UCD180 questions

[Jaka Racman]

Hi Bruno,

4)PFC, if present, overshoots at around 17Hz (current feedforward never heard of, although many of these controller chips have dedicated input pins for this)

.

Well, PFC is designed for it. If you want to limit input current THD, then voltage loop must be slow or you are feeding second line harmonic into the input multiplier. Current feedforward is used only in B version of L4981 regulator of all the chips I am aware of. The same second you feedforward load current into input multiplier, THD will suffer also. And the main problem will be noncompliance with EN61000-3-3 (flicker) requirements. You might as well speed up the voltage loop and increase THD or use a rather large bank of capacitors. As far as i know, audio amplifiers are the last dinosaurs that are not subject to EMC harmonics and flicker standards. How do you do that? And why would you want to use PFC for power supply, when there is no requirement for that?

And BTW, output capacitor current control loop is used in SMPS design for some time now. ONsemi has 6 chips that use this technique, not counting older Cherry semiconductor ones.

Best regards,

Jaka Racman

[Bruno Putzeys]

Originally posted by Jaka Racman
Current feedforward is used only in B version of L4981 regulator of all the chips I am aware of.

Oops there you go... Extrapolation never works (it was this precise chip I'm using for my smps experiments so I supposed that current feedforward was commonplace)

Originally posted by Jaka Racman
The same second you feedforward load current into input multiplier, THD will suffer also. And the main problem will be noncompliance with EN61000-3-3 (flicker) requirements.

I don't exactly see why THD (actual harmonics) would increase, but surely the input waveform won't be a sinewave anymore. I was not aware of a thing like "flicker requirement".

Originally posted by Jaka Racman
As far as i know, audio amplifiers are the last dinosaurs that are not subject to EMC harmonics and flicker standards. How do you do that? And why would you want to use PFC for power supply, when there is no requirement for that?

IMHO audio amplifiers are exempt from these requirements precisely because it would force nearly the whole audio power amp industry out of business. Once a few consumer electronics companies have good PFC based power supplies you'll see it become a requirement rather quickly.

Originally posted by Jaka Racman
And BTW, output capacitor current control loop is used in SMPS design for some time now. ONsemi has 6 chips that use this technique, not counting older Cherry semiconductor ones.

As I said - everything is there for the right people to use, but when I look at the power supplies currently co-packaged with power amplifiers it's not happening (I haven't checked the supplies used by IcePower - presumably these are in a different league).

[Jaka Racman]

Hi Bruno,

don't exactly see why THD (actual harmonics) would increase, but surely the input waveform won't be a sinewave anymore.

Actually you are right. You have just found a way to push incredible amounts of non mains related harmonics into the mains network and not be punished for that. It is always good to have someone thinking out of the box. I actually wonder how much time will it take to the standardizing committees to fill this hole.

But the flicker problem still remains, and this will be a larger problem to fill if they impose this standard on audio industry like they did on mine (medical field). Because of that standard I am currently designing a flicker free power supply which will have more than 3.7kJ stored energy in capacitors additional to current feedforward. Some of our competitors are forced to specify dedicated power lines because of that. Audio industry must have a really good lobbyists.

Best regards,

Jaka Racman

[Ouroboros]

The 4981B simply has the ability to add a bit of spread-spectrum modulation to the oscillator to lower the conducted noise when measuring with an average responding EMC receiver.

I've designed in the 4981 as the PFC stage in a 250W PSU here at work. The chip works very well and nothing has blown up yet on the prototype! (The main isolating stage that follows the PFC is a two-transistor forward convertor producing 46V at 5A)

The site http://henry.fbe.fh-darmstadt.de/smps_e/#smps is extremely useful to help design and simulate various power conversion stages.

[Bruno Putzeys]

Originally posted by Jaka Racman
Actually you are right. You have just found a way to push incredible amounts of non mains related harmonics into the mains network and not be punished for that. It is always good to have someone thinking out of the box. I actually wonder how much time will it take to the standardizing committees to fill this hole.

Well it'll always remain something of a balancing act between energy storage and mains pollution. However the situation, I think using a pfc even with heavy current ff will still be much preferrable over a straight cap-loaded rectifier.

Also the non-harmonic components are not going to contribute to distribution losses (which is why we want good power factors) and the requirements don't need to be strict because the additional rubbish is asynchronous/noncorrelated so over a large number of stereo sets it'll average out (unless everyone in the country is playing the same radio station at full blast). Harmonics, being synchronous, do cumulate, so strict regulation is necessary there.

I'm not sure if audio has a such a good lobby. It's more likely we're quantité négligeable.

[Jan-Peter]

Guys,

Perhaps a good moment to start a new thread about how to design a good SMPS for an amplifier, analog or Class-D.

In this way we keep the thread about the UcD180 more clean to the subject.

Cheers,

Jan-Peter

www.hypex.nl

[Hans L]

Originally posted by Jan-Peter
Hi Xman737,

I just send you an email about details of ordering. Within a few weeks we will have a webpage ready were everybody can order the Class-D modules, together with cable assemblies and powersupplies.
...
Best regards,

Jan-Peter

www.hypex.nl

I did it... I read 18 pages of posts and feel like

Anyway, is the powersupply already available? I hope I'm not too impatient... I am however a complete twit when it comes to electronics and wouldn't want to buy a kit that isn't foolproof.

Does it need a soft-start circuit to be able to use it for tweeters in an active design? I noticed 'Pop-free stop mode' in the specs, is that enough? I saw someone stating it wasn't necessary in an active design, but another builder did have a softstart in his amp most likely designed for a passive speaker...

Thanks!
Hans.


P.S. I'm also looking forward to a paper with the answers to these questions by wytco0

Things that I think would be useful :-)
Description of power supplies recommended, possibly some actual designs, eg dual mono, single; tranformer ratings etc
Description of signal connection, balanced vs. unbalanced.
Protection information, Switch on etc.
Cooling recommendations.
Opamp discussion
Info re cooling requirements, eg making it clear that although they run cool some heatsinking is needed.

[classd4sure]

Hi,

You only really require a soft start circuit with huge toroidal transformers as they induce a good surge of current when you first power them up, also large capacitor banks coupled to said transformer make it worse.

At what point does soft start become manditory? 300VA? 500VA?

I also would like to know if Hypex has plans for offering soft start circuits?

I've read on some sites who do sell them that they improve the sound by starting it without a punch of current and reduces "warm up" time by hours before it starts to sound good... true or false? ?

Thanks

[Bruno Putzeys]

Originally posted by classd4sure
You only really require a soft start circuit with huge toroidal transformers as they induce a good surge of current when you first power them up, also large capacitor banks coupled to said transformer make it worse.

At what point does soft start become manditory? 300VA? 500VA?

I also would like to know if Hypex has plans for offering soft start circuits?

I've read on some sites who do sell them that they improve the sound by starting it without a punch of current and reduces "warm up" time by hours before it starts to sound good... true or false? ?

Yup, soft start is a courtesy to your rectifier diodes and the circuit breakers in your house, but the amp doesn't need it.
If you read through the thread, you will find posts on power supply dimensioning, and how the amount of storage capacitance depends only on rated load impedance, not rated power. Once you got that, you'll see it is unnecessary to stack up such an amount of capacitance as to necessitate a softstarter.

IMHO soft start has no effect on warmup time. "Warmup" (as defined as the slow change in sound, usually for the better, during a certain time after powerup) is an electrochemical affair in the electrolytics. If you want to reduce warmup time, keep the power supply up all the time and turn the amp on/off by the enable pin (if at all you would bother turning it off).

[classd4sure]

Yeah I saw that as marketing hype but thought I'd ask

So if the reservoir capacitance isn't a problem, or, much of the problem, at what point does the transformer size necessitate soft start, given the standard 25 amp breaker?

From http://www.powertronix.com/html/body_in-rush.html
Transformer Rating
Recommended Protection

15 VA - 300 VA
None

300 VA - 1.0 kVA
Slow blow fuse

1.0 kVA - 2.0 kVA
Small external resistor in the primary circuit

2.0 kVA - 10.0 kVA
NTC thermistor or soft start circuitry