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Old 4th March 2013, 02:02 AM   #1
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Default RGN and RGP after RQ?

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RGN and RGP after RQ?
what if an another output pair added does it require RQ again?
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Old 4th March 2013, 10:02 PM   #2
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The purpose of the gate resistor is to isolate the gate capacitance from the driver so yes,
it always has to be duplicated for each gate the driver feeds. If you read a few other threads
here, you'd soon realise that this how all multiple Mosfet output arrays are arranged.

Seeing as you've already looked at some commercial Mosfet designs such as Aussie Ampliers',
I'm quite sure you know this already. If you're serious about learning something worthwhile
and pieced together to make useful sense of the topics, read Bob Cordell's book, which goes
into Mosfet amplifier designs with more than average detail and explanation.
Designing Audio Power Amplifiers: Bob Cordell: 9780071640244: Amazon.com: Books
At that bargain price, think how much you'll save on bad ideas, burn-outs and waiting for replies.
It might also mean you don't need to start a new thread every time you have a moment of doubt.
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Old 4th March 2013, 10:45 PM   #3
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Sorry, missed RQ in your question. It would be a guess but if you duplicate that between subsequent N/P pairs,
there is bound to be trouble with oscillation. My preference would be not to fit it, even if there is benefit for a single pair.
There are fancier techniques that are probably better there.
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Old 5th March 2013, 05:47 AM   #4
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Gate resistors should be repeated (one per gate). Depending on the predriver circuit you may also need to worry about capacitively loading it. With multiple output transistors and the associated routes to the gates and close proximity gate resistors you might consider putting a smaller resistor directly on the predriver outputs (can always short them out).
Not sure of the function of RQ, I suspect it may be needed when in mute, from the simplified schematic (not familiar with the part in general) it may be serving to keep the predriver outputs biased as the vas current is reduced. If so then just one of these before the gate stoppers would suffice.

Thanks
-Antonio

Last edited by magnoman; 5th March 2013 at 06:01 AM. Reason: RQ typo
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Old 5th March 2013, 05:52 AM   #5
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Quote:
Originally Posted by Ian Finch View Post
Sorry, missed RQ in your question. It would be a guess but if you duplicate that between subsequent N/P pairs,
there is bound to be trouble with oscillation. My preference would be not to fit it, even if there is benefit for a single pair.
There are fancier techniques that are probably better there.
RQ i think using one is fine but for every gate there should be a resistor asusual... but I think RQ should come before the gate resistor the schematic shows it as after the gate resistor..
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Old 6th March 2013, 12:35 AM   #6
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www.ti.com/lit/an/snaa058a/snaa058a.pdf
The link is to TI's app. note for the LME49830, which is probably the actual matter here. It includes a muting app. but no RQ anywhere within sight. Perhaps because the original Natsemi team is not around to update with comments, the designs are a bit old but I'm not convinced about RQ. If it's better before the gate stoppers, then surely it would also be for the single pair schematic of the OP.
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Last edited by Ian Finch; 6th March 2013 at 12:38 AM.
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Old 6th March 2013, 01:55 AM   #7
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its in the datasheet...
http://www.ti.com/lit/ds/symlink/lme49830.pdf
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