National's 170w Class D amplifier Inductors - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 2nd June 2002, 11:47 PM   #1
diyAudio Member
 
Join Date: Jun 2002
Default National's 170w Class D amplifier Inductors

I was interested in building National's 170w Class D amplifier with the LM4651 driver IC and the LM4652 mosfet IC. However, on their schematic it shows the output and ground having 50uH inductors on them. I checked inductor prices and this would be at least $10 an inductor. Is there any way to make or get these cheaper, or eliminate them from the design? I am afraid the inductors might be necessary in a switching amp though.
  Reply With Quote
Old 4th June 2002, 07:19 PM   #2
diyAudio Member
 
Join Date: May 2002
Location: Cincinnati, OH now Columbus,OH USA
Send a message via AIM to BeanZ
The output inductors are absolutely necessary in a class-D amp and the amplifier will not produce audio without them. The inductors and caps form a lowpass 2nd order or higher LC filter to remove the constant switching frequency and recove the audio. Ten bucks a piece are a pretty good deal and I dont think that you can make them for cheaper. You are lucky that you even found an off the shelf part to use for the application. Typically, for switching power applications a custom magnetic component must be designed and wound. I would buy the inductors.

BeanZ
__________________
BeanZ
  Reply With Quote
Old 4th June 2002, 08:56 PM   #3
diyAudio Member
 
Join Date: Jun 2002
If the amp was only going to be used as a subwoofer, would it be possible to use inductors with lower uH?
  Reply With Quote
Old 4th June 2002, 11:21 PM   #4
diyAudio Member
 
Join Date: May 2002
Location: Cincinnati, OH now Columbus,OH USA
Send a message via AIM to BeanZ
The LC filter is to remove the switching frequency. If the switching frequency is not removed completely there will be all kinds of garbage all over the place. An option would be to use a lower value inductor but a higher capactior value. The cutoff frequency is: 1/(2*pi*sqrt(L*C)) where L is in Henries and C is in Farads. The cutoff frequency is chosen to be much less than the switching frequency but higher than the audio region. Make sure that the inductor that you choose is rated for adequete current. This should be at least 10Amps. This is enough current for the output plus a few amps of ripple current. If you are going to buy an inductor make sure that it can run at the switching frequency. Hope this helps.

BeanZ
__________________
BeanZ
  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
FS: National Overture Class-D Demo Board Amp speaker Swap Meet 3 24th March 2009 03:05 PM
WTS: National 170W Class-D Amp Demo Board speaker Swap Meet 1 3rd March 2008 02:41 PM
I don't know how to go to the page that have audio power amplifier ic at national.com jinkuchi Chip Amps 5 16th May 2005 04:06 AM
Class D amplifiers on National Chips jmateus Chip Amps 4 8th April 2005 06:10 AM
National's 170w Class D amplifier vish_zn Solid State 11 24th May 2002 02:12 PM


New To Site? Need Help?

All times are GMT. The time now is 08:59 AM.


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