Arduino buck-boost converter

Discussion in 'General Electronics Chat' started by R-allen25, Feb 21, 2015.

  1. R-allen25

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    Feb 21, 2015
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    can anyone explain step by step how this circuit works? it is a arduino operated dc-dc buck-boost converter? arduino buck boost.JPG
     
  2. Jony130

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  3. R-allen25

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  4. MrChips

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    Resistors serve a number of functions.

    In your circuit shown most are there to limit the current.
     
  5. R-allen25

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    Feb 21, 2015
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    any
    thing else?
     
  6. MrChips

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    C2 and R8 constitute a filter circuit with a certain frequency response.

    R2 and R7 are bias resistors. In this case, they are bleeder resistors to remove the charge from the gates of the MOSFETs when the input voltage is supposed to be zero volts.
     
  7. R-allen25

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    Feb 21, 2015
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    there is another thing im not sure on, is the two transistor connected base to base. are they acting as switches?
     
  8. Jony130

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    Q2 and Q3 are act like a emitter followers, and they job is to quickly charge (Q2) and quickly discharge (Q3) the P-MOS (Q4) gate parasitic capacitance.
     
  9. MrChips

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    That is called a class B push-pull amplifier. When one transistor is on, the other is off.
    In your circuit shown, yes, they are acting as opposing switches as the purpose of that circuit is to drive Q4 fully on hard or fully off as quickly as possible, i.e. you want the time spent during transition to be as short as possible.
     
  10. MrChips

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    R9, R10 and R11 constitute what is known as a voltage divider circuit that provides a sample of the output voltage fed back to A0. The wiper arm on R10 is adjustable to allow you to set the voltage feedback.

    Zener diode D3 prevents the feedback voltage from exceeding 4.7V which could potentially damage the Arduino ATmega328 MCU chip.
     
  11. R-allen25

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    Feb 21, 2015
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    you mentioned C2 and R8 is acting as filter circuit, but what is it filtering?
     
  12. MrChips

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    Your buck-boost converter is a switching supply, isn't it? Driven by a PWM signal?

    There will be lots of high frequency noise on your supply output.
     
  13. R-allen25

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    Feb 21, 2015
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    driven by pwm and 12 volt supply but yes your are right
     
  14. R-allen25

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    Feb 21, 2015
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    which mosfet will be turned on first during the supply of 12 volts Q3 or Q4?
     
  15. Shagas

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    Why is R2 even necessary? If the pin is high then there is nothing to bleed , when the pin is low then the gate can bleed through the pin.
     
  16. kubeek

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    Becasue when the micro is in reset the pins will likely be high impedance leaving the gate floating.
     
  17. R-allen25

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    Feb 21, 2015
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    what does the feedback to the arduino do?
     
  18. kubeek

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    It tells the program what the output voltage is, and the program changes the pwm accordingly.
     
  19. R-allen25

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    Feb 21, 2015
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    does anyone know the formulas to calculate the components for the circuit?
     
  20. Dodgydave

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    Jun 22, 2012
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    which components they're all listed?
     
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