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Class D Switching Power Amplifiers and Power D/A conversion

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Old 9th June 2003, 05:38 AM   #71
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the file can be uploaded FTP and thats at his discretion as you said
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Old 9th June 2003, 05:49 AM   #72
ssanmor is offline ssanmor  Spain
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I think we can use Yahoo Briefcase to share any files.
I have create an account. Just tell me your Yahoo ID (if you don't have one, it is easy to sign in at:

http://es.briefcase.yahoo.com/

Once you have an ID, please e-mail it to me at ssanmor@canal21.com and I will add you to the users list able to share the contents of my folder.
I have just added an App. Note from On Semiconductor which describes an implementation of a ClassD amplifier with both N and P mosfets.

Best regards.Sergio
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Old 9th June 2003, 08:01 AM   #73
ssanmor is offline ssanmor  Spain
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I have finally found the schematics of the Crest LT amplifier in a web page, so there is no need to upload them.
The link is:

http://linxlabs.by.ru/crest.htm


I suppose that the one we have been talking about is the second one. I will have a look at it.

Best regards and, anyway, a lot of thanks, Charles. This info will be VEEERY useful .

Sergio
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Old 9th June 2003, 12:52 PM   #74
ssanmor is offline ssanmor  Spain
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After studying the Crest LT schematics a little bit, here are some thinks I would like to point:

-The circuit is fairly simple, specially if you remove all the fancy protecions (Autoramp, IGM, ACL, refer to Crest webpage for details).
-The output stage is accomplished with a simple level shifter using a PNP transistor, then it is inverted with an XOR gate (the other non-inverted branch is also passed through another XOR gate to equalize delays) and then goes to a IR2113 driver. It is exactly the same as IR2110, which is the very similar to the above discussed IR2121/25 pair.
-The output filter is very clever: it uses a 2-pole LC filter (L5/C93) and then a notch filter. This can be adjusted to cancel just the switching frequency.
-The dead-time is only accomplished with a diode and a resistor in the gate of the mosfets, relying on the gate capacitance to form the time constant. It effectively delays the rising edges thus minimizing the shout-through effects.

The circuit can be very simplified and still work. I have noticed also that it doesn't use strange or sophisticated components as fast comparators or opamps.
It has given me a lot of ideas and just when I can I will be making a first prototype with a totally different PWM modulator based on a MAX038 triangle generator and a few opamps and comparators.

Thanks, Charles, for pointing to the right direction.

Best regards.
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Old 9th June 2003, 08:21 PM   #75
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The circuit is based on the work of Brian Attwood (using a double-feedback loop topology).
It is more or less the same one as used by Peavey within their DECA series back in the eighties, although with more modern components (Attwood is also stated as inventor on the Peavey Patent).

Regards

Charles
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Old 10th June 2003, 05:32 AM   #76
ssanmor is offline ssanmor  Spain
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Hello again, Charles.
Why is it a "double feedback" loop topology? I only see one point from the output to the modulator stage, apart from the protection circuits.

Best regards
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Old 11th June 2003, 10:47 AM   #77
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It is not that easy to see but let us have a look at the diagram (channel 1):


The feedback signal is taken off the output filter via R99 (forming a lowpass together with C41). Then it is divided into an inner loop and an outer loop.

The inner loop is consisting of the lead circuit formed by C40 and R62, the lag circuit formed by C39, R58 and R64, followed by the lowpass R65/C30.

The outer feedback loop is consisting of another lag circuit around U38.

Regards

Charles
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Old 11th June 2003, 10:53 AM   #78
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Found this the other day, may be of interest

http://www.planetanalog.com/features/OEG20030326S0055
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Old 11th June 2003, 01:57 PM   #79
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Quote:
Originally posted by ssanmor
The dead-time is only accomplished with a diode and a resistor in the gate of the mosfets, relying on the gate capacitance to form the time constant. It effectively delays the rising edges thus minimizing the shout-through effects.
I think the output stage is basically the same as the Crown cct that I used. I wonder how they got around the patents? I think the gate resistors for slower turnon is to reduce reverse recovery effects in the diodes that carry the inductor current, not fot shoot-through problems which this topology does not have.
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Old 11th June 2003, 02:14 PM   #80
ssanmor is offline ssanmor  Spain
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Well, Circlotron, you are right in that the BCA topology doesn't have shout-through problems, because botch mosfets are not ON at the same time (except for 0V input). The driving signals for the high and low side mosfets are obtained, respectively, by PWM modulation of the input signal and its inverted version.

BUT, the Crest LT topology is a conventional Half-bridge output. That is, the driving signals are, for the high/low side, the PWM modulation of the input signal and the inverted version of the modulation. Thus it CAN have shout-through problems.

I am not sure if the diode and resistor in the gates is for the dead time control or for the effects of the diodes as you suggest , but what I am sure is that the Crest LT output topology and working principle is not the same as the BCA amplifier's.

I think that I will try with the conventional half-bridge topology first. I am doing some tests with a SG3535 as the modulator, now that the level shifting stage and mosfet driving is clear. I will tell you how it goes.

By the way, Circlotron, how are you going with your experiments? Yesterday I found a little program to aid in the calculation of LC filters. If have done some simulations of its results with Pspice and it works fine. You can adjust your output filter to get optimal ripple rejection.



This is starting to get hoooot!
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