yet another UcD

[classd4sure]

Hi, Chris, Constantine,

Good news, I succesfully fix the minor thing for my 'UCD'. The problem solved when R1 is replaced with series 150ohm and trim pot 100ohm.

The second, the heat already solved. I was using small heatshink like Constantine. The problem is the the heat rise when played louder. Then I have experiment to use small fan to blow the amp. Then after that known that the heatshik pretty cool an no temp rise. Even at played very loud. Yup... the amp need good air circulation.

I got the idea from PC PSU. FYI, I use cheap and dirty rewinded PC PSU to supply the AMP at 30V+/-.

Now the amp became my favorite amp. I find new 'color' of sound at my amp.

Best Regards,
Kartino

Hi Kartino,

That's great.

It's funny but when I was working on mine I had the hardest time of it while at idle or lower volume, it was sure to cook, even with a fan aimed right at it set to high speed. Playing it very loudly was the only way it would survive. Wouldn't it by nice if we all had scopes?

Hey Chris,

Just comming up to speed on this very interesting thread.

Ever bothered to simulate with very high inductor ripple currents.
In real life, it drops the distortion down.
When the load current is less than the peak inductor current ripple the dead time doens't matter much.
The switching occurs when the switch turns off rather than being dependent on when the switch turns on.

I'd love to try this on a big UcD, and say set the ripple current to say 10 amps. then you could get 5^2 * Rload/2 or 50 Watts of very low distortion output.

My guess is the UcD400 is running at about 1.5~2A ripple current, so you only get about 1A*Rload/2 or 2Watts in this mode.
Notice the UcD distortion curves are very good at 1W!

The smaller inductance, say 5uH, will mean you need to increase the output filter cap to keep all the same though. Like 5.6uF
Not really an issue in UcD. This will raise the Q of the LC with nominal loads, but UcD is pretty invariant to this.
That, and the high Q means its out of band too.

Best Regards,

Mike

Best Regards,

Mike

Hi Mike,

I haven't tried that but I have a good idea what you're talking about.

I can't say if the ucd modulator would be a good candidate for such a thing.

I'm imagining more of a ZCS hysteretic current mode ripple regulator, or other ways of making it more robust against this. Do you think it's the body diode conduction that is the sole cause of this added distortion? Or perhaps it's more miller effect.

Worth looking at anyway.

Regards,
Chris

 

[kartino]

Hi Chris,

You are right, We need scope to do this job.


Hi Constantine,

(Not too much to talk PSU here?) rewinding is cheapest for me. I got $7.0 for new ATX PSU. I remove the transformer. Still keep primary winding, replace secondary with smaller wire to get more space. Then add another secondary winding as you like. Add diodes, filter and caps, just it. It works, regulated, and protected. I may failed started when use big caps, because PSU detect as short circuited. Just add 0.5 ohm resistor before caps will work well.

About dismantling the transformer is very easy. Soak the transformer with thinner (for paint) for 5 hours, then the transformer can be dismantled. Use power glue to reassembling again.

I got more than 100W for that idea at 30+/- Volts.

OK, back to class D thread!

Best Regards,
Kartino

 

[Portlandmike]

Hi Kartino,


Hi Mike,

I haven't tried that but I have a good idea what you're talking about.

I can't say if the ucd modulator would be a good candidate for such a thing.

I'm imagining more of a ZCS hysteretic current mode ripple regulator, or other ways of making it more robust against this. Do you think it's the body diode conduction that is the sole cause of this added distortion? Or perhaps it's more miller effect.

Worth looking at anyway.

Regards,
Chris

Chris, the distortion is due to the error in the transition time. For example, if the top switch is on, and turns off, and the inductor has current flowing into it, the switch node falls when the top switch shuts off. If the inductor current is flowing out of the inductor, the top switch shuts off, but the switch node doesn't fall until the bottom fet sinks more current than the inductor current.
That typically in my experience is a delay of the dead time.

So, when ever the load current exceeds 1/2 the ripple current, you get this error pulse.

Now, having put up this idea a few times, I've simulated some of this, and it seems the UcD comparator switch driver scheme is pretty good at minimizing dead time. And, in affect, the frequency seems to shift to maintainn the poloarity current change every cycle for much larger current excursions than the topology I did my investigation on. That by the way was the MPS 7720. That IC had clear and measurable dead time of about 80nS. In that amp, running in high ripple current dropped the distortion over 20dB or 10X.

UcD, is more like 20nS from what I picked up from a bruno post.
I do have a scope, and an AP ATS-2. So one of these days, I'll measure the hell out of it, and post it.

I think I'll tweak the dead time adjust too, but this is the wrong thread. ;>)

Regards,

Mike

 

[Portlandmike]

Got some inductors if anybody is intersted

Hey,

You guys need inductors.

I have about 5 lbs of good ferrite gapped pot core inductors that are 16uH and a solid 11-12 Amps. I actually measured 20A before sat, but I don't know if that's limited by copper loss.

They are tri-filer wound, and if so inclined, easy to take apart.

Less inductance, more current. More inductance, less current.

1/2 L i^2

Best Regards,

Mike
p.s. It might be tough to ship out of north america.