Harold Hallikainen wrote about zero crossing:

> I think in my next design I'll add a diode between the FW center tap
> rectifier output and the filter capacitor.  A pull-down resistor will
> result in full-wave rectified but unfiltered DC at the anode of the
> added diode.  I can then add the 10K to the INT pin.

  Fine, but don't add a diode between the bridge output and filter
capacitor, add *two* from the ends of the power transformer to your
junction of pulldown and current limit resistor.

  This way you are not reducing the efficiency of the power supply.  And
you can use the same two diodes for a bridge rectifier situation.  Not
that you couldn't have used the series diode here too ...
--
  Cheers,
        Paul B.