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Old 14th January 2005, 03:57 PM   #1
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Default schematic of my future D amp for the pb12

Here is my simplified D amp, sourced from the IR AUDAMP.

There is no protections on it. Its the prototype.
No components values on this schematic yet...

It will be supplied with a 37v rail, on a 4 ohm load. IR papers suggest as high as 95% eff with this kind of amp, so,
(0.707x37)/4=171w...-5%=162w rms...that will be good enough as a first real D amp project.
Board will be able to accept 60v rails to go close to the 500w claimed by IR.

Any comments?

thanks group.
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File Type: pdf cam output.pdf (55.9 KB, 2086 views)
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Old 14th January 2005, 05:24 PM   #2
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Default Re: schematic of my future D amp for the pb12

Quote:
Originally posted by pat allen
Here is my simplified D amp, sourced from the IR AUDAMP.

There is no protections on it. Its the prototype.
No components values on this schematic yet...

It will be supplied with a 37v rail, on a 4 ohm load. IR papers suggest as high as 95% eff with this kind of amp, so,
(0.707x37)/4=171w...-5%=162w rms...that will be good enough as a first real D amp project.
Board will be able to accept 60v rails to go close to the 500w claimed by IR.

Any comments?

thanks group.
Hello,

Very nice

It's easier to follow if you use VCC and VEE for the op amp stuff, VSS for positive high voltage (output stage) and VDD for negative output stage.

Might consider removing those resistors in the bootstrap circuit. Especially the one between the diode and bootstrap capacitor.

Check out the datasheet for the IR2011, they don't show any resistors. You want it to be able to refresh the cap really fast and hold a charge as long as possible.
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Old 14th January 2005, 05:28 PM   #3
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that resistance is there into the original schematic of the IRAUDAMP.
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Old 14th January 2005, 06:30 PM   #4
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Default Re: Re: schematic of my future D amp for the pb12

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Originally posted by classd4sure


Hello,

Very nice

It's easier to follow if you use VCC and VEE for the op amp stuff, VSS for positive high voltage (output stage) and VDD for negative output stage.

Might consider removing those resistors in the bootstrap circuit. Especially the one between the diode and bootstrap capacitor.

Check out the datasheet for the IR2011, they don't show any resistors. You want it to be able to refresh the cap really fast and hold a charge as long as possible.


in my use of electrical terms for my job, i am used to see VDD as the + source while VSS is the return or ground...
Microchip, Ti, Atmel use it that way...(microcontrolers that i work with all day)
They were labeled with the voltage before, i tougt it was easier like that, it is a personal choice i think.

The resistor you talked about is a very small value, 10 ohm.
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Old 14th January 2005, 09:27 PM   #5
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Default Re: Re: Re: schematic of my future D amp for the pb12

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Originally posted by pat allen




in my use of electrical terms for my job, i am used to see VDD as the + source while VSS is the return or ground...
Microchip, Ti, Atmel use it that way...(microcontrolers that i work with all day)
They were labeled with the voltage before, i tougt it was easier like that, it is a personal choice i think.

The resistor you talked about is a very small value, 10 ohm.

You're right I meant to say VDD+ VSS-.

I just found it confusing due to there being multiple sources.. meant no insult of course.

Please read page 9:

http://www.powerdesigners.com/InfoWe...ive/an-978.pdf

A bootstrap cap even so big as 100uF would be better too.
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Old 14th January 2005, 09:58 PM   #6
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Hi, please look at the .pdf, if not done. There is the original schematic of the IRAUDAMP. I have not invent anything, it is a copy-paste of theirs desing.
Please, look at it, maybe they are wrong??
They sell this amp for around 600$ (2 channel+protections on board.)
thanks.

IRAUDAMP ORIGINAL PAPERS
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Old 14th January 2005, 10:48 PM   #7
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Hi Pat,

I know.. I know, it's there demo board, I've seen it.

The app note I linked to are discussing these very drivers though.
Guess who the app note is by?

Here's what's likely an updated version of that same app note:

http://www.irf.com/technical-info/appnotes/an-978.pdf

They took that line out, yet show the same IC and everything, changed their minds? I think so, all the same..... let's think about.

Some of their diagrams (most of them) do NOT show this resistor, the odd one does.

This app note discusses it more:

http://www.irf.com/technical-info/designtp/dt04-4.pdf

600$..... Doesn't make it right.

I'd use a cheap electrolytic 100uF bypassed by a small low ESR... ceramic?

It's only ever going to be charging from 12Volts there's no great need to limite the current and the ESR should do something for it.

If you really feel the need for a resistor though, I'd try a few ohms but placed before, the diode, not after it. (R49?) removed.

But you know.. you can experiment.

They selection of cap size is pathetically small though, minimum calculated ? It should be 10X that at least.
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Old 15th January 2005, 01:42 AM   #8
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Hi, thanks for the links, they are very helpfull. I didnt realisez how far they gives equations to optimise every aspects of this topology.

I have done some average calculation with the formulas for the bootstrap cap, it always came very small, below 1uf, considering the esr and frequency of the overall switching gizmo...anyway, i build it as a demo test prototype to eventualy make it burn on its limit...who knows, maybe it works good as is ??

I realy plan to do several test on this board, as well as many components swaping, i will try to optimise it myslef with the help of the app notes. Scope snap shots are on call to show them to all of you.

As for the caps on the board, yes they are small, but they claims that they are not to store or to filter the ac from a transfo, and one have to build its own regulated power supply with enough caps to power up theses boards..

I do have 6x 34 800uf caps and a 60v ct 12 amp toroidal transfo for the task...it should be good enough for the tests...

thanks.
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Old 15th January 2005, 01:57 AM   #9
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Hi,

You know how those OEM's like to pinch every penny right?

Those calculations give you an estimate of the bare minimum requiremed value, good design practice say's take that value X10, other app notes say the bigger the better (less odds of overcharging, less ripple((less ripple.... better drive to the mosfet, don't want your Rdson varying with duty cycle right)))...

I'm using 100uF electrolytic in my little amp, paralleled with a 100nF ceramic across the 12V zener. Works fine. Up to you.

You could also make the driver /output stage on a seperate PCB, that way you can try other kinds of amps out with it too.
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Old 15th January 2005, 03:06 AM   #10
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Quote:
Originally posted by pat allen
Hi, please look at the .pdf, if not done. There is the original schematic of the IRAUDAMP. I have not invent anything, it is a copy-paste of theirs desing.
Please, look at it, maybe they are wrong??
They sell this amp for around 600$ (2 channel+protections on board.)
thanks.

IRAUDAMP ORIGINAL PAPERS
IR have two different version of IRAUDAMP1 on its site.

one have a capacitor paralled at the input of the integrator:
http://www.irf.com/product-info/audi...sdtutorial.pdf
one not:
http://www.irf.com/technical-info/re.../iraudamp1.pdf

the appearence is also slightly different:
http://www.irf.com/graphics/nr/nr040826.jpg
v.s.
http://www.irf.com/technical-info/re.../IRAUDAMP1.jpg

Another thing is, there seems to be no hystresis,so it may be using 180 deg phase shift to oscillate like UCD's. (though the feedback is taken from switching stage, not filtered output)
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