Hi Kalvin,
My intention here is to collect information from the knowledgeable people on this forum, and trying to figure out whether my ideas are realizable. Maybe someone else will also learn from this discussion, as I will.
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My two bobs worth regarding switchers are pre regs, I have a psu that uses a LM2576 as the pre reg, it tracks the linear output so it sits 5 v above the output. For a few weeks I fought with the noise spikes on the output, even though I had carefully designed the pcb there was a good 50mV noise. What I did was change the position of the catch diode so it is cathode end on through board, fitted a small ferrite bead to the longer anode.
I then fitted two 470n ceramic smd caps as close as possible to the pcb side of the switchers input and ground then added a common mode choke and some caps, I ended up with a rather low noise output, on full load it produces around 1mV p-p noise, thats at 25 volts @ 3 A, most of that is low level ripple.
So with careful planning of the pcb around the switcher and some filtering noise can be reduced, however, using leads from the psu to say a plug board for your project would require a small cap across the boards input to reduce any further noise picked up in the leads.
I also note from my painful experiments that if I connect the ground output of the psu to earth then noise levels rise, mostly common mode noise.
On another prototype pcb I have the switcher separate from the rest of the circuit, it feeds the linear part via two jumper cables that pass a toroid ring with two turns, then into a series of ceramic caps, early tests do show a reduction in switching noise but I need to fully evaluate the idea further.
Regarding the thyristor pre reg, its an old design that I first saw in the same mag way back in 94, I had to build it, it worked, I think I still have my modified version laying in the loft. ( last part added due to the image bringing back memories ).
EP