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  • Author Author: Andrew J
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YAPS Part Twelve Reprise - Design revisited

Andrew J

Edit: 22/11/19 - updated navigation link

 

Following the rather disastrous last PCB update, I had it remade with a footprint that could take a 50uH inductor - and 10uH if I wanted to experiment.  Required a little jiggery pokery to fit the other parts around it but I also took the opportunity to rework some of the silk screen, layout, addition of a TVS on the input (D3) and re-size the mounting holes.

image

It’s all soldered up and back to working again thank goodness - I’m still kicking myself for misreading the 50nH inductor - with a controllable output voltage and current and nothing overheating or blowing. 

 

So the big reveal - has this improved?  For some reason, the scope has stopped recognising the USB key that’s plugged in so excuse the photos of the screen (and the dust!!)  I suspect something wrong with the firmware but that’s a problem for another day.  These readings were measured at the output capacitor with the short-wire ground probe, AC coupled, BW limited, 1x.

 

1.5A / 15V

10Ohm load with no voltage or current limiting:

image

 

0.050A / 0.5V

10Ohm load with current limited to 0.050A and voltage following:

image

 

I think I’ve every reason to be happy with these results right?  Mean Pk-Pk ripple voltage of 0.288mV and a max of 1.04mV from a Vin of 24V to an output of 0.5V is worth writing home about, right?

I’ll do more testing - soak testing, voltage overshoot and so on - but I’ve described these on previous posts so I’ll only repost if I see problems, or someone specifically wants to see them.

 

I’m on to encasement next.  I see the light at the end of the tunnel at last!

 

Next: Part 13 - Encasement and Wrap Up

Back: Part 12 - Design revisited: reworking the layout and PCB

  • in reply to DAB

    I will be revisiting some of my early experiments and I’ll take the opportunity to see how it impacts, particularly how I have impacted the transient characteristics.

  • You might also put the design under various loads. You will find that the noise may change depending upon what you are driving.

     

    DAB

  • I know I said I wouldn't add more details unless significantly different, but I did get a chance to test the ripple at 15V 3A:

     

    image

     

    Still pretty good in my view.  At this power, the LT3081 Linear Regulators run about 20c hotter than the first version.  I've also traded transient response for ripple with the larger inductor so this isn't going to be a power supply that can be used for highly dynamic loads.  At some point I may try it with a 10uH inductor again and see what difference it makes in terms of the trade-offs.  However, for what I have, and where I've got to I'm happy to settle for this.

  • in reply to three-phase

    Thanks Don - it's taken a little while to get the board updated, manufactured and delivered but it hasn't been abandoned.  And a jaunt to Italy didn't speed things up either! 

     

    Max specs are 0-15V, 0-3A so not quite maximum load (or minimum load) - tomorrow/tuesday I will be testing further, including with a 5Ohm load to get it to the full 15V 3A.  Functionally, I've already done this as I've documented in previous posts so I'm not expecting any issues, but I will be checking the ripple at 3A.  Famous last words image

  • Great to see an update and that you are moving forwards with the project. The results look good to me, was the power supply on its maximum load?

     

    Kind regards.