Opto-isolated zero crossing detector
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From: Joerg on 19 Jul 2010 22:00 Jim Thompson wrote: > 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. > I saw that. Might want to add 1M or something like that between line and neutral, for discharge. > 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 :-) >> 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 :-) -- 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 22:14 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 ;-) > > >> 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'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. ...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: Grant on 19 Jul 2010 22:18 On Mon, 19 Jul 2010 17:31:57 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> 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. > >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. > Decades ago there were iffy 741 opamps coming in, so we had to test them prior loading into boards. I made a little 2 opamp triangle wave oscillator with LED, if a new opamp work in the integrator section it was okay, but if a bad opamp worked as a comparator, we binned separately them for that use ;) Ones that could do both were binned to make up for the others. Can't remember which brand they were, probably the cheapest available. Didn't use a separate comparator chip, & response time didn't matter. Grant.
From: John Larkin on 19 Jul 2010 22:50 On Tue, 20 Jul 2010 12:18:09 +1000, Grant <omg(a)grrr.id.au> wrote: >On Mon, 19 Jul 2010 17:31:57 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> 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. >> >>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. >> > >Decades ago there were iffy 741 opamps coming in, so we had to test >them prior loading into boards. > >I made a little 2 opamp triangle wave oscillator with LED, if a new >opamp work in the integrator section it was okay, but if a bad opamp >worked as a comparator, we binned separately them for that use ;) > >Ones that could do both were binned to make up for the others. > >Can't remember which brand they were, probably the cheapest available. >Didn't use a separate comparator chip, & response time didn't matter. > >Grant. The first switcher I ever did, hysteretic 24 to 5 volts buck, used an uncompensated uA709 as the comparator, feeding a 2N2905 and then a 2N3055. A 709 was an OK comparator. The 3055 was reasonably fast because it ran as an emitter follower, unsaturating. I ran it at 24 KHz because I could hear 22K in those days. I recall that a uA709 needed three external compensation parts to work as an opamp. It had some nasty latch modes, too. We got a lot of bad parts in those days, especially RTL and TTL. We rarely get a bad IC any more. John
From: Jim Thompson on 19 Jul 2010 23:10
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. Buy a cooler, you need the lesson ;-) ...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 | |