Forward Converter topology confusion

[khatus]

Hello guys i have some confusion about forward converter Topology.
Here What does it mean by catch action of diode ??

I can not understand how does Dot end of Nr will be clamped at one diode below ground?? Can anybody explain with pictures??

 

[d123]

Hi,

a) Not entirely sure what (level of knowledge) you're asking about for this. b) My knowledge is shaky on this topic. c) Sorry if picture isn't what you're asking for.

'Catch diode' means limiting/blocking diode - it limits (in this direction) negative excursions to one whole diode drop below ground/common/0V in this case, sadly not to an ideal and very desirable 0V. Instead of Vdc passing through dot end of Nr to ground, and then I ask myself what voltage 'ground'/'common'/'0V' would be at during that time, it is limited to the diode forward voltage, , e.g. -0.7V for a silicon diode, as far as I remember. In the picture of Q1 on, the input signal (green line) is allowed to return to ground through the transistor, in the picture when Q1 is off, the green path ends at the end of the diode, it is not allowed to go any further.

many people here who are far smarter than I am will correct my possible errors and explain better later, I suppose.