Question on zero-crossing circuit

Douglas Beeson · May 1, 2014

Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Thanks!

--
Douglas Beeson <c.difficile@gmail.com>

George Herold · May 1, 2014

On Thursday, May 1, 2014 8:10:51 AM UTC-4, Douglas Beeson wrote:

Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Hmm, We'll have to wait for Jim, 'cause it's not obvious to me how it works.

Why not just a transformer and then a comparator with some hysteresis. You still would want to capacitively couple it I think.... let the average voltage be your "zero". And that looks to be what C1 is doing.

George H.

Thanks!

--

Douglas Beeson <c.difficile@gmail.com

Phil Hobbs · May 1, 2014

On 05/01/2014 09:39 AM, George Herold wrote:

On Thursday, May 1, 2014 8:10:51 AM UTC-4, Douglas Beeson wrote:
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Hmm, We'll have to wait for Jim, 'cause it's not obvious to me how it works.

Why not just a transformer and then a comparator with some hysteresis. You still would want to capacitively couple it I think.... let the average voltage be your "zero". And that looks to be what C1 is doing.

George H.

It's only complicated-looking because it's drawn badly, with the power
supplies mixed up with the signal wiring.

The top and bottom rails (after R2 and R3) are the power supplies, Cap
C1 turns the AC mains into essentially a regulated AC current source.
R1 limits the inrush to an amp or so so you don't pop the rectifiers,
and the two zeners clip off the tops to keep the voltage regulated.
R2/C3 and R3/C4 are the supply filters. (The positive supply lead on
the LM339 isn't shown, which adds to the confusion.)

So apart from whatever incidental voltage there is on the neutral, you
can think of the junction of D1 and D2 as sitting still at ground
potential. The other ends of D1 and D2 sit at +- a diode drop from there.

AC current is applied to the junction of D4 and D5 via R4 (plus a bit of
despiking from C5, to get rid of switching hash and so on). On the
positive half cycle, D4 conducts and the D3/D4 junction goes to +2 diode
drops, so U1 pulls low.

On the negative half cycle, D3 conducts in the same way, and U2 pulls low.

Within a diode drop of the zero crossings, neither D3 nor D4 conducts,
and both U1 and U2 are high. So the result is a brief pulse on each
zero crossing.

It's not a circuit you'd want to do anything much with, except drive an
optocoupler, because there are safety issues.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Jim Thompson · May 1, 2014

On Thu, 1 May 2014 06:39:00 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Thursday, May 1, 2014 8:10:51 AM UTC-4, Douglas Beeson wrote:
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Hmm, We'll have to wait for Jim, 'cause it's not obvious to me how it works.

Why not just a transformer and then a comparator with some hysteresis. You still would want to capacitively couple it I think.... let the average voltage be your "zero". And that looks to be what C1 is doing.

George H.

Thanks!

Douglas Beeson <c.difficile@gmail.com

The impedance of C1 is ~12K @60Hz, limiting the recirculating current.
Transformers are expensive, and bulky.

The object of that path is to provide the power supply current for the
339 comparators.

Contrary to Phil, it is not drawn badly... it's quite easy to follow

John Larkin · May 1, 2014

On Thu, 1 May 2014 08:10:51 -0400, Douglas Beeson <c.difficile@gmail.com> wrote:

Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Thanks!

That's a lot of parts for a simple function. It's from an old s.e.d. thread.

Here are a few that I suggested:

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD.JPG

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD_2.JPG

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD_3.JPG

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD_x.JPG

That last one powers the gate from the line input, via the esd diodes.

(Beeson. I knew a Dr Beeson, a physicist, in New Orleans.)

--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

John Larkin · May 1, 2014

On Thu, 1 May 2014 06:39:00 -0700 (PDT), George Herold <gherold@teachspin.com>
wrote:

On Thursday, May 1, 2014 8:10:51 AM UTC-4, Douglas Beeson wrote:
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Hmm, We'll have to wait for Jim, 'cause it's not obvious to me how it works.

Why not just a transformer and then a comparator with some hysteresis. You still would want to capacitively couple it I think.... let the average voltage be your "zero". And that looks to be what C1 is doing.

C1 is mostly a current limiter.

Three interesting things:

C1 and C2 need to be "XY" type caps, safe to put across the AC line

C4 appears to be not connected

It has 20 parts and its output is still not isolated from the AC line.

A transformer, or a wall-wart equivalent, doesn't need a cap.

--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

Phil Hobbs · May 1, 2014

On 05/01/2014 11:11 AM, Jim Thompson wrote:

On Thu, 1 May 2014 06:39:00 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, May 1, 2014 8:10:51 AM UTC-4, Douglas Beeson wrote:
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Hmm, We'll have to wait for Jim, 'cause it's not obvious to me how it works.

Why not just a transformer and then a comparator with some hysteresis. You still would want to capacitively couple it I think.... let the average voltage be your "zero". And that looks to be what C1 is doing.

George H.

Thanks!

Douglas Beeson <c.difficile@gmail.com

The impedance of C1 is ~12K @60Hz, limiting the recirculating current.
Transformers are expensive, and bulky.

The object of that path is to provide the power supply current for the
339 comparators.

Contrary to Phil, it is not drawn badly... it's quite easy to follow

There'd be something seriously wrong if the guy who drew it couldn't
follow it. I'd much prefer flags on the PS leads (and it would be
easier for beginners if VCC were shown on the 339s.

And... there is a whole world that doesn't need opto-couplers... think
the appliance control industry where everything is operated directly
off-line.

...Jim Thompson

But if you're going to go to all that trouble, why put up with a
floating output? You aren't going to drive much off those rails, not
with 330 ohms in series.

And a 6N138, one BR, one resistor, and one cap will do the whole shebang
and give you isolation besides. (Or a 2-channel opto, as John suggested.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Jim Thompson · May 1, 2014

On Thu, 01 May 2014 13:25:01 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/01/2014 11:11 AM, Jim Thompson wrote:
On Thu, 1 May 2014 06:39:00 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, May 1, 2014 8:10:51 AM UTC-4, Douglas Beeson wrote:
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Hmm, We'll have to wait for Jim, 'cause it's not obvious to me how it works.

Why not just a transformer and then a comparator with some hysteresis. You still would want to capacitively couple it I think.... let the average voltage be your "zero". And that looks to be what C1 is doing.

George H.

Thanks!

Douglas Beeson <c.difficile@gmail.com

The impedance of C1 is ~12K @60Hz, limiting the recirculating current.
Transformers are expensive, and bulky.

The object of that path is to provide the power supply current for the
339 comparators.

Contrary to Phil, it is not drawn badly... it's quite easy to follow

There'd be something seriously wrong if the guy who drew it couldn't
follow it. I'd much prefer flags on the PS leads (and it would be
easier for beginners if VCC were shown on the 339s.

It's not meant for use as a PCB netlist. The 339 is totally
behavioral (model is on the Device Models & Subcircuits page of my
website), thus needs only IN+, IN-, OUT and a GND reference to
function.

(I'm actually working up a nice model of (OpAmp & Comparator) output
stages that properly reflects VDD and VEE currents with load, but have
been too busy to put the final touches on it.)

And... there is a whole world that doesn't need opto-couplers... think
the appliance control industry where everything is operated directly
off-line.

...Jim Thompson

But if you're going to go to all that trouble, why put up with a
floating output? You aren't going to drive much off those rails, not
with 330 ohms in series.

Huh? The output is at the 339, with a 10K pull-up. A _logic_ signal,
and it worked great in the washing machine it went into.

And a 6N138, one BR, one resistor, and one cap will do the whole shebang
and give you isolation besides. (Or a 2-channel opto, as John suggested.)

Whoopee doo ;-) Everything to the right of the bridge rectifier
(except capacitors) went onto a single chip along with a ton of other
goodies, timers, OpAmps, and a 3.3V output to power a micro.

And lots of things don't need much power... I recently designed a 1kHz
oscillator (for a medical application) that consumes only 6nA! And a
1MHz version that runs on 1.3uA.

Cheers

Phil Hobbs

Phil Hobbs · May 2, 2014

On 05/01/2014 01:50 PM, Jim Thompson wrote:

On Thu, 01 May 2014 13:25:01 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/01/2014 11:11 AM, Jim Thompson wrote:
On Thu, 1 May 2014 06:39:00 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, May 1, 2014 8:10:51 AM UTC-4, Douglas Beeson wrote:
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Hmm, We'll have to wait for Jim, 'cause it's not obvious to me how it works.

Why not just a transformer and then a comparator with some hysteresis. You still would want to capacitively couple it I think.... let the average voltage be your "zero". And that looks to be what C1 is doing.

George H.

Thanks!

Douglas Beeson <c.difficile@gmail.com

The impedance of C1 is ~12K @60Hz, limiting the recirculating current.
Transformers are expensive, and bulky.

The object of that path is to provide the power supply current for the
339 comparators.

Contrary to Phil, it is not drawn badly... it's quite easy to follow

There'd be something seriously wrong if the guy who drew it couldn't
follow it. I'd much prefer flags on the PS leads (and it would be
easier for beginners if VCC were shown on the 339s.

It's not meant for use as a PCB netlist. The 339 is totally
behavioral (model is on the Device Models & Subcircuits page of my
website), thus needs only IN+, IN-, OUT and a GND reference to
function.

(I'm actually working up a nice model of (OpAmp & Comparator) output
stages that properly reflects VDD and VEE currents with load, but have
been too busy to put the final touches on it.)

And... there is a whole world that doesn't need opto-couplers... think
the appliance control industry where everything is operated directly
off-line.

...Jim Thompson

But if you're going to go to all that trouble, why put up with a
floating output? You aren't going to drive much off those rails, not
with 330 ohms in series.

Huh? The output is at the 339, with a 10K pull-up. A _logic_ signal,
and it worked great in the washing machine it went into.

So you had a completely separate power supply just for the zero crossing
detector? Why? There must have been circuitry on the other side, which
would have needed its own power.

And a 6N138, one BR, one resistor, and one cap will do the whole shebang
and give you isolation besides. (Or a 2-channel opto, as John suggested.)

Whoopee doo ;-) Everything to the right of the bridge rectifier
(except capacitors) went onto a single chip along with a ton of other
goodies, timers, OpAmps, and a 3.3V output to power a micro.

And lots of things don't need much power... I recently designed a 1kHz
oscillator (for a medical application) that consumes only 6nA! And a
1MHz version that runs on 1.3uA.

Yeah, I suspected it was just a doodle. Parts are free in ICs, which
(like a trust fund) leads to lots of bad habits if you don't fight it.

Cheers

Phil Hobbs

Cheers

Phil Hobbs

...Jim Thompson

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

John Fields · May 2, 2014

On Thu, 01 May 2014 21:39:44 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 02 May 2014 08:04:26 +1000, "David Eather" <eather@tpg.com.au> wrote:

On Fri, 02 May 2014 01:37:17 +1000, John Larkin
jjlarkin@highnotlandthistechnologypart.com> wrote:

On Thu, 1 May 2014 08:10:51 -0400, Douglas Beeson
c.difficile@gmail.com> wrote:

Hi all,

I did a search the other day on zero crossing detector circuits and
came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What
does it do?

Thanks!

That's a lot of parts for a simple function. It's from an old s.e.d.
thread.

Here are a few that I suggested:

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD.JPG

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD_2.JPG

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD_3.JPG

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD_x.JPG

That last one powers the gate from the line input, via the esd diodes.

(Beeson. I knew a Dr Beeson, a physicist, in New Orleans.)

John,
those first three won't work. If the LED's pass enough current so it
detects 0 volts somewhere near 0 volts then they burn out at the top of
the mains cycle.

You can buy dual optos with guaranteed CTRs of 2 or so (or darlingtons much
higher).

---
OK, but the CTR isn't as important as the CTR match for the same
current into the LEDs.

have you got a part number for something that'll supply reasonable
(?) accuracy around the zero-cross as the current falls to zero?

And, BTW, what would you consider to be "reasonable accuracy"?
---

So pick the input resistors for, say, 5 mA peak current, hardly a danger to an
LED in an optocoupler. That would be 10 mA peak collector current. Depending how
close to "zero" you want, you could work with 1 mA, or 0.5 mA out. That's plenty
of signal.

The totem-pole opto, my first circuit, needs very little phototransistor current
to drive CMOS rail-to-rail. As noted in the old SED thread, if you don't like
the delay from the opto speed, add a cap in series with one of the input
resistors, to add some phase lead... and reduce power dissipation.

---
The problem with that is the reactance of the cap is going to lower
the current into the LED, spoiling the CTR match between the
sections.

Will it matter? Offhand, I dunno.

Do you have a clue?
---

It's perfectly feasible. The reason to keep the current down isn't to protect
the LEDs, it's to keep the power dissipation down in the input resistors.

One dual opto, two resistors. Or even one resistor. Output is a clean, isolated,
r-r square wave.

---
Not from #3, since it's essentially a De Morgan equivalent "OR" with
an output which will be a narrow positive-going pulse which will
straddle the zero-crossings.
---

Compare that to some of the other dozens-of-parts hairballs
posted here that don't even isolate.

---
Isolation is easy to get, accuracy isn't so easy, and "Hairballs" is
a derogatory term and has no place in an emotion-free discussion,
especially from an engineer who demeans emotionality in technical
discussions.
---

>What's wrong with my second one, ZCD_2?

---
If the 2.5V is really stiff it seems OK, but what voltage are you
specifying across the transformer secondary?

And for all the ones using optos, how about specifying an acceptable
+/- error with respect to the true zero-crossing and an opto part
number so we can figure out how bad they really are?

John Fields

Don Kuenz · May 2, 2014

Jim Thompson <To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote:

On Thu, 1 May 2014 06:39:00 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, May 1, 2014 8:10:51 AM UTC-4, Douglas Beeson wrote:
Hi all,

I did a search the other day on zero crossing detector circuits and
came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1.
What does it do?

Hmm, We'll have to wait for Jim, 'cause it's not obvious to me how it works.

Why not just a transformer and then a comparator with some hysteresis.
You still would want to capacitively couple it I think.... let the
average voltage be your "zero". And that looks to be what C1 is
doing.

George H.

Thanks!

Douglas Beeson <c.difficile@gmail.com

The impedance of C1 is ~12K @60Hz, limiting the recirculating current.
Transformers are expensive, and bulky.

Amen! And there's not always a handy power outlet nearby to plug a wall
wart into.

The object of that path is to provide the power supply current for the
339 comparators.

Contrary to Phil, it is not drawn badly... it's quite easy to follow

It's easy enough for me to follow. It looks like most of the other
production schematics out there. Your schematic "keeps it real" for
novices. The real world often lacks the time to "hand hold" or provide
"one on one" answers. So one learns to be grateful for any schematic
whatsoever.

It looks like you used LTSpice to draw it. LTSpice is the lingua franca
of usenet.

And... there is a whole world that doesn't need opto-couplers... think
the appliance control industry where everything is operated directly
off-line.

Hot power "keeps it simple" for journeymen. The WARNING - RISK OF
ELECTRIC SHOCK sticker advertises that journeymen skills are required.

--
Don Kuenz

Rick · May 2, 2014

"Wayne Chirnside" <w.faux@doentexist.com> wrote in message
news:WIE8v.3672482$kl4.3059748@fx10.iad...

On Thu, 01 May 2014 08:10:51 -0400, Douglas Beeson wrote:

Hi all,

I did a search the other day on zero crossing detector circuits and came
across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What
does it do?

Thanks!

Provides filtered smoothed DC to the comparators

http://www.fairchildsemi.com/pf/MI/MID400.html
I have used this with good results.

Phil Hobbs · May 2, 2014

On 5/2/2014 8:05 AM, Rick wrote:

"Wayne Chirnside" <w.faux@doentexist.com> wrote in message
news:WIE8v.3672482$kl4.3059748@fx10.iad...
On Thu, 01 May 2014 08:10:51 -0400, Douglas Beeson wrote:

Hi all,

I did a search the other day on zero crossing detector circuits and came
across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What
does it do?

Thanks!

Provides filtered smoothed DC to the comparators

http://www.fairchildsemi.com/pf/MI/MID400.html
I have used this with good results.

Another approach, which I've always thought was pretty, is the one
Tektronix uses in their scopes. They heat-shrink a piece of hookup wire
to each of the AC input leads, and use the few-pF capacitance to get a
line-isolated 60 Hz signal into their low-level circuitry.

That avoids having to have mains voltage on the PCB at all. They
probably have to use higher-rated insulation on the AC leads, but it's
still a win.

You would have to worry about the resulting phase shift if you need the
actual zero crossings as opposed to just line sync and power fail
detection, so you wouldn't want to use it for triggering a triac, say.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Douglas Beeson · May 2, 2014

On Thu, 01 May 2014 08:37:17 -0700
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Thu, 1 May 2014 08:10:51 -0400, Douglas Beeson <c.difficile@gmail.com> wrote:

Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Thanks!

That's a lot of parts for a simple function. It's from an old s.e.d. thread.

Here are a few that I suggested:

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD.JPG

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD_2.JPG

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD_3.JPG

https://dl.dropboxusercontent.com/u/53724080/Circuits/ZCD_x.JPG

That last one powers the gate from the line input, via the esd diodes.

(Beeson. I knew a Dr Beeson, a physicist, in New Orleans.)

--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

Thank you, John. My interest in ZCD circuits stems from a need to limit "clicks" when an amplified, audio-like signal is gated. I am looking at 13.8 Vp-p and 0.1-20kHz frequency. I want to trigger a uController with the leading or trailing edge of a comparator pulse so that the turnon or shutoff occurs only when voltage is near zero. I will have a look at your circuit ideas.

The Beesons arrived from England in the late 17th century, settled in Pennsylvania (Uniontown used to be called Beesontown), and family genealogy has it that some went south and some went west. I'm a western Beeson, but have since migrated north to Canada.

doug

--
Douglas Beeson <c.difficile@gmail.com>

Douglas Beeson · May 2, 2014

On Thu, 1 May 2014 17:01:49 -0400
WangoTango <Asgard24@mindspring.com> wrote:

In article <20140501081051.f2341ef5d60270d968a0bc7b@gmail.com>,
c.difficile@gmail.com says...
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Thanks!

Are you just looking at it to understand it, or are you looking for a
Zero Crossing Detector to actually use?

I have one that I have used for many moons that is a heck of a lot less
convoluted that this one and has proven to be quite reliable.

Thanks for your reply. I do have an actual need, but only at lower voltages (13.8 V max). It has to cutoff closer to zero than the 1 diode drop of Jim's circuit, though. I'm interested in seeing your design if you're willing to post it.

-doug

--
Douglas Beeson <c.difficile@gmail.com>

John Fields · May 2, 2014

On Fri, 2 May 2014 09:49:11 -0400, Douglas Beeson
<c.difficile@gmail.com> wrote:

..
..
..

My interest in ZCD circuits stems from a need to limit "clicks" when an amplified,
audio-like signal is gated. I am looking at 13.8 Vp-p and 0.1-20kHz frequency.
I want to trigger a uController with the leading or trailing edge of a comparator
pulse so that the turnon or shutoff occurs only when voltage is near zero.

..
..
..

>doug

---
From your description it sounds like you have an AC signal which you
want to switch into a load, but only after the switch is turned on
and then close to when the next AC zero crossing occurs.

Once that happens and the AC is feeding the load, you want the
switch to stay ON for some time and then, when it's switched OFF,
disconnect the AC from the load close to when the next AC zero
crossing occurs.

Is that what you're looking for?

John Fields

Jim Thompson · May 2, 2014

On Thu, 01 May 2014 21:53:39 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Thu, 01 May 2014 17:41:13 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Thu, 1 May 2014 08:10:51 -0400, Douglas Beeson
c.difficile@gmail.com> wrote:

Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Thanks!

This one might be better for those who are afraid of "hot" circuits...

http://www.analog-innovations.com/SED/ZeroCross_LM339_SED.pdf

(Next to last listing on the S.E.D/Schematics page of my website.)

...Jim Thompson

21 parts! A personal best!

I aims to please >:-}

Most LM339s will do horrible goofy things, in all four sections, if you pull one
input a little below ground. D3 won't prevent that. See the National data sheet,
notes 3, 6, and 8. They warn about this *three* times. Also see their ZCD
example on page 14.

D3 does prevent substrate diodes from conducting. Besides, those of
us intimately familiar with the LM339 know why those "horrible goofy
things" can't happen in my circuit.

And you don't. So you just throw your usual sand in the air.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice

Jim Thompson · May 2, 2014

On Thu, 01 May 2014 21:57:20 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Thu, 1 May 2014 18:45:50 -0400, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:

In article <h6r4m9h23tvdtggm7g6rvbkhp08mtei4rk@4ax.com>,
jjlarkin@highNOTlandTHIStechnologyPART.com says...

On Thu, 1 May 2014 06:39:00 -0700 (PDT), George Herold <gherold@teachspin.com
wrote:

On Thursday, May 1, 2014 8:10:51 AM UTC-4, Douglas Beeson wrote:
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Hmm, We'll have to wait for Jim, 'cause it's not obvious to me how it works.

Why not just a transformer and then a comparator with some hysteresis. You still would want to capacitively couple it I think.... let the average voltage be your "zero". And that looks to be what C1 is doing.

C1 is mostly a current limiter.

Three interesting things:

C1 and C2 need to be "XY" type caps, safe to put across the AC line

C4 appears to be not connected

It has 20 parts and its output is still not isolated from the AC line.

A transformer, or a wall-wart equivalent, doesn't need a cap.

Yeah, I also noticed there isn't any (+) rail powering up the LM339
cheap, so don't worry about isolation, it's only connected to the
noodle!

Jamie

Good point, no power to the 339s. Probably Spice powers them up, for free.
Simulation is wonderful!

Jim Thompson · May 2, 2014

On Fri, 2 May 2014 09:51:26 -0400, Douglas Beeson
<c.difficile@gmail.com> wrote:

On Thu, 1 May 2014 17:01:49 -0400
WangoTango <Asgard24@mindspring.com> wrote:

In article <20140501081051.f2341ef5d60270d968a0bc7b@gmail.com>,
c.difficile@gmail.com says...
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Thanks!

Are you just looking at it to understand it, or are you looking for a
Zero Crossing Detector to actually use?

I have one that I have used for many moons that is a heck of a lot less
convoluted that this one and has proven to be quite reliable.

Thanks for your reply. I do have an actual need, but only at lower voltages (13.8 V max). It has to cutoff closer to zero than the 1 diode drop of Jim's circuit, though. I'm interested in seeing your design if you're willing to post it.

-doug

Jim Thompson · May 2, 2014

On Fri, 02 May 2014 08:18:11 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Fri, 2 May 2014 09:51:26 -0400, Douglas Beeson
c.difficile@gmail.com> wrote:

On Thu, 1 May 2014 17:01:49 -0400
WangoTango <Asgard24@mindspring.com> wrote:

In article <20140501081051.f2341ef5d60270d968a0bc7b@gmail.com>,
c.difficile@gmail.com says...
Hi all,

I did a search the other day on zero crossing detector circuits and came across this nice one by Jim Thompson:

http://www.analog-innovations.com/SED/Zero_Crossing.pdf

I think I have figured out how it works, except for capacitor C1. What does it do?

Thanks!

Are you just looking at it to understand it, or are you looking for a
Zero Crossing Detector to actually use?

I have one that I have used for many moons that is a heck of a lot less
convoluted that this one and has proven to be quite reliable.

Thanks for your reply. I do have an actual need, but only at lower voltages (13.8 V max). It has to cutoff closer to zero than the 1 diode drop of Jim's circuit, though. I'm interested in seeing your design if you're willing to post it.

-doug

Straddle zero, or just one side of zero? What voltage level do you
want?

...Jim Thompson

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