b*cat had a peculiar feeling whilst reading
4C's comment about
D1 being the reason for the frequency division to 25 Hz.
That statement cannot be correct.
Perform a thought experiment by connecting a 50 Hz AC source to an oscilloscope. Look at the display. Connect a diode in series with one lead and look at the display, once again. Both traces show 50 Hz waveforms.
Grummaging about, I found a description of
CONVERTERS RINGING No's 4, 5, 6 & 7 and Section 3, Operation, states the following --
3. Operation
Consider the converter transformer as having two cores with identical secondary windings and a common primary winding.
These cores saturate in turn on alternate positive half cycles of the half-wave rectified mains supply. During the time a core is saturated no energy is transferred to the output. During the time a core is not saturated (i.e. it is working normally) a pulse of energy is transferred to the output. The saturation pulses are at SO c/s. The secondary windings are connected in series opposition relative to the primary winding, therefore these output pulses will be alternately in opposite senses, giving rise to an output at a frequency of 25 c/s. The optimum value of the capacitor which is connected to the secondary windings of the transformer is determined by the behaviour of the converter at low mains-input voltage and the starting of oscillations on load. Unlike a normal LC resonant circuit, the value of this capacitor does not influence the frequency of the output current.
When the loading on the output terminals is increased beyond full load, the output voltage falls rapidly and the production of 25 c/s ceases. On removing the excess load, the oscillations restart. This provides a useful self-protecting feature.
I think I understand that explanation . . .
