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Class D Switching Power Amplifiers and Power D/A conversion

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Old 3rd April 2013, 10:20 AM   #3381
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I took the temperature after about a hour running at moderate volume into a 2 ohm load: UcD type Class D Amplifier - YouTube
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Old 3rd April 2013, 11:07 AM   #3382
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Tekko,
Nice job man! �� It sounds great - very easy and lots of volume there for such an unassuming little circuit. It wasn't clear if the temps displayed by the IR thermometer was in degrees C or F?

Which circuit schematic did you end up using for your build? Can you point me to link?
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X
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Old 3rd April 2013, 11:19 AM   #3383
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The temp was in deg C.

This is the basic circuit used: http://i.imgur.com/poN8eVz.png

But i replaced the shunt regulators with some LM7x series 5V regs.
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Old 3rd April 2013, 11:27 AM   #3384
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Tekko,
Thanks for the circuit. What is the main difference between this one and he circuit posted at the beginning (post 13 I think)? Sorry for the newbie questions. Can you also point me to a description of how the circuit works in words? I am having a hard time seeing how a single op amp is able to serve as the input buffer amp, comparator, and sawtooth pulse generator to make then PWM modulator. Amazingly simple design but it is described in words somewhere that would be very helpful.
Thanks in advance.
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Old 3rd April 2013, 11:31 AM   #3385
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The difference is the way the comparator output is configured, instead of beeing open emitter in the original, i made it open collector.

The circuit is self-oscillating, using post filter feedback. It is not clocked.

You can find some info by googling "Universal Class D"

Last edited by Tekko; 3rd April 2013 at 11:33 AM.
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Old 3rd April 2013, 12:10 PM   #3386
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Ok thanks. Is the feedback through R11 and R12? In the diagram is speaker load represented by the 4 ohm resistor R15 connected to the center tap of the power supplies? What voltages ate you using for the rails?
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Old 3rd April 2013, 12:18 PM   #3387
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The feedback is what goes between the speaker output and the inverting input on the comparator.

The speaker is represented by the 4ohm speaker.

I'm using 2x25V for the first tests, then 2x35V for further tests.
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Old 3rd April 2013, 12:53 PM   #3388
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Quote:
Originally Posted by Tekko View Post
Anyone has a guess on how hot a 3A(source/sink) gate driver such as IR2010 or FAN7392 will get with 20 ohm gate resistor and mosfets with a total gate charge of 100nC at 400kHz ?

At 400ish kHz even with 30nC gate charge(IRF540) a IR2010 gets pretty hot.

Something tells me this will not even work at all.

These gate currents are scary!!
I've created a spreadsheet for calculating the approximate dissipation of the gate driver IC (based on AN-978) (Must be opened on libre office/open office) Feel free to edit if you found errors in calculation.

2pcs mosfets with total Qg of 200nc running at 400kHz is not safe without active cooling. Calculated dissipation is 1.1W (close to 1.4W max of 14pin PDIP IC case) and in reality, the actual dissipation might be worse than the calculation.
The result of the approximate dissipation shows that the surrounding air at the IC must not exceed 41 deg celsius for safe and reliable operation. I think it can be done with a heatsink on the top of the IC and active cooling to move the air around it. (Active cooling is needed because the ambient temp (inside the amplifier case) will rise when the IC or the amp itself is emitting heat)
Attached Images
File Type: png dissipation.PNG (24.8 KB, 562 views)
Attached Files
File Type: zip IR2110 Dissipation.zip (23.3 KB, 96 views)

Last edited by jlester87; 3rd April 2013 at 01:03 PM.
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Old 3rd April 2013, 01:00 PM   #3389
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Default 3kw 0.5 ohms

can schemtic be stimulated in LT SPICE



SAMEERX1
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File Type: jpg class d 2500w.JPG (156.7 KB, 559 views)
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Old 3rd April 2013, 01:04 PM   #3390
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I did notice that with IRFP150, the switching frequency had dropped to just 250-300kHz, wheres with IRF540 it was somewhere around 400-450kHz.

However the amp ran for hours until i shut it off when going to bed and there were no issues with overeating gate drivers, even though the whole thing had been heat soaked to around 70deg C due to the IRFP150s beeing hard to drive and thus dissipating alot due to spending time in the linear region.
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