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Old 23rd December 2001, 03:55 AM   #1
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Default Linear Tech. LT1166 chip

Anybody tried using this auto-biasing chip for a power Mosfet output stage? It controls the currents in the top and bottom Mosfets so that their current product is a constant. Elliminates the need for a bias adjustment and automatically controls crossover for minimum distortion. The technical press reviews were pretty good a few years ago when it first came out, but I haven't seen any published power amplifier designs using it. I purchased a few LT1166 chips recently to try out in a design, but haven't gotten around to it yet. The app. notes for it show it used in an Op. Amp. controlled power amp., but it appears to be perfect for a fully discrete amplifier too. Won't work with lateral mosfets easily though due to operational voltage requirements. But the usual hexfets or vertical mosfets are cheaper and higher current anyway.
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Old 24th December 2001, 05:55 PM   #2
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Default Lt 1166

This chip also has built in optional single or dual slope output overload protection. It really makes designing your own amplifier a breeze.
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Old 24th December 2001, 06:05 PM   #3
PH104 is offline PH104  United States
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I haven't tried these myself, but I have read of others measuring some high frequency distortion when using the LT1166.

I have used the output error correction scheme published by Hawksford in JAES some years ago with good success.

I'd be very curious to hear your opinion if you give the LT part a try.

Phil
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Old 24th December 2001, 06:38 PM   #4
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Default amp design

Thanks for the tip! I am thinking of using the chip in an amp. design using an output linearization scheme by Steve Gunderson in JAES Vol 32 No. 6 1984 June pg 430. This approach uses a cascode stage in the voltage amp. stage to provide a connection point for the compensation capacitor which is linearly related to the output rather than to the usual output base or gate drive signal. The cascode's base is slaved to the output. Another interesting variation is apparent if one looks at Seals Optimos Amp. which slaves the cascode to a ratio of the output signal but doesn't impliment the Gunderson compensation pickoff point. Gundersons idea's main attraction is a claimed reduction in high frequency distortion where feedback is least effective, so will be interesting to see if the aforementioned high frequency distortion is cleaned up or not when using the LT1166 chip too.
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Old 24th December 2001, 06:56 PM   #5
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Both the schematics for this and the Hawksford circuit
bear a lot of similarity to the original dynamic bias patent
# 3,996,228 from 1976.

I have to say from looking at the data sheets for the LT1166
that I wouldn't be inclined to use it based on performance,
which doesn't seem to be all that great.
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Old 24th December 2001, 07:13 PM   #6
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Thanks for the additional info. I have a copy of that Gunderson article somewhere and will have to look it again in a different light. I'm going to be building an amp using a topology that I think is similar to Gunderson's example (if my memory is right). That amp won't be for music but for a synthesized AC power supply, but the experiment would be fun and educational.

Nelson
Your right! I had seen your patent before (at least the first page from your website) but never noticed the similarities or even thought to compare the different schemes until you pointed this out. Is a complete version of that patent available? And please let me add my thanks to all the others for your new DIY website and all the information you have published over the years for DIYers.

Phil
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Old 24th December 2001, 09:21 PM   #7
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www.uspto.gov

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Old 24th December 2001, 10:09 PM   #8
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Old 26th December 2001, 06:24 AM   #9
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Nelson,

I believe your dynamic bias patent should be 3,995,228??
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Old 26th December 2001, 09:34 PM   #10
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Doh!
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