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Original question:

UCC39002: The Principle of Control Mode

UCC39002: Paralleling 2 or 3 Forward Isolated Converters for increased power

Devesh Agarwal
Prodigy 90 points
Part Number: UCC39002
Other Parts Discussed in Thread: TL431, , UC3907

Tool/software:

Greetings.

We have a 75W 12V DC isolated forward converter with voltage mode TL431AIDBZR+PC357 control using a voltage divider circuit.

We have a customer who would like to parallel 2 or 3 of our converters to achieve 150W or 225W 12V output. Our existing converter delivers to +/- 3% accuracy but we can reduce by another 0.5% by using a higher precision TL431.

We are unable to find any reference schematic that shows how to interface and use the UCC39002 to a isolated PWM converter. May I request for some help with a reference schematic interfacing UCC39002 to an isolated circuit. I have read SLUA147 but that is for a non-isolated converter.

We have to be careful of transient response since input inrush to our converter is limited. We can, if needed, add additional inductors and capacitors on the paralleling daughter board for this, but then might need a timer circuit to delay output till the capacitors charge.

Thanks in advance.

  • +1
    TI__Mastermind 40580 points

    Hello Devesh, 

    I wish to assure you that the UCC39002 can work with isolated and non-isolated power supplies with equal design considerations. 
    The UCC39002 does not "care" whether the power sources to be paralleled are isolated or not; it only cares that a remote-sense connection is available with which to be able to adjust the modules output voltage.  

    This app-note (TI Literature #SLUA270) illustrates one way to connect three modules together for sharing. 
    https://www.ti.com/lit/pdf/slua270
    In this app-note, it is unspecified and simply does not matter whether the modules are isolated or not.  

    The app-note that you referenced (TI Literature #SLUA147) has examples of isolated supplies shown in Figures 6, 7, 10, and 11.  This app-note features an older controller UC3907 (still supported, no longer promoted), but many of the sharing-control principles are the same and apply to the UCC39002 as well. 

    I don't think you will need to add more inductors or capacitors for paralleling purposes.  The transient response of the modules will be unaffected.
    The loop-response of the current-sharing is designed to be much slower than the PSU response so it will not interfere with regulation or introduce instability. 

    Regards,
    Ulrich