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veioloko
Joined: 18 Aug 2006
Posts: 36
Helped: 3
Location: Brazil
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 24 Aug 2006 12:17 zero crossing using moc |
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hello
does anybody know an ic that detects the zero cross directly from the ac line 85~265?
without transformer? because i don´t want to use transformer and neither big resistors.
i wan´t to do a digital dimmer.
thanks and sorry for my english
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SplinterCell
Joined: 24 Aug 2006
Posts: 3
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24 Aug 2006 13:04 zero crossing moc |
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Not sure if there are discrete ICs that operates in the voltage range that you want.
National Semiconductor's LM1815 allows you to operate upto 120V using external resistors.
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IanP
Joined: 05 Oct 2004
Posts: 6661
Helped: 1577
Location: West Coast
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veioloko
Joined: 18 Aug 2006
Posts: 36
Helped: 3
Location: Brazil
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24 Aug 2006 13:22 why we use fuse |
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thanks but i don´t want to use moc....i just want to detect the zero cross and pick a low or high digital signal, that the microcontroler will use.
does anyone knows how is the circuit that is inside moc? that detects the zero?
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on1aag
Joined: 30 Jun 2006
Posts: 155
Helped: 36
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25 Aug 2006 7:41 zero crossing 110 220v |
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Hi Veioloko,
What about a discrete solution ? The width of the output pulse is
200 µS, the steep trailing edge is the reference.
Be careful, it could be a shocking experience! 
on1aag.
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alex_eng
Joined: 27 Aug 2006
Posts: 5
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27 Aug 2006 10:34 zero cross detect optocouplers |
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| you can detect zero crossing using amplifiers connect (-)pin to ground and the(+) to the signal u want when the wave be zero as ground the output will be zero other will give -VCC or +VCC as the signal move in the negative part or possitive one
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BigBenG
Joined: 26 Aug 2006
Posts: 3
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27 Aug 2006 21:15 Re: Zero crossing |
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HV Zero crossing detection is almost always done with simple optcoupler circuits and then maybe some other passives to tailor the waveform to your needs.
Please see the picture for a simple example of how to do crossover detection with very few components.
Hope it helps
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veioloko
Joined: 18 Aug 2006
Posts: 36
Helped: 3
Location: Brazil
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28 Aug 2006 13:29 Re: Zero crossing |
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Hello
thanks but i´m using a full wave rectifier.....
The ideia that you give is good becuase it use only a half..consequently less power....
However the power in both circuits are very high...
I made a circuit using the 6n139 that requires only 1mA at imput...so i could turn the circuit in 110 and 220. But i used two 22k 7w in series. I get +- 40ºC ....
How can i reduce the size of the circuit and the heating?
I want a 120hz signal in the microcontroler....
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mexfi571
Joined: 01 Feb 2007
Posts: 7
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01 Feb 2007 15:44 Re: Zero crossing |
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| BigBenG wrote: |
HV Zero crossing detection is almost always done with simple optcoupler circuits and then maybe some other passives to tailor the waveform to your needs.
Please see the picture for a simple example of how to do crossover detection with very few components.
Hope it helps |
Can you explain me how this circuit works? I didn't understand why we use fuse and another devices. there is anyone to help me in this subject? Thanks so much.
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veioloko
Joined: 18 Aug 2006
Posts: 36
Helped: 3
Location: Brazil
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08 Feb 2007 12:20 Re: Zero crossing |
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The circuit is simple to understand
The fuse is there only for security.
Resistors are used to "limit" the voltage in the optocoupler.
When we have less than +-1.2v,the optocoupler will not work, so we have the zero cross
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egemen
Joined: 20 Feb 2009
Posts: 3
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20 Feb 2009 18:17 Re: Zero crossing |
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| BigBenG wrote: |
HV Zero crossing detection is almost always done with simple optcoupler circuits and then maybe some other passives to tailor the waveform to your needs.
Please see the picture for a simple example of how to do crossover detection with very few components.
Hope it helps |
but the diode reverse-peak voltage is about 3V.so 220 ac damages the opto-coupler.Am I wrong?does the circuit in the picture work?
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btbass
Joined: 20 Jul 2001
Posts: 1267
Helped: 115
Location: Oberon
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20 Feb 2009 19:05 Re: Zero crossing |
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| Just use a high value resistor, something like 4M7 and feed it into one of your micro input ports. Use clamping diodes to supply and ground on the input pin.
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egemen
Joined: 20 Feb 2009
Posts: 3
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20 Feb 2009 19:31 Re: Zero crossing |
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| btbass wrote: |
| Just use a high value resistor, something like 4M7 and feed it into one of your micro input ports. Use clamping diodes to supply and ground on the input pin. |
secondly a normal opto-transistör input current 60-80 mA.if 120 K resistor is used
then opt-coupler input current will be very low to operate opt-coupler.(120K resistor in picture ).for example at 22v ac voltage level,about 300 ohm resistor must be used for acquiring 60-80 mA.But at peak level (220 volt ) this resitor will be too low.Consequently there is a dilemma.
I think the curcuit in the picture is not a good idea.Do you agree?If not why?
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max0412
Joined: 26 Oct 2003
Posts: 312
Helped: 31
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20 Feb 2009 19:53 Re: Zero crossing |
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| btbass wrote: |
| Just use a high value resistor, something like 4M7 and feed it into one of your micro input ports. Use clamping diodes to supply and ground on the input pin. |
How does that work with 60Hz slow moving waveforms? Is it possible to detect just the falling edge zero cross?
I’ve read of doing it using the internal ESD diodes in PIC’s never tried it yet though.
If I get sometime this weekend I'll try it on a low voltage AC.
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egemen
Joined: 20 Feb 2009
Posts: 3
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20 Feb 2009 20:07 Re: Zero crossing |
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| max0412 wrote: |
| btbass wrote: |
| Just use a high value resistor, something like 4M7 and feed it into one of your micro input ports. Use clamping diodes to supply and ground on the input pin. |
How does that work with 60Hz slow moving waveforms? Is it possible to detect just the falling edge zero cross?
I’ve read of doing it using the internal ESD diodes in PIC’s never tried it yet though.
If I get sometime this weekend I'll try it on a low voltage AC. |
of course resolution will be low.because 220v volt will be reduced 5,1 v.
at low level ac it can ce useful.A/D of pic should be used.under zero level detection can not be done without op-amp curcuit or etc.
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20 Feb 2009 20:07 Ads |
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btbass
Joined: 20 Jul 2001
Posts: 1267
Helped: 115
Location: Oberon
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20 Feb 2009 21:26 Re: Zero crossing |
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If the pic is supplied by a rectified ground ref. from a single supply, the ac swings above and below this. The input is just pulled high and low on the crossings and clamped by the diodes.
A dimmer is a hot circuit anyway, just be careful, make sure the whole thing is isolated!
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xulfee
Joined: 27 May 2008
Posts: 431
Helped: 32
Location: Pakistan
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21 Feb 2009 6:40 Zero crossing |
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| u can use opamp in open loop configuration for zero crossing
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tonybg
Joined: 17 Mar 2007
Posts: 18
Helped: 2
Location: bulgaria
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28 Feb 2009 13:18 Re: Zero crossing |
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Here is some example. GP3 is the input for sensing zero crossing.You can use the part connected to it for your project.Or the whole project.Have fun:D
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