Electronics > Projects, Designs, and Technical Stuff
Ideal buck converter for high current
CoteRotie:
--- Quote from: David Hess on August 03, 2020, 10:17:26 pm ---
It could be done at the expense of power density and closed loop bandwidth. The higher operating frequency of smaller parallel multiphase converters allows for higher bandwidth for faster response and higher power density.
But winding and using high current inductors like that is more like plumbing.
--- End quote ---
Absolutely, I didn't mean to suggest it couldn't be done in a single phase, only that the (much) better solution from an efficiency, input ripple, input cap size, output response, and ease of design and build would be a multi-phase design. I have seen a 10kW single phase converter, but it was ugly ;)
You can do 30A/phase comfortably for lower voltage outputs but off the top of my head I would probably go with 4 phases for this design. I agree with comments that it's not a good design for a beginner to start with.
CoteRotie:
--- Quote from: anishkgt on August 03, 2020, 09:53:54 pm ---
--- Quote from: Jay_Diddy_B on August 03, 2020, 08:16:07 pm ---Hi,
So you 360F in a 3S2P configuration.
This is 240F
After the weld the voltage drops to 6V and you need to charge back to 8.1V
CV=It
240F x 2.1V = 504 As
If you use 20A charge current the charge time will be about 25 seconds to charge from 6V to 8.1V
Designing a poly-phase high current buck is NOT a good project for somebody who hasn't built one before.
Jay_Diddy_B
--- End quote ---
Thank you mate appreciate your concern.
I know the traces has to be routed bearing mind to keep the digital, analog and the inductors traces separated. There is always a first time for everything. To begin with i am looking at the ADP1850. Seems to be built for the kill.
--- End quote ---
Well, if you're happy with 20A of charge current instead of 84A you could do a single phase buck. The dual phase would be fine too. But if you want to charge using the full 84A the ADP1850 says on the datasheet "Output current to more than 25 A per channel". But probably not THAT much more so you would need a different part, like https://www.analog.com/media/en/technical-documentation/data-sheets/ltc7871.pdf
anishkgt:
That part is a bit too much with the extra gate drivers. I think i will go with the ADP1850, two in parallel. 25/phase would run them at 23 or 24 per phase give close to 92 to 96A. Inductors rated above 20A is hard to find and are less common.
Siwastaja:
Note that ending voltage of 8V means the average voltage is at 4V, which can be used for a rough loss calculation.
So while at 8V you could theoretize going without synch rectification, at 4V average it's almost a must.
Indeed, building it in single phase requires massive components and heatsinking, which easily blows your layout loop area up.
The more phases you use, the smaller the loops, and the easier cooling becomes; you can safely increase the distance between the phases (not going to extremes, of course, or you lose the benefits of shared DC input bus capacitance) to spread the heat.
These smaller transistors in smaller loops enables you to use higher frequency, which enables you to use smaller inductance values; making the off-the-shelf inductor selection current ratings go up!
As you have noticed, going below about 20A/phase gets you a wide selection of cheap off-the-shelf inductors.
Note you need a control IC that can do unlimited current-mode. Proper CC-CV would be optimal, but assuming you don't need good CC regulation, just pick one which limits current below the ratings of your components and doesn't go in a hickup or latched overcurrent modes.
I agree 4 phases would be the minimum. Some 2-phase control ICs have sync outputs phase-shifted by 90 degrees so you can built a 4-phase thing with two such chips. With more than 4 phases, the options for control ICs get more scarce.
Pawelr98:
--- Quote from: anishkgt on August 03, 2020, 09:26:08 pm ---Not sure how practical it would be to have an inductor in series.
--- End quote ---
This is in order to stop the thing from tripping OCP and blowing the switch that connects the capacitor bank.
If you connect a massive capacitor bank and there is a big voltage difference then massive current will start to flow.
We don't want that.
A series inductor will limit the current.
The only problem I see is the possible kickback which can overvolt the capacitors.
Computer power supplies are not equipped with constant current mode.
Once the current goes too high they just switch off.
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