Badly in need of help on output inductor design for ZXCD1000 based 500 watts amp - diyAudio
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Old 8th November 2005, 07:33 AM   #1
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Question Badly in need of help on output inductor design for ZXCD1000 based 500 watts amp

Hello audiophiles,

Though new to Class D amplifier design; i had completed a design for 150 watts.

Using a standard, off-the-shelf 20uH gapped toroid PG0058 from pulse. Now I consider myself confident enough to port it to a 500 watts output power.

The problem is finding an easily available gapped (or something similar toroid, RM or EE core) capable of handling 20 amps current without saturation.

With level of discussions everyday happening here at diyaudio.com Can somebody please guide me to an informative link or share horizons to success... All suggestions are most welcome...



_______________________________________

Regards
Chaturvedi

The good news is that nothing is compulsory.
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Old 8th November 2005, 08:43 AM   #2
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I am attaching the circuit diagram for reference.

I would really appreciate and modification and suggestion from DIYers...
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Old 8th November 2005, 09:10 AM   #3
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Quote:
Originally posted by Razor_Edge
I am attaching the circuit diagram for reference.

I would really appreciate and modification and suggestion from DIYers...

Hi,

While I can't help you with the inductor question, and I know others will, I think your driver and output stage will fall apart at 500 watts.

It seems most wouldn't consider using a comp. output stage past 200 watts.

I dont' know anything about the IC you're using either, but it seems strange to me that it's driving the MOSFETs directly with no buffers.

I think for a 500 watt amp you're looking at upgrading to a dual N channel output stage driven discretly or via a good driver IC.

Best Regards,
Chris
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Old 8th November 2005, 09:49 AM   #4
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I dont' know anything about the IC you're using either, but it seems strange to me that it's driving the MOSFETs directly with no buffers.

I think for a 500 watt amp you're looking at upgrading to a dual N channel output stage driven discretly or via a good driver IC.



Firstly: The datasheet for this IC states that it can drive a Mosfet for a Ciss upto 2200pf with a similar configuration. The datasheet can be downloaded from link below.

same as defined in the datasheet for IR2010 driver.

I would like your critics on this part. (where am i lagging... )



Anyways, thanks for the valuable feedback Chris...


Best Regards

http://www.zetex.com/audio/audio05-1-2a.asp
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Old 8th November 2005, 10:04 AM   #5
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Quote:
Originally posted by Razor_Edge
I dont' know anything about the IC you're using either, but it seems strange to me that it's driving the MOSFETs directly with no buffers.

I think for a 500 watt amp you're looking at upgrading to a dual N channel output stage driven discretly or via a good driver IC.



Firstly: The datasheet for this IC states that it can drive a Mosfet for a Ciss upto 2200pf with a similar configuration. The datasheet can be downloaded from link below.

same as defined in the datasheet for IR2010 driver.

I would like your critics on this part. (where am i lagging... )



Anyways, thanks for the valuable feedback Chris...


Best Regards

http://www.zetex.com/audio/audio05-1-2a.asp

This part right here:

"The ZXCD1000 class D controller IC is inherently
capable of driving even higher power solutions, with
the appropriate external circuitry
. However as stated
above the maximum supply voltage to the ZXCD1000
class D controller IC is 18V and the higher supply
voltages must therefore be dropped. Also due
consideration must be given to the ZXCD1000 output
drive levels and the characteristics of the bridge
MOSFET’s. The latter must be sufficiently enhanced by
the OutA and OutB outputs to ensure the filter and load
network is driven properly.If the gate drive of the
ZXCD1000 is too low for the chosen MOSFET then the
OUTA and OUTB signal must be buffered using an
appropriate MOSFET driver circuit. Additionally,
suitable magnetics are essential to achieve good THD
performance."


Not to mention parasitics, trust me at 500W you're in for some real trouble, call it a feeling.

Regards,
Chris
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Old 8th November 2005, 10:43 AM   #6
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Quote:
trust me at 500W you're in for some real trouble, call it a feeling


I thought this issue would be a bit easier to address that getting the optimum magnetics designed for high power... was i so wrong in my interpretation..

Can anybody suggest be a good Mosfet driver (which can handle more that 3000 pf of input gate to source capacitance within 50 nSec)

I stongly believe in keeping the dead time to less than or equal to 15nS for good THD performance (please comment)...


Thanks Chris for redefing my immediate objectives. I still dont know how to go about magnetics capable of handling 20~25 Amps of pulsed current into the transducer.

NOTE: The current design works on 200Khz +/- 50 Khz operating frequency with THD below 0.01%.
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Old 9th November 2005, 08:09 AM   #7
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Chris is right, you will want to go with an all N-channel setup at 500W. It would be easiest to use a gate driver like the National LM5104 that requires a single input and provides dead time control. That way you can keep the ZXCD1000 and not have to add any additional circuitry between the PWM controller and gate drivers. However, I am currently using the LM5104 and it looks like it handles dead time control poorly. Plus there are better gate drivers [IMHO, which I unfortunately am finding out the hard way] with separate high and low inputs. I would suggest using a discrete design by taking the complimetary outputs from the ZXCD1000 and using one to drive each side of the bridge with the other output connected to a RC dead time adjustment and then inverted [HC04]. Does that make sense? Then you can use a myriad of different gate drivers - I suggest the IR2010 or HIP2100.

As far as magnetics, my best suggestions from others that I am passing on is to use a distributed gap common toroid. That gies you a smaller footprint and keeps your flux fringing down. I'd stay away from split gap toroids or separate inductors. You can achieve good results with any method, but I am just pasing on what I have heard. Sorry I can't help you with core material or anything.

Best regards in getting some great performance out of your amp!
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Old 9th November 2005, 08:31 AM   #8
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Namaskar Chaturvedi bhai,

Are yaar tum Air core inductor kiyon nahi use karte ho,

I have used air core inductors upto 50A , as they are unsaturable types...

K a n w a r
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Old 10th November 2005, 09:09 AM   #9
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What kind of output MOSFETs? Q1...Q4 is not marked on the schematic.
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Old 10th November 2005, 10:44 AM   #10
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Quote:
What kind of output MOSFETs? Q1...Q4 is not marked on the schematic.
the output mosfets are from zetex ZXM64N035L3 and ZXM64P035L3 50.

Quote:
Are yaar tum Air core inductor kiyon nahi use karte ho,
I have used air core inductors upto 50A , as they are unsaturable types...

At 500 watts of output power the amount of radiation would be very very high. that is y I am keeping myself from air core inductance KANWAR sahab... (hindi mein peheli baar post kar raha houn, acha laga...)

I have got very good results by using gapped core inductor from pulse.

Actually getting ferroxcube gapped core at a competitive pricing from local vendor is giving me a hard time...

yesterday, I tried using a N67 based EE core (air gap in the central limb). Its getting very hot at just 155 watts...!!!

No success absolutely in this direction...


hey kenshin,

I am thinking of keeping the rail voltages at 70 volts(good mosfets with better THD performance at lower voltages). Please comment...
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