My Class D Schematic... Will it work? - 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 5th November 2007, 01:45 AM   #1
thefish is offline thefish  United States
diyAudio Member
 
Join Date: Oct 2006
Default My Class D Schematic... Will it work?

So I have had this project kicking around in my head for about a year now, but finally it is looking like it will become a reality. Back in January I drew up this schematic and I even got a prototype PCB made (since I was ordering a lot of other boards at that time). I never got around to building it. Before I spend all the time/money on the last few parts and building this thing does it look like it will work?

One concern I have is the finally output stage, the IR2011 (wired up as in the data sheet) is operating on a single supply, but wont this limit the range of the speaker? How can I get around this? Is there a better driver out there that will allow me to use a split supply (I have a nice +/- 30V one ready to go).
Attached Images
File Type: jpg class-d_sch.jpg (67.5 KB, 2004 views)
  Reply With Quote
Old 6th November 2007, 02:11 AM   #2
diyAudio Member
 
raidfibre's Avatar
 
Join Date: Jan 2003
Location: Boston, MA, USA
Send a message via AIM to raidfibre
You'll blow out the driver if you run it straight from a half bridge because the AC signal will be based around half of your rail voltage (15v). You either need to use a full bridge or use a filtering series capacitor. You should also have an LC filter before the signal leaves the amp chassis.

50kHz is too low unless you're only driving a subwoofer.
Using OPA134 to generator a triangle wave is a waste. Use a TL072 or something. There are other things but I didn't look really closely at your circuit. It's not a bad start, you're understanding the concepts.

--
Martin K
  Reply With Quote
Old 6th November 2007, 02:23 AM   #3
diyAudio Member
 
raidfibre's Avatar
 
Join Date: Jan 2003
Location: Boston, MA, USA
Send a message via AIM to raidfibre
The circuit you pasted from the IR2011 datasheet is really generic. For the half bridge you would drive the high and low with the same signal ( I think one of the inputs is inverted on chip )

The only reason you would run separate PWM into the IR2011 is if you are doing phase shifting, which you are not. I don't really understand what you're trying to accomplish with your comparator outputs..

The analog audio input should be filtered to prevent any audio signals over 1/2* Fsw.

The MOSFET gates should be run at 12v unless you're using logic level FETs...
__________________
--
Martin K
  Reply With Quote
Old 6th November 2007, 03:44 AM   #4
thefish is offline thefish  United States
diyAudio Member
 
Join Date: Oct 2006
Thanks for the reply, this has been very helpful! I did not realize that one of the inputs on the IR2011 was inverted that is why I was using that comparator. For the output LC filter how do I size the inductor?

P.S.
This amp will be used purely for a subwoofer @ less than 120hz
  Reply With Quote
Old 10th November 2007, 11:20 PM   #5
thefish is offline thefish  United States
diyAudio Member
 
Join Date: Oct 2006
Can anyone confirm that one of the inputs on the IR2011 is inverted? I have found no other mention about this and looking at some other amp schematics on the net leads me to think that is not correct.

Here is my new schematic, what do you all think? I have simulated it using opamps instead of the twin IR2011 drivers (using TI-TINA does not allow the IR2011) and it looked ok to me.
Attached Images
File Type: jpg amp-1-build.jpg (76.2 KB, 1450 views)
  Reply With Quote
Old 11th November 2007, 12:01 AM   #6
diyAudio Member
 
raidfibre's Avatar
 
Join Date: Jan 2003
Location: Boston, MA, USA
Send a message via AIM to raidfibre
It looks like it would work. What you should do is start at a lower voltage and a lower frequency (12v and 10kHz) and ramp up the frequency and power from there.

The diodes in the IR2011 drivers must be rated for at least 50v and should be schottky or very fast recovery.

The Vb-Vs capacitor should be at least 10 times the Cgs capacitance of the MOSFET. I usually use 1uF ceramic caps.

The Vcc caps on the IR2011 should be at least a few uF ceramic as well. Keep every trace having to do with the gate drive as short as possible.

I like to put 15v zener diodes from the gate to source of the MOSFETs to try to circumvent spikes.

I'm not sure if you will be able to drive your MOSFETs up to 200kHz with those gate drivers. They don't sink very much current. I would use 10 ohm gate resistor to start and you will probably end up wanting to put ferrite beads on the FET gate pins to get cleaner switching waveform.

Good luck!
__________________
--
Martin K
  Reply With Quote
Old 11th November 2007, 12:16 AM   #7
thefish is offline thefish  United States
diyAudio Member
 
Join Date: Oct 2006
Quote:
Originally posted by raidfibre
It looks like it would work. What you should do is start at a lower voltage and a lower frequency (12v and 10kHz) and ramp up the frequency and power from there.

The diodes in the IR2011 drivers must be rated for at least 50v and should be schottky or very fast recovery.

The Vb-Vs capacitor should be at least 10 times the Cgs capacitance of the MOSFET. I usually use 1uF ceramic caps.

The Vcc caps on the IR2011 should be at least a few uF ceramic as well. Keep every trace having to do with the gate drive as short as possible.

I like to put 15v zener diodes from the gate to source of the MOSFETs to try to circumvent spikes.

I'm not sure if you will be able to drive your MOSFETs up to 200kHz with those gate drivers. They don't sink very much current. I would use 10 ohm gate resistor to start and you will probably end up wanting to put ferrite beads on the FET gate pins to get cleaner switching waveform.

Good luck!
Thanks for your comments. I will do as you say and slowly ramp up the frequency and the power while watching it on my scope. If 200khz does not work 100KHZ should be ok since this is only going to be a bass amp. Cheers!

P.S.
I am a mechanical engineer by education/trade; I have worked with plenty of simple electronics but this is the first “complex” system I have tried to design.
  Reply With Quote
Old 14th November 2007, 04:41 PM   #8
diyAudio Member
 
Join Date: Sep 2007
thefish can u supply me with a schematic of your design. My email is kyu333@gmail.com. thanks and good luck with your project
  Reply With Quote
Old 14th November 2007, 04:41 PM   #9
diyAudio Member
 
Join Date: Sep 2007
Hello everyone I'm working on a triangle generator for a class D amplifier so far I tried the LM566(discontinued) and the NTE994m(discontinued) now this two are gone and I can't get anything that will work. I have tried the 8038 bt I cant get the 180Khz to 200Khz that I desired. Does anyone know what other options are out there?
  Reply With Quote
Old 14th November 2007, 04:49 PM   #10
diyAudio Member
 
raidfibre's Avatar
 
Join Date: Jan 2003
Location: Boston, MA, USA
Send a message via AIM to raidfibre
Is the problem distortion or what?
What amplitude are you trying to get?
__________________
--
Martin K
  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
How does Class D work? travis Class D 16 17th April 2009 10:49 PM
350.5 modding the amp to work in more class A jfrago Pass Labs 26 24th April 2008 05:26 PM


New To Site? Need Help?

All times are GMT. The time now is 01:22 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