| Electronics > Beginners |
| how does blackdog's PSU work? |
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| exe:
Thank you very much, guys, for all the information you provided. I entered EE about three years ago (as a hobby). My first device supposed to be a DIY power supply. Now, three years later, after hundreds of hours of reading forums, tech literature, experimenting and building multiple prototypes I'm nowhere near finishing my very first project :). But, anyway, please keep discussing. Topics such as frequency compensation or choosing the pass element are quite rarely discussed (at least I didn't find much info, yet alone measurements). Who knows, may be after this thread I'll finish designing my "ideal bench power supply". |
| Wortel:
Hi Bram, Sorry to hear about your family going bad, hopefully things are going better now. You mentioned a smaller version of the NA-01 low noise PSU on Circuits Online if I remember correctly. Is the schematic available somewhere? That would be nice! Wortel |
| Zero999:
--- Quote from: blackdog on March 21, 2018, 08:02:09 pm ---Hi Carrot, No, the project was not dead, but when I was busy with the extended testing of the 230V net filtering, it went very badly with one of my family members. So it is still a bit of a sensitive point... But I had already decided to make a smaller finnishd version first (2.5A), so that I can place it better between my other equipment in my LAB. And 2.5-Ampere is sufficient for most of my applications, i started building of the next test version, see the picture below. The 5V Reference on this board is a MAX6350, also a fine part. --- End quote --- Oh no, don't build it like that. The creapage between the primary and secondary is very unlikely to be sufficient, for isolation from the mains. All that's needed is a voltage spike and the tiny gaps on the perf board will arc over, connecting the secondary side to the mains. Put the mains and secondary sides on different boards, that way you can be sure they're properly isolated. |
| blackdog:
Hi Hero999, Thanks for the warning :) But i already now that, i dril out the holes around the 230V powerline connections before i do the real testing, this is only the reference section build. This is not a final circuit board, i drill a lot in these boards, like in one of my high performance preamps to get the paracitics down. If you want, take a look at this design of one of my low noise preamp, design for measuring at power supply's and some extra holes in the circuits board! Date/time: vrijdag 17 maart 2017 16:35:45 https://www.circuitsonline.net/forum/view/135863 Back on topic, The most important point in the development of a linear power supply is the phase margin of the control loop. A standaard opamp has about 60 degrees phase margin, every component you place in the loop will bring this phase margin down. Placing a power transistor(s) in the loop brings it down, if don't place a capacitor over your feedback resistor, almost certainty there will be instability horror. Look at the many power circuits on the Internet, most of them are compensated to "dead"... This is because the person who developed the circuit has not understood how the circuit works. Two examples, Dave Jones fist power supply, I knew from the beginning that it would fail. He finally learned his lesson with version-2 :-) The second example is e.g. Gerry Sweeney power supply, look at his video's. Hi did a fine job, except for the loop stability... Do not think that I am a gentleman who knows everything, as someone declaimed here on the forum... In the beginning of the 1974 i started with opamps like the uA709, my college and i were complaining about it alway was oscillating, what a bad opamp! But of course we were bad technicians, we did not read the datasheet and aplication notes, we were fools. Take a look at the LM709 data sheet, and see how universel this opamp is, even gains of 80 dB are possible with reasonable bandwidth. Would I still use the uA709, no there are now much better opamps for sale, this was only just to make a point clear. And regularly I have to learn, make stupid mistakes, I am just a human being. :-DD Thus e.g. only using a fast opamp does not make a good power supply. The intention is that when you develop the power supply, and that all parts of the schematic are well matched to each other. The Harrison design i use (from the late 1950's) is really beautiful. And my part of it, is using modern parts and tuning these for optimum performance. All designs with extra transistor and opamps in the loop will never reach the performance of this simple design. And again, most LAB power supply do not need this High End performance. I have a Dutch famos brand switching power supply, 30V and 5-Ampere, the dynamic performance is "not so good", why? There is a lot of capacitance on the output en the loop is not fast. But i still use it regular wen i need higer currents then 1-Ampere and when its not critical. The time is up, have to work, laters more. Kind regards, Bram |
| Cerebus:
--- Quote from: exe on March 22, 2018, 10:00:52 am ---Topics such as frequency compensation or choosing the pass element are quite rarely discussed (at least I didn't find much info, yet alone measurements). --- End quote --- Don't forget that a power supply is just - in essence - a DC coupled power amplifier. So, texts covering power amplifiers go over much of the same ground. If you want a discussion of pass element choice that's a place to look for it. Just make sure you stick to reliable sources, otherwise you'll find yourself going down the audiophool rabbit hole. |
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