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LM5023: Compensation for CCM and DCM

Jamie Shaffer1
Prodigy 220 points
Part Number: LM5023

I have an application which requires a minimum load of 2W and a maximum load of 75W for a flyback converter, which I would like to use the LM5023 for. However, to achieve CCM at 2W, I would potentially need a 10mH magnetizing inductance, which may not be feasible at my power levels and input voltage. A much more reasonable magnetizing inductance of 1mH would result in my CCM/DCM boundary lying at roughly 20W, which is my estimated typical load. The LM5023 datasheet does not make mention of CCM, and only mentions DCM once by saying that it is designed for high efficiency in DCM. The control loop compensation for the two modes is significantly different. Is there any guidance on how to compensate this controller for both CCM and DCM operating modes?

  • +1
    TI__Guru 71565 points

    Hello,

    The LM5023 is a QR flyback controller, which means it operates almost near critical conduction. The device adds a slight delay before FET turn-on to valley switch, so the device is running in DCM and CCM.  So you only have to setup the voltage loop for controlling DCM.

    You select your transformer primary magnetizing inductance (Lp) base on 75 kHz minimum frequency, max load at critical conduction.  The following equation should be used just solve for Lp.

    Regards,