The simplistic Salas low voltage shunt regulator

[Salas]

There is no "B" so it does not. Do you use the short coil gnd pin on the probe or its 5 inch crock lead?

 

[dimkasta]

I m using the short coil thingy

 

[Salas]

Stick another 47uF on the sense lines at the BIb's side for good measure then see if the random noise falls any further. Don't hit auto, it takes the BW limit out.

 

[dimkasta]

I ll try the 47uF thanks.

If you check the first capture, you ll see that it detects the 5Mhz with the limit on too

 

[dimkasta]

Quick question. Between the sense lines you mean O3 and O4 right?

 

[Salas]

First is a dense noise like pattern though when the other is some shape. It may gets its peaks mixed in the noise too. But the amplitudes are very different still. Is there some clock related frequency that explains circa 5MHZ possible emission on the Shiga? Harmonically related up or down a crystal fundamental even?

 

[Salas]

Quick question. Between the sense lines you mean O3 and O4 right?

I mean on S+ & S0 on the output connector.

 

[dimkasta]

Yep that s them.
Thanks a lot for the quick after-hours helpdesk 🙂

The crystal is at ~16Mhz if I remember correctly.

However I was getting something similar with the plain 7808 psu before separating the digital parts from the motors. It was about same size, but bit different freq

I found the capture... Don t know if it s related...

 

[Salas]

Its not that far in freq, the other is broken in shape and it could be counting somewhat off. There is no way a 7808 can be producing anything in the 6-7MHZ. Emissions from the digital stuff and the way they couple most likely.

 

[dimkasta]

At the time I was suspecting the FRs with their low ESR making the 7808 ring...

By the way the cap at the sense seems to have made things worse

The 5Mhz seem to dissapear some times though... it seems to depend a lot on how I attach the probe...

 

[Salas]

It has a more noise like shape and a more logical relation of Vpp to RMS. Do you always measure the same point at the Shiga or the rail at different points also?

 

[Salas]

P.S. Go to 200nS again to have steady reference.

 

[dimkasta]

Yep it s the same spot always for all these measurements.

 

[Salas]

Which is the Shiga PSU receive point?

 

[dimkasta]

It s a temporary screw connector connecting the 5cm twisted pairs with 2 5cm wires going to shiga entry points.

Here s a capture at 200ns. Image is the same with BW limit off

No 5Mhz...

 

[Salas]

Alright, see with what cap where does least possible Vpp of whatever circulates or emits and you can't do much more, then leave it alone.

 

[dimkasta]

You mean experiment with sense cap size?
Or the ones on C103 and Shiga too?

 

[Salas]

On the Shiga is more effective as the experiments have shown, see if value or type can help further than that 2.84mV RMS you had best.

 

[schultzsch]

Salas what would be the disadvantage/s to use the ccs between 4-4.6Vdrop

 

[Salas]

More capacitance in the CCS due to Mosfet VDS VS Ciss curve says lower drop gives more but still potent.