I am trying to simulate a circuit for Zero Cross Detection. The end goal is triac phase control. My simulation using proteus hangs up and with message "Simulation is not running in real time" and proteus freezes untill crash.

For the ZCD Circuit, I referred to the following post.

The circuit i am trying to simulate is this

Simulation screen shot:

enter image description here

Is there anything wrong with the circuit or am i not simulating it right?

Please advice.

  • \$\begingroup\$ For the simulation purposes add a ground to the bottom side of the input source, it should speed the simulation and prevent errors. \$\endgroup\$
    – alexan_e
    Mar 21, 2015 at 11:06
  • 1
    \$\begingroup\$ A circuit doesn't have to be wrong for a simulator to get into difficulty. \$\endgroup\$
    – Andy aka
    Mar 21, 2015 at 11:22

1 Answer 1


I have tested this that and found that there are something unstable over it. It develops a form of "noise" which disturb the signal. This takes place between every 30 seconds to 1 minute. (Perhaps my setup?)

This is a simple one

enter image description here


About the message "Simulation is not running in real time" here, try the following.

Select 'Set Animation Option' from the menu system and simply push the 'SPICE Options button'. Try to put [ABSTOL] down to, for example 1e-08 and see if it helped.

If it has not helped, try to go further down or if it helped, try to go one up by one until the error recurs, then go one down.

  • \$\begingroup\$ You may want to put rectifier diodes "antiparallel" across the optoisolator LEDs, or at least verify that the optocoupler LEDs are capable of holding back 1.5*230V when reverse-biased. \$\endgroup\$
    – akohlsmith
    Jun 28, 2015 at 14:46

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