Help in understanding how this chip works

Discussion in 'Homework Help' started by Senorjohnny, Feb 24, 2018.

  1. Senorjohnny

    Thread Starter Member

    Feb 18, 2018
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    Hello,

    There's a block diagram and description of the operation in the datasheet however i don't understand it. Can anyone help me clear my confusion

    Thank you in advance.
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    1,361
    What exactly you do not understand? The Boost converter? Or current mode control?
     
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  3. OBW0549

    Distinguished Member

    Mar 2, 2015
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    No, not unless you can tell us exactly what you're confused about. If you would post some specific questions, we could probably answer them.
     
  4. Senorjohnny

    Thread Starter Member

    Feb 18, 2018
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    0
    Yes, how does current mode switcher work?

    What difference do i get from using this chip compared to a mosfet?

    How does the comparator in the block diagram function?

    Thank you
     
  5. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    ()
    In the Voltage mode control, we only feedback the output voltage and we change the duty cycle to correct the output voltage.
    In Current mode control, we are also sensing the inductor current (cycle by cycle) and we use this as a reference "ramp" for a PWM comparator.
    CM.png

    As you can see we have a output voltage sensing error amplifer, and additional we hava a current sensing resistor and the current comparator.
    Notice that current sensing is much faster because we are sensing the inductor current cycle by cycle. And "voltage seensing" is "slow" because more switching cycles is needed to change the output voltage.

    You cannot compare chip with a MOSFET. Because inside LT1370 chip you have almoust the whole circuit needed for building switching regulator.
    Mosfet alone is just a transistor nothink more.

    Exactly in the same whay as is FIGURE 1.31
    https://www.mhprofessional.com/9780071823463-usa-switch-mode-power-supplies-second-edition-group (sample chapter)
     
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  6. ebp

    Well-Known Member

    Feb 8, 2018
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    I recommend searching TI's website. A great deal has been written about the benefits and drawbacks of current mode versus voltage mode control methods. If you can find them on the site, the publications from the Unitrode Power Supply Seminars are very good (TI acquired Unitrode several years ago). Different topics are covered each year, but some of the fundamental details are included in most of the earlier Seminar books. I don't know how many of them are available free.

    Also read all the ap notes Jim Williams of Linear Tech wrote on switch mode power supplies.
     
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