Opto-isolated zero crossing detector
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From: Jim Thompson on 19 Jul 2010 12:49 On Mon, 19 Jul 2010 08:25:55 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Mon, 19 Jul 2010 08:15:10 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> 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 >> >>Of course "The Bloviator" will claim too many parts, at the same time >>not providing component values on his own "designs". >> >>You can build my representation as shown... and it WILL work. >> >>Simplistically, from a years ago (1978) disco design... >> >>www.analog-innovations.com/SED/Zero_Crossing.pdf > >Make that... > >http://analog-innovations.com/Disco.PDF > >> >>Also mentioned recently here in... >> >>Message-ID: <bfuu265c7k3eile075vjkbpqe9ggg78amm(a)4ax.com> >> >>Adequate for non-critical Triac synchronization >> Elaborating... Use output pulse to drive an NPN to drive your opto-coupler input. Or... as I'd likely do, use the two spare comparators in the LM339 package. ...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 |
From: Spehro Pefhany on 19 Jul 2010 14:41 On Mon, 19 Jul 2010 11:26:33 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >> >>(Mine has the output high (nominally) for |Vin| < Vdd/2) >> > >So a "Cluck-Cluck" to Larkin's circuit IS in order ?:-) A cluck anyhow. >Mine is high for �Vbe about the zero-crossing. > > ...Jim Thompson For triac pulse triggering you need the load current to rise above the worst-case holding current by the end of the pulse for it to remain on for the rest of the half cycle. A lot of triacs have pretty high holding currents ( >100mA worst case). I guess ideally you'd use something like +/-Vbe on line voltage (or my circuit operating on a lower voltage such as 3.3V with 1.7V thresholds) and stretch the pulse by 100usec or so.
From: Jan Panteltje on 19 Jul 2010 14:38 On a sunny day (Mon, 19 Jul 2010 11:26:33 -0700) it happened Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in <h26946953v2v6suqb8jkrg0tv3m483tj2o(a)4ax.com>: >>>> >>>> 1M --> <-- pulse width >>>> ___ >>>> + -|___|------------------+ +--+ >>>> | ___ | | | >>>> + -|___|- | ------+ +----- >>>> | | | __ >>>> | 1M | __ +-\ \ Zero cross >>>> | +-------\ \ | |o----- output >>>> | | | |o-----/__/ >>>> | +-------/__/ >>>> AC HOT | >>>> .-. >>>> AC NEUTRAL | | >>>> | | | >>>> | '-' 510K >>>> GND | >>>> >>>> VCC > >Mine is high for �Vbe about the zero-crossing. I like Spheros's circuit. For just +-Vbe you can do much simpler: +5V | 10M _ |----------------------- ___| |______ in c | --- 1M ------ b NPN | | e c | | ---b NPN | /// | e | /// | |______________________|
From: Jim Thompson on 19 Jul 2010 14:48 On Mon, 19 Jul 2010 14:41:54 -0400, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >On Mon, 19 Jul 2010 11:26:33 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >>> >>>(Mine has the output high (nominally) for |Vin| < Vdd/2) >>> >> >>So a "Cluck-Cluck" to Larkin's circuit IS in order ?:-) > >A cluck anyhow. > >>Mine is high for �Vbe about the zero-crossing. >> >> ...Jim Thompson > > >For triac pulse triggering you need the load current to rise above the >worst-case holding current by the end of the pulse for it to remain on >for the rest of the half cycle. A lot of triacs have pretty high >holding currents ( >100mA worst case). I guess ideally you'd use >something like +/-Vbe on line voltage (or my circuit operating on a >lower voltage such as 3.3V with 1.7V thresholds) and stretch the pulse >by 100usec or so. Yep. Somewhere in my chip repertoire is a design that goes high AT the zero crossing (either slope) and stays high for awhile. I did it for GenRad about 30 years ago, so it's _on_paper_ (before PSpice :-) Hopefully I still have it. IIRC it did not require a time delay... scratching head and doing a vague memory dump... I seem to remember it detected that the TRIAC did reach holding current. ...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 |
From: Joerg on 19 Jul 2010 20:10
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. [...] -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |