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Old 21st March 2006, 07:09 PM   #1
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Default Re-thinking of my D-amp...full bridge or not.

Hi. I was just thinking about full bridge topo, and found that i could be very easy to implement this on what i did...

Can someone confirm.

the added parts are in the shaded box. It just mimicks what the already amp does, but inverted...
Could it be that easy??

Forget the rest of the schematic, it is not updated.
If it works, it will require some modifications to the protection board and the output relay.

thanks

Pat Allen
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File Type: pdf test.pdf (85.9 KB, 178 views)
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Old 23rd March 2006, 07:34 AM   #2
SSassen is offline SSassen  Netherlands
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That's not going to work well if low harmonic distortion is what you're after, the 2nd half of the bridge is just 'floating' with no feedback whatsoever. You need at least a summing amplifier to add the two output signals together and make the signal single ended for you single-ended front-end.

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Sander Sassen
http://www.hardwareanalysis.com
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Old 23rd March 2006, 12:46 PM   #3
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Hi, thank you for your reply.

i was just thinking about something simple to make bigger power from a minimalistic way.

I didnt find any schematics of full bridge Damp that uses the LT driver.
any idea?

thanks

Pat Allen
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Old 23rd March 2006, 12:48 PM   #4
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Hi Pat,

I already gave you a hint:

Quote:
You need at least a summing amplifier to add the two output signals together and make the signal single ended for you single-ended front-end.
Best regards,

Sander Sassen
http://www.hardwareanalysis.com
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Old 23rd March 2006, 01:09 PM   #5
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Hi.

yes, i saw it, thank you.

Im gona try something...
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Old 23rd March 2006, 02:01 PM   #6
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Hi.

I have looked at my schematic and came to this conclusion:

To add feedback for the second bridge, it will require as much parts as to just build two completely separate amps...no gains there...

There is no way to keep the lower bridge totaly independant of the analogue signal...someone may want to argue about this.

i came on a app note from LT about a full bridge application with a LT1160/1162 (page 13). I studied it a bit.

I found two interesting parts, wich are LT1016 and TC4428.

I will continue to investigate anyway

thanks for any kind of inputs. I think it could be cool to have an open project for a full bridge D amp that uses the LT driver. I think it could end to something very interseting and simple.

Pat Allen
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Old 23rd March 2006, 02:18 PM   #7
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Hi Pat,

It is much simpeler, just use a single opamp as a summing amplifier and take the feedback off of the two outputs, the summed signal can then be fed back into the feedback loop as you normally would. Hence the summing amplifier replaces the resistor at the output that is now used in the feedback loop of the half bridge.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com
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Old 23rd March 2006, 02:43 PM   #8
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Quote:
Originally posted by SSassen
Hi Pat,

It is much simpeler, just use a single opamp as a summing amplifier and take the feedback off of the two outputs, the summed signal can then be fed back into the feedback loop as you normally would. Hence the summing amplifier replaces the resistor at the output that is now used in the feedback loop of the half bridge.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com


Summing amplifier????
Sum of both outputs is more or less zero!
I would guess a difference amp would be the right thing.
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Old 23rd March 2006, 02:44 PM   #9
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coming from you it sound so simple

questions if you dont mind...

the resistor in the feedback loop sets the gain of the amp.
how the gain will be set if an opamp is inserted into the feedback loop? you sayd to remove the resistor feedback.

the feedback is taken before the lc filter, does it affect what you are saying? how the opamp will see the voltage swing?

i took what you sayd word to word and inserted it into my test sch.


I carefully inverted the added half signal of the bridge to the amp, hence the signal that goes to the inverted input of the opamp.

the value of the resitors are randomwly choosen for now.

thanks

Pat Allen
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File Type: pdf cam output.pdf (60.1 KB, 86 views)
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Old 23rd March 2006, 02:50 PM   #10
SSassen is offline SSassen  Netherlands
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ChocoHolic,

Quote:
I would guess a difference amp would be the right thing.
Correct, a common confusion of nomenclature, now where did I put my coffee? Pour me another!

Best regards,

Sander Sassen
http://www.hardwareanalysis.com
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