Devil's Staircase

There's nothing special about audio:

Why would you add that output decoupling capacitor when it is not needed?

None of the designs I have seen has a capacitor. Dig into it and find that you are chasing ghosts and just making a bad design by add a highly unlinear device

Notice that Class D is all about removing or compensating non linearities of the output stage.

Cheers

Klaus

Why class D? Doesn't seem like an obvious first choice for audio unless it's for a PA system or something of that sort.

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You have 15mV offset on the output

See page 8 of the datasheet:

For a 4 ohm coil that is only 4mA

You have no problem, get rid of the caps

Cheers

Klaus

To maybe avoid saturating the transformer. A good toroid has low DCR. I could easily circulate a few amps DC in the primary.

A capacitor looks easier.

he wants an amplifier not a space heater

We plan to do three channels, 150 watts each, in a 2U rackmount chassis.

It will simulate a 3-phase PM alternator hung on the gearbox of a jet engine. We'll be able to program frequency, voltage, and complex output impedance.

Huh, I have more questions than ideas. (How can you use a polarized cap.?)

but some sort of neg feedback that sense's DC current? George H.

why do you need a transformer?

and why not some COTS amplifier, you can a 4 channel several 100watt amplif ier in 2U for a few hundred $

For isolation, to make 3-phase and other configurations, and to get various output voltages.

Some of the downstream voltage regulators are weird. People like to short out PM alternators for regulation. Our box will have to tolerate that.

We'll probably do our own class-D modules. We could use one of the TI eval boards, but they are big and have a zillion jumpers and goofy connectors.

We can get a 48V, 600 watt MeanWell power supply for $75!

We were thinking about putting the TPA3255 on the bottom of the board and heat sinking it to the bottom of the box, which avoids a fan. It has a huge, grounded power pad on the top of the chip.

Isn't most audio power class D now?

Most polarized caps don't mind a bit of back bias. Polymers don't mind a lot. A couple of power diodes would guarantee that a cap would never see more than +-1 volt.

I should run a lot of AC current through some supercaps and see what happens.

Sure, but a cap is a lot less thinking.

That looks rather special!

OK, just my only 'other' idea.

I was going to report an almost first time pcb spin today. (Silk screen was a little off in places.*) I then I blew up the TCA3072... I forgot bypass caps, and had some hanging things... that shorted or something.

Otherwise it all looked good.

George H.

• I also forgot the pads for the output connector. I did say almost, :^)

Doesn't sound so bad. Add a little series R.

if it needs to support shunt regulation it would probably need some to meas ure current any way

Feed back a (heavily) filtered signal to the input? The problem is that they don't really tell you what the input of the 3255 looks like, IIRC (none do). It's intended to be AC coupled.

Most, except in automotive (where the TPA3255 is intended to play). Automotive is still mostly class-AB, or some "high efficiency" variation of AB (i.e. 'SB', 'KB', or 'TB'). It's changing though.

What's their ESR? High temperature is death to capacitors.

But I thought electronics was fun?!