Opto-isolated zero crossing detector
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From: Jim Thompson on 19 Jul 2010 11:15 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 Also mentioned recently here in... Message-ID: <bfuu265c7k3eile075vjkbpqe9ggg78amm(a)4ax.com> Adequate for non-critical Triac synchronization ...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: Jim Thompson on 19 Jul 2010 11:25 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 > > ...Jim Thompson ...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 11:48 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 > >Also mentioned recently here in... > >Message-ID: <bfuu265c7k3eile075vjkbpqe9ggg78amm(a)4ax.com> > >Adequate for non-critical Triac synchronization > > ...Jim Thompson I have this (perhaps) amusing NON-isolated contribution, but anyone using it does so _entirely_ at their own risk. ;-) 1M --> <-- pulse width ___ + -|___|------------------+ +--+ | ___ | | | + -|___|- | ------+ +----- | | | __ | 1M | __ +-\ \ Zero cross | +-------\ \ | |o----- output | | | |o-----/__/ | +-------/__/ AC HOT | .-. AC NEUTRAL | | | | | | '-' 510K GND | VCC Width of the pulses is (1/(pi*f)) * sin^-1(Vdd/(sqrt(8)*Vline(rms)), so for a 10V supply and 120VAC/60Hz line input it would be ~150usec. It will be offset a bit because of the input capacitance, but only a few microseconds.
From: markp on 19 Jul 2010 12:27 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:bjq846lfqpvcd0d3u27t45dfba73ju1e93(a)4ax.com... > 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 > Funnily enough I did something very similar for another project, that is use a bridge rectifier with a capacitor to create a low voltage 'off-line' DC supply for a micro, then used the neutral wire as a reference into the micro with a current limiting resistor. What actually happens is the low voltage DC supply goes up and down wrt neutral, the micro sees + and - edges when it crosses the neutral potential. That works fine, LTSpice simulated and built. But it's non-isolating. Mark.
From: markp on 19 Jul 2010 12:49
"markp" <map.nospam(a)f2s.com> wrote in message news:8ajc97F9erU1(a)mid.individual.net... > > "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote > in message news:bjq846lfqpvcd0d3u27t45dfba73ju1e93(a)4ax.com... >> 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 >> > > Funnily enough I did something very similar for another project, that is > use a bridge rectifier with a capacitor to create a low voltage 'off-line' > DC supply for a micro, then used the neutral wire as a reference into the > micro with a current limiting resistor. What actually happens is the low > voltage DC supply goes up and down wrt neutral, the micro sees + and - > edges when it crosses the neutral potential. That works fine, LTSpice > simulated and built. But it's non-isolating. > > Mark. Actually what you get is not exact zero crossing with this. There's a phase delay introduced by the capacitor and resistor of the off-line DC source. If you know the frequency (50 or 60Hz) you can, to some extent, compensate for this with a delay (as I did in software). My application was to turn on a relay as close to zero crossing as possible, but in fact anywhere close enough that didn't have too much voltage across the contacts at the point of switching was acceptable. Mark. |