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Old 14th July 2005, 07:51 AM   #21
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Location: Alps:Tube amp designs over 150W, SMPS guru.
We have to examine the maths and physics of pfc digression in the 1kW domain: Continuous/average mode running f= 60KHz; required core volume would be around 73cm3 i.e E65 core size. Boost diode losses around 7W. Inductor 300uH at 25% ripple.

Looking at 100KHz operation the core size would come down to around 44cm3 i.e E55. However boost diode and switching mos losses rise to 10W % 35W for Mosfet. Inductor value around 180uH. Clearly with rising freq, switching losses begin to mount.
A magnetic snubber would improve efficiency at 88V.

Theres alot to reiterate. At 1kW a lowRds value of mosfet is quite important. The sense resistor value roughly 20milli-ohm 3W is going to be troublesome. (A mosfet could be used in lieu). Current transformers add complications i.e require extra knowledge. The EMI noise is also an issue and is related to ripple current in the inductor. Choosing a higher value inductor lowers this proportionally but the size goes up.
Another issue is to run both DC/DC and pfc at the same frequency; this then becomes too low for the DC/DC converter when one can realistically see a running freq over 100Khz.
With the efficiency figure I previously mentioned may seem pessimistic. However the pfc inductor value and core volume is important...that is any peak current that might saturate the core would be devastating for both switching devices. At a kW a fail would be quite dramatic.
AN overall efficiency of just 70% for both DC/DC and pfc combined
running at 1KW o/p power was suggest designinging for 1400W.....that would be the case for Telecom......but for music rating your peak condition is unlikely to be reached. As a designer I would go for the expected peak figure. Only my opin.

The hardest part is to <see a spec what one wants> and eventually arrive at a compromise sep and build round it. There is also the aspect of the build time. The other poss is just build the DC/DC part and swallow the grim cap input power factor. I'm against this.

I can look at the required input cap values; but this cap-input policy is fast disappearing and I'm against this.........Note recent energy legistation in CA.
EVA has seen the audio end through, again as she mentions the european mains volts sort of rescues the pfc.

I hope you can see what happens between steady music conditions and actual worst case peak power.
Cold water on ideas ? still luke warm.

richj
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Old 14th July 2005, 02:04 PM   #22
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Eva, sounds like you have some solid hueristic knowledge of audio. I'm not following your numbers, though. If the amp is 100W rms, then wouldn't the peak power be 141 watts (100 * root 2)? Then a 6 channel system would need 846 watts peak. How did you come up with 1200 watts worst case?

You confirmed my gut feeling that the real world average power consumption is going to be significantly less - I just don't have the experience to back that up. I used to do some audio work for telephone systems, and I recall looking at the crest factor - but don't remember the details except that peak to average was a big number.

So getting back to your description, I would need to supply 200 watts average with enough capacitance/storage to handle the transient peaks?
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Old 14th July 2005, 02:30 PM   #23
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600 * sqrt(2) [for peak voltage] * sqrt(2) [for peak current] = 600*2 = 1200
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Old 14th July 2005, 03:20 PM   #24
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Quote:
Originally posted by DonoMan
600 * sqrt(2) [for peak voltage] * sqrt(2) [for peak current] = 600*2 = 1200
Doh!

Absolutely correct, thanks for correcting me.
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Old 14th July 2005, 11:39 PM   #25
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Quote:
Originally posted by gearheadgene
So getting back to your description, I would need to supply 200 watts average with enough capacitance/storage to handle the transient peaks?
Exactly. Note that this requires careful pulse by pulse and average current limiting in the PFC section, and a lot of capacitance in the PFC bus. However, a compromise between output power and capacitance may be found, I would recommend 400W or 500W for the PFC as these numbers are somewhat easier to reach than 1000W. There are even 500W evaluation boards for sale, I think.
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Old 15th July 2005, 10:59 AM   #26
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(my son wanted to see that


Can you elaborate on the pulse by pulse limiting? What type of regulator would you recommend for this power level - half-bridge, 2 transistor forward, flyback, other?

I am going to look to see what eval boards are available. As I said before, On-semi has a 1KW pfc available as eval board but am not sure if they also have a 500W dc-dc eval board. Let me check. If anyone knows of some, feel free to chime in.
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Old 15th July 2005, 11:16 AM   #27
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Why do you want a smps this big ??? Driving car power amplifiers in your home ?
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Old 15th July 2005, 11:22 AM   #28
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Quote:
Originally posted by Tekko
Why do you want a smps this big ??? Driving car power amplifiers in your home ?
Just working on a 6 channel amp (5.1) for the home.
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Old 15th July 2005, 11:32 AM   #29
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You wont need one kilowatt spms for that, just use a 500VA transformer for the 5 main channels like any home vinema amp/receiver and a separate subwoofer amp mounted on the sub "plate amp"
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Old 15th July 2005, 11:49 AM   #30
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Tekko:

Sorry, this is an SMPS discussion, there is no place for bulky 50Hz transformers and unregulated rails sagging 30-40% under full load.
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