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Homework Help: Non-Inverting Buck/Boost Converter Question

  1. May 6, 2014 #1
    Function of the Circuit:
    • Provide a constant voltage of 3.7V at the load for battery charging when there is an input ranging from 0V to 5V.
    • When SW1 driven by PWM 1 and SW2 is always OFF, the device will work in Buck Mode. That is if input voltage goes above 3.7V.
    • When SW1 is always ON and SW2 is driven by PWM 2, the device will work in Boost Mode. That is if input voltage is below 3.7V.

    How to create a feedback system at the output which will cause the output to stay constant at 3.7V?
    • The circuit have to boost the voltage to 3.7V if the voltage at the input is below 3.7 V
    • The circuit have to buck the voltage to 3.7V if the voltage at the input is above 3.7V

    Note: The circuit is attached in the thread.

    Attached Files:

    • 1.jpg
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  2. jcsd
  3. May 6, 2014 #2


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    Science Advisor

    The usual solution to this situation is to first boost to say +12V, then buck that to +3.7V.

    The reason for using +12V rather than +5V is that efficiency is better with the higher intermediate voltage and the capacitor between the stages can be smaller.

    You have not specified the charge current output required at +3.7V.
  4. May 6, 2014 #3


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    Staff: Mentor

    As it is required to supply 3.7V output even when there is no input, you'll be deriving full power from another source under some conditions.
  5. May 6, 2014 #4


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    Staff: Mentor

    Since this is your schoolwork problem, you need to show a fair amount of initial effort, before we can be of tutorial help. Can you show us some techniques that can be used for this problem?
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