IRS27951 / IRS27952 - Page 12 - 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 14th January 2013, 01:05 AM   #111
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by nigelwright7557 View Post
I looked at the power up pulse train and the 27951 is resetting well before the power up sequence ends.
If I remove the 470uf smoothing capacitors it powers up OK.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 14th January 2013, 05:11 AM   #112
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by nigelwright7557 View Post

...Values...
It still overloads and stops.
...
Just to eliminate power up timer problems I used 47uF to stretch the power up delay.
But what is your soft start frequency? What is the soft start frequency setting resistor (Rss)? Without a resistor a soft start capacitor (Css) does nothing!
__________________
Olyan nem volt még, hogy ne lett volna valahogy
  Reply With Quote
Old 14th January 2013, 02:05 PM   #113
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Soft start frequency is 400KHz from 3k9 and 10uf.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 14th January 2013, 05:33 PM   #114
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
The circuit wont power up off mains but it does run on 90 volts DC.
I can see the high frequency power up sequence working then the frequency slowly drops to 25KHz. It is going to the lowest frequency as the 90 volts doesn't give enough voltage to make the opto-coupler output go low.

My problem is I don't have an isolation transformer to look at the primary side of the circuit.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 14th January 2013, 06:05 PM   #115
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by nigelwright7557 View Post
I worked through the spreadsheet and input all my values:
Lm 800uH
Lr 85uH
Cr 100nf
k 7
.
If you have an Lm=800uH and a Lr=85uH, how can you have a K=7 ?
Your K is 9,4
(The spreadsheet uses function to calculate values. Cells with input are marked yellow. Don't write into cells with function)

From these values (k=9,4) i get a fmin of 33kHz. (19kHz will lead you to capacitive mode)
The primary peak current is 2,70A. This means you need a FET with Rdson < 0,74 Ohm, which is true for you. The IRS27951 starts with swtiching on the lower FET, and puts a bigger impulse out first.

What is your timing capacitor? 270pF?
Now its getting interesting...
If your Cr Lr, and freqs right, it should start up without a problem now.
__________________
Olyan nem volt még, hogy ne lett volna valahogy
  Reply With Quote
Old 14th January 2013, 06:12 PM   #116
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Sorry my Lm is 600uH and Lr is 85uH.
k = 7.

Timing capacitor is 390pf.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 14th January 2013, 06:27 PM   #117
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by nigelwright7557 View Post
Sorry my Lm is 600uH and Lr is 85uH.
k = 7.

Timing capacitor is 390pf.
With 600uH - 85uH - 100nF combination the primary peak current is 3,6A. But it would also work with your 0,4Ohm FET (its on the limit but should).

Do you power with no load at output?
When you power up does the output voltage increase to some level?
__________________
Olyan nem volt még, hogy ne lett volna valahogy
  Reply With Quote
Old 14th January 2013, 06:34 PM   #118
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by lorylaci View Post
With 600uH - 85uH - 100nF combination the primary peak current is 3,6A. But it would also work with your 0,4Ohm FET (its on the limit but should).

Do you power with no load at output?
When you power up does the output voltage increase to some level?
I have 660r across 45 to -45 volt lines.
I currently also just have 100uf per rail for smoothing.

I get a very brief but small voltage on the output.

The 27951 is resetting on the power up high frequency.
Its not getting a chance to get to the normal working frequency.

If I run off 90 volts I can see the power up frequency is fine and then it slowly settles down to about 21000Hz.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 14th January 2013, 07:04 PM   #119
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by nigelwright7557 View Post
I have 660r across 45 to -45 volt lines.
I currently also just have 100uf per rail for smoothing.

I get a very brief but small voltage on the output.

The 27951 is resetting on the power up high frequency.
Its not getting a chance to get to the normal working frequency.

If I run off 90 volts I can see the power up frequency is fine and then it slowly settles down to about 21000Hz.
The IRS27951 first low output impulse has a double length (datasheet page 15). Do you use one 100nF capacitor, or 2x47nF split capacitor?

If you use a single, then at startup it has no voltage on it. And this (and the IRS27951 longer first impulse) causes a current transient, which triggers the OC of the IRS27951.
__________________
Olyan nem volt még, hogy ne lett volna valahogy

Last edited by lorylaci; 14th January 2013 at 07:09 PM.
  Reply With Quote
Old 14th January 2013, 07:15 PM   #120
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
I used a single 100nf 500 volt AC capacitor.

Do you mean put two 47nf in parallel ?
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  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



New To Site? Need Help?

All times are GMT. The time now is 04:01 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