the wire wrapped around the coil the zero crossing of the vm can serve as the reference time instant for the synchronization of power transistor signal the detection of zero crossing time instant is carried out with an electrical signal conditioning circuit which is already applied in today standard control board for white good appliance market thus the period of the power converter that is sensed can be calculated directly considering the time intervals between consecutive vm zero crossing fig4 5 and 6 show examples of implementation of the invention with 2 and 3 power converters the parameter measured for synchronization is the magnetic flux in the coil ferrite bar i e the voltage u03bd m induced on the wrapped wire in fig4 and 5 the two power converters start up sequence is as follows reference coil 1 power converter 2 acquires a synchronization signal from coil 1 power converter 2 synchronizes its timers with the signal power converter 2 starts delivering power with same frequency that uses converter 1 in fig6 the three power converters start up sequence is as follows reference coil 2 power converters 1 and 3 acquire a synchronization signal from coil 2 power converters 1 and 3 synchronize their timers with the signal power converter 1 and 3 starts delivering power with same frequency that uses converter 1 it is important to notice that by using the magnetic flux induced in a coil ferrite bar as reference electrical parameter no electrical connection between power converters is required and they are electrically isolated moreover the.