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Old 26th April 2006, 07:53 AM   #1
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Default Crackle !! can't solve ??

I use IR2110 to build a class-d amp.
But It always has Crackle sound , when output amplitude get clipping.
I don't have any ideal why it happen and don't know how to improve it ...
The class-d is different with class-ab , i know.
But why class-d amp get clip will occure the crackle ???
They were getting clip , but class-ab will not get crackle....
somebody said the crackle is normal ,, perhaps....
But can not we solve it or improve it ???
Or it is the disadvantage with class-d amp???

I use HIP4080 to build a class-d amp before and try to clip the output amplitude.
It get very stable ...
The amplitude can rise up to +RAIL and clip.
So , i think it has other way can do it .
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Old 26th April 2006, 09:51 AM   #2
Eva is offline Eva  Spain
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There are several reasons for "crackle sound" to be introduced when clipping:

- IR211x boostracp capacitor being drained too quickly and under-voltage lockout protection kicking in.

- The control loop can no longer control the output filter during clipping, so the filter will resonate at its natural frequency until normal operation is resumed. RC damping may improve that a bit, altough filter resonance should be chosen above the audio band to start with.

- Control loop instability. In practice, phase margin of systems using global feedback is reduced when the output comes very close to the rails, so careful adjustment of compensation networks is required. Also, for oscillator based designs, sawtooth edge precision is critical there.

There are too many ways to get it wrong.
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Old 26th April 2006, 01:08 PM   #3
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Quote:

- The control loop can no longer control the output filter during clipping, so the filter will resonate at its natural frequency until normal operation is resumed.
Control loop instability. In practice, phase margin of systems using global feedback is reduced when the output comes very close to the rails,.
Is that only happen when i connect the feedback after LC-Filter??

Quote:
RC damping may improve that a bit, altough filter resonance should be chosen above the audio band to start with.
Is The RC damping serial and connect between output and gnd ??
Or is that the Zoble Network ???

Quote:
- Control loop instability. In practice, phase margin of systems using global feedback is reduced when the output comes very close to the rails, so careful adjustment of compensation networks is required. Also, for oscillator based designs, sawtooth edge precision is critical there.
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Old 26th April 2006, 05:29 PM   #4
fredos is offline fredos  Canada
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Eve put you on the good way. First check your bootstrap capacitor if it can handle long pulse at clipping. In my design, I use a 47uF and 2X 0.1uF Tantal dip. Look to at the recovery time of your bootstrap diode...Check the output wave with a scope if their any wave over the signal when your near the clipping, this will indicate that your core is saturing. Try to reduce the overall gain too and drive your amp with more voltage. Reducing too the amplitude of the triangle wave could improve thing. Maybe another source, try to add more decoupling on the main power supply, between power supply and ground, and a place that nobody try, between the aux power for the Ir2110 and the -15V of your drive circuit. This will canmcle lot of noise between low voltage power supply and hight power power supply..

Fred

www.d-amp.com
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Old 26th April 2006, 05:50 PM   #5
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Originally posted by fredos
. Check the output wave with a scope if their any wave over the signal when your near the clipping, this will indicate that your core is saturing.
Thanks ....
I have added the bootstrape cap to 47uF Tantal .
I use SF14 be the recovery diode , I think it fast enough.

Do you mean check the wave , when it get clip??
If the output wave get clip , how to indicate the core is saturing ??
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Old 27th April 2006, 06:15 AM   #6
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In my amp...I used a seperate floating supply of 15VDC to power the IR2110 Highside ... to handle the Low Frequency Clipping perfectly...no crackes only nice clipping....

K a n w a r
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Old 27th April 2006, 08:20 AM   #7
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Quote:
Originally posted by Workhorse
In my amp...I used a seperate floating supply of 15VDC to power the IR2110 Highside ... to handle the Low Frequency Clipping perfectly...no crackes only nice clipping....

K a n w a r

That's sounds so good ,,,
could post some circuit here ??
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Old 27th April 2006, 09:34 AM   #8
Pierre is offline Pierre  France
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Not too much to think there... just use a separate transformer/rectifier/regulator/filter to get 15V, and connect the - to the midpoint between fets, and the + to the IR2110 VB voltage. Do you need a schematic for that?
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Old 27th April 2006, 10:04 AM   #9
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Originally posted by Pierre
Not too much to think there... just use a separate transformer/rectifier/regulator/filter to get 15V, and connect the - to the midpoint between fets, and the + to the IR2110 VB voltage. Do you need a schematic for that?

I can image it , it seems ever looked in some application note.
So , the Vcc and Vb pin will get two different base gnd 15v???

You said not to think ,, Isn't that a good way ???
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Old 27th April 2006, 11:05 AM   #10
Eva is offline Eva  Spain
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It's not so easy to get a floating power supply because the "midpoint between MOSFETs" is being switched back and forth at speeds grater than 1V/ns. Anything connected to that node will be a nice antenna, and the required common-mode filter to solve that problem may be bigger than the output inductor itself!

The bootstrapped resistor/capacitor or diode/capacitor supply is far more practical and quiet. Also, IR211x ICs draw less than 0.5mA supply current on each output cell as long as output state is not changed, so a 4.7uF capacitor already allows for more than 10ms of clipping while discharging by just 1V. Figure out that I'm using 2.2uF without any starvation problems (with IGBTs and feeding 18V to the gates).

The crackle is probably being caused by more complex phenomena. Your oscilloscope will tell you...
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