class d design

bob123 · 11th February 2006, 05:23 PM

This is a design of a self oscillating amp with no need for a ouput filter if you dont mind a bit of EMI being splashed around the room. Any suggestions of how to improve this circuit would be more than welcome as i plan to build it or something similar in a week. Sorry for the croc clips but its SO easy.

The ouput trannies are actualy fets.

Any suggestions / comments?

myanmar · 13th February 2006, 01:29 PM

Hi Friend,

Do you know the slew rate of LM311?
http://www.fairchildsemi.com/ds/LM/LM311.pdf
In that datasheet
Response Time TRES Note 2 - 200 - ns
Note. 2. The response time specified is for a 100mV input step with 5mV over drive.

How can I calculate for slew rate in that datasheet?
Pls, explain me, if you can.
Because I am a starter.

For TL084 slew rate is not enough in my circuit.
classd woofer amplifier
Can I replace LM311 in my circuit instead of TL084?

I also want to test your circuit.
But alittle difficult to buy AND gate.
Can I change +/- 15V to +/- 50V in your design?
Because I want large POWER.

Bye.

bob123 · 13th February 2006, 02:01 PM

hi because the lm311 is not a linear device, and the output is either 1 or 0. There is not a slew rate that can be measured accuratly. Therefore the response time is what is used. This is the time it takes for it to go from one state to the other, 200ns is fine for this amplifier.

This schematic is just a concept and has not been tried or simulated in anything more accurate than crocclips, therefore i cannot assure you that it is correct.

I would suggest that you get swCAD III and build it on that.

As for the +-50v supply, A voltage level shifter would need to be added to allow the fets to switch, Dead time would need to be added because otherwise it would turn in to a mosfet killing machine.

I suggest you start off on a 10w - 20w amplfier first and then move on to more powerfull ones, because the difficulty level realy steps up when trying to use higher voltage rails than the op-amp output.

Rember that when using a voltage compairitor you need a resitor from +vcc to the output in order to get a voltage at the output!

The operational amplifier in the intergraitor needs to be quite fast as it needs to slew 0.7v for every oscillation. a voltage comp CAN NOT be used here.

As for the and gates, they are essential to the working of the circuit and cannot be removed.

You can only replace a opamp with a voltage comp if the opamp is open loop.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Class D amp design	Thys	Class D	1	20th July 2007 09:45 PM
Hybrid Class A / Class B design.	GK	Solid State	27	1st January 2007 02:30 AM
class H design	csl113	Solid State	5	23rd June 2006 05:53 PM
My 50W class A design!	PanzerLord	Solid State	90	11th August 2004 06:17 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

13th February 2006, 01:29 PM	#2
myanmar diyAudio Member Join Date: Feb 2006 Location: Yangon	Hi Friend, Do you know the slew rate of LM311? http://www.fairchildsemi.com/ds/LM/LM311.pdf In that datasheet Response Time TRES Note 2 - 200 - ns Note. 2. The response time specified is for a 100mV input step with 5mV over drive. How can I calculate for slew rate in that datasheet? Pls, explain me, if you can. Because I am a starter. For TL084 slew rate is not enough in my circuit. classd woofer amplifier Can I replace LM311 in my circuit instead of TL084? I also want to test your circuit. But alittle difficult to buy AND gate. Can I change +/- 15V to +/- 50V in your design? Because I want large POWER. Bye.

13th February 2006, 02:01 PM	#3
bob123 diyAudio Member Join Date: Jun 2004 Location: Southampton UK	hi because the lm311 is not a linear device, and the output is either 1 or 0. There is not a slew rate that can be measured accuratly. Therefore the response time is what is used. This is the time it takes for it to go from one state to the other, 200ns is fine for this amplifier. This schematic is just a concept and has not been tried or simulated in anything more accurate than crocclips, therefore i cannot assure you that it is correct. I would suggest that you get swCAD III and build it on that. As for the +-50v supply, A voltage level shifter would need to be added to allow the fets to switch, Dead time would need to be added because otherwise it would turn in to a mosfet killing machine. I suggest you start off on a 10w - 20w amplfier first and then move on to more powerfull ones, because the difficulty level realy steps up when trying to use higher voltage rails than the op-amp output. Rember that when using a voltage compairitor you need a resitor from +vcc to the output in order to get a voltage at the output! The operational amplifier in the intergraitor needs to be quite fast as it needs to slew 0.7v for every oscillation. a voltage comp CAN NOT be used here. As for the and gates, they are essential to the working of the circuit and cannot be removed. You can only replace a opamp with a voltage comp if the opamp is open loop.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)