High speed comparator

bigbulb · 5th April 2005, 04:06 PM

Hi Guys,
I'm designing a self oscillating class d amplifier, with feedback from the mosfet.
Can you guys suggest a good comparator other than LM311, LM319? and I had search for self oscillating class d amp and found thet most are half bridge. may I know how to use full bridge for self oscillating? (2 output from masfet output stage, output from full bridge is float from ground)

regards,
Bigbulb

sovadk · 5th April 2005, 11:17 PM

Hi I use LMV7239 by National Semiconductors. It's very fast and best of all, it has a push-pull output configuration.
I know that maxim makes a lot of fast comperators, if that can help.

www.maxim-ic.com
www.national.com

bigbulb · 6th April 2005, 01:03 AM

Thanks sovadk.

I still searching for self osc type of class d in full bridge configuration. I had build the half bridge one and wish to try full bridge. Can't figure out how's the feedback connection, since the speaker output is floating. Please help!

tiki · 7th April 2005, 08:42 PM

If you understand German a bit, you may want to give this thread a try.
At least the user Beobachter develops a so called (by himself) SODFA as a full bridge version with pre filter feedback. He posted links to the schematics too.
Regards, Timo

bigbulb · 9th April 2005, 01:11 PM

Thanks Tiki for the link!

classd4sure · 11th April 2005, 05:45 AM

You can take it differentially across the load, then use a diff amp to convert to single ended (ugly) or be really slick and keep it fully differential, subtract with differential input, like UCD.

You might want to start with a half bridge though, you'll cook less mosfets getting through the ol learning curve that way.

If you go for the fully differential idea you won't even need to change much of anything to go with a full bridge later on.

I believe Linear Technologies has some insanely fast comparators and offer some of them with differential outputs as well, might want to have a look at their selection.

Cheers

Kenshin · 17th September 2005, 06:37 AM

LM319 has two compararors per chip. Now use one chip in double channel UcD (or any other self-osc configuation), one comparator for a channel.

Would the parastic coupleing (via inside or via supply railes) mix two switching frequencies and cause the "whistling" problem?

Do I need to use one LM319 chip per channel (and waste half of them)?

Jaka Racman · 17th September 2005, 07:04 AM

Hi Kenshin,

I would not even recommend that you put both amplifiers on the same PCB if you intend to use them for audio. I once used three LT1394 comparators on the same board, and noise level was not Hi-Fi. But for motor control (intended application) it was OK. There was no whistling since this was a clocked design.

Best regards,

Jaka Racman

Kenshin · 21st September 2005, 12:24 PM

put different amplifiers on different board... would it cause more noise from grounding?

classd4sure · 23rd September 2005, 10:29 PM

Just view them as two lines interconnecting at a star point beyond the amps themselves.

5th April 2005, 04:06 PM	#1
bigbulb diyAudio Member Join Date: Aug 2004 Location: klamazoo	High speed comparator Hi Guys, I'm designing a self oscillating class d amplifier, with feedback from the mosfet. Can you guys suggest a good comparator other than LM311, LM319? and I had search for self oscillating class d amp and found thet most are half bridge. may I know how to use full bridge for self oscillating? (2 output from masfet output stage, output from full bridge is float from ground) regards, Bigbulb

17th September 2005, 06:37 AM	#7
Kenshin diyAudio Member Join Date: Jan 2005 Location: China	LM319 for double channel UcD LM319 has two compararors per chip. Now use one chip in double channel UcD (or any other self-osc configuation), one comparator for a channel. Would the parastic coupleing (via inside or via supply railes) mix two switching frequencies and cause the "whistling" problem? Do I need to use one LM319 chip per channel (and waste half of them)?

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5th April 2005, 11:17 PM	#2
sovadk diyAudio Member Join Date: Sep 2004 Location: Kaspar Sinding Meyer @ DTU in Lyngby	Hi I use LMV7239 by National Semiconductors. It's very fast and best of all, it has a push-pull output configuration. I know that maxim makes a lot of fast comperators, if that can help. www.maxim-ic.com www.national.com

6th April 2005, 01:03 AM	#3
bigbulb diyAudio Member Join Date: Aug 2004 Location: klamazoo	Thanks sovadk. I still searching for self osc type of class d in full bridge configuration. I had build the half bridge one and wish to try full bridge. Can't figure out how's the feedback connection, since the speaker output is floating. Please help!

7th April 2005, 08:42 PM	#4
tiki diyAudio Member Join Date: Feb 2004 Location: Dresden	If you understand German a bit, you may want to give this thread a try. At least the user Beobachter develops a so called (by himself) SODFA as a full bridge version with pre filter feedback. He posted links to the schematics too. Regards, Timo

9th April 2005, 01:11 PM	#5
bigbulb diyAudio Member Join Date: Aug 2004 Location: klamazoo	Thanks Tiki for the link!

11th April 2005, 05:45 AM	#6
classd4sure Account Disabled Join Date: Feb 2004	You can take it differentially across the load, then use a diff amp to convert to single ended (ugly) or be really slick and keep it fully differential, subtract with differential input, like UCD. You might want to start with a half bridge though, you'll cook less mosfets getting through the ol learning curve that way. If you go for the fully differential idea you won't even need to change much of anything to go with a full bridge later on. I believe Linear Technologies has some insanely fast comparators and offer some of them with differential outputs as well, might want to have a look at their selection. Cheers

17th September 2005, 07:04 AM	#8
Jaka Racman diyAudio Member Join Date: Dec 2002 Location: Slovenia	Hi Kenshin, I would not even recommend that you put both amplifiers on the same PCB if you intend to use them for audio. I once used three LT1394 comparators on the same board, and noise level was not Hi-Fi. But for motor control (intended application) it was OK. There was no whistling since this was a clocked design. Best regards, Jaka Racman

21st September 2005, 12:24 PM	#9
Kenshin diyAudio Member Join Date: Jan 2005 Location: China	put different amplifiers on different board... would it cause more noise from grounding?

23rd September 2005, 10:29 PM	#10
classd4sure Account Disabled Join Date: Feb 2004	Just view them as two lines interconnecting at a star point beyond the amps themselves.