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zero crossing

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be80be

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Z.png

I was just thinking about this today would it be usable to use 2 resistors and to diodes a zener to clamp to max of 5 volts like the sch.
 
D1 and D2 are both redundant.
 
You want isolation if this is from the mains voltage. A optisolator, as 4pyros mentioned, is a cheap way to provide that as well as give you the zero crossing signal. Just add a series resistor and a inverse connected diode across the opto input.
 
I was playing with it just to see how it looks in a simulator it's giving crazy reading in mV like -47mV then +47mV
I was thinking without the zener I would read a 0 to 60 volt maybe up to 75 But that's not showing up
 
I was playing with it just to see how it looks in a simulator it's giving crazy reading in mV like -47mV then +47mV
I was thinking without the zener I would read a 0 to 60 volt maybe up to 75 But that's not showing up
What simulator?
What diodes are you using?
Post the simulated circuit and sim results.
 
Im using Multisim I figured out the bad readings Im getting what it should be -754mV to +754mV I was using there virtual diode
testReadings.png


Thats with a 4006 diode its lower then the virtual but still what I figured is should be
 
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I shouldn't but; does the last zener clip the signal?

kv
 
A zener will clamp to its rated voltage when reverse biased and clamp to a about 0.7V negative when forward biased (with the anode grounded).
 
hi burt,
D2 will start conducting long before the Zener diode reaches it zener breakdown and clamp the output at ~0.7V
Remove D2
Eric
 
This is what I think id go with. Let me know what you see wrong with it. Hope you all had a wonderful Christmas
Thanks Burt
 

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D2 may clamp the voltage too low and prevent Q1 turning on. You could replace D2 with two diodes in series, or simply eliminate it, to overcome that.
BTW R3 has much too low a value. Try 220k or more.
For safety's sake the 120V supply should come via a transformer.
 
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R3 should only drop 120 mA In simulator it shows It at about 119mA But I'm with you On that I think a bigger 100K or more would be safer but that didn't let the Q1 pull to ground.
I'm trying for a short low at At Q1 when the AC line hits zero.

I do all the live testing with a transformer I was just looking to make this small.
 
R3 should only drop 120 mA
120mA x 120V = 14.4W !! You'll need a mighty big resistor and a heatsink.
I'm trying for a short low at At Q1 when the AC line hits zero.
Not possible. If the AC volts are zero then Q1 will be switched off, not on.
 
Hi Burt nice to hear from you again.

Just so happens I'm working on something remotely similar, my mrs's pyrography wood burner power controller.
A lot of designs use an opto, however you can do it with a transistor like I have (wit a diode to protect the base from inverse voltage), then you dont need a zener, and theres a low risk of the voltage going above vcc, of course a transistor doesnt give isolation, but then whats the point when my circuit is powered by a line transformerless supply?

One thing to bear in mind is the voltage rating of the resistors, might be ok in the US on 110, however here in the UK its better to use 2 47k resistors in series than 1 100k, if there was any kind of spike on the mains theres a risk of flashover.
 
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