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Old 4th June 2005, 07:16 PM   #11
SSassen is offline SSassen  Netherlands
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Alright, another update, got some feedback from a few helpful subscribers to the hifi-forum.de website. The latest schematic is listed below. You'll see the transistors are now connected differently, this should allow for better interfacing with the mosfet driver. I've also switched to the IR2011 mosfet driver as it has better parameters overall and is better suited for high-frequency (>200KHz) operation.

class_d_amp_004
http://hardwareanalysis.com/images/a...arge/11524.gif

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Sander Sassen
http://www.hardwareanalysis.com
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Old 4th June 2005, 07:45 PM   #12
SSassen is offline SSassen  Netherlands
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Chris,

I'd love to simulate it, but to be honest I wouldn't know how, many of the parts I used aren't in the Spice library and to be honest I haven't used a simulator for a long time. If you'd like to help out and sim it for me you're most welcome of course. You can just omit the driver stage and the mosfets and connect the output of the comparator right up to the output coil in the sim if I'm not mistaken?

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Sander Sassen
http://www.hardwareanalysis.com
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Old 5th June 2005, 06:01 AM   #13
SSassen is offline SSassen  Netherlands
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And another update, we're up to version 005 already with the latest changes being a simpeler input buffer and optimized values for the resistors around T1 and T2 to guarantee proper switching.

class_d_amp_005
http://hardwareanalysis.com/images/a...arge/11527.gif

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Sander Sassen
http://www.hardwareanalysis.com
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Old 6th June 2005, 07:19 AM   #14
subwo1 is offline subwo1  United States
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You may like to remember to adjust the values of R15 and R16 at some point in time.
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Old 6th June 2005, 08:41 AM   #15
Pierre is offline Pierre  France
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Sander, looking at your schematics, I have seen that the only way you have accounted for dead-time addition is the diode in antiparallel with the gate resistor.
I don't know if you have built this circuit and hence if you have found shoot-through currents, but that's something you may need to have in mind if you find that the mosfet reliability is not good when you test it.

Perhaps other people that have built similar designs can say that it is not necessary to add more dead-time before the driver. What are your opinions on this issue?

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Old 6th June 2005, 08:59 AM   #16
SSassen is offline SSassen  Netherlands
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Subwo1, Pierre,

Yes, I might be looking at changing some resistor values to account for more deadtime, but the same mosfet driver (IR2011) and output stage is used by IRF in their reference design and their deadtime, and hence THD figures, are very respectable.

I've already ordered parts (at Farnell and RS) and should be getting them in shortly. I'll then construct a prototype on some proto-pcb and she if she'll run. If she does I'll hook her up to a load and see if I can get some good measurements on the scope and modify the design accordingly.

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Sander Sassen
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Old 6th June 2005, 09:10 AM   #17
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Hi Sander

I had a look at it and I'd say that I like it. I would also recommend a large parallel resistor to C7.

The working principle is from one of the guys on the German forum, isn't it ? What is his experience with DC drift ?

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Charles
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Old 6th June 2005, 09:24 AM   #18
SSassen is offline SSassen  Netherlands
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Phase_accurate,

It is a bit of everything really, but indeed the feedback topology is from the German guys, as you can see the feedback loop feeds both the integrator and the comparator input and is slightly different from the classic self-oscillating class-D implementation.

As you're the 2nd person suggesting I add a large resistor across C7 to avoid drift, Chris also mentioned it, I added R2 - 4.7-MOhm, which should be sufficient I guess, see latest version of the schematic below. Fortunately I have all the tools here to evaluate the proto, such as a dual channel 100MHz storage scope, a DDS function generator and I just ordered a dozen 50-watt resistors to build a dummy load, and not to be forgotten new batts for my DMMs.

class_d_amp_006
http://hardwareanalysis.com/images/a...arge/11529.gif

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Sander Sassen
http://www.hardwareanalysis.com
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Old 6th June 2005, 12:20 PM   #19
Pierre is offline Pierre  France
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Sander, why do you like the last transistor arrangement more than the version-3?
I mean, what's the difference between having the base connected to the comparators and the upper resistor to Vcc (as it was before) and connecting the base to GND and the upper resistor to each comparator's output?

About level shifting, it is surely needed, unless you operate all your circuitry with the same supply as the IR2110, but then input should be capacitively coupled, as well as feedback signal. I don't know how that would perform during startup, however.

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Pierre
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Old 6th June 2005, 12:25 PM   #20
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Quote:
I mean, what's the difference between having the base connected to the comparators and the upper resistor to Vcc (as it was before) and connecting the base to GND and the upper resistor to each comparator's output?
Apart form the fact that one of these arrangements is inverting and the other one isn't - there is a difference in speed. Driving the emitters should be faster since it eliminates the miller effect.

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