Re: Help with power supply noise., Please.

On 1 Aug, 20:28, Mike <nomtrxs...@xxxxxxxxxxx> wrote:
I am building a homebrew bench power supply and it is working very well except for too much noise on the
output. It is a single output with adjustable CV from 0 to 40V and adjustable CC from 0 to 4A. I have posted a
schematic of the regulator section and a digital photo of the noise waveform under no load on a.b.s.e in PDF
format. I posted it using the same suject line. I would greatly appreciate it if someone could give me some
ideas of what to try in order to reduce the noise. I fear it is doomed to have a noisey output since it is
point to point wired on perfboard, but I sure hope not. I tried very very hard to get the ground connections
right and have rearranged them to try minimize the noise, but those changes didn't affect it much either way.
This noise is very stable in that it doesn't change much from no load to the full 4A load, It gets fuzzy under
full load, maybe from some low level high frequency oscillation. It doesn't change with output voltage. I
increased the value of C5 to .047uf to get the noise down to where it is now. With C5 at 2200pf the noise is
about 2 1/2 times what it is now and increasing C5 further decreases the noise very little.

There is another curious thing that happens that has me stumpped. I intended to use an OPA2277 for U1. With
the 2277 installed the transition from CV to CC mode in very abrupt, I.E. with a 10ohm load resistor
connected, the voltage set to 20v, and the current set to 2.5A it draws 2A as expected. When I lower the CC
setting it has no affect on the output untill it is set to about 400ma below the current being drawn or 1.6A
in this case. The current then snaps down to 1.6A and decreases smoothly from there down. It did this no
matter what current level I used to test it. It also does it if I increase the output voltage to excede the CC
seting. With an LM6132, LF412, or a TL082 installed it transitions to CC mode quite smoothly.

Mike

When truth is absent politics will fill the gap.

Think I'd be schrieking with fear if my own supplies ran that
clean :).
It's capacitor ripple breaking through. Seems a very non linear
control loop from sampling the output to taking corrective action.
From pic', control action seems slightly lopsided. Maybe assymetrical
lags. I'd be inclined to lose D2 and drop R8 R17 to maybe 1/10 their
present values and then add some local linearising with a (say) 220ohm
in Q4's emitter.
Puzzled by U3, it seem way overkill.

.

Relevant Pages

  • Re: Beginners Guide to Classical Music
    ... but don't forget you're just listening to horse hair ... what appears to be a load of elitist snobbish barriers. ... music history. ... Nice Noise ie making people actually listen the music. ...
    (rec.music.classical)
  • Re: Help with power supply noise., Please.
    ... schematic of the regulator section and a digital photo of the noise waveform under no load on a.b.s.e in PDF ... ideas of what to try in order to reduce the noise. ... This noise is very stable in that it doesn't change much from no load to the full 4A load, ... It doesn't change with output voltage. ...
    (sci.electronics.design)
  • Re: Very low current in amplifiers
    ... basic amplifier configuration are very large and the current is ... amplifier cease to work as intended assuming no load? ... but with BJTs noise is lower at low bias currents. ... resistors also introduces increased thermal and other noises ...
    (sci.electronics.design)
  • Re: 6SN7 Mu Follower Distortion Paper
    ... This way the working Ea for top and bottom ... load line for 200k. ... load R to replace the top triode acting as a follower and buffer between ... For measuring noise in such a circuit, the bottom grid should be taken ...
    (rec.audio.tubes)
  • Re: Help with power supply noise., Please.
    ... Mike wrote: ... ideas of what to try in order to reduce the noise. ... This noise is very stable in that it doesn't change much from no load to the full 4A load, ... It also does it if I increase the output voltage to excede the CC ...
    (sci.electronics.design)