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Author Topic: Fool proof zero crossing detector  (Read 2148 times)
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max
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« on: August 23, 2020, 11:32:09 11:32 »

Hi,

Please suggest a fool proof zero crossing for a noisy environment.
I need it for scr triggering in a spot welding machine, the machine
input voltage is 400vac.

Regards
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token0
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« Reply #1 on: August 23, 2020, 01:06:09 13:06 »

Maybe you'll be happy with zero-cross triac driver optocoupler? There are a bunch for various voltages. For example MOC308xM is rated for 800VAC. You could use it to trigger some beefy solid-state relay. If your AC is too noisy, add some AC filter before triac.
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metal
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« Reply #2 on: August 23, 2020, 03:33:32 15:33 »

start reading this: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.640.7504&rep=rep1&type=pdf, look at Fig. 2
I used this one: https://dextrel.net/design-ideas-2/mains-zero-crossing-detector.html which is the same as Fig. 2 in the paper.
I have already used this ZC for a 12V halogen lamp dimmer, look at the attachment, this was my prototype for this ZC while testing ZC.

Finally, look at https://www.onsemi.com/pub/Collateral/AN-3004.pdf.pdf Figure 17.

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« Reply #3 on: August 23, 2020, 08:48:02 20:48 »

also check scr snubber.
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cicos
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« Reply #4 on: August 24, 2020, 09:02:46 21:02 »


Photocoupler TLP620 ?

Pozzz, JaMi
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cicos
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« Reply #5 on: August 26, 2020, 08:28:01 08:28 »

40A 100A Single Double Pulse Digital Spot Welder Weldering Controller Board Spot Solder Soldering Machine Time Control Module
Search on aliexpress, ebay ...
MOC3021 + BTA100-800B

Pozzz,JaMi
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max
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« Reply #6 on: September 10, 2020, 12:00:51 12:00 »

Hi,

There are also some PLL based zero cross detector, but did not find any practical
circuit, can someone share the practical circuit.

I think the PLL circuit will give better result.


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bobcat1
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« Reply #7 on: September 13, 2020, 07:57:23 07:57 »

Hi

PLL based zero cross detector, are as good as there time base , you can build one using some logic circuit (4060 ,4046 etc) where several IC needed and some glue logic , but I can't see any advantage over simple opto-isolated as line frequency in most country are accurate enough to be used as time base

All the best

Bobi
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mbyka
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« Reply #8 on: September 13, 2020, 06:25:20 18:25 »

I can suggest you my own design for zcd circuit.

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PM3295
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« Reply #9 on: September 14, 2020, 04:58:37 16:58 »

Below is a circuit that gives clean edges at the zero-crossing point while having very good noise immunity. Most if the cleanup is actually done by the RC low-pass filter on the input, and the PLL restores the phase locking with the input line frequency. The RC filter causes some phase shift that the PLL action restores. Fine-tuning of the zero crossing point is with P1.
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cesare
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« Reply #10 on: September 19, 2020, 03:37:21 15:37 »

Hi Max,

it's not clear if you need to implement a phase control on SCR in order to control the power.

If you only need to trigger the thyristor on zero crossing you only need a phototriac rated for mains voltage because you need to trigger when voltage across the Thyristor is almost zero and not necessarily at a exact frequency. For example the timings generated from a PLL can happen on non zero voltage due to noise and small PLL bandwidth.

If you need power control you can also consider burst mode by skipping some conduction cycles but in this case beware of flicker issues.

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max
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« Reply #11 on: September 20, 2020, 12:19:14 12:19 »

Hi cesare

As I described I am using it for welding power control, to vary the welding
current using the phase control.

Regards
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bobcat1
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« Reply #12 on: September 21, 2020, 08:13:29 08:13 »

Hi cesare

As I described I am using it for welding power control, to vary the welding
current using the phase control.

Regards


Hi Max,

The best way to do what you ask is to use mosfet not thyristor's (SCR TRIAK)
I know someone who design a similar system with great success
using a mosfet is a bit more complex in compare to thyristors but this type of design can handle far more power needed for welding.

All the best

Bobi
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cesare
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« Reply #13 on: September 21, 2020, 11:19:15 11:19 »

Hi Max,

using mosfets you can implement " reverse phase control".

Here you can find some material

https://www.avrfreaks.net/forum/reverse-phase-control-dimmer-based-cool-mosfet-transisor

Reverse phase controlling has some advantages over traditional dimmers in many dimmer applications. The manufactuers of inverse phase dimmers adverstise their products to be more efficent and less noisy. Because turning on point is always exact at the zero phase there are no huge current spikes and EMI caused by turn on. Using power MOSFETs it is possible to make the turn-off rate relatively slow to achieve quite operations in terms of EMI and acoustical or incandescent lamp filament noise.

Read more at: https://www.epanorama.net/documents/lights/lightdimmer.html#reverse

Regards
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PM3295
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« Reply #14 on: September 21, 2020, 06:17:26 18:17 »

Rod Elliot has a good page on a functional trailing-edge control circuit.

https://sound-au.com/project157.htm
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