Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Check my figures for LM317 ripple
Check my figures for LM317 ripple
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 9th November 2017, 09:34 PM   #1
dotneck335 is offline dotneck335  United States
diyAudio Member
 
Join Date: Dec 2012
Default Check my figures for LM317 ripple

My figgerin' gets me 0.083 mV of ripple from an LM317 with 10,000 uF on the input side, 10 uF on the adjustment leg, and 1 amp of current. Or about 82 db below a 1 volt rms audio signal. Correct?
  Reply With Quote
Old 10th November 2017, 04:40 AM   #2
mchambin is offline mchambin  France
diyAudio Member
 
Join Date: Mar 2011
This is pretty good.
10 000 uF, 1A. should give about 0.6 V peak to peak Ripple.
LM317 datasheet gives Ripple rejection 64dB typical with Cadj 10uF.
So, output Ripple is 0.6 Vpp/1585 = 0.37 mV peak to peak.
That is about 0.1 mV rms Ripple.
__________________
Transistor junction temperature is not transistor case temperature.
  Reply With Quote
Old 10th November 2017, 04:51 AM   #3
abraxalito is offline abraxalito  United Kingdom
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Send a message via Yahoo to abraxalito
What's very interesting is that the original (National) DS and TI's current datasheet do not agree on ripple rejection vs frequency. I'm inclined not to believe TI - NS shows its not flat with frequency but rather has a peak about 100Hz and then falls off.
__________________
'The total potential here must be nothing less than astronomical.'
'Nothing less. The number 10 raised almost literally to the power of infinity.'
  Reply With Quote
Old 10th November 2017, 11:59 AM   #4
trobbins is offline trobbins  Australia
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
Ahhh, but can you measure that? :-)
  Reply With Quote
Old 10th November 2017, 12:05 PM   #5
mchambin is offline mchambin  France
diyAudio Member
 
Join Date: Mar 2011
Sure, a serious oscilloscope can show better than 1 micro volt. Here we have about 100 uV output ripple
__________________
Transistor junction temperature is not transistor case temperature.
  Reply With Quote
Old 10th November 2017, 12:25 PM   #6
mchambin is offline mchambin  France
diyAudio Member
 
Join Date: Mar 2011
In post #2 the 64dB ripple rejection is from a TI datasheet.
64dB typical at 120 Hz Vo=10V.
I did not use the graph dB versus frequency.
Where they bugged, the curves for Cadj=0 and Cadj=10uF are in the wrong order.
Furthermore, I guess the raw figure, 64dB is for a 120 Hz saw tooth shape ripple, while the graph is for a sine AC ripple at Vin.
__________________
Transistor junction temperature is not transistor case temperature.
  Reply With Quote
Old 10th November 2017, 12:29 PM   #7
abraxalito is offline abraxalito  United Kingdom
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Send a message via Yahoo to abraxalito
The 'ripple reduction' graph isn't plotted for a real ripple waveform (which contains plenty of harmonics) rather for a simple 120Hz sinewave. So its optimistic in practice because the rejection falls above 100Hz. Meaning the actual output of the reg sees a higher proportion of higher harmonics than the input.
__________________
'The total potential here must be nothing less than astronomical.'
'Nothing less. The number 10 raised almost literally to the power of infinity.'
  Reply With Quote
Old 10th November 2017, 12:46 PM   #8
trobbins is offline trobbins  Australia
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
Quote:
Originally Posted by mchambin View Post
Sure, a serious oscilloscope can show better than 1 micro volt. Here we have about 100 uV output ripple
Sorry - the query was directed at the OP. Not everyone has accurate uV measurement capability, whether a meter or cro, although a soundcard spectrum analyser would likely be easier to calibrate at a higher level, and then assume accurate scaling.
  Reply With Quote
Old 10th November 2017, 01:00 PM   #9
mchambin is offline mchambin  France
diyAudio Member
 
Join Date: Mar 2011
I understand.
I see that my Digitek QM1323 Multimeter
$51.80 at autObarn Lismore NSW has:
AC resolution 0.1 mV
So, it is not good enough to measure such a low ripple.
__________________
Transistor junction temperature is not transistor case temperature.
  Reply With Quote
Old 10th November 2017, 02:34 PM   #10
dotneck335 is offline dotneck335  United States
diyAudio Member
 
Join Date: Dec 2012
Another interesting thing on the LM317 datasheet is that, with 500 mA and 15 volts of Vin to Vout, that the 120 Hz ripple rejection goes all to hell when the output voltage ventures beyond 25 volts---getting 24db worse by the time the output approaches 30 volts!! This may, indeed, call for a MUCH higher value cap on the output than otherwise expected. I wonder if this also applies when the Voltage I/O is a more reasonable 5 to 7 volts.
  Reply With Quote

Reply


Check my figures for LM317 rippleHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
LM3886 Power Supply Ripple and using a DMM on AC to measure Ripple swamp Chip Amps 6 27th January 2016 05:53 PM
PP PSU: How much ripple is too much ripple? DrewP Tubes / Valves 10 11th September 2011 06:59 AM
Lissajous figures rtarbell Everything Else 1 28th October 2005 02:23 AM
Noise Figures northsiderap Solid State 12 7th May 2005 09:48 AM
help, need some figures Alex_B Multi-Way 54 9th December 2002 01:36 AM


New To Site? Need Help?

All times are GMT. The time now is 05:25 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki