How to sense the zero crossing of current?
How about an optocoupler in series with the load? You would need a small circuit to rectify (BR1) and limit (D2, D3, R3) the current. D2 and D3 at the same time limit the voltage over the circuit, but worst case there is still about 3V voltage drop from load perspective. V1 should therefore be much higher than 3V.







simulate this circuit &ndash; Schematic created using CircuitLab

The output will be pulled high when the LED stops conducting current, hence during the zero crossing.