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Old 21st September 2011, 11:04 PM   #11
Zaaphod is offline Zaaphod  United States
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Originally Posted by Frank Berry View Post
You could add an audio transformer to feed the input of the TPA3122D2.
The secondary of the transformer, feeding the L and R inputs of the TPA3122D2, must have a center tap which should be connected to the analog grounds of the TPA3122D2s.
I'm sure that would work, I just want to try to keep the cost down on these, because I want to make a lot of them. Since my signal is defiantly floating, could I do something like 2 resistors to ground like this schematic?
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Old 21st September 2011, 11:32 PM   #12
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Perhaps this would be better with a HF filter capacitor. I saw this when doing a search for differential receiver, but it was going into an op amp, and did not use the ac coupling capacitors.
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Old 22nd September 2011, 01:17 AM   #13
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That sounds like a really cool idea! Could I just use my TPA3122D2 as a PWM signal generator? or does that require the load to operate correctly? What would I use for my remote power stage? could I just use some mosfets or would I need an op amp or something?
This whole idea sounds like a lot of fun... perhaps something like this? perhaps there is some kind of power mosfet half bridge device I could use?
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Old 22nd September 2011, 05:45 PM   #14
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Sort of like that, actually one double-output comparator can be a good enough PWM modulator.
For a ready-made half bridges you can try some low side drivers, like TC4429, they are powerfull enough power stages themselves for below 20V supplies.
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Old 22nd September 2011, 11:19 PM   #15
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Sort of like that, actually one double-output comparator can be a good enough PWM modulator.
For a ready-made half bridges you can try some low side drivers, like TC4429, they are powerfull enough power stages themselves for below 20V supplies.
Could you please tell me how I could use a double output comparator to make a PWM modulator?

I had a look at the TC4429, that looks really cool. Does anyone happen to make a dual version of something like that? I was fixing to order some parts soon, I think I may get a few of those to play with.. this whole idea of sending the PWM signal down the twisted pair instead of differential audio really has me fascinated.
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Old 22nd September 2011, 11:27 PM   #16
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I had a look at the TC4429, that looks really cool. Does anyone happen to make a dual version of something like that? I was fixing to order some parts soon, I think I may get a few of those to play with.. this whole idea of sending the PWM signal down the twisted pair instead of differential audio really has me fascinated.
They come in 8 pin packages so no big deal using two.
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Old 23rd September 2011, 07:42 AM   #17
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Could you please tell me how I could use a double output comparator to make a PWM modulator?
Try a hysteresis-based relaxation oscillator.
File:OpAmpHystereticOscillator.svg - Wikipedia, the free encyclopedia

Just feed one of the "grounds" with audio signal and use differential output to drive the UTP (sinlge output should work too).
Any simulator will help you find the values for passives to get required switching frequency and input sensivity, around 10 minutes of trials and errors.
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Old 23rd September 2011, 03:15 PM   #18
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How about something like this using the TC4420?
That op amp oscillator looks interesting, and very simple. When I looked up PWM methods, I saw a lot of things like running a triangle wave into one input and the signal into the other one.. but then I need a triangle wave generator too.

I can't seem to find a double output comparator, any suggestion on a chip for that? I am guessing it is like a regular op-amp but with both inverted and non-inverted outputs.
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Old 23rd September 2011, 04:31 PM   #19
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Some information I came across... the microchip website suggests MCP1407 instead of the TC4420. I guess it's the new version of it. Looks like it is slightly faster and wider temperature range. I checked the prices on Digikey, the TC4420 is $1.72, and the MCP1407 is only $1.06, so it's a bit less expensive as well.

I also came across this application note

http://ww1.microchip.com/downloads/e...tes/00763c.pdf

about latchup of the driver.. it mentions this could happen driving and inductive load, which I would be doing. It says to put reverse biased diode clamps from both the input and output to each power supply rail. Does anyone have any experience with this? Do I need these on my inputs since I am using optocouplers?
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Last edited by Zaaphod; 23rd September 2011 at 04:55 PM.
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Old 23rd September 2011, 06:36 PM   #20
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Originally Posted by Zaaphod View Post

I can't seem to find a double output comparator, any suggestion on a chip for that? I am guessing it is like a regular op-amp but with both inverted and non-inverted outputs.
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