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Class D Switching Power Amplifiers and Power D/A conversion

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Old 29th March 2006, 03:24 PM   #11
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This is my final circuit ....
do i have to use the dead time control ??
because i feel it doesn't has any advantage for me.
I really feed the dead time circuit will break the square waveform of input of IR2110.
Thanks for your circuit ... really ....
It looks only the level shift is different from mine.
do you think my level not good or something else ???
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Old 29th March 2006, 04:11 PM   #12
zkaiser is offline zkaiser  Yugoslavia
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Quote:
do you think my level not good or something else ???
yes you actually passing a way more voltage into ir2110 inputs, than it is supposed, it is true that you have resistor for voltage drop, but if input stage of schmit trigger in ir2110 doesnt have clamping diodes and it does not you risking burning it out or some latchup issues. So beware what u doing with maximal ratings of
ICs


Best regards
Zeljko Kaiser
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Old 29th March 2006, 11:52 PM   #13
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you mean the input signal level of ir2110 too high.
But i probe the signal , It only get about 12Vpp square wave from -55v to -43v.
It that in save range ???
Because i think that is ok ...
So , i do not doing anything to prevent it. Like you see in my circuit.
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Old 30th March 2006, 06:03 AM   #14
zkaiser is offline zkaiser  Yugoslavia
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well, baybe is problem in pcb layout, and do you have 470uF caps very near the mosfets, if not you should use some low esr at least 63V and if its not bugging for you it would be nice to measure all relevant wave forms, like triangle ramp voltage
output of u12a (pin 1)
outputs of u13 (pin 7,8)
inputs of ir2110 (lo,hi)
outputs of ir2110 (lo,hi and Vsource input)
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Old 30th March 2006, 12:51 PM   #15
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Quote:
Originally posted by zkaiser
you should use some low esr at least 63V

I layout a copper for mosfet output.
The C25 just near by the output of the mosfet pcb layout.
i don't think does it near or not ....
you said i have to use a low esr cap ,, at least 63v...
does it just need only 25V ???

I will probe these waveform and post them later....

now i only do the current limit circuit ...
No DC protect and clipping protect...
do you think it that need ???
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Old 1st April 2006, 03:55 AM   #16
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Question :
could someone tell me , if +/-RAIL = 55V,,,
In normally , the output signal that after LC output filter , will i get how much Voltage Peak to Peak ???
Now , i only can get 80Vpp signal output
If output signal more big a little , it get clip and distrotion!!
And speaker will get strange sound ,,,
So , the output signal in normal , will get how many output amplitude ???
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Old 1st April 2006, 07:06 AM   #17
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Quote:
Originally posted by titanchen68
Question :
could someone tell me , if +/-RAIL = 55V,,,
In normally , the output signal that after LC output filter , will i get how much Voltage Peak to Peak ???
Now , i only can get 80Vpp signal output
If output signal more big a little , it get clip and distrotion!!
And speaker will get strange sound ,,,
So , the output signal in normal , will get how many output amplitude ???
Have a look a the section on Class D amplifiers on

http://www.genomerics.org

Part of it deals with deadtime distortion and later explains how deadtime will introduce the effect you are describing if you use feedback.

DNA
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Old 1st April 2006, 02:33 PM   #18
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Quote:
Originally posted by Genomerics


Have a look a the section on Class D amplifiers on

http://www.genomerics.org

Part of it deals with deadtime distortion and later explains how deadtime will introduce the effect you are describing if you use feedback.

DNA

Thanks for your reply.....
After i saw the content in that webside ,
It seems causing clamp the output of error-amp.
And Yes , i do clamping my output of pre-amp.
I limit the output of pre-amp to 75% of triangle wave amplitude.
Because i see a paper writen by IRF , It has a example.
It set the input to 75% of triangle wave amplitude.
So , i think that is causing by it....

doesn't the deadtime only effect the THD??
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Old 1st April 2006, 04:20 PM   #19
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Quote:
Originally posted by titanchen68



Thanks for your reply.....
After i saw the content in that webside ,
It seems causing clamp the output of error-amp.
And Yes , i do clamping my output of pre-amp.
I limit the output of pre-amp to 75% of triangle wave amplitude.
Because i see a paper writen by IRF , It has a example.
It set the input to 75% of triangle wave amplitude.
So , i think that is causing by it....

doesn't the deadtime only effect the THD??
Clamping the input to the error amplifier by clamping your pre-amp input may or may not achieve the desired result. You need to take the gain from pre-amp in to error amp out into account and then the feedback will mess things up as well.

For the moment I'd say you need to apply the clamp around the error amplifier to gaurantee things. Unfortunately getting an accurate clamp may prove to be difficult. I've used ideal zeners in my models but real ones are.... rubbish.

Since deadtime affects the transfer function then it does affect the distortion. The low level effect didn't seem to upset the feedback..... I'll have to go and check that now, bum.

However the transition from deadtime to no deadtime at high outputs appears to be much nastier. Bear in mind that when these things happen the gain of the power stage (its transfer function) changes and that upsets the overall feedback. If you have designed for one set of circumstances and they change then there is a good chance that things will fall over.

Mind you, as I say.... I'm making this up as I go along.

Just for the fun of it one thing you might try is to re-connect the outputs of your comparator to the level shifting transistors. Tie the base of the transistors to signal ground. Then drive the emitters via your 1K resistors, R32 and R42, from the comparator outputs.

Watch out because that loses a stage of inversion so you'll have to swap the inputs on the IR2110. However it becomes a common base connection which should be much faster than what you have at the moment.

DNA
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Old 2nd April 2006, 08:03 AM   #20
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Thanks a lot ....
So , if the clamp circuit put in the error-amp will get better than clamp in the pre-amp , right ???
You said it will not getting an accurate clamp by using zener, but it seems to be a good ideal for now.

I still do not understand the different between the clamping around the error-amp and in the pre-amp.
Isn't it to clamp the input signal not exceed the triangle wave amplitued ??

what do you feel that i clamp the input signal amplitude to be 75% of triangle wave amplitude ??
Is it too lower or higher???
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