Hello,
I'd like to use the LM5017 to generate a primary 5V supply and secondary isolated 5V supply from an input of 12 to 75V.
Looking at some reference designs and the LM5017 datasheet example for an isolated output (Fig. 17 of datasheet), I have some questions:
1. The datasheet example shows the transformer coils as opposite polarity (looking at the dots in the schematic). Are both outputs positive? I guess it just depends on how the secondary load is connected (regards polarity). The LM5017ISO eval board also shows the transformer connected this way but some other reference designs do not (e.g. PMP7818, PMP7383).
2. Reference design PMP7383 shows diode D1 in the primary output path. Why is this included? This diode is not shown in other similar topology designs (e.g. PMP7942).
3. Reference design PMP7138 shows diode D2 connecting the 5V output back to the Vcc pin. Why is the diode used in this circuit? My understanding is that this diode can improve efficiency & power dissipation but only if the output is higher than the max. threshold voltage of Vcc.
Thanks,
Kieran