Ban wrote: > The book I'm referring to is giving this model: >
You're just discovering this now?- after shooting your ignorant mouth off and posing as the big power supply expert- laughing at other people and ridiculing their "state of knowledge?"
...because it's so readily available everywhere else....
Then you're so damned dumb you started this thread attempting to capture the whole of the design philosophy after a few elementary and incomplete SPICE model runs....too much- what gall.
Why not skip the 3rd edition, I'm told the 4th edition is better ;)
-- Thanks, Frank. (remove \'q\' and \'.invalid\' when replying by email)
You're right, I forgot this. Plus I was dumb enough to mix some figures with another xformer, reverse the turn ratio and count it across 2 secondaries. I guess it's time for some vacation.
So it is 630VA, 230V 2x(2x34V) Lp=12.7H N=1:0.1474 Lf1a=Lf1b=16uH Lf2a=24uH, Lf2b=22uH Rp = 2.13R Rs = 0.22R for all the secondaries.
The transformer ratio was measured (I didn't design it).
A funny story is that this is an old transformer I had custom made about 20 years ago (many more auxiliary voltages). In order to be sure to have the right voltages under load I told the manufacturer the bypass caps values, the current loads, and let they do their job... Doing so, I was sure enough (well hoping) the transformer would be spot on on the first attempt.
...so they "clerverly" took a previous same size transformer they had done, wired it with the caps, load resistors... and a variac transformer to "fine adjust" and then "correct" the turn ratios. They then sent me the transformer, probably without testing it in the setup.
The requirements was for 35V DC under load, and the transformer was of course "a bit" off specs. I was astonished when they told me how they worked out the turn ratio.
Needless to say that another firm did it right the first time and got the market.
-- Thanks, Fred.
Well, I put my measured values in: for my small 50VA toroid with 17% loss 220/18V I got from primary to secondary 25uH leakage inductance and 240pF interwinding capacity with both secondaries in parallel. From one secondary to the other it was 6uH and
3500pF, seem to be wound bifilar. I have not corrected the reading for the DC-resistance(0.7R each secondary, 36R primary), so the actual values should be smaller.IMHO a high leakage induction is bad. The pulse is not spread out, but the peak is delayed and the pulse has a much longer risetime, whereas the falltime gets shortened. This *creates* the problem with the spike. The peak current and rms value stay almost identical. Since the charge stored in the diodes is carrier_lifetime * current it will be better to take a faster diode. There is *no spike at all*, when the carriers recombine before the voltage gets reversed. One big mistake would be to put a capacitor across the secondary, or capacities to gnd from there. now the current which is stored in the leakage induction will oscillate nicely through this cap instead of the diffusion capacity of 2*2 diodes in series. People think it is good to put 10nF across the diodes, but this is almost as bad. Sure the frequency gets lower, but the damping not, unless you also use a resistor in series with C. Anyway, to spread out the pulse you will need a resistor in series. To dampen the ringing, a resistor across the secondary which is big enough not to dissipate too much will serve better against the "high voltage spike". Also the current of this ringing is really low, so I doubt it will have too much effect. The higher the frequency, the more damping because of skin effect etc.
-- ciao Ban Apricale, Italy
Well, I measured the loss and it was exactly ohmic, so you could actually use my simulations. And I was only joking to provoke you, because you can not give any constructive critics but just negativity. I also called for commentaries and was sharing *my insights* not the absolute truth. And I'm revising and learning as you can see.
-- ciao Ban Apricale, Italy
Unobtanium. But at least you keep us drooling.
Ed
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.