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Old 13th July 2005, 07:26 AM   #11
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OK, so half-bridge config looks good. Can anyone recommend some good regulator IC's for that?
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Old 13th July 2005, 07:47 AM   #12
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Have you decided on current mode or voltage mode......?
There are masses of switching ic's about for such apps.
UC3825;UC3525;
Current mode is best for half bridge.... takes care of inductor staircasing.
Have you worked out the cap input filter requirements and output inductor ?

richj
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Old 13th July 2005, 02:17 PM   #13
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Hi Rich,

I haven't worked out much at all, actually. This is all pretty much new to me, so I am learning as I go.

If you go back in the thread, you'll see that the plan is to use PFC preregulator. I've found at least 2 reference designs from On-semi, plus have seen some from other manufacturers too. This should hopefully be an ok starting point.

Other than that, I'm still poking around trying to get as much info into my tiny brain that I can Couldn't sleep last night, so was up 'till 4 am reading through the various posts. Haven't finished reading yet, though.
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Old 13th July 2005, 03:26 PM   #14
Eva is offline Eva  Spain
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Could you tell us about each of the required outputs? ie: output voltage, cross-regulation requirements and allowable voltage error margin, minimum load, typical load and maximum load expected for each output.

Could you also tell us about the input? ie: minimum and maximum input voltages.
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Old 13th July 2005, 06:04 PM   #15
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Quote:
Originally posted by Eva
Could you tell us about each of the required outputs? ie: output voltage, cross-regulation requirements and allowable voltage error margin, minimum load, typical load and maximum load expected for each output.

Could you also tell us about the input? ie: minimum and maximum input voltages.
why soytenlee (my best 3 stooges impression). . .

Universal input - standard stuff, 85 VAC to 240 VAC
feeds PFC
PFC output (around 400 VDC) feeds isolated DC-DC converter.

Output voltage, probably around 35 VDC
Output current MAX, around 30 A.

I'm thinking that only a single output will ok, but will consider other distributed topologies if needed.

Regarding the load, well that's going to be all over the map. I'd say minimum is pretty low - maybe 50 Watts when idle, and max will be around 650 or 700 W. As an estimate, the typical power consumption will be 200 W.

I've rationalized the 1KW requirment as having enough room for growth without having to redesign - although this may remain as overkill. Started out as needing 650W, then thought to add a little comort zone, then considered some future plans, and then next think I knew - bam, 1KW was just about right.
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Old 13th July 2005, 07:49 PM   #16
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Your requirements seem not too complex, but at first you mentioned several outputs, what are you going to power?
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Old 13th July 2005, 08:55 PM   #17
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Quote:
Originally posted by gearheadgene
Hi Rich,

I haven't worked out much at all, actually. This is all pretty much new to me, so I am learning as I go.


okay you got a few boundary conditions set up........ ...there are some tricky bits which we shall eventually arrive at and be prepared for compromises.

You mention the pfc rated worst case at 1kW (the inductor size would be based on that figure and run at a lowish frequency)... at 88 V AC the pfc would require nearly 13A from AC supply. This is bad news for EMI input chokes and the input bridge rectifier.

Food for thought....If you assume DC/DC conv 30AX35V =1050 Watts, the overall efficiency or both PfC+ DC-DC 1/2 bridge forward converter would be around 0.85x0.8=0.68.
The loss of efficiency with the pfc at 88V at 13A is to be expected ....You will have to give us some idea of expected physical size of both units
You mentioned <quote> "that all is pretty new to me". Do you have a good oscilloscope and other test gear ?

richj
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Old 13th July 2005, 09:02 PM   #18
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Why do you need a ps with this mutch power ?
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Old 14th July 2005, 03:21 AM   #19
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Quote:
Originally posted by Eva
Your requirements seem not too complex, but at first you mentioned several outputs, what are you going to power?
Maybe I'm giving mixed signal here. Let me be a bit more specific - I want to power a 5.1 style amplifier. Each stage is going to be 100 watts into 8 ohm, so that accounts for 600 watts. I plan to run the amps at 35'ish volts, so each channel is going to require
2.9 Amps. I still have to figure out what to do about 4 ohm loads.

Additionally, there's some low voltage circuits that need power (5V, 3.3V, etc.) that may or may not be derived directly from the off-line portion of the supply. Rough estimate of 50 Watts for that stuff.

I am completely open minded on how to handle this supply. That's why I was suggesting other topologies. Heck, I even considered a transformer (torroid) to drop line voltage down to something lower, then run a individual AC-DC supplies on each channel. Then, I could use flyback stuff, simpler (perhaps) and maybe cheaper. Overall, I'm not sure the cost winds up less. For certain, the torroid isn't cheap - and then again, I'd have to handle the switching from 120 or 240.

Quote:
Originally posted by richwalters



okay you got a few boundary conditions set up........ ...there are some tricky bits which we shall eventually arrive at and be prepared for compromises.

You mention the pfc rated worst case at 1kW (the inductor size would be based on that figure and run at a lowish frequency)... at 88 V AC the pfc would require nearly 13A from AC supply. This is bad news for EMI input chokes and the input bridge rectifier.

Food for thought....If you assume DC/DC conv 30AX35V =1050 Watts, the overall efficiency or both PfC+ DC-DC 1/2 bridge forward converter would be around 0.85x0.8=0.68.
The loss of efficiency with the pfc at 88V at 13A is to be expected ....You will have to give us some idea of expected physical size of both units
You mentioned <quote> "that all is pretty new to me". Do you have a good oscilloscope and other test gear ?

richj
That's a bitter pill to swallow - even though you are right! It crossed my mind before, but I have conveniently forgotten about the power loss. With such a lousy loss of power between the PFC and dc-dc, why would anyone bother? Maybe the regulations over in Europe get in the way, or maybe the pfc stuff makes sense for all the other reasons - but the power loss is really ugly.

So where does that leave me now? I could run without PFC, that's another option. If I don't though, and am losing 32% in conversion inefficiency, then the power requirements go up - ugh.

Equipment? Right now, the only stuff I have access to is at work. Moving forward, I'll need to get some here at home.


There is something that I can't put my finger on, and has a big impact on my requirments. In my example of 5.1 system, each channel rated at 100 watts - what are the odds that the system would have to supply 600 watts continuously? Given the nature of audio, it's more like random noise. But what about music? Anyway, I'm rambling.

gene
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Old 14th July 2005, 07:22 AM   #20
Eva is offline Eva  Spain
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Audio is tricky because peak to average ratio of power consumption may be as high as 10. Also, tight regulation is not strictly required, so you may use the 400V DC internal bus to drive an unregulated DC-DC converter and still get some (average) regulation while making things much simpler.

If you are going to power 6 100Wrms channels then the worst-case peak power consumption will be 1200 W, the worst-case average power consumption will be less than 900 W. The real-world worst-case peak power consumption with music signals at maximum volume may still be near 1000 W, but the average power consumption will hardly reach 200 W, even with everything starting to clip (trust my experience).

With so high peak to average power ratios, having a power supply with poor efficiency at 1000W is not a problem as long as it can repetitively handle 1000W for small amounts of time in a reliable way. Furthermore, you can use a lot of capacitance on the 400V bus in order to isolate the PFC converter from high peak currents, since 400V capacitors store more energy in less space and at less cost in comparison with 35V capacitors.

If you live in an area with 230V mains, you could also discard the universal mains requirement and just cover 176V to 240V in order to make PFC thingy easier.

The low-voltage housekeeping outputs may be derived from the main DC-DC transformer or even from the PFC inductor in order to get power as soon as posible. Then, it's easier to just shut down the main DC-DC converter in case of fault, over-current, over-temperature, etc....
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