I am constructing Optocoupler based Zero cross detection circuit for power factor correction.How to find zero crossing of current wave?please recommend the circuits with resistor calculations.



closed as too broad by PeterJ, Enric Blanco, laptop2d, Dmitry Grigoryev, Wesley Lee Jun 30 '17 at 19:41

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    \$\begingroup\$ Please show that you have done some research and then ask for help on something you don't understand. This is not a free design service. \$\endgroup\$ – Transistor Jun 22 '17 at 6:27
  • \$\begingroup\$ Convert current to voltage, repeat the zero crossing circuit. \$\endgroup\$ – JWRM22 Jun 22 '17 at 6:30
  • \$\begingroup\$ Welcome to the site. Please quickly realise that this is not a free design house, homework-answering service or an on-line technical encyclopedia, copied out to you on demand. People will help you take the next step if your question shows that you've done as much as you possibly could on your own - which your post doesn't, I'm afraid. Please revise your question showing your work and findings so far, in considerable detail. Or delete the question if Internet searches give you your answer anyway. Again, a warm welcome to the site. \$\endgroup\$ – TonyM Jun 22 '17 at 6:47
  • \$\begingroup\$ will send you the worked out circuit \$\endgroup\$ – Lavanya Maruthakutti Jun 23 '17 at 17:19

To measure current, use a CT (current transformer) - this converts the current taken by a load or appliance into an isolated and manageable signal voltage that is proportional to load current but, beware, if your currents are not sinusoidal, then trying to compare the zero crossing point of voltage and current is going to be a big problem. Consider an appliance such as a TV or HiFi and look at the typical current taken: -

enter image description here

With these sorts of appliances (and many others too), the current drawn from the AC line comes in very non-sinusoidal blips coincident with the recharging of a reservoir capacitor after the bridge rectifier.

If you were to take a zero-cross point of the current waveform, where would that be in the picture above? In other words, for many household and some industrial loads, you can't use zero-cross detectors to give any indication of the relative phase angle between voltage and current.

Simultaneously sample v and i at a fast rate such as 1 kHz minimum, then multiply and average to get power taken. Also compute Vrms and Irms and compute power factor of load using: -

PF = \$\dfrac{Power}{V_{RMS}\times I_{RMS}}\$

See this Q&A for further information. Ditto this answer too.


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