Current surge limiter for toroidal capacitors

Lots of circuit variations exist on this theme. We would like to add one more, however, that’s not easily beaten for simplicity and reliability. It seems that toroidal mains transformers can only be switched on by a hefty initial current. The current surge is especially high when initially the residual magnetism stored in the closed core has to be built up because of the instantaneous phase angle. This design tip presents an inexpensive solution to ‘soft-starting’ toroids.