Power Supply Resevoir Size

[liching1952]

Originally Posted by dadod

I am sorry to intrude in this very interesting thread, but I was provoked by this guy telling nonsense about C multirplier .
dado

So explain why its not nonsence.

[homemodder]

Originally Posted by jacco vermeulen

The latest Dartzeel 458 monaurals each have a 2KVA toroidal with a huge oversized core, 4.5 times the nominal power rating.
Mr Hervé Delétraz is from your turf, the things cost 150K a pair, you must find that Hilarious too.

150k

These must have more carats of gold in the front plate than the Goldmunds

What do these designers (company) ( used in the absence of a more appropriate smiley ) ??

[jacco vermeulen]

$

[liching1952]

Originally Posted by liching1952

amps need a big cap not to minimize ripple but for another reason. This is neglected and even canceled by the circuit you called C multiplier. In fact its a Cap divider. Huh?

Me tupid you smart, where is the answer?
And why you people so seeking low ripple. Good Ampi dun need ripple free supply and ripple will not reach speaker.
Looks like you people dun know how much ripple is tolerable.

[Terry Given]

liching1952, you could try reading the thread. for comprehension this time.

[liching1952]

Originally Posted by Terry Given

liching1952, you could try reading the thread. for comprehension this time.

Me inglish is too bad to read all that. As me understand its very simple and only me newcomer dun understand. So tell me in simple Inglish what much ripple do you want and why cause at me electronic level, ripple is not an issue for good profesional design ampi.

[MagicBox]

This thread isn't much about ripple; ripple is just *one* small factor in the main subject called "Transient Response" of the whole chain.

[Terry Given]

liching1952, that is just trolling. you are at least trilingual, and from what you've posted so far your english is more than sufficient for the task at hand - Ni Shuo Huai Hua. besides, with your MSc you should be able to follow the schematics and plots. that you have not and will not do so suggests you are either lazy or stupid. I'm assuming lazy.

As MagicBox points out, the thread is about transient response.

Why low ripple? stupid question. have you ever heard of PSRR? what about Early Voltage? cascoding?

[Nico Ras]

Every village has a fool.

[Terry Given]

I'm just playing with the xfmr-rectifier-cap setup. Toms model, one transformer driving a MBR20100 full bridge into a 5R load with N * 1.2mF 26mOhm caps in parallel.

and I didnt see quite what I expected to see - above about 10mF the conduction angle is constant. thats odd. so I started looking a bit harder. it looks like its the combined effect of ESR (xfmr + diodes + cap bank) & leakage inductance that prevents the conduction angle from narrowing further - IOW it limits the peak current.

The transformer winidng resistances are interesting. Its a forward-mode transformer so the RMS primary and secondary currents are closely related - Ip = Is/N + Imag (this aint necessarily so in a coupled inductor).

generally one designs Imag = small (this is why the huge ratio of Lmag to Lleak - Lmag must be >> Lbase and Lleak << Lbase) so Ip = Is/N. One normally assigns equal volume to equal power windings - so the primary winding area Aw_p should be roughly equal to the secondary winding area Aw_s. Filling this up with Cu then results in Rp = Rs*Np^2. and the resistive losses in each winding are therefore equal (casually ignoring skin & prox effect)

yet in this case Rp/N^2 = 157mOhm but Rs = 290mOhm - the secondary resistance is 1.85x what I would expect it to be. so ignoring magnetising current the secondary accounts for 1.85/2.85 = 65% of the total copper losses.

I might expect to see that in, say, a microwave oven transformer where the poor thing runs hard into saturation (some MOTs draw less current under load because the voltage droop across the primary leakage pulls the core out of saturation. it makes it hard to spot a dead transformer if you dont know this). But nobody in their right mind would do that to a transformer running continuously. and beside with Lmag = 52H the mag current is < 10mA.

It might be to do with the thermal behaviour - if the secondary is on the outside of a toroid it will cool better. I dont know, I havent designed any LF toroidal transformers, but it still seems like a poor idea - especially as it hurts regulation.

the high Lmag seems odd too - 6mA magnetising current is stupidly low* at 120VA thats 0.6% of load.

One would normally pick a number, say 10% full load and design Imag = that much. this reduces the number of turns, and the leakage goes down (and regulation improves). Maybe the manufacturer was trying to get stupidly low Bmax for some reason? who knows, but its certainly odd.

*I used to have a 100kW three-phase 400V:208V transformer with Imag = 200mA (about 0.1%), but that was designed to be switched on and off hundreds of times per day, so was not allowed to "boing" so it had a peak flux density of about 400mT IIRC.

that might be whats happening here - if this transformer were designed for minimum inrush (which is utterly pointless if it then drives a thumping great rectifier-capacitor load) it explains the low Imag and the high leakage.

this transformer might turn out to be a TERRIBLE choice for modelling power supply interactions