Inrush current-limiting

Show your math.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

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** A simple simulation or test will show the claim is not wrong.

If you have some dark reason to doubt it - time to out it.

..... Phil

The 'if there is no limiting' is the key phrase here. ESR of the filter capacitor, series resistance in the rectifiers (required for hot-spot reduction in many power diodes), and even the power cord are significant limiters of inrush current.

Power cord and capacitor are the components best able to deal with a bit of waste heat, so putting the losses there would be sensible. A common-mode inductor, in many larger power supplies' AC line, is another candidate, as are fuses (slow-blow preferred).

supply - the M-400 "Carver Cube" and Carver PM1.5 models.

At switch on, the triac firing point ramps up from zero crossings to about

65% of the peak voltage of the AC supply over about 2 seconds. Of course th is eliminates any transformer of filter electro inrush surges.

In use, the firing point constantly changes to keep the internal DC rails s teady as possible. It's a simple pre-regulator scheme that permits the use of a MUCH smaller AC transformer than otherwise.

However, if on bench test you hold the amp at full power with both channels running for a couple of minutes - smoke soon oozes out of the transformer. "

You might be off base on this one. He is talking 15 uF here, which is defin itely something else.

Actually though, zero crossing has been used with alot more filter cap than 15 uF. Sony TVs did it, and when the micros did not get a zero crossing si gnal it would not come on. Fixed a bunch of them and actually it was just a slightly leaky diode. The board actually had space drilled and everything for two diodes in series but they jumped one with piece of wire. when the other diode's leajage got too high the set would ot coe on. But the idea wa s to turn the relay on at zero crossing to minimize stress on the compoents .

Other options exist, as you stated, the Carver design just picked it up gra dually, but then that was a fully regulated system. For most applications a n engineer would not go to the trouble of all that. Especially because now cheap rules.

I bet you remember the days when transformers were used between transistor stages because of cost. the transformers were a cost conscious idea, as the y saved money. Later transistors got so cheaper and better, and with so muc h gaun and bandwidth that these transformers became obsolete. It was simply a matter of money.

But many schemes have been used to linit the inrish current. They also used a secondary relay ot let in a resistor before giving the full current to t he cap.

But on an engineering level, I think they use too much capacitance these da ys. They do it mainly, I think because of the ripple current. Well my siste r's PC monitor quit and I replaced a BANK of 1,000 uFs with ONE 100 uF at 1

60 volts and it has lasted a log time. you think maybe caps used to be bett er ?

Maybe it is just my imagination but if you ever want to brave pur cities an d come here gunless and vulnerable I can show you the picture on this monit or.

I stop now.

was to protect the limiter's *pass* transistor."

Perhaps you areunfamiliar with for example the 1.5t. You have probably seen commutating power supplies in amps but that thing used an extra stage. Thr ee rails. the TRIAC was there to try to keep the rails up. And Phil is righ t, you push these things they blow up. They depend on the variable load of normal audio to live. that is about when I gave up o Carver designs. In fac t I just sold my PL 400 - 2 because I simply do not need that much power. i f I had a carver 1.5T I would never have hooked it up. But really, the 1.5T is not that great audio wise, the PL 400-2 is though. Not in every way, bu t I heard the difference with the 1,000 damping factor. But I had speakers at the time.

Bottom line, maybe Phil will get with me here, why the hell does a SMPS run ning at 150 KHz need like 2,000 uF filtering the damn AC coming in ? It doe sn't.

I cme up with a circuit that eliminated most of that and people said is was not practical, well with a few modifications that cn change. Ever see the VFDs that run stright off the 50 or 6o Hz mains ? running off of three phas e they can make any frequency and do not even have a rectifier. When I prop osed my one output device audio output here and was thinking of patenting i t, I dropped it after seeing that design because I was sure that is prior a rt. Without a patent I am not all that interested in persuing it. I am done working and if anyone doesn't like it they can get the f*ck out.

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** Lemme see - when "jurb" snips the prior context post out of sight the fool acts like it never existed in the first place.

Wot totally insane crap !!!!!!!!!!!!!!

FYI to all:

I've sniped yet another of this boring retard's tedious "Concertos for Solo Trumpet" out of sight.

Cos nobody alive needs to see it.

..... Phil

If ou need that you do ot belong here.

Drop and Vfw of the rectifiers and forward resistance then add the ESP of t he cap.

I am a ninth grade dropout and I know that.

It can be 200 amps, but only for microseconds. As it charges the cao the su rge goes away. Just like your incadescent lamop they measures three ohms wh en cold, but once warmed up it only pulls 100 watts because its resistance has risen to like 130 ohms and it is only pulling one amp.

How many people here can design a video game or an IC but don't know basic amps and ohms ? Maybe I should start a school. You know now you can't just put a new battery in a car because the alternator cannot handle it. It will fry out and there goes another hundred bucks if you get off that easy. You are not getting what you used to get. We put completely dead, even shorted batteries in cars and the alternator just handled it as we drove around.

Another thing is that in the TV field I saw a like foot long piece of foil evaporated off the circuit board in a Panasonic, going to the rectifiers. I checked for shorts and there were none so I just hooked it up and the set worked. If that doesn't tell you about the difference between peak and aver age current I don't know what will.

You don't even need ten ohms. One ohm would do it for 120 volts. that limits it to 120 amps at worst. This is assuming zero resistance or drop i the rectifiers and zero ESR in the main filter.

Even all that, most power switches can handle it, as well as the fuses. Even going into the wiring and circuit board foil dimensions, when that amperage is passed it is a matter of time. A ten amp fuse can handle 100 amps, but only for a short time.

Time is one thing that engineers forget but I have neither the time or inclination to teach them.

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( snip off key trumpet music )

** If the PSU is to deliver 1500 watts of DC to the output it very much does.

AC supply side filtering must reduce the p-p value of the 120Hz ripple voltage to an acceptable level - usually not exceeding 15% of the average DC voltage.

WTF makes you think otherwise?

On second thoughts, I don't need to her your reasons.

Bad trumpet music offends my delicate hearing.

.... Phil

The problem isn't intrinsically the couple hundred amp spike that occurs when the filter cap is connected at the peak of the line waveform and the voltage leaps from 0 to ~170. Most components can handle a narrow pulse of a couple hundred amps for a few microseconds - the pulse is gone before it "knows" what hit it.

The problem is that the rectifier, cap, and lead/trace inductances form a resonant circuit and when hit with the material equivalent of a 170V Heaviside step the thing rings out like a bastard! Like a 50 amp RMS waveform going on for hundreds of usec. Definitely long enough to hammer any resistive components in series silly enough to be in the way of it.

1 ohm isn't enough to damp the resonance.

Just a representative example in LTSpice:

Could be much larger, goes on for days...

I guess 3/4 ohms is passable for 15uF. 110v gives 155v peak.

NT

The problem isn't the maximum possible value of the initial current spike as given by Ohm's law for DC, it's the RMS value of the _surge_ current into an under-damped resonant circuit that goes on for the better part of eternity when compared with the length of the spike.

You need to damp that shit and 3/4 ohm, 1 ohm etc. won't cut it.

Maybe you could argue for the behavior's reliability from entropy. What are the chances a little SMT resistor can be blown apart by having X number of joules dumped into it and reassemble itself into a wire?

Cool. Show your math.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Doing a full time-domain nonlinear analysis of a bridge rectifier + cap

• parasitic inductance + load hit with a truncated sine is a pretty damn nontrivial math problem! And I think it would need to be that complete to show the problem.

IIRC someone only did a full time-domain mathematical treatment of a bridge rectifier + cap with a sine input in like 2008 or something.

OTOH you can set up a representative LTSpice circuit and appropriate input waveform in about 10 min and it shows the spike and surge just fine.

You could get a pretty good estimate with a 4-function calculator. But none of the experts here seem able to do that.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

You don't even need a calculator ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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