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| A niche chip (LT4320) for mains powered AC -> low volt DC "linear" based psu ? |
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| johansen:
a zero loss diode bridge would not be very useful for high power high voltage circuitry anyway.. because you would need a high volume inductor after the bridge to keep the power factor within reason. there are a few diode-less pfc topologies available, most produce a lot of common mode noise. there is a topology i like but i haven't developed a controller for: see attachment |
| Phaedrus:
Well right now the most common topologies in PCs go like this: Common Mode Filter --> Bridge Rectifier --> Interleaved boost converter PFC --> PWM --> Transformer --> Secondary The most common PWM topologies are either Double Forward (for 80%-87% efficient PSUs), or LLC Resonant Half or Full Bridge (for 87-92% efficient PSUs). There's also some high-end ZVS Phase-Shift Full Bridge units, and a popular Active Clamp Forward platform. Anyway, efficiency is an important marketing feature, and the big efficiency certification is 80PLUS. Currently the top of the line runs 80PLUS Platinum, which requires 89-92% efficiency at 115VAC at room temperature. There are about a half dozen ODM vendors who can currently reach this and still maintain "enthusiast grade" voltage regulation and ripple. But 80PLUS is working on a new standard, called 80PLUS Titanium. The spec isn't finalized, but word is the efficiency at 50% load will have to be either 94% or 95%. That's 2-3% that we need to gain over current designs, most of which just clear Platinum. We've adopted the DC-DC secondary topology which netted the 1-2% boost needed to hit 80PLUS Gold back in the day. It's hard to improve that much more, considering we're already using synchronous rectification both for the main +12V rail and for the minor rails. Assume we can boost the efficiency of the DC-DC modules, call that a 0.25% gain. The transformer and other magnetics efficiency is improving slowly but surely. We can probably get another 0.5-1% there by end of next year. With improvements to layout, connectors, shortening power traces, using thicker copper, etc, we might get an extra 0.25% there. So we need *at least* 1% more gain. PWM topologies are currently close to maxed out, it's unclear how much more we can gain there. So where do we have obvious losses we could cut? The bridge rectifier and the PFC diodes. Replacing the diodes in a boost converter is a classic power electronics problem that has yet to be solved. I don't think anyone's made one that doesn't nuke itself yet. So that leaves the bridge rectifier. The current trend is to go bridgeless PFC, which replaces the bridge rectifier with active MOSFET rectification. No one has built an adequate analog controller to do this yet (the LT4320 is the closest I've seen), so currently you have to use MCU control. This normally ends up with the entire PSU being MCU controlled, instead of analog, which is a $30-$50 increase to BOM cost. If someone could figure a way to do it analog, without requiring a digital control loop, for $20 BOM or less, that would be a killer advantage in the market. If we could get 0.5% efficiency there that would put us in reach of 80PLUS Titanium certification at a lower cost than the competition. |
| digsys:
--- Quote from: Phaedrus ---The transformer and other magnetics efficiency is improving slowly but surely. We can probably get another 0.5-1% there by end of next year. --- End quote --- I find it interesting that they can't get better? We've had MPPT chargers (which have a much more difficult task) at app 97-98% for many years. Our current design, by one of our members, runs at 98.5% at 4:1 In/Out range over most the power range. It's a resonant synchronous design. They even have resonant controller chips out now. Mainstream doesn't seem to be interested in efficiency unless they're forced to. |
| Phaedrus:
--- Quote from: AcHmed99 on December 28, 2013, 11:45:06 am --- --- Quote from: digsys on December 28, 2013, 08:31:07 am --- --- Quote from: Phaedrus ---The transformer and other magnetics efficiency is improving slowly but surely. We can probably get another 0.5-1% there by end of next year. --- End quote --- They even have resonant controller chips out now. Mainstream doesn't seem to be interested in efficiency unless they're forced to. --- End quote --- Because the end consumer isn't going to want to pay for it. Look how competitive the PC power supply market is. You have a never ending flood of cheap bogus rated chinese crap going for 20 bucks or so. Thats all most consumers care about price. In order to get high efficencies you need more complex resonent topologies and sync rectification. Even for those to hit high efficencies you have to use more expensive semiconductors. Most PC supplies I've looked at are junk. They use the cheapest fets or IGBT's, cheapest rectifiers minimal if any line filtering, heatsinking that would be woefully inadequate to deliver rated power given the crap semi's they use. --- End quote --- Actually there's quite a large market for quality power supplies. The gamers, enthusiasts, and Litecoin miners all want quality kit, and will pay for it. The cheap $20 crap may move in volume, but it's not particularly profitable most of the time. The $50 - $150 segment is extremely competitive and usually quite profitable. In the US, 650W, 750W, and 850W power supplies that are 80PLUS Bronze (82-85%) or 80PLUS Gold (87-90%) sell very well; total market size of 25,000-40,000 of those wattages a month. Average price near a hundred bucks. Crack open one of our CoolerMaster V850 power supplies and tell me that's cheap crap. It may not be lab grade, but it's solid engineering and good build quality. ;) |
| M. AndrĂ¡s:
if the damn psu is as reliable as it can be like those decades old hp lab power supplies then i will gladly pay a fair price for it, not like the cheap 50-100bucks cheap 500+watts shit what cant even deliver its rated power and when i dies kills the attached things too. im wondering if this chip could be used with pretty low rdson fets and its power supplied externally it doesnt need much so a small bridge rectifier from the main ac feed maybe? high power losses would be minimal too |
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