Opto-isolated zero crossing detector
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From: Jim Thompson on 19 Jul 2010 20:19 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 -- | 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: John Larkin on 19 Jul 2010 20:31 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. > >[...] Not really. He said he'd ground one end of the transformer, or the other, or the CT. My little differential comparator thing works fine in all those cases. 4 resistors, one comparator or opamp. The right opamp can make a nice comparator when you don't want a lot of speed, like when you want to ignore line spikes. Somebody semi-famous said to never use an opamp as a comparator and never use a comparator as an opamp. He was half right. John
From: Joerg on 19 Jul 2010 20:35 Jim Thompson wrote: > 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. > 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. 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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 19 Jul 2010 20:39 John Larkin wrote: > 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. >> >> [...] > > Not really. He said he'd ground one end of the transformer, or the > other, or the CT. My little differential comparator thing works fine > in all those cases. 4 resistors, one comparator or opamp. > Ok, yes, if non-iso then it's fine. > The right opamp can make a nice comparator when you don't want a lot > of speed, like when you want to ignore line spikes. Somebody > semi-famous said to never use an opamp as a comparator and never use a > comparator as an opamp. He was half right. > I have used opamps as comparators a lot, never had any issues. The other way around is a pain in the neck because most are open collector. The fun really begins when using CD4000 logic for stuff like this. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 19 Jul 2010 21:49
On Mon, 19 Jul 2010 17:35:37 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> 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. >> > >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. One does assume that he has a regular isolated power supply on the other side (that needs the zero-crossing info :-) > >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. ...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 | |