Circuitry needed to make these Paralleled Buck converters share current equally between them?

[Flyback]

Hi

The attached (LTspice sim and pdf schem) is two paralleled Buck converters. Please assist us in making out the circuitry required to make these Bucks share current equally between them.

The circuitry shown inside dotted lines is what we have so far. However, we need the sharing to be done over the entire load range of zero to 8A.

Clearly what we have here will not do the job over the load range. So we need circuitry to indicate the difference between the load currents, and then accordingly adjust the individual reference voltages into the error amplifiers of each Buck…to make them share current. As you know, the circuitry should reduce the reference voltage of the highest current Buck, so as to make it peg back its current and Vice Versa for the other Buck….to make them share equally.

 

[ronsimpson]

????
The input voltage (24V) is the same to each buck? or different 24V supplies?
The output load is the same for each buck? There are multiple 2 ohm resistors, in parallel. The loads will share.
Why? From experience, there are things you have not told us.
What is the load?
Share to 10%? How accurate?

 

[ronsimpson]

More parts can be removed but this is just a start.

 

[Flyback]

Thankyou Ron, that’s an excellent solution…

The thing is, we are considering a way of making totally separate voltage regulating output power supplies to share with each other, into a single voltage regulated output….and really, the solution with the single error voltage for both controllers needs them both to be on the same PCB……sorry I didn’t say this at first….

So I do apologise because the reason we are looking into this isn’t specifically because of the Buck example that I gave here in the top post…its because we wish to do a 12.5Kw, 800V power supply, from a 400V PFC’d output. (input is mains 240vac)…..(but I thought it would have been too much detail to come forward with this in the top post)

...The best way we can think of is to have four sets of 3.15kW converters each comprising an interleaved 3.15Kw Boost PFC, feeding a 3.15kw Dual LLC converter with isolated stacked outputs (2*400v for 800v)……..then we will make the four 3.15kw, 800v outputs go into one 800v output…by use of a sharing technique between the four of them...this is why we are interested in "sharing" techniques.

(Basically, we need a 800V, 12.5Kw power supply from a 240vac mains input.)

 

[ronsimpson]

I can see stacking four 200V supplies. Each will regulate at 200V. This will make the error amps simple. By series the supplies will share current. (parallel-series sounds strange)

When I have paralleled; I used one error amp and over rode the error amps in the IC. That is what I wanted to show you.

Because I have not done 12.5kw in 40 years I would not want to start one. But 3kw PWC sounds better. Do you have a way to interleave them? And interleave the LLC?

 

[Flyback]

Thanks, We may even consider sixteen 50V , 780W output converters all stacked (ie in series) for the 800V, 12.5kW....Eg, Sixteen two transistor forwards each with sync rectifiers....Big heatsinks, since this 800V power supply will be on the ground and weight isnt so important. (its to power a tethered drone of 56kg weight)
Interleaving would be nice, but with them being separate power modules, i dont think we can do that.

 

[ronsimpson]

When stacking supplies to get higher voltage, put a diode across each output to keep any supply from being driven negative.