2 Designs for Class D Power Supply - Which One? - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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 May 2006, 02:40 PM   #21
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
No not because the amp loads them, but because being connected individually to the winding of the transformer (albeit through a bridge, but that makes no real difference) they by default cannot have major voltage imbalance.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 9th May 2006, 04:54 PM   #22
diyAudio Member
 
sx881663's Avatar
 
Join Date: Nov 2003
Location: so. ca.
Default To bleed or not to bleed, that is the question.

The point of bleeders is 2 fold; first they help regulation by providing a minimum current set point. Second and more important is in the case of failure of the rail fuses, you will have them right? Where does the stored energy go if you don't have the bleeders? After the failure will be the time you are poking around in the amp with a probe and will inadvertently short out one of the caps. BANG! There goes your probe tip and now a trip down the hall to change your shorts!
The stored charge can last a very long time and if the dead amp has been sitting for some time we tend to discount thoughts of danger like this. Safety first!
Roger
__________________
Happiness is being owned by a cat
  Reply With Quote
Old 9th May 2006, 05:10 PM   #23
diyAudio Member
 
sx881663's Avatar
 
Join Date: Nov 2003
Location: so. ca.
Default Latest drawing

Back2diy,
The new drawing looks very good but please do include rail fuses. This setup still is not as good as separate transformers or even separate windings. The separated grounds are really an illusion as when the diodes are forward biased they are really connected together. Signal current will transfer between channels freely at this time. I did a design like this some time ago and had the transformer manufacture do separate windings so I could do full bridges for each needed voltage. At the same time you can get the exact voltage and power rating you need. Most of these transformers are done by hand one at a time so customs arenít much of a problem or very much more costly. All you need to do is ask!
Roger
__________________
Happiness is being owned by a cat
  Reply With Quote
Old 9th May 2006, 06:26 PM   #24
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
Default Re: To bleed or not to bleed, that is the question.

Quote:
Originally posted by sx881663
Second and more important is in the case of failure of the rail fuses, you will have them right? Where does the stored energy go if you don't have the bleeders?
The stored charge can last a very long time and if the dead amp has been sitting for some time we tend to discount thoughts of danger like this. Safety first!Roger
Yes you are right here. I do use 10k bleeders for this on my 60V lines of the PSU's but thats only for discharging not for something else. This consumes hardly any energy.
__________________
Kind regards,
Bert
  Reply With Quote
Old 10th May 2006, 12:58 PM   #25
bck2diy is offline bck2diy  United States
diyAudio Member
 
Join Date: Aug 2004
Location: Da Bronx
richie00boy, I will keep C2, C3 close to the rectifier bridges. Yes, I am keeping the diode caps only for curiosity :-) Initial build will be without them, then I plan to add them to see if there is any sonic difference to my ears and I'll take them out if I can't find any. On the bleeders, I had planned on soldering one to each cap (across the terminals so to speak) - your option would mean I put them in the circuit potentially after the last caps. I guess that is ok (from a safety point - will it drain both caps if resistor rating is calculated correctly)? For the initial stages of my diy steps, I don't plan on using more than 300VA transformer - from what I have read, a soft start is unnecessary in this case? I do plan to use one when I move to the mono amp (which will most likely include a more powerful amp kit also - UcD400 for e.g.).

Bert and all, the reason I went for bleeders is mainly due to the safety factor. I plan to keep them that way.

Roger, on the rail fuses - from what I have learnt, they need to be fast blow type. What I couldn't figure out is the amp rating on those fuses - how do I calculate them (for calculating transformer primary fuse value I divide the VA rating of the transformer secondary by input voltage and add 10% for transformer loss, etc: e.g. - 300VA / 120V = 2.5A + 10% ~ 3A slow blow type fuse for F1 in previous diagram). Is it the same as the primary fuse except being a fast blow type?

[Edited to add comment below]:
Roger/Bert I understand your comments about separate windings/transformers - I do plan to get there in later stages of my diy steps. The intermediate step I had outlined is to educate myself on calculating the right values for the transformer, capacitors, bleeder resistors, etc., before I can take on the challenge of designing a psu for a mono amp with the various add-on circuits mentioned (previously).

Thanks again!
-bck2diy
  Reply With Quote
Old 10th May 2006, 01:39 PM   #26
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
It's looking good. You don't need soft start for 300VA. Rail fuse sizing is tricky. I work out the sine wave RMS current at full power then use the next fuse up from that.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 10th May 2006, 05:55 PM   #27
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
-bck2diy,
primary fuse a 3.15AT fuse(300W toroid) and dc line fuses for the UCD400 is 8AF per supply line. UCD180= 6.3AF. So 2 modules 4 fuses. This is how I use it with a fast type of output protection relay. You don't need a softstart for a 300W toroid with a 230V AC mains. At 115AC I don't know? Bleeders for safety are wise as stated by Roger.
__________________
Kind regards,
Bert
  Reply With Quote
Old 10th May 2006, 06:15 PM   #28
diyAudio Member
 
sx881663's Avatar
 
Join Date: Nov 2003
Location: so. ca.
Default Lots of questions

The bleeders should not be mounted on the caps. If you use a low enough resistance value to drain the caps quickly they will run quite warm or even hot enough that you wouldn't want the cap to be the heatsink. Only one on each rail is necessary.
400VA seems to be the dividing line according to most and me as well. Above this number you would be better served with a soft start. Inrush current can get very high with the bigger transformers. I would guess in the 50-100 amp range. This is enough to stress parts and cause premature failures.
Rail fuses? 180 watts/4 = 45, SQ root= 6.7 amps total shared by 2 rails + some margin = 5 amps. This should be a workable value for the 180 modules. This is also the value Hypex recommends.
Roger
__________________
Happiness is being owned by a cat
  Reply With Quote
Old 11th May 2006, 12:03 PM   #29
bck2diy is offline bck2diy  United States
diyAudio Member
 
Join Date: Aug 2004
Location: Da Bronx
richie00boy, Bert, Roger ... thanks once again!!

Roger, I'll take up your advice on not mounting the resistor across the capacitor terminals. I didn't think of the heat issues - I assumed a heatsinked wirewound resistor (as shown in the picture below) would take care of the heat dissipation issues! Also, thanks for showing an example of how to calculate the rails fuse.

Now, I ought to be able to complete step 2 without any further questions! I'll be back to ask more questions when I take on soft start, dc protection, etc!!

-bck2diy
Attached Images
File Type: gif 16027.gif (34.4 KB, 177 views)
  Reply With Quote
Old 11th May 2006, 05:19 PM   #30
diyAudio Member
 
sx881663's Avatar
 
Join Date: Nov 2003
Location: so. ca.
Default Heat removal

Of course if you are remote mounting those resistors to a panel or something they could be connected to the cap as not much heat would go through the wires. I assumed you were talking about the typical sand cast or axial types mounted with short leads right on the cap pins.
I do hope that isnít the actual resistor you are thinking of using. 100 ohm is way too low of value and will waste around 20 watts each. A value like 2000 2 watt would be far more appropriate using only around 1 watt. Anything from 2k to 10k will do fine with out generating excessive heat.
Roger
__________________
Happiness is being owned by a cat
  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
Class D Power Supply??? Co_Driver Class D 19 17th December 2010 01:05 PM
Looking for nice power supply designs Progg70 Power Supplies 6 15th January 2008 09:23 AM
Class D Power Supply kuda Class D 7 12th May 2006 07:58 AM
DC-DC Power converter for Class T amp power supply? rtalk Class D 2 7th December 2004 04:02 AM


New To Site? Need Help?

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