ucd 25 watts to 1200 watts using 2 mosfets - Page 152 - 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 10th December 2011, 08:22 PM   #1511
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by CPX View Post
I am using resistive load(1 ohm)..no speaker..i have headphones connected to the output with a resistive network.
Any way 50hz and 20 hz distorsions that i hear are not visible on the scope/fourier..
If you cannot see the sine distorted in a scope, than it could have some harmonics. But if you cannot see harmonics on the Fourier Transform, then THEY ARE NOT THERE, whatever your ear tells.
Your brain is just fooling you then.
__________________
Olyan nem volt még, hogy ne lett volna valahogy
  Reply With Quote
Old 10th December 2011, 08:28 PM   #1512
CPX is offline CPX  Romania
diyAudio Member
 
Join Date: Nov 2004
Location: Cluj
They are there...the scope is not sensitive enough(cheap digital scope)...
I made simulations and there are around -40 db.If you want i will post a file with alternating distorsion zones at -40 db so you can see if they are hearable for you.
  Reply With Quote
Old 10th December 2011, 08:47 PM   #1513
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by CPX View Post
They are there...the scope is not sensitive enough(cheap digital scope)...
I made simulations and there are around -40 db.If you want i will post a file with alternating distorsion zones at -40 db so you can see if they are hearable for you.
-40dB distortion means 0,01%. If you want distortions lower than that with this simple schematic, then stop screwing with me

Just to be sure I made some test, generated some sines in audacity. Base is 50Hz, i can hear 150Hz down to -36dB, 100Hz down to -27dB. But this is also because ears sensitivity drastically increases from 50 to 100-150hz, and also because of headphone sensitivtiy incease...

I am usually satisfied with distortions lower than 0,1%. If you want distortions lower than 0,01% then you have to adjust lot of things: very good compator, fast gate drive, minimise dead time, imcrease feedback etc...
And you will need very good instruments.
__________________
Olyan nem volt még, hogy ne lett volna valahogy
  Reply With Quote
Old 10th December 2011, 08:59 PM   #1514
CPX is offline CPX  Romania
diyAudio Member
 
Join Date: Nov 2004
Location: Cluj
I am sorry but i know that -40 db means 1 % distorsions(0.01 level)..for 0.01% -80 db it is needed.I would be happy with -60db distorsions
  Reply With Quote
Old 10th December 2011, 09:06 PM   #1515
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by CPX View Post
I am sorry but i know that -40 db means 1 % distorsions(0.01 level)..for 0.01% -80 db it is needed.I would be happy with -60db distorsions
According to the manual of my THD meter (HAMEG), THD is the ration of the POWER of harmonics to the POWER of the base signal (or for small distortions the total signal).
So 10mV harmonics to 1V base signal, lets assum at 1Ohm is 0,1mW to 1W, so it is -40dB both at level, and both at distotions. So 0,01% distortion is -40dB
But just to make sure I searched wiki, and found that there are to mismatching definitions Total harmonic distortion - Wikipedia, the free encyclopedia
So you are right by the other definition. But to measure that distortion a digital scope's bitdepth is usually not enough, so measurements with soundcard is needed.
__________________
Olyan nem volt még, hogy ne lett volna valahogy

Last edited by lorylaci; 10th December 2011 at 09:11 PM.
  Reply With Quote
Old 10th December 2011, 09:20 PM   #1516
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
In case of low distortion (say < 1%), both methods will deliver almost identical values, because if the distortions are low, then the difference of magnitude of the fundamental vs the magnitude of the entire signal becomes neglectible.

But I am massively wondering why you say -40db would be 0.01% ?
In fact -80dB would equal to 0.01%.

xxdb = 20*log(U1/U2) = 10*log(P1/P2)

I guess you just mixed up some zeros.
In your example of U1=10mV and U2=1000mV the ratio is 0.01=1/100=1%
  Reply With Quote
Old 10th December 2011, 09:21 PM   #1517
CPX is offline CPX  Romania
diyAudio Member
 
Join Date: Nov 2004
Location: Cluj
For me if i can hear the distorsions the amp is bad and when i can no longer hear them the amp is acceptable and if they measure at <80 db the amp is excelent.
The software that i am using also has this scale:
0.01% means -80 db
Click the image to open in full size.

Last edited by CPX; 10th December 2011 at 09:25 PM.
  Reply With Quote
Old 10th December 2011, 09:31 PM   #1518
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by CPX View Post
For me if i can hear the distorsions the amp is bad and when i can no longer hear them the amp is acceptable and if they measure at <80 db the amp is excelent.
The software that i am using also has this scale:
0.01% means -80 db
Click the image to open in full size.
Okay, so I can give you the following advices to reduce distortion
You said that decreasng dead-time decreased distortion. Try changing the gate-depleting dioda at gate drive to a PNP transistor. This would make turn off faster, then you can decrease the resistor. So overall gate driving will be better.
__________________
Olyan nem volt még, hogy ne lett volna valahogy
  Reply With Quote
Old 10th December 2011, 09:44 PM   #1519
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Quote:
Originally Posted by CPX View Post
Decreasing inductance increases the point(in Amps) where abnormal distorsion and noise begins.With 10uH that zone is near clipping at 18kz and 2 ohm load.With 1 ohm load and 15khz,18khz and beyond i still have problems and I do not want to decrease inductance any further.

distorsion begins here far beyond clipping level - 18khz 1 ohm load.
Click the image to open in full size.

So..as load impedance decreases and frequency increases heavy distorsion(white noise and lower frequency sounds) apear bofore clipping level..why?
This looking like just being the transfer function of the output filter.
As I understood you have 10uH and 1.5uF? And 1 Ohms load.
At 18kHz this will deliver almost 3db attentuation.
Means behind the filter clipping must start at approx 70%...72% of the clipping limit in front of the filter.

80% efficacy, might have multiple reasons.
- Measurement errors.
- Slow or ringing gate drive
- Heavy overlap of ON-times (but you would see this in massive heating of the MosFets, even without any load)

In order to say something about the gate drive, we would need to see in one screen shot Ugs and Uds ( time scale 50ns/grid) of the lower MosFet during a switching event in the upper area of a positive signal half wave at high load.
  Reply With Quote
Old 10th December 2011, 09:45 PM   #1520
CPX is offline CPX  Romania
diyAudio Member
 
Join Date: Nov 2004
Location: Cluj
Decreased dead-time decreses distortion somowhat but 20-50 hz distorsion is bad with low and ultra low gate charge mosfets(tested irfb5615) and i do not think adding a transistor will solve it,in my opinion the main problem is in feedback/filtering section.

ChocoHolic i have 10 uH and 1 uF output filter with 1 ohm load..so i have to change the filter to have 0 db attenuation at 16 khz(18 khz is to much) ..is that posible?
I will post gate drive wave forms tomorrow,eficiency is 80% at 1 ohm load and 90%(3% error) at 4 ohm load but using lower rds on transistors didn't improve it so power is lost in switching.
Thanks for your help

Last edited by CPX; 10th December 2011 at 09:54 PM.
  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
Philips 40/25/15 watts amplifier with Universal preamplifier circuit. renjiish Solid State 64 28th July 2014 11:33 AM
Decibel Watts VS Watts ? fivestring Solid State 11 1st April 2009 01:08 PM
AMP1-B: why only 25 watts @8ohms? theAnonymous1 Class D 10 15th August 2005 06:55 PM
Sound quality of amps at 0.3 watts vs @ typical 5 watts rick57 Solid State 2 26th March 2005 06:25 AM
Need 2 watts Vivek Everything Else 4 17th July 2003 08:29 AM


New To Site? Need Help?

All times are GMT. The time now is 07:25 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