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LM5046: full bridge converted to phase shifted full bridge

Marcello Deluca
Prodigy 210 points
Part Number: LM5046
Other Parts Discussed in Thread: LM5045,

We currently use LM5045 in full bridge DC-DC converter; the Xfmr sec. output is a single winding and it too is a full bridge topology using 4 synch rectifiers controlled by two UCC21225's, one for each half of SR bridge. How could we use the LM5046 to obtain the ZVS benefit in the same topology? i.e., could it work with a single Xfmr output winding?

  • 0
    TI__Guru* 78306 points

    Hello,

    Your inquiry is under review.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 78306 points

    Hello,

    The LM5045 and LM5046 look to be very similar devices with SR control for a phase shifted full bridge.  I would think you would be able to use them in a similar fashion.   Could you tell me why you want to switch to the LM5046?

    Regards,

  • 0 in reply to Mike O'
    Prodigy 210 points

    to possibly avoid or at least reduce voltage transients / ringing stemming from Xfmr leakage and cct parasitics.

    My question remains un-answered - how do I make this chip work with a single Xfmr sec. winding?

  • 0 in reply to Marcello Deluca
    TI__Guru* 78306 points

    Hello,

    The way your inquiry was written it sounded like you had this design working with a LM5045 and wanted to switch it to the LM5045.

    "We currently use LM5045 in full bridge DC-DC converter; the Xfmr sec. output is a single winding and it too is a full bridge topology using 4 synch rectifiers controlled by two UCC21225's, one for each half of SR bridge. How could we use the LM5046 to obtain the ZVS benefit in the same topology? i.e., could it work with a single Xfmr output winding?"

    If you want to use a single winding on the secondary you can do with a full bridge rectifier and a output filter stage.  This would require only one inductor and a output capacitor bank.

    If you want to use secondary rectifiers you could use half bridge drivers and control them with the outputs of the L5045/6.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 210 points

    Thanks. Another issue has arisen in the same design. We have two identical power rails ea. controlled by their own LM5045 (48V @ 12A) and in future we want to be able to parallel them to get double output current / power. Is there an easy way to parallel / share two LM5045 converters? I would like to combine them / parallel them after the output inductors i.e., at the load, since that means the converters can be kept independent on the converter board so we could keep one common PCB and provide two solutions, 12A and 24A. Unfortunately the two LM5045's wont be that close together so I would worry about trying to combine / sum the RAMP and CS signals together to facilitate current sharing and stability - I suspect noise would interfere with this method.

  • 0 in reply to Marcello Deluca
    TI__Guru* 78306 points

    Hello,

    I am reviewing your inquiry and will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 78306 points

    Hello,

    Since both controllers are peak current mode controllers.  If you make one feedback path to both outputs they should share current because the peak currents will be controlled to the same level.  I would suggest synchronizing the two controllers to make EMI filtering easier.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 210 points

    I take it you want me to drive both LM5045 COMP pins (the feedback input) with a single FB signal that is the sum / average of the combined / shared outputs. Since I am using opto couplers for ea. LM5045, in the case where the two are being combined / shared, one of the optocouplers will be depopulated and the other one will sum /average both outputs and drive both LM5045 COMP pins shorted together. 

    Is that right?

    I don't know that the offsets / tolerance errors within the two LM5045's (and the individual current sense signals) will be small enough to not cause instability or inequity between the two acting together, do you?