine the dead center along with some +/- offset too. The key thing for this situation is to have a pulse that is very stable from zero crossing to zero crossing. For people who are using it for a integillent light dimmer, running this pulse into the trigger of a hardware timer is perfect, because the software takes the pulse offset into account for leading the timer value.

If "sjjm" is using this to drive hardware-only (no-cpu) circuits, then it is another issue.

 

• Jul 27, 2006

• #15

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dfullmer

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zcd circuit using op-amp

I agree With enlightenment. It could also be that the timing is not so critical and you just want to know that the event has happened +/- a millisecond. In the processor world this is a life time. For someone standing at a machine pushing a button to get a response 1-2 milliseconds is not even enough time to start to blink. It is all very application specific.

dfullmer

 

• Jul 28, 2006

• #16

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electronrancher

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mains zero cross detector

a 741 uses npn input stage with pnp common mode feedback - it can't sense a voltage near ground unless you use a negative supply of about 2 volts or so lower than ground.

probably, you should use one of the suggested schematics unless you can supply both a positive and negative supply voltage.