Description of SMPS

AN4414

8/20

DocID025611 Rev 1

This clearly states that selecting a higher duty cycle at a minimum input voltage will cause

the peak primary current to decrease and requires a high magnetizing inductance. To attain

the required inductance, we will require a larger number of turns and the transformer would

be very bulky if no high permeability ferrite material is used to require that inductance.

Moreover the DCR of windings will increase due to a long wire length and copper losses will

be more, impacting the efficiency and metering standard norms. For 3-phase metering, the

power supply consumption should be limited below 8 VA.

Looking into the above challenges, we need to define a very low value of a maximum duty

cycle and hence the peak primary (or drain current) at somewhat higher value. On the other

hand, this would require lesser turn ratio (n) and there would be a large number of

secondary turns in comparison with a traditional flyback transformer.

Note:

Maximum primary peak (or a drain current of the device) < Idlim (maximum specified value

in the VIPER17 datasheet).