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I have simulated the following circuit on MultiSim, and it seems to work well doing its job. The first element is a full wave bridge rectifier. At its output is connected the input of the zero-cross circuit and also to another diode which is connected to a bulk capacitance. I plan to run a flyback power supply from the capacitor's voltage (10uF).

My doubt is about the circuit in practice. Will there be current leak from the capacitor the the bridge output sufficient to make the zero-cross circuit have an unexpected different behavior? Is there any problem on connecting a flyback PSU and the that zero-cross circuit on the same bridge-rectifier? Will the power supply / capacitor of 10uF interfere on the working of my zero-cross?

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edit: zero cross circuit

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Why do you feel your zero cross circuit needs to be behind the rectifier instead of before it? I assume the only reason D7 exists is to prevent C1 from holding the output of the rectifier at a DC value when the AC source swings negative which would interfere with the zero-cross circuit.

Get rid of D7. It's bad solution to a problem that doesn't need to exist. Just move your entire zero-cross circuit (which is R1/R2 and everything to the right of it) before the rectifier instead. You also do not need R3. It is not doing anything.

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  • \$\begingroup\$ topic was edited. How about the second circuit? Do you think it is better than the original? \$\endgroup\$ – abomin3v3l Jul 5 '20 at 1:45
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    \$\begingroup\$ Don't remove your original circuit since it makes the text in your question and my answer non-sensical (I don't think you meant to do this but what's what happened and your new circuit got double posted). Your zero-cross circuit with R3 removed looks fine to me. \$\endgroup\$ – DKNguyen Jul 5 '20 at 1:45
  • \$\begingroup\$ R1 and R2 I will change to 150K only. Do you suggest any improvement (second circuit)? \$\endgroup\$ – abomin3v3l Jul 5 '20 at 1:55
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    \$\begingroup\$ @abomin3v3l It's not like R3 was doing anything before. It was always being shorted out by D3 so if it was fine before it will be fine now. There was only 240K total limiting the current to begin with. \$\endgroup\$ – DKNguyen Jul 5 '20 at 1:56
  • \$\begingroup\$ C2 = 47nF seems to produce better output regarding the input zero crossing. \$\endgroup\$ – abomin3v3l Jul 5 '20 at 2:06

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