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Understanding Half Bridge Driver

  1. Aug 5, 2013 #1
    I'm trying to understand what this IC is doing and what the "typical application" circuit is doing

    http://www.onsemi.com/pub_link/Collateral/NCP1392-D.PDF

    It looks to me like this is the basic idea. AC comes in, PFC is done, signal is rectified so that a DC signal is coming into the IC. Then, the IC converts back into AC, but this time at a higher frequency, driven through an isolation transformer and then rectified AGAIN, but this time at a lower ripple current due to the higher frequency.

    Do I have this correct? If that is the case, what is the purpose of the feedback loop, since it looks like it varies the frequency of the driver, not the output voltage?


    Thanks,
     
  2. jcsd
  3. Aug 5, 2013 #2
    In my book this is really a controller, more then a driver, but it includes the "driver" stage.

    Your description is about right - it is set up for a Half Bridge DC/DC converter ( ref http://www.ti.com/lit/sg/sluw001e/sluw001e.pdf )

    The front end rectifier / PFC is part of a typical application - but not a requirement - highlighting that the chip has a PFC delay - allowing front end - DC to get to voltage and stabilize.

    The frequency varies to maintain a given Vdc on the output - this seems odd at first, but the idea is that each pulse through the transformer - carries a fixed amount of energy (think voltage and current)- to hold the voltage steady as the current varies you adjust the number of pulses over time = Frequency. When you got to resonant mode, it gets a little trickier in the logic, but the current is nearly a sine, as the F increased you are "over Resonant" putting more energy in the tank circuit - but this is to support the output that is taking more energy out - to keep the tank balanced ( E in = E out)
     
  4. Aug 5, 2013 #3
    Thank you! That makes sense and that TI webpage is a very good reference.

    One more question, what is the reasoning for doing this? The only benefits I see are:
    1. Reduced Ripple Currents
    2. Easier to regulate voltage by varying the frequency of the oscillator

    Are these the only reasons? It seems to me if you are not required to keep a low ripple requirement and do not require careful regulation of voltage/current, it would be easier to just go

    120VAC->Step up/step down Transformer->rectifier
     
  5. Aug 5, 2013 #4
    Yes, this topo is for higher quality dc, good regulation, efficency, large voltage changes, etc, and gendrally for lower power. For a basic dc supply there a lot of ways to go.
     
  6. Aug 5, 2013 #5

    berkeman

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    Staff: Mentor

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