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
MFOS Dual Power Supply
Post new topic   Reply to topic Moderators: dnny, Uncle Krunkus, v-un-v
Page 1 of 1 [7 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
ronmexico



Joined: Mar 05, 2012
Posts: 3
Location: Cincinnati

PostPosted: Mon Mar 05, 2012 7:42 pm    Post subject: MFOS Dual Power Supply Reply with quote  Mark this post and the followings unread

I building the MFOS dual power supply.....and I have run in to a problem.

I am trying to use the design to give me an adjustable dual power supply in the 3V-9V range (roughly). Instead of a 24V transformer, I am using a 13V center tapped transformer such that I get about +- 8V when rectified.

I have also swapped out the 1K resistors @ R3 and R7 for 240ohm resistors.

So everything has gone well but I am having a issue that is driving me crazy.

The rectification/filter "stage" of the board works fine... one side puts out ~8V+ and ~8V-. However the adjustable voltage regulator "stage" doesn't seem to be working.

I am turning the 2K trim pots and no matter what I do, the output voltage only changes by +- ~.5V e.g. between 7.25 and 7.75. That is to say, I cannot get the voltage down to say 4V.

This problem is true of both the + and - supply "side" of the board.

I have gone so far as to model the circuit in LTSpice to make sure my resistor changes work as they are supposed to.... and Spice tells me as the resistance of R4/R8 drops, so does the voltage.

I have gone over the board again and again.... verifying the values of the resistors/capacitors, no short circuits, diode orientation etc....

The circuit is so simple, I feel stupid for having to ask for help but I hope someone can give me a pointer to think of something I haven't yet.... probably something rather obvious Smile.


Thanks in advance!
Back to top
View user's profile Send private message
Sound



Joined: Jun 06, 2006
Posts: 842

Audio files: 1

PostPosted: Mon Mar 05, 2012 9:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

arrow
Back to top
View user's profile Send private message
Osal



Joined: Aug 16, 2011
Posts: 145
Location: Here

PostPosted: Mon Mar 05, 2012 9:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

You should obtain within 2.5V and 11.9V with this configuration. To obtain roughly 3 to 9V (2.5 to 8.9) you could use 330 resistors instead 240

The transformer is insufficient to output 9V. The minimum transformer to output +/-9V should be a 24VCT.

What is the maximum current output you desire to output?
What is the value of filter capacitors?

_________________
electronic-sea.net
Back to top
View user's profile Send private message
prgdeltablues



Joined: Sep 25, 2006
Posts: 162
Location: UK
Audio files: 10

PostPosted: Tue Mar 06, 2012 4:49 am    Post subject: Reply with quote  Mark this post and the followings unread

A few thoughts..

Are the trimmers wired correctly -centre pin connected to one end - it sounds as if you are not actually changing the resistance when you turn them.

Check the pinouts of the LM317/337 note they are different.

Have you checked the ground is properly connected (voice of experience)

The positive regulator should work without a load, but the negative one likes a load - try connecting an led with say 1k series resistor between V- out and ground.

Peter
Back to top
View user's profile Send private message
ronmexico



Joined: Mar 05, 2012
Posts: 3
Location: Cincinnati

PostPosted: Tue Mar 06, 2012 7:46 am    Post subject: Reply with quote  Mark this post and the followings unread

prgdeltablues wrote:
A few thoughts..

Are the trimmers wired correctly -centre pin connected to one end - it sounds as if you are not actually changing the resistance when you turn them.

Check the pinouts of the LM317/337 note they are different.

Have you checked the ground is properly connected (voice of experience)

The positive regulator should work without a load, but the negative one likes a load - try connecting an led with say 1k series resistor between V- out and ground.

Peter


I thought the same thing regarding the trimmers not being connected correctly. I have the "3" pin of the pots connected to the center "ground" rail/trace and the other to pins are connected together and is in series with the 240 ohm resistor (and I did double check that is 240 ohm not 240K ohm). I've checked these and rechecked these stupid trimmers.


Not sure about the ground... the transformer is wire to 2 prong A/C outlet....i.e. there is no ground pin.

I tried the applying a load idea.... stuck a 4.7K ohm resistor across the outputs....no change.


To the other poster(s).... the capacitors are as specified in the project except for the big filter capacitors, I believe I am using something slightly smaller. Also any DC voltage under 6V-7V is fine.

The only other thought I has was the output filter capacitors are not draining after being charged up to ~8V. e.g. when I fire it up the output is 8V.... as I turn down the resistance, the capacitors are not discharging fast enough.... I kind of doubt this as there is 4.7K ohm resistor that should drain them and provide a little bit of bias current.


Grrr.... this is so frustrating!
Back to top
View user's profile Send private message
prgdeltablues



Joined: Sep 25, 2006
Posts: 162
Location: UK
Audio files: 10

PostPosted: Tue Mar 06, 2012 9:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Could you measure the voltage between the output pin and the adjustment pin - it should be about 1.25 V (that's the reference voltage) - ie across R1.

The readings you're getting do sound suspiciously like CR1 and CR3 are in backwards - that would provide a path from input V to ouput V with a diode drop of 0.6V - about 8V down to 7.4V. You could try disconnecting those and CR2 and CR4 - they are all good for protection but are not essential to the operation of the regulators.

Post a picture?
Back to top
View user's profile Send private message
ronmexico



Joined: Mar 05, 2012
Posts: 3
Location: Cincinnati

PostPosted: Tue Mar 06, 2012 7:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

prgdeltablues wrote:
Could you measure the voltage between the output pin and the adjustment pin - it should be about 1.25 V (that's the reference voltage) - ie across R1.



So I measured that and discovered I was getting something like 7V across it!

So I traced down the circuit to figure out where they voltage was coming from and found it! Apparently part of the trace on the PCB I etched didn't survive between R2 and the VPOS output.... I soldered those 2 together and now the board is working as expected/designed...

I just knew it was going to be something stupid like that!


Thanks for getting me on the path to finding the problem!!!!
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 [7 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
emSynth

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