Is there any thing wrong with this design - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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 24th February 2013, 01:09 AM   #11
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
You are dissipating at least 2.35W in that resistor, which should be at least 10W for good thermal stability.

Use a fixed resistor between out and ref which should not be more than 1.21K if you want good regulation. (1mA of reference current) You could use a 392K + 7.87K if you need ~400V out. If you need to make the output voltage adjustable the pot should be placed in series with these resistors. Note that the LM317 can require as much as 10mA of load current to regulate correctly depending on maker, so make sure that the load current is sufficient when the load is warmed up.

The accuracy of the LM317 is sufficiently good that with 1% resistors you should be able to get close enough to the target output voltage without trimming.

Note that 100uF capacitor on the reference terminal is not a great idea, I'd not make it more than a few uF at these operating voltages. Don't expect the regulator to survive a short on the output either.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 24th February 2013, 05:44 PM   #12
tony Ma is offline tony Ma  United States
diyAudio Member
 
Join Date: Feb 2011
Dear All, tks for the input

@kevinkr, it's hard to find resistor with 10W (I checked with Digikey, mouser and etc)

Btw the output that I need is 400V DC 100mA

tks
  Reply With Quote
Old 24th February 2013, 05:44 PM   #13
tony Ma is offline tony Ma  United States
diyAudio Member
 
Join Date: Feb 2011
Quote:
Originally Posted by vacuphile View Post
Does it actually work at all? I really don't see how you could subject an LM317 to these voltages. How could you send AC straight through a 10mH inductor? What happens if you put 100uF straight over AC? Where does the DC come from? Etc.
Actually I don't use any inductor
  Reply With Quote
Old 24th February 2013, 06:06 PM   #14
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
A quick look at Digikey appears to show 11 pages of 10W resistors, though none are that value. But it's probably safer to use 2 or 3 resistors to make the 68k anyway.
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 25th February 2013, 02:35 AM   #15
diyAudio Member
 
rfengineer2013's Avatar
 
Join Date: Feb 2013
Location: Colorado
I'll echo what KevinKR and Sofaspud said. A 3W resistor with a constant 2.4W load it will most certainly run hot.

Since you have the pot for adjustment, the 68k value isn't that critical. Series and/or parallel several resistors as needed to get something close to 68k with at least a 10W equivalent - you should run a lot cooler then.

RF Dude
  Reply With Quote
Old 25th February 2013, 02:50 AM   #16
diyAudio Member
 
rfengineer2013's Avatar
 
Join Date: Feb 2013
Location: Colorado
You also might want to increase the breakdown voltage rating of C4 - using a 400V cap across a 400V potential is a bit sporty...

If you put caps in series to increase the breakdown voltage, you will want to use equalizing resistors - a simple solution would be to stack a couple of 5W 33k resistors in series and put one 0.22 250V cap across each resistor. Digi has TDK 0.22uF, 250V caps, P/N FK20X7R2E224K in stock at 0.73 ea. - this will give you a 0.11uF 500V equivalent for C4 which should be plenty safe.
  Reply With Quote
Old 25th February 2013, 03:06 AM   #17
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
The better resistors tend to have temp rise graphs in their datasheets to give you an idea as to how hot they will get. Attached is an example from this http://www.farnell.com/datasheets/1449996.pdf welwyn datasheet.

Tony.
Attached Images
File Type: png temp_rise.png (23.3 KB, 92 views)
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 25th February 2013, 03:45 AM   #18
diyAudio Member
 
rfengineer2013's Avatar
 
Join Date: Feb 2013
Location: Colorado
I must be in full design review mode... Occupational hazard, I guess.

Looking at the schematic further, my comment above on C4 also applies to C3 and C6. C6 is running right at its rated limit, and C3 is likely seeing a voltage above its rated limit sitting at the input to the LM317.

I would definitely use higher voltage rated caps for both of these - you risk blowing the caps as the applied voltage is going to stress them over time.

OK, just a few more things to chew on - good luck with the supply, hope you get 'er running happily and can move on to other parts of the design.

Last edited by rfengineer2013; 25th February 2013 at 04:06 AM. Reason: Added explanatory note.
  Reply With Quote
Old 25th February 2013, 05:09 PM   #19
tony Ma is offline tony Ma  United States
diyAudio Member
 
Join Date: Feb 2011
Quote:
Originally Posted by rfengineer2013 View Post
I must be in full design review mode... Occupational hazard, I guess.

Looking at the schematic further, my comment above on C4 also applies to C3 and C6. C6 is running right at its rated limit, and C3 is likely seeing a voltage above its rated limit sitting at the input to the LM317.

I would definitely use higher voltage rated caps for both of these - you risk blowing the caps as the applied voltage is going to stress them over time.

OK, just a few more things to chew on - good luck with the supply, hope you get 'er running happily and can move on to other parts of the design.
Tks for the input
I will replace all the capacitor with more higher rating maybe like 630V
Also for resistor, i just checked there is 68K at higher watt like 14W at digikey
  Reply With Quote
Old 1st March 2013, 04:28 PM   #20
tony Ma is offline tony Ma  United States
diyAudio Member
 
Join Date: Feb 2011
Hi guys,

just want to give update

I am ending up changing Resistor 68K with Caddock 14W and change all capacitor with 1000V from Digikey

What a big different. The sound is more smooth.

So I believe what ever comes out from PS to any board (ex PA or pre-amp board) will effect the quality of the board itself

i learn some thing here tks guys
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Wrong Voltage / current on BoZ... or Wrong Measuring ? gionag Pass Labs 8 14th May 2008 12:24 PM
Is % open area the wrong parameter for ESL stator design? Few Planars & Exotics 6 23rd May 2007 10:58 PM
help!!! design a T-line enclosure for the "wrong woofer" ningures Multi-Way 4 7th October 2006 08:24 PM
Anything wrong with my first sub design? angsuman Subwoofers 9 23rd November 2005 02:38 AM
Anything wrong with this design? FrancoB Tubes / Valves 4 27th April 2005 07:50 AM


New To Site? Need Help?

All times are GMT. The time now is 11:51 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2