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Ultra-High performance OpAmp-based MOSFET Power Amp
Ultra-High performance OpAmp-based MOSFET Power Amp
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Old 7th September 2005, 11:57 AM   #11
tlf9999 is offline tlf9999  United States
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Quote:
Originally posted by amplifierguru
Howsat? Looks more like 12mA to me given 15V supplies for the chip - a lot for the following stages to deal with and also your chip supplies.
Because the opamp isn't swinging 10v in either direction. its actual gain is much lower than that.

the supplies are 12v actually.

here is the current through R15.
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Old 7th September 2005, 12:29 PM   #12
tlf9999 is offline tlf9999  United States
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Quote:
Originally posted by Eva
That soft-clipping behaviour is just a side effect of very low open-loop gain.

you are right about it: open loop gain is about 100x.
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Old 7th September 2005, 04:05 PM   #13
dimitri is offline dimitri  United States
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I think something like this:
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Old 7th September 2005, 04:07 PM   #14
dimitri is offline dimitri  United States
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Transfer characteristic and diff gain for the output stage vs Rbias=10...50kOhm
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Old 7th September 2005, 05:01 PM   #15
Mr Evil is offline Mr Evil  United Kingdom
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Default Re: Ultra-High performance OpAmp-based MOSFET Power Amp

Quote:
Originally posted by tlf9999
a) insufficient voltage gain for high power applications: opamps run off low rail voltages...
Try an OPA445. They will run off up to +/-45V and are surprisingly good quality for a specialized op-amp. I've use them to make hybrid amps similar to yours before with good success.
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Old 7th September 2005, 05:17 PM   #16
dimitri is offline dimitri  United States
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OPA445 has 40db of gain @ 20kHz and costs $9.5 (digikey)
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Old 7th September 2005, 05:23 PM   #17
tlf9999 is offline tlf9999  United States
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Default Re: Re: Ultra-High performance OpAmp-based MOSFET Power Amp

Quote:
Originally posted by Mr Evil

Try an OPA445. They will run off up to +/-45V and are surprisingly good quality for a specialized op-amp. I've use them to make hybrid amps similar to yours before with good success.

thanks. you can also use 541/549 or those lm chips.

The purpose of this exercise is to find out how to expand an opamp's voltage and current output capability.
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Old 7th September 2005, 07:01 PM   #18
mzzj is offline mzzj  Finland
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Default Re: Re: Re: Ultra-High performance OpAmp-based MOSFET Power Amp

Quote:
Originally posted by tlf9999



thanks. you can also use 541/549 or those lm chips.

The purpose of this exercise is to find out how to expand an opamp's voltage and current output capability.
How about bipolars and CFP output stage with some gain like 4x?

might call this one with CFP as a "ultra-stable", if yours is "ultra-high performance"
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Old 7th September 2005, 08:05 PM   #19
nuvistor is offline nuvistor  United States
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Default Re: Re: Re: Ultra-High performance OpAmp-based MOSFET Power Amp

Quote:
Originally posted by tlf9999
The purpose of this exercise is to find out how to expand an opamp's voltage and current output capability.
Bootstrap the op amp power pins from the op amp output for more voltage output range?

EDN article

LTC Magazine June 1994 p. 20
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Old 7th September 2005, 08:42 PM   #20
tlf9999 is offline tlf9999  United States
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Default Re: Re: Re: Re: Ultra-High performance OpAmp-based MOSFET Power Amp

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Originally posted by nuvistor


Bootstrap the op amp power pins from the op amp output for more voltage output range?

EDN article

LTC Magazine June 1994 p. 20

those are the ones I was thinking about. But I wanted to get a little "creative", .
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