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Old 11th September 2012, 06:36 PM   #1071
Krisfr is offline Krisfr  United States
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Quote:
Originally Posted by danielwritesbac View Post
A spreadsheet would be wonderful!
I thought something like this would be kinda cOOL
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Old 11th September 2012, 06:37 PM   #1072
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for simplicity.
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Old 11th September 2012, 06:42 PM   #1073
Krisfr is offline Krisfr  United States
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Can all of those Dynamics be taken care of by a little capacitance over kill ?

Way too many variables...
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Old 11th September 2012, 07:00 PM   #1074
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Obvious that 8700uF is not big.
condition is simple:
ac1 & ac2 probe on secondary of trafo.
c_Main = probe on main caps (8700uF)
r2P = probe on dissipation load (650w) it is a burst 1Khz with duration 16ms as see, connected at output of this psu (on main capacitor). this is all.
Orange track= same condition but probe at output of experimental regulator...ahah yes, this is vcc i need
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Old 11th September 2012, 08:27 PM   #1075
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Quote:
Originally Posted by AP2 View Post
This is a fantasy that a psu with transformer, drop only 1-5V. sorry for this. if you have measure, please show.
Ew. The diode noise, the power line noise and loop noise all contributes higher charge to the capacitors when in unloaded conditions (a major problem for preamps); likewise, weak current noise makes artificially inflated voltage drop in power amplifiers. Yuk! If you didn't want that, then please filter it. For reference, see ham radio style power filtering. You should be able to reduce your voltage fluctuations by at least 2v. After filtering, the end result can meet AndrewT's 1v to 5v spec.

Also check out your under-load bridge rectifier forward voltage drop graph. Compare to the graph for KBPC3502 (looks almost like a straight up wall). A well snubbed KBPC3502 plus a transformer that has RC's applied across primaries and secondaries, will give you a more steady voltage due to reduced noise content. Noise filtering (parallel filters) and sturdy diodes--this works!

P.S.
Other possible problem for too much fluctuation is inrush resistors, crc, etc. . . that make caps take longer to charge, since series filters make a given transformer work like a much smaller transformer, and thus installing series filters IS re-visiting the question of whether or not your transformer is big enough. Earlier, I posted about a method for constraining the voltage drop of series filters by setting diode(s) parallel to the resistors for your choice of voltage drop limits (that resistors alone can't do because resistors work with current, not voltage). SO, you can have a CRC without epic voltage drop at high power.
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Last edited by danielwritesbac; 11th September 2012 at 08:38 PM.
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Old 11th September 2012, 10:54 PM   #1076
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AP2, measuring the secondary voltage does not give a scaled-down (by turns ratio) version of the AC line voltage. your rectifier-capacitor load is producing the flat-topped waveforms in conjunction with the transformer secondary leakage inductance. Although your AC line may well be slightly non-sinusoidal, in order to tell that you need to measure the AC line itself - or measure the unloaded secondary if you dont have isolated voltage probes.

Unless you have an amplifier as large as, say, a rolling stones concert, you wont affect the AC line voltage (hint: what is the rated power of the AC connection your house is connected to?).

And just for fun, try calculating the voltage THD
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Old 11th September 2012, 11:49 PM   #1077
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Originally Posted by Terry Given View Post
Unless you have an amplifier as large as, say, a rolling stones concert, you wont affect the AC line voltage (hint: what is the rated power of the AC connection your house is connected to?).
Unfortunately, the mains is affected by all the ratty devices dragging power off it, which adds yet another layer of complexity upon this matter; it can be quite a mess. I've posted this link a couple of times, but for the sake of the conversation I'll add it here again: www.acoustica.org.uk.

... (there is an eery silence as several sim's bite the dust) ...

With all this it's a wonder that amp's can produce anything like decent music ...

Frank
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Old 12th September 2012, 03:37 AM   #1078
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Frank, thats not bad - I've seen a much nastier picture than that: entirely missing cycles. it was at the end of a reasonably long transmission line (a few hundred km) and a local business had a spot welder making (IIRC) mattress assemblies. 20MW or so. every time it turned on the local supply collapsed completely. Some friends of mine were hired to fix the resultant power quality problems the rest of the small town experienced. their solution? buy everyone a UPS. which AIUI the company did.

you'll get the worst power in, say, an office block, where there may be hundreds or even thousands of rectifier-capacitor loads. this can and does set neutral conductors on fire (non-sinusoidal currents do not cancel in three-phase systems)


when it comes to measuring things like THD & PF of unity-PF SMPS, this is a real problem - most PFC work by forcing the line current to follow line voltage - so when testing you must use a clean voltage source, to get accurate, repeatable results. One simple test is to measure the PF & THD of a purely resistive load. if it aint 1 & 0, then all is not well with ones voltage supply.

we can draw some interesting conclusions from this:

1. even with perfectly sinusoidal mains, the rectifier-capacitor load at the end of the secondary (and primary) leakage inductance will still give a flat-topped secondary output voltage.

2. this is yet another good reason for a well laid out broadband DC bus (parallel plates again) if your cap bus is < 100mOhms up to 1MHz (easy to do) then it will attenuate the bajesus out of the AC line noise & harmonics

3. its also another good reason for the split DC bus approach, with the rectifier & first bank at the xfmr - all the mains harmonics & noise must still flow in the secondary wiring to & from the cap bank, so short (twisted) wiring will prevent it magnetically coupling elsewhere

4. Unless there is something horribly wrong with ones capacitor bank (say for example it is a typical audio one /snark), the attenuation of harmonics will be quite good - after all, they are designed to be nice and low-Z at the fundamental. This is where the transformer leakage is actually useful. Using Toms xfmr with L_leak_sec = 1.4mH and Cbus = 3mF, thats a 2nd order LPF with a corner frequency of 78Hz. rectified 3rd harmonic => 300Hz (yeah, I know, thats not the actual spectral characteristics of |sin(3wt)| but tis a reasonable approx & im lazy) so thats > 20dB attenuation.

4a. above some frequency the xfmr stops helping due to P-S capacitance - which is why screened xfmrs are used. But as with all EMI, the connection of the screens is paramount - any inductance in the screen connection to Earth is bad, as it not only now has a resonant peak, but above that frequency the screen shielding drops off with increasing F.
(I havent seen screened toroidals, but thats because I havent looked)

5. this is however a good reason to beef up the capacitor bank above the Gootee Minimum (although thats still pointless if the layout & wiring is lousy)

6. one sincerely hopes ones amplifier PSRR is good at LF, so any harmonic ripple that does get thru the cap bank wont modulate the output

7. using encapsulated CM/DM filter AC line sockets is a good idea, to clean up any nasty HF noise. these have excellent Earth connections, so you pretty much cant screw it up. any EMI filter that you have to supply the earth to is just asking for trouble...

I promise not to talk about PCC impedances.

Last edited by Terry Given; 12th September 2012 at 03:39 AM.
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Old 12th September 2012, 05:03 AM   #1079
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Yes I do keep an eye on you thread. We started by aiming for large caps, then aimed for smaller caps but in all we have reached a conclusion we reached at the beginning . Keep up the good work guys.

But one thing is clear, its good to have a healthy transformer. Everything had already been sorted out here Power Supply Resevoir Size , Power Supply Resevoir Size, Power Supply Resevoir Size , Power Supply Resevoir Size .
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Old 12th September 2012, 06:02 AM   #1080
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I have another potentially dumb trick with diodes.
The following example is using a 36vct (18,0,18) transformer and a CRC power supply.

For drainer resistor and a bonus light:
Per each rail. . . 10 of 2v orange led with each a 22k resistor.
That array looks like a 2v diode drop series to a 2.2k drainer resistor.

Notice that when the fridge or AC or vacuum cleaner is on, the diodes light up a bit brighter. Proportionately, this rather bright 2.2k bleeder resistor arrangement is wasting more noise than DC.

Since the example power board is a CRC, where do I put the diode+resistor drain for best effect (to waste more noise than DC), transformer side of the pi resistors (the "R" of the CRC) OR reservoir side of the pi resistors?

And, could I use power diode series to 2.2k to accomplish the same effect as the led's?
I ask because a black diode doesn't give an obvious indication.
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Last edited by danielwritesbac; 12th September 2012 at 06:11 AM.
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