Opto-isolated zero crossing detector
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From: markp on 14 Jul 2010 20:53 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? Thanks! Mark.
From: Spehro Pefhany on 14 Jul 2010 20:58 On Thu, 15 Jul 2010 01:53:54 +0100, the renowned "markp" <map.nospam(a)f2s.com> 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? > >Thanks! > >Mark. > Maybe a bridge rectifier, resistor or FET current limiter, and an optocoupler. Depends a bit on how close to the zero you want to go (should the pulses vary in width with voltage, for example, and at what voltage threshold should the output go "true"). Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Joerg on 14 Jul 2010 20:58 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 http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 14 Jul 2010 21:23 On Thu, 15 Jul 2010 01:53:54 +0100, "markp" <map.nospam(a)f2s.com> 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? > >Thanks! > >Mark. > Ooh, you could use a variant of one of my favorite trick circuits, the totem-pole optoisolator: ftp://jjlarkin.lmi.net/ZCD.JPG John
From: krw on 14 Jul 2010 21:44
On Thu, 15 Jul 2010 01:53:54 +0100, "markp" <map.nospam(a)f2s.com> 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? > How close to "zero" does it have to detect? The output has to be isolated from both the primary and secondary? |