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  1. #1
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    The "cheap, quick and easy" way to do high power SMPS's?

    Hi,
    Is this the “cheap, quick and easy way” to do high power SMPS’s?

    The attached shows two identical Two Transistor forward converters in parallel…..each is 1.2Kw (50vout and 24iout)
    If any one trys to hog all the current…its current limiter kicks in and stops it from doing so.

    Many more can be similarly paralleled to build up a higher power SMPS.

    No feedback loop fighting.
    Nice thermal spreading.
    No interconnecting electronics needed to ensure sharing.

    What’s not to like?
    (attached is the pdf schem and LTspice sim)

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    Re: The "cheap, quick and easy" way to do high power SMPS's?

    and if it's built symmetrically - the thermals will be even-ish too - but ...!

    how are you doing the volt feedback on each one ...? if one is a few mV higher than the other it will do al the current up to current limit...

    ever heard of electronic droop current sharing? needs only one resistor in the Volt error op-amp to drop the volts with load, e.g. 54 to 53.5 from 0 - full current

    this is also a quick & dirty way to get good easy current sharing with no oscillations ...... ;o) you're welcome ...

    - - - Updated - - -

    Also - in your pdf - why not have one IC and have the same gate drive ( buffered ) to both ( and more ) of the power stages ... for the same Tx in each case the pri currents should be very close ...!


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    Re: The "cheap, quick and easy" way to do high power SMPS's?

    My starting point would be to choose a current mode controller/topology and, as we've discussed elsewhere, you can then have one voltage loop driving as many inner current controllers as you want. Perfect sharing. No risk of weird converter starts and stops as they hit their limit.

    It's just as easy to find CMC as voltage mode controllers so there is little downside that I see.


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    Re: The "cheap, quick and easy" way to do high power SMPS's?

    the circuit appears to be current mode already - just need to link the comp pins - for all stages to do the same current ...

    - - - Updated - - -

    if you synch the oscillators too - then they would all switch at the same time ( if desired ) ...


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    Re: The "cheap, quick and easy" way to do high power SMPS's?

    "1.2Kw (50vout and 24iout)" works fine if that's what you need.

    way back when I started engineering, there was a cartoon near one guy's desk
    cost, quality, schedule - pick 2.

    cheap quick and easy just sounds too good to be true.
    and usually, if it seems too good to be true, it is.



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    Re: The "cheap, quick and easy" way to do high power SMPS's?

    Ok then.

    Ideally you’d phase shift them for interleaving.



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    Re: The "cheap, quick and easy" way to do high power SMPS's?

    Thanks, I admit that one controller is better…..(eg one error amplifier for multiple units etc etc)……though in some ways I like the idea of a totally independent unit, that doesn’t need its control linking up to other units…where the local ground may not be the same due to current flows, etc……and indeed, different units are likely to be on different PCBs and a single error amp signal would need wiring between units.
    Yes I agree that any of them may just go into current limit….though to be honest I am accepting of that.
    I suspect that when on say 70% load……with say 10 SMPS’s in parallel like in the way of the top post…..then maybe one unit might be totally off…and if a sudden 100% load transient then occurs…..that “off” unit (with its error amplifier railed low) may take some time to get “compus mentus”, and so sudden transients may not be as well served.
    Last edited by treez; 14th February 2020 at 09:05.



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    Re: The "cheap, quick and easy" way to do high power SMPS's?

    having 4 oscillators, 90deg apart looks like a good idea ( single 555 osc with 4 connections to local boards ) - linking the comp pins would be easy - job done ... ...



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    Re: The "cheap, quick and easy" way to do high power SMPS's?

    the beauty of the two switch - two diode - forward converter, is that it is very easy to get going at full power, near 50% duty cycle a little bit of slope comp is useful for maximum stability ...



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    Re: The "cheap, quick and easy" way to do high power SMPS's?

    Thanks,
    The principle of the top post…..can it equivalently be done with two vicor DCM modules in parallel?....but this time with an error amplifier pulling down the TRIM pin on any DCM module which tries to deliver over 5A of current?
    (as in the attached schem)
    The DCM datasheet doesn’t state enough detail on the TRIM pin for us to know if this is workable.

    The power supply is for 40Vin and 48vout at 10A.....thats 5A from each DCM module.

    DCM3623x50M53C2yzz
    http://www.vicorpower.com/documents/...53C2yzz_ds.pdf



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