electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Large voltage drop in PSU
Post new topic   Reply to topic Moderators: dnny, Uncle Krunkus, v-un-v
Page 1 of 1 [23 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Thu May 28, 2020 8:22 pm    Post subject: Large voltage drop in PSU Reply with quote  Mark this post and the followings unread

Hi,

I recently built a power supply based on the MFOS adjustable PSU.
After designing and etching the board, i am experiencing voltage drop of a whopping 600mV (12.4V to 11.8V) under load.The load is a 20 Ohm 10W cement power resistor which drew about 500mA.
I fucked up initially by testing without heatsinks and then to be safe i replaced both regulators and tested with heatsinks installed. The heatsinks were salvaged from broken KRK monitors, which are hefty and dissipated the heat well enough.

The transformer is rated at 36VA CT 15-0-15V.
Input voltage is about 20-21V which ensures there is enough headroom.
So what issues could be causing this significant loss in voltage?

I am thinking of breadboarding the circuit and testing again before i etch the final board 2nd time around, with that said the circuit is straight forward enough..

Thanks!

Update: edited the circuit to include missing wire(in red)


12v_linear_psu_951.pdf
 Description:

Download
 Filename:  12v_linear_psu_951.pdf
 Filesize:  41.23 KB
 Downloaded:  12 Time(s)


Last edited by Gingoism on Wed Jun 03, 2020 12:22 am; edited 2 times in total
Back to top
View user's profile Send private message
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Fri May 29, 2020 8:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

just to update, after breadboarding and testing the results were better but i think my dvm is just not good enough for accurate readings but here is what i noted :

Load = 20R 10W / 510mA - the voltage actually went up 12.05V to 12.15V
= 12R 10W / 895mA - 12.05 to 12.10V
= 8R 10W / 1100ma - 12.05 to 11.20V

so i think the fault must have been in the design or the etching of the board.
i was also thinking maybe i should add a current limiting circuit to cap the current to below 900mA. Any recoomendations?
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 4863
Location: Moon Base
Audio files: 650

PostPosted: Sun May 31, 2020 3:23 am    Post subject: Reply with quote  Mark this post and the followings unread

I am reading, just so you know you are not screaming into the void.
Not really sure what can be causing it, but it seems to be a little bit higher than I would expect.
Does the input voltage drop under load ?

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Sun May 31, 2020 4:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Phobos, yes on the faulty PSU board the input voltage did drop to about 3-4V, so it hovered around 17-18V. With that said the breadboard circuit is relatively stable up to about 890mA but as you can see under a 1A load i lose about 800mv and input voltage drops from 20V to 17V is that normal for a LM317/337 regulator? I know they can handle up to 1.5A correct?
Back to top
View user's profile Send private message
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Sun May 31, 2020 6:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

also side note i was wondering if i can use this Led driver (i have 2 of these) -

http://www.007swz.com/zsdwzg/products/dianyuan_130278.html

and convert it to a either a 15V or 12V PSU, my question is which method would be better?

1. DC/DC Converter
2. Linear Voltage Regulator
Back to top
View user's profile Send private message
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Sun May 31, 2020 7:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Gingoism wrote:
Hi Phobos, yes on the faulty PSU board the input voltage did drop to about 3-4V, so it hovered around 17-18V. With that said the breadboard circuit is relatively stable up to about 890mA but as you can see under a 1A load i lose about 800mv and input voltage drops from 20V to 17V is that normal for a LM317/337 regulator? I know they can handle up to 1.5A correct?


as for heatsinks i tried 2 different ones. see attached pics
heatsink from krk monitor is about 110cm(L)x60(W)x60(H)
the size of the mosfet heatsink is 42mm(L)×35mm(W)×25.4mm(H)


mosfet-hs.jpg
 Description:
 Filesize:  38.16 KB
 Viewed:  749 Time(s)

mosfet-hs.jpg



KRK Heatsink.JPG
 Description:
 Filesize:  1.78 MB
 Viewed:  7 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

KRK Heatsink.JPG


Back to top
View user's profile Send private message
gabbagabi



Joined: Nov 29, 2008
Posts: 610
Location: Berlin by n8
Audio files: 23

PostPosted: Tue Jun 02, 2020 2:46 am    Post subject: Reply with quote  Mark this post and the followings unread

by just fishing in the dark, i would risk to consider that may transformer is not "strong" enough
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 4863
Location: Moon Base
Audio files: 650

PostPosted: Tue Jun 02, 2020 6:56 am    Post subject: Reply with quote  Mark this post and the followings unread

just checked the schematic (was that here all along, did I check it before ?!) where did you get the idea of putting a diode between the
output and the adjust input ? There should be a resistor there (240 ohms) or is that only missing in the schematic ?

as for heatsinks as long as you can still touch it without burning your fingers it's ok. If you touch it with a wet finger and it sizzles it's getting too hot.
(note: they can get VERY hot).

Breadboards are probably not the best way to test a supply under load. You need solid connections and also wire gauge can make a difference.

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Tue Jun 02, 2020 6:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

gabbagabi wrote:
by just fishing in the dark, i would risk to consider that may transformer is not "strong" enough


Hi gabba,

That was my initial thought then i tried a a different transformer from that pictured below. this one was 40VA and i got similar results..


CT Transformer.jpg
 Description:
 Filesize:  2.29 MB
 Viewed:  3 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

CT Transformer.jpg


Back to top
View user's profile Send private message
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Tue Jun 02, 2020 6:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
just checked the schematic (was that here all along, did I check it before ?!) where did you get the idea of putting a diode between the
output and the adjust input ? There should be a resistor there (240 ohms) or is that only missing in the schematic ?

as for heatsinks as long as you can still touch it without burning your fingers it's ok. If you touch it with a wet finger and it sizzles it's getting too hot.
(note: they can get VERY hot).

Breadboards are probably not the best way to test a supply under load. You need solid connections and also wire gauge can make a difference.


you are right phobos, the schematic above is wrong and was edited after the 1st iteration.

the circuit is basically from the datasheet

i simulated the circuit in spice and i was stumped by the results..the circuit performed as expected until i changed the load to 10 ohms and below, the voltage dropped from 12.5V to 10V and the load current flat lined at about 1A and remained the same even when i increased the input voltage to 40V...so im not sure what to make of this. has anyone made a lm3XX PSU with an excess of 1.5A?


lm317_VReg.png
 Description:
 Filesize:  401.74 KB
 Viewed:  8 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

lm317_VReg.png



lm317_Reg_20-Ohm_Load.pdf
 Description:

Download
 Filename:  lm317_Reg_20-Ohm_Load.pdf
 Filesize:  34.75 KB
 Downloaded:  9 Time(s)


lm317_Reg_10-Ohm_Load.pdf
 Description:

Download
 Filename:  lm317_Reg_10-Ohm_Load.pdf
 Filesize:  34.96 KB
 Downloaded:  11 Time(s)

Back to top
View user's profile Send private message
gabbagabi



Joined: Nov 29, 2008
Posts: 610
Location: Berlin by n8
Audio files: 23

PostPosted: Wed Jun 03, 2020 1:25 am    Post subject: Reply with quote  Mark this post and the followings unread

ok i was thinking this:

10 Ohm mean 1,5Amp

your transformer is rated 2x15VA 36W

from my experience that means each side of the transformer is rated 18W.

that means because of RMS and 0,707, you could write the rating as 2x (21,21V @18W)

if you draw now 1,5A out of one --> u are well beyond the power rating


in my opinion u are reaching the theoretical limits if u draw 0,85A Shocked
Back to top
View user's profile Send private message
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Wed Jun 03, 2020 3:55 am    Post subject: Reply with quote  Mark this post and the followings unread

yes gabba that makes sense in theory and also in practice...
explains why it was stable up to the point when the load current was around 0.8-0.9A.
Which now i think is pushing it too much and probably would perform much better with full load at 0.6-0.7A.
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 4863
Location: Moon Base
Audio files: 650

PostPosted: Wed Jun 03, 2020 5:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Still, with the voltage dropping to about 17V it's still more than enough for the LM317 to produce a stable 12V.
So why is the output dropping ?

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube

Last edited by PHOBoS on Wed Jun 03, 2020 7:05 am; edited 1 time in total
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
JovianPyx



Joined: Nov 20, 2007
Posts: 1970
Location: West Red Spot, Jupiter
Audio files: 222

PostPosted: Wed Jun 03, 2020 6:33 am    Post subject: Reply with quote  Mark this post and the followings unread

That is odd PHOBoS, has the DC input to the regulator been checked with a scope (especially while under the load causing a problem)?
_________________
FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
corruptio optimi pessima
Back to top
View user's profile Send private message Visit poster's website
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Wed Jun 03, 2020 4:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

No, not with a scope, ill etch a new board over the weekend and run some tests. What am i to observe with the scope beside the Vin at the regulator? As for transformers i don't have anything higher than 40VA on hand.
Back to top
View user's profile Send private message
JovianPyx



Joined: Nov 20, 2007
Posts: 1970
Location: West Red Spot, Jupiter
Audio files: 222

PostPosted: Wed Jun 03, 2020 6:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

If everything is happy, it should be a straight line. However, under some conditions, such as weak transformer or insufficient capacitors, it will be a flat line with dropouts or voltage dips at your mains frequency times 2. This will show up as a lower DC voltage on a DMM. If the dips go low enough, the regulator can drop out. That would also be momentary and would cause the regulator's output to have a DMM measured voltage lower than the spec.
_________________
FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
corruptio optimi pessima
Back to top
View user's profile Send private message Visit poster's website
Blue Hell
Site Admin


Joined: Apr 03, 2004
Posts: 23280
Location: The Netherlands, Enschede
Audio files: 255
G2 patch files: 320

PostPosted: Wed Jun 03, 2020 6:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
If everything is happy, it should be a straight line.


Flat is a bit optimistic .. pre regulator and under load there will always be ripple .. but, as pointed out by you later on, and to clarify things maybe .. the important thing is:

that the lowest dip should still be sufficiently high to keep the regulator happy .. that is .. some 0.2 to 3 Volts above the desired output voltage

(This depends on the regulator specs, it's a number that will be in the data sheet - I didn't look it up .. but IIRC about 2 Volts for the LM317 family - look it up though when it happens to go below 3 Volts, to make sure it's all okay still).

You can lower the amount of ripple by using larger filter caps .. the big pre regulator - post rectifier electrolytic ones.

Larger ones will increase the inrush current tho, the current that will flow to firstly charge them filter caps .. but this is about a low power PSU so not likely an issue .. but might your rectifier diodes pop out occasionally, that would be the thing causing it .. this can be calculated too .. of course . but you would need some detailed specs of the transformer to be able to - specs usually not available.

Anyways .. just some remarks that popped up here after reading the thread.

_________________
Jan
also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Back to top
View user's profile Send private message Visit poster's website
JovianPyx



Joined: Nov 20, 2007
Posts: 1970
Location: West Red Spot, Jupiter
Audio files: 222

PostPosted: Wed Jun 03, 2020 7:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

My main point was to look at the PSU input (and output) with an oscope. Yes, a straight line is optimistic, but if under a light load, it can be quite straight.

The problem occurs when the dips go below the drop out voltage. Every regulator has one. LDO regulators are "Low Drop Out", but you should find the drop out voltage in the datasheet for your regulator. It's good to keep those dips well above the drop out voltage because the input mains voltage can change. If mains goes down, the dips get closer to the drop out voltage. In my own building, I like to over-design a supply, a bit extra current capacity and good size caps.

_________________
FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
corruptio optimi pessima
Back to top
View user's profile Send private message Visit poster's website
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Tue Jun 23, 2020 6:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Took a while to get my stuff in order, but finally did some tests and here are the results:

Vin@Reg= 21.69V @ no load
Vout@Reg= 12.00V

Vin@Reg= 18.8V @ 0.285A
Vout@Reg= 11.95V

Vin@Reg= 17.6V @ 0.550A
Vout@Reg= 11.9V

Vin@Reg= 15.2V @ 1A
Vout@Reg= 11.80V

attached pics from the scope, the post rectifier cap voltage is quite noisy. I believe 10,000uF is big enough?


Vin22V@noLoad.jpg
 Description:
 Filesize:  198.42 KB
 Viewed:  2 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

Vin22V@noLoad.jpg



Vin18.8V@0.28A.jpg
 Description:
 Filesize:  209.03 KB
 Viewed:  2 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

Vin18.8V@0.28A.jpg



Vin17.6V@0.55A.jpg
 Description:
 Filesize:  176.55 KB
 Viewed:  3 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

Vin17.6V@0.55A.jpg



Vin15.2V@1A.jpg
 Description:
 Filesize:  219.25 KB
 Viewed:  6 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

Vin15.2V@1A.jpg



LoPHS.jpg
 Description:
 Filesize:  304.9 KB
 Viewed:  7 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

LoPHS.jpg


Back to top
View user's profile Send private message
JovianPyx



Joined: Nov 20, 2007
Posts: 1970
Location: West Red Spot, Jupiter
Audio files: 222

PostPosted: Tue Jun 23, 2020 7:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

That is definitely more droop than the datasheet specifies, so unless it's damaged, it wouldn't be the LM3xx IC at fault.

PSUs need to transfer rather large amounts of current. To do that efficiently, all of the connections must be very low resistance. It would take only one marginal connection giving a little too much resistance to cause voltage droop. Problems in the Vadj part of the circuit could cause it to inaccurately follow the output and make inaccurate adjustments to the output. If not already done, I'd consider re-flowing all of the solder connections.

Dunno, pretty weird, so I'd suspect something weird.

_________________
FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
corruptio optimi pessima
Back to top
View user's profile Send private message Visit poster's website
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Tue Jun 23, 2020 7:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
That is definitely more droop than the datasheet specifies, so unless it's damaged, it wouldn't be the LM3xx IC at fault.

PSUs need to transfer rather large amounts of current. To do that efficiently, all of the connections must be very low resistance. It would take only one marginal connection giving a little too much resistance to cause voltage droop. Problems in the Vadj part of the circuit could cause it to inaccurately follow the output and make inaccurate adjustments to the output. If not already done, I'd consider re-flowing all of the solder connections.

Dunno, pretty weird, so I'd suspect something weird.


but the results measured are consistent while on the breadboard and also on the pcb. I do have an identical CT transformer thats 36VA 18-0-18, will give that a try later and if the results are the same what should i look at, that might me causing this behaviour. will also reflow the the connections.

With that said I am already designing another PSU with an LM723 but i do hope to at least figure out why this is happening so i can learn from my mistake.


PSU_Bottom.jpg
 Description:
 Filesize:  3.89 MB
 Viewed:  4 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

PSU_Bottom.jpg



PSU_Top.jpg
 Description:
 Filesize:  3.68 MB
 Viewed:  5 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

PSU_Top.jpg


Back to top
View user's profile Send private message
JovianPyx



Joined: Nov 20, 2007
Posts: 1970
Location: West Red Spot, Jupiter
Audio files: 222

PostPosted: Tue Jun 23, 2020 7:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

I looked again at the scope traces. What I noticed is that it seems that under little to no load, there's no in-your-face ripple, but as you increased the load current, there began to appear more and more of a sort of sawtooth. It looks like it might be 50 Hz. I would look also at the regulator's input voltage with a scope, it may be coming within the dropout voltage. What that would mean is a transformer that just can't supply the current needed.

The circuit boards look well made.

_________________
FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
corruptio optimi pessima
Back to top
View user's profile Send private message Visit poster's website
Gingoism



Joined: Feb 01, 2017
Posts: 14
Location: Singapore

PostPosted: Tue Jun 23, 2020 7:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

i am thinking the same with regards to the transformer, also it began "whirring" audibly at 1A Shocked .
ok will look at getting a higher rated transformer in the meantime.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: dnny, Uncle Krunkus, v-un-v
Page 1 of 1 [23 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
e-m mkii

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use