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Old 19th December 2008, 07:56 PM   #1
Sponkii is offline Sponkii  Denmark
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Default Op amp pwm design

Any one who has a design on a class D amplifier based on opamps ??
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Old 19th December 2008, 11:59 PM   #2
Sponkii is offline Sponkii  Denmark
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Default Is it possible ?

Hey, i was wondering if it is possible to use som of following components, for a D-class?..


Mosfet:
http://docs-europe.electrocomponents...6b8097ae0f.pdf

Amplifier for triangle wave and comperating:
http://docs-europe.electrocomponents...6b80aa53c6.pdf

Possibly this comperator:
http://docs-europe.electrocomponents...6b80032b90.pdf

Or can i use this as a "all in one":
http://docs-europe.electrocomponents...6b80026a9e.pdf


i have mosfet drivers an fets..
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Old 20th December 2008, 10:02 AM   #3
Pafi is offline Pafi  Hungary
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You can use almost anything for class D. But why would you choose these? Your MOSFET limits supply voltage to 30 V, wich means approximately 24W @ 4 ohm. If you need only 24W, then there are truly one-chip solutions. And why would you use such an expensive OPA, when a comparator is cheaper and better?
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Old 20th December 2008, 10:55 AM   #4
GGEC is offline GGEC  China
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very very good, They are can use at D-class amp.
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Old 20th December 2008, 04:51 PM   #5
Sponkii is offline Sponkii  Denmark
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Default components

what i have calculated i can get around 80-100watt in to 8 ohm at 30V if i use bridge..

30V^2 = 900
900/8ohm = 112.5watt

as for the op amp, it is not That expensive..
but what do you want to recommend?
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Old 20th December 2008, 05:13 PM   #6
Pano is offline Pano  United States
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Hmmmm.... I don't think so.

You might squeek by with 50W RMS into 8 ohms with a 30V supply. That's not bad, plenty of power for most jobs. You'll need to keep the chips cool.
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Old 20th December 2008, 07:01 PM   #7
Sponkii is offline Sponkii  Denmark
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Default ...

okay..

i was thinking of half and full bridge.

what is the main factors that i should compare the N - P channel?

On resistance, rise/fall time ? and what is the margin max 10% off??..
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Old 20th December 2008, 09:40 PM   #8
Pafi is offline Pafi  Hungary
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Quote:
what is the main factors that i should compare the N - P channel?
It depends on the gate driver, power level, and the quality demand. N an P channel FET's are completely different, so you can't expect too much.

I think IRFZ24N and IRF9Z34N are well enough. I attached a simple schematic. In this circuit your OPA can be quite useful because of its high short circuit current. (But it's just an idea!) You have to change some values! (Gate-resistors and 100 ohm must be reduced significantly if you use AD818.)

Take special attention on supply decoupling, and ground plane, if you build it!
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File Type: gif switching_amp_by_pafi_2.gif (8.0 KB, 734 views)
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Old 20th December 2008, 10:32 PM   #9
Sponkii is offline Sponkii  Denmark
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Default reply..

Pafi..

I might have explained it wrong, how do i match a N and a P mosfet for a bridge ..

the schematic that you made, i guess it is self oscillating?..

i have already made a test breadboard. looks like the pic i attatched,

i just need to know, where and how to add "dead time" ??


the op amp i use right now is lm833n, the carrier is around 120khz..

when i connect my 8ohm speaker, it actually sounds great..
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Old 20th December 2008, 11:54 PM   #10
Pafi is offline Pafi  Hungary
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Quote:
I might have explained it wrong, how do i match a N and a P mosfet for a bridge
For a bridge? Why do you think it is different from matching for a half-bridge?

You explained your question well for the first time, but the answer depends on some unknown things, as I said. Don't bother, there are more serious other problems!

Quote:
the schematic that you made, i guess it is self oscillating?..
Yes.

Quote:
i just need to know, where and how to add "dead time" ??
Between gate-driver and FET, or between comparator and gate-driver if your gate driver has 2 channels. How? R||D, C

In any cases you must disconnect two gates from each other! And you need level shifting between gate-driver and FETs.

Quote:
when i connect my 8ohm speaker, it actually sounds great..
Where do you connect it, if power stage is "not yet tested"?
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