Before you discuss switcher chips and their synchronization features, you would decide for a topology.
- which AC/DC stage, simple rectifier? PFC? 1 or 3 phase?
- multiple or a multiphase transformer?
- which primary switch configuration, multiple single switches? H6 bridge?
Load sharing is enforced by operating all phases with current mode control. The current control loops must be fed the same current setpoint, which is the output of one voltage-mode error amplifier. So if you combine multiple controllers, one will act as a master, controlling the clocks and voltage error signals of the other phases.
I'm not sure what you mean by synchronous supplies. Usually that means they use transistors instead of passive catch diodes, maybe you meant to say synchronized?Well, i can see this working for synchronous supplies, all supplies will operate at the same time and give a little to satisfy the demand. But for multiphase supplies, each controller next in line would use 100% of it’s power to satisfy the control loop. The last of the controllers would rarely be used. This would negate the usefulness of multiphase controllers to reduce ripple current.
I'm not sure what you mean by synchronous supplies. Usually that means they use transistors instead of passive catch diodes, maybe you meant to say synchronized?
In any case, that approach does ensure sharing between interleaved phases, and is the standard method. Could you explain your reasoning a little clearer?
No, you misunderstand. Each phase has its own independent current control loop, and all of them are fed with the same setpoint. This means that all phases will always try to carry equal current. The ordering of the clock phases doesn't make any difference. There is no "first" phase, since the cycle is periodic.Yes i did mean synchronized.
Let’s say 6 interleaved supplies. 360 deg / 6 = 60 degrees, each supply supplies current 60 degrees after one another. If each supply is fed the same current set point then the first supply that the clock triggers will be the only supply supplying power at that instant. It will try to satisfy the full demand of the sagging power supply. Each subsequent power supply will supply less and less power.
Peak current mode control is normal, but average or valley current mode control can also be used.mtweig:
Through nothing less than superhuman effort of 3 days of Googgling, I found a total of two sentences from a Linear ap note on “how to” of interleaved power supplies.
“The current-sharing can be easily achieved by implementing peak current mode control. In a current mode control regulator, the load current is proportional to the error voltage in the voltage feedback loop. If the paralleled regulators see the same error voltage, they will source equal currents.”
Which sounds like the same thing you had said.
To implement it, you just need synchronizable controllers whose current setpoint can be overridden with an external signal (easy to do when they use transconductance error amplifiers). And you also need a way to generate the interleaved clocks. Beyond that there's no real trick behind this. Just look up "polyphase" on linear's website, they make dozens of suitable parts.I am still searching the internet for an actual design example using separate controllers. So far i have not found even one design.
FlapJack;
your lack of success in your search may have a silver lining.
It may mean that there is no prior art to it, and if you can actually solve the problem, you may have a patentable circuit.
What's the actual problem? The concept of current sharing is simple, if you understand the operation of switcher ICs, you'll know how to use it in multiphase topology.
Right, we're just pointing out that implementing multiple phases isn't a great leap from implementing a single phase supply. The controller(s) just need to have the capabilities I described above.As i said in my original posts i am trying to learn how to design switching power supplies. I did not say i know everything.
Peak current mode control is normal, but average or valley current mode control can also be used.
To implement it, you just need synchronizable controllers whose current setpoint can be overridden with an external signal (easy to do when they use transconductance error amplifiers). And you also need a way to generate the interleaved clocks. Beyond that there's no real trick behind this. Just look up "polyphase" on linear's website, they make dozens of suitable parts.
I looked the block diagram over for any sign of the double overlapping circle that usually indicates a transconductance amplifier but did not see anything. Here is the link for the data sheet. If this controller does not have a transconductance amplifier can you recommend one that does.
Most of them are meant to handle one phase per each chip, but they are capable of being combined and interleaved easily.I looked at the polyphase controllers on Liners site. They are all single chip solutions for low voltage low power aps and only one output per phase.
Yes, but I implemented external isolated gate drivers and amplifiers for the current and voltage sense, so it was significantly modified from the typical low power application it was designed for. This is typical for high power applications, the control IC does not directly interface to any of the actual high power circuitry.mtwieg:
Are you saying you only used one UCC28070 PFC controller for 20kw.
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