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UC3825 Power limit

Flavio Souza
Prodigy 50 points
Other Parts Discussed in Thread: UC3825, UC2825, UC3825A

Hi everybody,

I was reviewing the Power management guide and in the colunm "Typical Power Level" of UC3825 that says 50 to 750W.

Despite this information I guessed that the limitant would be the peripherals. So I resolved go on in my project at 1200W, then worked at 2 minutes, and burned(mosfets). I need increase the efficiency, but, historically anybody got works above 750W?

  • 0
    Prodigy 200 points

    Hi you are right about the importance of periferial components.

    I assume that you did use hefty gate drivers between the controller and your bunch of mosfets.

    I think that UC2825´s internal gate drivers would be stressed hard driving enough fets to get the 1.2KW out.

    The guidelines of Power Management Guide http://www.ti.com/lit/sg/slvt145n/slvt145n.pdf

    do indeed state that the recommended range of power suplies to be implemented with UC3825 and UC3825A

    if 50 to 750W, but it does not say if the 750W would be reasonable with which of the topologies.

    I have done 25W (611KHz)converter using UC2825, and as you see it is outside guide range.

    If I was doing 1.5KW 250KHz converter, from say 500VDC TO 60vdc  I might consider UC3825A using half  bridge

    with three to five parallel output stages depending on requirements for redundancy (  if all resnant converter topologies would be banned by other factors.)

    If certain controller can achieve 750W output using single half bridge output stage, it should be able to do 1.5KW using single full bridge output stage.

    I have partcipated in design of  100KW output power supply (sort of amplifier actually) and it was finally implemented using 48 parallel 2.5KW output stages because failures using 6 parallel 20KW stages was too frequent. The main problem was that keeping 200A transistors from blowing was way too difficult and having 75A transistors each current limited to 40th of required current made the thermal design easier.

    also it was more feasible to test and tuneand select   the 50+ output stages that were made individually .

    Parallelling powerstages driven by same controller is not trivial, you might want to have same length coaxial/optical cables from driverboard to powerboard and star shaped parallelling of output inductors and grounds. Also it creates a whole lot of EMC/EMI issues that must be addressed. also system can become a weird oscillator if the output stages behaviour  vary too much under varying loads.