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 30th November 2011, 11:08 PM   #1
epilot is offline epilot  United States
diyAudio Member
 
Join Date: Jul 2006
Default LM3886 transformer/bridged diode...

Hi guys,

I am designing an amplifier out of an LM3886. The load impedance is 4 ohms.
I want to use two filter caps (6700 0r 10000uF) for the dual power supply which supply the LM3886 chip.

I have got just 2 questions.
1: how to choice the best suited bridged diode (foe instance if a 10A bridged diode is good enough for this purpose (the large filtering caps are shorted at first when the amplifier starts to work, So I would like to know how to select the best bridged diode so that it works just right and does not fry due to shorted filtering caps at the start point of amplifier working)).

2: what is the best choice for the toroid and non toroid transformer for this job? I mean the transformer current delivering and so on.

Thanks for any help.
  Reply With Quote
Old 30th November 2011, 11:29 PM   #2
Bazukaz is offline Bazukaz  Lithuania
diyAudio Member
 
Bazukaz's Avatar
 
Join Date: Nov 2005
Location: Vilnius
Send a message via Skype™ to Bazukaz
Default Hi

Hi, in general I would recommend bridge of around 25 amps(better have safety due to surge current when caps are charged on turn-on).
Toroids are mostly better(usually lighther for the same power, less hum).

Regards,
Lukas.
  Reply With Quote
Old 30th November 2011, 11:52 PM   #3
diyAudio Member
 
Join Date: Sep 2006
Location: Santa Rosa Beach, FL
What voltages do you want to run, for your +/- rails??
  Reply With Quote
Old 1st December 2011, 12:05 AM   #4
epilot is offline epilot  United States
diyAudio Member
 
Join Date: Jul 2006
Quote:
Originally Posted by Bazukaz View Post
Hi, in general I would recommend bridge of around 25 amps(better have safety due to surge current when caps are charged on turn-on).
Toroids are mostly better(usually lighther for the same power, less hum).

Regards,
Lukas.
Hi And thanks,
a 25A bridged diode is not a way to high plz?
  Reply With Quote
Old 1st December 2011, 12:08 AM   #5
epilot is offline epilot  United States
diyAudio Member
 
Join Date: Jul 2006
Quote:
Originally Posted by CanAm Man View Post
What voltages do you want to run, for your +/- rails??
Something like +-20Vrms (56Vp-p) or a bit higher or lower is a good choice for the power supply I think.

I do not how to choice a transformer for this job so that it works 24 hours a day...?
  Reply With Quote
Old 1st December 2011, 12:57 AM   #6
diyAudio Member
 
ByronInPortland's Avatar
 
Join Date: Nov 2010
Location: Portland, Oregon
Coincidentally, about a year ago I built a 2-channel LM3886 amp, which I've been using with a pair of 4 ohm speaker for a while now (though not 24hrs/day). I'm very happy with it. The rectifier uses MUR860s by On semiconductor ON Semiconductor MUR860: 600 V, 8.0 A Ultrafast Rectifier.
I'm using the Antek AS-3218 Antek - AS-3218 which has built-in shielding and 18V secondaries.

Good luck and be sure to post photos of your build!
  Reply With Quote
Old 9th December 2011, 02:43 PM   #7
epilot is offline epilot  United States
diyAudio Member
 
Join Date: Jul 2006
Quote:
Originally Posted by ByronInLawrence View Post
Coincidentally, about a year ago I built a 2-channel LM3886 amp, which I've been using with a pair of 4 ohm speaker for a while now (though not 24hrs/day). I'm very happy with it. The rectifier uses MUR860s by On semiconductor ON Semiconductor MUR860: 600 V, 8.0 A Ultrafast Rectifier.
I'm using the Antek AS-3218 Antek - AS-3218 which has built-in shielding and 18V secondaries.

Good luck and be sure to post photos of your build!
Hi and thanks for the replys.

2 questins:

isnt a 8A diode a way too low for 2 channeled power ampifier?
why you did use an ultrafast diode for the job? is it nessesery to use an ultrafast diode?
  Reply With Quote
Old 11th December 2011, 05:26 PM   #8
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
There is a sequence that you can follow, to arrive at the sizes and values for the components.

If you know the desired output power and the load impedance, then you can estimate the required supply voltage. That will also enable you to estimate the voltage and Volt-Amp (VA) rating for the transformer, and the maximum steady-state current required. The desired maximum ripple-voltage amplitude and max load current will give you the total smoothing capacitance needed. The capacitors' ESR (equivalent series resistance) spec will let you estimate the possible initial inrush current magnitude (and with cap values would give an estimate of its duration and profile vs time). If a regulator is to be used, then max ripple voltage amplitude, rectifier voltage drop, the regulator drop-out voltage spec, and the worst-case transformer regulation and worst-case line voltage excursion will also need to be accounted for, when the transformer voltage is selected, to make sure that the bottom of the ripple voltage waveform can't make the regulator go into dropout, which would be quite ugly (smile).

Note that the initial inrush current might be many tens of Amps, but its time duration might be short-enough that lower-rated rectifier diodes or bridges could handle it OK.

Some of the basics that you need are here: Unregulated Power Supply Design .

The Chipamps forum has a "sticky" thread (at the top), that's all about power supplies for chipamps.

Last edited by gootee; 11th December 2011 at 05:35 PM.
  Reply With Quote
Old 12th December 2011, 10:54 AM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by gootee View Post
Some of the basics that you need are here: Unregulated Power Supply Design .

The Chipamps forum has a "sticky" thread (at the top), that's all about power supplies for chipamps.
I like/love your reply. It seems to remind me of what I advise.
Give some guidance and tell them/him/her to go and read.
__________________
regards Andrew T.
  Reply With Quote
Old 13th December 2011, 01:04 AM   #10
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
Originally Posted by AndrewT View Post
I like/love your reply. It seems to remind me of what I advise.
Give some guidance and tell them/him/her to go and read.
Thanks. It wasn't entirely consciously planned that way. (smile) I just thought that the process-level view was what was needed the most, at that moment. And, maybe like you, I thought that the details would probably be best-learned by just churning around in them for a while. Either that or I was in a hurry. (grin)
  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
My Bridged LM3886 robertj88 Chip Amps 12 31st October 2010 03:47 PM
100w Bridged lm3886 Ted205 Chip Amps 2 3rd April 2009 07:29 AM
Bridged LM3886 (again ?) Puffin Chip Amps 24 14th February 2008 08:10 AM
resistors before the diode in a bridged rectifier: what does it do? jarthel Parts 2 5th September 2006 04:38 PM
Looking for a PCB for bridged LM3886 zafira1981 Chip Amps 1 29th March 2006 03:39 AM


New To Site? Need Help?

All times are GMT. The time now is 09:19 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