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Class D Switching Power Amplifiers and Power D/A conversion

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Old 14th April 2005, 09:35 AM   #1
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Default My DIY UCD

Hi folks,

Well, I've mentioned my projects from time to time, fully intended on doing this P2P to keep costs as low as possible, and things have taken a turn that's forcing me to abandon my project for the time being, though I fully intend on getting back to it as soon as I can, maybe even sooner than I think right now.

In the meantime, I've decided to post what I consider to be a fairly final version of what I was going to wire up, have at it as you will.

I still have a very high powered full bridge design in the works that I started long before this, however I've learnt more during this half bridge project and know things need to be changed on it, so you won't be seeing that anytime soon.

I strongly recommend if you want an excellent amplifier, buy it from Hypex, but this is a good DIY project and much can be learned by it from many, I believe.

I'm not at all claiming it's 100%, but I think it's OK and should give a reasonable start to a working circuit.

This was made for ~65W RMS, but should handle much more, gain as shown is 27dB.

About the only thing not shown is the current source (it's ideal) and the delay circuit to switch it on via said current source.

However, this has zero protection circuitry whatsoever.

This simulates in transient very respectably, but since that's meaningless.. keep in mind alot of these values will need tweaking in a real world circuit.

Please excuse the untidyness of the circuit, I didn't have time to clean things up. I think you can all manage to figure it out though.

For a 1V input @ 20kHz:

TOTAL POWER DISSIPATION 1.04E+00 WATTS
DC COMPONENT = 7.670111E-03
TOTAL HARMONIC DISTORTION = 5.350052E-02 PERCENT

Regards,
Chris
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Old 14th April 2005, 09:40 AM   #2
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Output waves,

Enjoy.
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Old 14th April 2005, 11:19 AM   #3
subwo1 is offline subwo1  United States
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Hi Chris, I like the cascode output from the discrete comparator.
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Old 14th April 2005, 12:48 PM   #4
SSassen is offline SSassen  Netherlands
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Classd4sure,

Excellent, I just PM-ed you about the current status of your design, only to find this post about an hour later (coincidence?). I'd be happy to help out with prototyping and design if needed, should be fun, and a welcome exercise on my part.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com
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Old 14th April 2005, 05:23 PM   #5
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Hi there,

Thanks Subwo1. You're most welcome to make use of it in your project should you so desire, or a variation thereof.. or not

I appreciate the comment anyway.

Hi Sander, it was actually a total coincedence! Hmmmmmm, or, was it?

I thank you for your offer and your interest. If you'd like to prototype it or anything.... I only intended on doing it P2P for cost reasons but a nice PCB would be something too.

It of course has to purely be done for the love of it for the obvious reasons.

If you're curious as to what my new full bridge looks like, its' very much like this half bridge, just double (mirror) the cascoded outputs, increase the current to the LTP as the quad outputs divide it, then adjust the mirror balance resistor accordingly , and also mirror the output section.

I'm not yet satisfied with it enough to post it as a few of the original component selections aren't as good as I'd originally thought, it did simulate extremely well though, but I think it can be alot better. I'd rated the parts to handle 2kW continuously, I figured the drivers would hit a ceiling long before that though, but you know, doesn't cost anything at all to do on spice.

I'll help out anyway I'm able to if you decide to take it on, and you're welcome to email me or post here, I should be getting them, just won't have the time to tinker for awhile is all.

Take care,
Chris
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Old 15th April 2005, 05:49 AM   #6
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Hi,

I already had a few more screens from simulations of this same circuit so I thought I'd post them as well.

This first one is of the same circuit prior to a few changes, where it had only ~20dB of gain, ideal power supplies for the mosfet drivers, aaaand.....yeah, only 2 ohm series gate resistors.

Next screen will be of the gate drive signals only. I know it seems like the gate signals intersect rather high ~2.5 to 3V, but that seems to be the sweet spot that keeps shoot through in check and power dissipation low, at least for the simulator.

Regards,
Chris
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Old 15th April 2005, 05:51 AM   #7
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Gate signals + switching instance of half bridge.

That's it for now.

Regards,
Chris
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Old 15th April 2005, 09:01 AM   #8
IVX is offline IVX  Russian Federation
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Hi Chris,
why irf540? stp14nf10 $.5
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Old 15th April 2005, 09:22 AM   #9
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Hi Ivan,

Simple. It is only my standard mosfet for simulating with, IRF540 advanced analysis model. It is the one component that has always been a constant, so other changes are better evaluated with things I've tried before.

I've also not found a better working model, and the parameters are fairly realistic.

The device I use currently in the actual circuit however is Fairchild's FDP3682, free samples. I've also tried FDP3672, they run a little warmer, bigger input capacitance, and I can only do so much as far as optimizing goes with no scope at hand, which will soon change. I'd say they're good mosfets though.

An IRF540Z might be fun to try though. Use whatever works anyway, it's all part of the fun of it.

Thanks,
Chris

PS:

Fairchild does have models of the mosfets I've mentioned using, however I've found that by the time you've tweaked settings enough for them to converge, it cant' simulate with any accuracy at all and still fails, so their newer spice models aren't worth trying.
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Old 15th April 2005, 11:06 AM   #10
subwo1 is offline subwo1  United States
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Hi Chris, thanks, and thanks for this thread on your project. I just have not decided what I will actually settle upon for my project. I have experimented with amps built around an IR2110 and around 6N137 optocouplers.

The discrete UcD is an attractive option because it can be assembled with discrete parts which allows more access to the signal path for tweaking. It also can pass the signal more smoothly like a linear amp.

Those gate drive waveforms show the timing shift between the upper and lower drives due to capacitive interaction. Another general class D problem is the energy storage of the output inductor causing MOSFET body diode conduction and subsequent shoot-through at high output levels.
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