Opto-isolated zero crossing detector
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From: markp on 20 Jul 2010 04:37 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:asq946tkoa9fg1q1iof4vl393erfiht0t8(a)4ax.com... > On Mon, 19 Jul 2010 17:10:59 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >>Jim Thompson wrote: >>> On Thu, 15 Jul 2010 07:29:45 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> markp wrote: >>>>> "Joerg" <invalid(a)invalid.invalid> wrote in message >>>>> news:8a74q8FbegU1(a)mid.individual.net... >>>>>> markp wrote: >>>>>>> Hi All, >>>>>>> >>>>>>> I have an sinusoidal AC signal between 30V and 160V AC and between >>>>>>> 200 >>>>>>> and >>>>>>> 600Hz in frequency, and I need an opto-isolated zero crossing >>>>>>> detector. >>>>>>> The >>>>>>> AC is actually from a transformer output but I don't want to add any >>>>>>> more >>>>>>> windings to it. I do however have a centre tap on the AC output. >>>>>>> Does >>>>>>> anyone >>>>>>> have any suggestions? >>>>>>> >>>>>> Why opto? Can't you use a modem transformer that gets a divided-down >>>>>> signal at the input and has the proper isolation specs? Then use a >>>>>> regular zero-crosser of your liking on the others side where things >>>>>> don't have to run isolated. >>>>>> >>>>>> From a size point of few such a signal transformer and an optocoupler >>>>>> aren't grossly different. A little, maybe. >>>>>> >>>>>> -- >>>>>> Regards, Joerg >>>>> It's an option, but may be a little more expensive. I'm sure it can be >>>>> done >>>>> with just an optocoupler. >>>>> >>>> Sure it can be. But the accuracy suffers greatly. You can only send so >>>> many milliamps into an optocoupler and then it signals "out" well >>>> before >>>> the real zero-crossing happens. >>> >>> Discrete representation (high transistor count of chip would scare you >>> :-) of what I do in off-line-powered appliance controller chips... >>> >>> www.analog-innovations.com/SED/Zero_Crossing.pdf >>> >> >>But Mark needs an isolated one. >> >>[...] > > Use that pulse (buffered) to drive the opto-coupler. > > ...Jim Thompson This doesn't provide accurate zero crossing because of the phase delay introduced by the capacitor and resistor (C1 and R1). That phase delay will change with frequency and will vary with voltage. Unfortunately I need between 30V and 160V AC and between 200Hz and 600Hz oherwise this could have worked - the problem is using a capacitor to limit current and the phase delay that creates.
From: markp on 20 Jul 2010 05:33 "markp" <map.nospam(a)f2s.com> wrote in message news:8al52jF1ogU1(a)mid.individual.net... > > "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote > in message news:asq946tkoa9fg1q1iof4vl393erfiht0t8(a)4ax.com... >> On Mon, 19 Jul 2010 17:10:59 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>>Jim Thompson wrote: >>>> On Thu, 15 Jul 2010 07:29:45 -0700, Joerg <invalid(a)invalid.invalid> >>>> wrote: >>>> >>>>> markp wrote: >>>>>> "Joerg" <invalid(a)invalid.invalid> wrote in message >>>>>> news:8a74q8FbegU1(a)mid.individual.net... >>>>>>> markp wrote: >>>>>>>> Hi All, >>>>>>>> >>>>>>>> I have an sinusoidal AC signal between 30V and 160V AC and between >>>>>>>> 200 >>>>>>>> and >>>>>>>> 600Hz in frequency, and I need an opto-isolated zero crossing >>>>>>>> detector. >>>>>>>> The >>>>>>>> AC is actually from a transformer output but I don't want to add >>>>>>>> any more >>>>>>>> windings to it. I do however have a centre tap on the AC output. >>>>>>>> Does >>>>>>>> anyone >>>>>>>> have any suggestions? >>>>>>>> >>>>>>> Why opto? Can't you use a modem transformer that gets a divided-down >>>>>>> signal at the input and has the proper isolation specs? Then use a >>>>>>> regular zero-crosser of your liking on the others side where things >>>>>>> don't have to run isolated. >>>>>>> >>>>>>> From a size point of few such a signal transformer and an >>>>>>> optocoupler >>>>>>> aren't grossly different. A little, maybe. >>>>>>> >>>>>>> -- >>>>>>> Regards, Joerg >>>>>> It's an option, but may be a little more expensive. I'm sure it can >>>>>> be done >>>>>> with just an optocoupler. >>>>>> >>>>> Sure it can be. But the accuracy suffers greatly. You can only send so >>>>> many milliamps into an optocoupler and then it signals "out" well >>>>> before >>>>> the real zero-crossing happens. >>>> >>>> Discrete representation (high transistor count of chip would scare you >>>> :-) of what I do in off-line-powered appliance controller chips... >>>> >>>> www.analog-innovations.com/SED/Zero_Crossing.pdf >>>> >>> >>>But Mark needs an isolated one. >>> >>>[...] >> >> Use that pulse (buffered) to drive the opto-coupler. >> >> ...Jim Thompson > > This doesn't provide accurate zero crossing because of the phase delay > introduced by the capacitor and resistor (C1 and R1). That phase delay > will change with frequency and will vary with voltage. Unfortunately I > need between 30V and 160V AC and between 200Hz and 600Hz oherwise this > could have worked - the problem is using a capacitor to limit current and > the phase delay that creates. Forget that! This would be tru if you used the neutral as the input, but it actually uses the hot line I forgot to look at the timing diagrams on the second page :(
From: Joerg on 20 Jul 2010 16:14 Jim Thompson wrote: > On Mon, 19 Jul 2010 19:00:39 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Mon, 19 Jul 2010 17:35:37 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: > [snip] >>>> Ok, yeah, then it's easy of course. But you'll have to either tap off >>>> primary power somewhere or send isolated power across. Not that it's a >>>> big deal to do though. >>> Did you look at the schematic? It's (the zero-crossing detection) >>> powered from the line via the 220nF capacitor. >>> >> I saw that. Might want to add 1M or something like that between line and >> neutral, for discharge. > > Why bother? The OP asked for a zero-crossing detector. Allusions to > opto-coupling indicates he has a transformer-isolated PS, so that > primary will dump any "Darwin" current ;-) > ROFL! Darwin current, classic! That was a good one. >> >>> One does assume that he has a regular isolated power supply on the >>> other side (that needs the zero-crossing info :-) >>> >> Assumptions have sunk many a ship :-) > > Did you read the thread, or do you just like to ramble ?:-) > I did read the whole thread and other than a transformer with too high a voltage I don't remember anything. You'd you be looking at yet another power supply. >> >>>> I'd use a li'l transformer with a resistive divider up front to tap off >>>> the signal and do all the rest on the non-iso side. Triad makes some >>>> nice small ones. Pretty, too, the ones I have are fire-engine red. >>> As I noted earlier in the thread... use the remaining spares in the >>> LM339 package to drive the LED in the opto-coupler. >>> >> But you'd still have one left over. What a waste of resources there :-) > > Transformers are unreliable for accurate zero-crossing timing. > Not if they are wideband enough. Check out the Triad Magnetics stuff. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 20 Jul 2010 16:16 Jim Thompson wrote: > On Mon, 19 Jul 2010 19:14:29 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >> On Mon, 19 Jul 2010 19:00:39 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> Jim Thompson wrote: >>>> On Mon, 19 Jul 2010 17:35:37 -0700, Joerg <invalid(a)invalid.invalid> >>>> wrote: >> [snip] >>>>> Ok, yeah, then it's easy of course. But you'll have to either tap off >>>>> primary power somewhere or send isolated power across. Not that it's a >>>>> big deal to do though. >>>> Did you look at the schematic? It's (the zero-crossing detection) >>>> powered from the line via the 220nF capacitor. >>>> >>> I saw that. Might want to add 1M or something like that between line and >>> neutral, for discharge. >> Why bother? The OP asked for a zero-crossing detector. Allusions to >> opto-coupling indicates he has a transformer-isolated PS, so that >> primary will dump any "Darwin" current ;-) >> > [snip] > > There IS a discharge path, without any additions. > Nope, upon a disconnect C2 dischargeth not. Well, except across the Darwin path you mentioned before ... bzzzt ... OUCH! -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 20 Jul 2010 16:50
On Tue, 20 Jul 2010 13:16:17 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> On Mon, 19 Jul 2010 19:14:29 -0700, Jim Thompson >> <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >> >>> On Mon, 19 Jul 2010 19:00:39 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> Jim Thompson wrote: >>>>> On Mon, 19 Jul 2010 17:35:37 -0700, Joerg <invalid(a)invalid.invalid> >>>>> wrote: >>> [snip] >>>>>> Ok, yeah, then it's easy of course. But you'll have to either tap off >>>>>> primary power somewhere or send isolated power across. Not that it's a >>>>>> big deal to do though. >>>>> Did you look at the schematic? It's (the zero-crossing detection) >>>>> powered from the line via the 220nF capacitor. >>>>> >>>> I saw that. Might want to add 1M or something like that between line and >>>> neutral, for discharge. >>> Why bother? The OP asked for a zero-crossing detector. Allusions to >>> opto-coupling indicates he has a transformer-isolated PS, so that >>> primary will dump any "Darwin" current ;-) >>> >> [snip] >> >> There IS a discharge path, without any additions. >> > >Nope, upon a disconnect C2 dischargeth not. Well, except across the >Darwin path you mentioned before ... bzzzt ... OUCH! Sorry you loseth ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | |