Driving Buck Converter

Discussion in 'The Projects Forum' started by niemand, Jun 2, 2013.

  1. niemand

    Thread Starter New Member

    Jun 2, 2013
    4
    0
    Dear electronics-experts,
    Im currently trying to design a variable duty cycle step-down buck converterto charge a battery(Vin=0-120V DC to Vout=24 V DC, Pmax~1kW). Now all my components are selected, except the MOSFET/MOSFET Driving Circuit.

    As Ive seen high voltage projects using the IRFP9240,I selected it.(http://www.calebengineering.com/high-voltage-variable-load.html)

    I will create the PWM using an Arduino board, which provides a 2.5-5 V output, but my Mosfet need V_gs=10 V. What is the most simple solution to drive my Mosfet with this signal?

    Ive read that one can use a second MOSFET(n-channel?) for this purpose, but I couldnt find an description/explanation of such a circuit.
    Any help will be appreciated,
    Nico
     
  2. niemand

    Thread Starter New Member

    Jun 2, 2013
    4
    0
    Maybe my question wasnt clear enough: Which circuit can I use to drive a p-channel MOSFET with a high Voltage(V_gs=10Volts), when I just have a 3 Volt PWM from the arduino?
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,023
    3,236
    It might be better to use a high-side N-MOSFET switch and drive it with one of these.
     
  4. niemand

    Thread Starter New Member

    Jun 2, 2013
    4
    0
    Hey crutschow, thanks for your fast reply!

    I think using a n-channel mosfet is a good idea,
    If I use the n-channel Mosfet SUM110P08-11L-E3 , which parameters do I need to check when selecting a Mosfet Driver?
    How do I need to connect this?

    Many thanks!
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Hi,

    Use an N-channel MOSFET with a high-side driver IC. You will need an extra 10V (min) to 15V (max) supply.

    Be aware that you need to use decoupling capacitors on your feedback signals and might need voltage buffers too.

    Also, you don't need the diode on the output.

    The current sensor is better to be placed before the output capacitor to measure transient current through the capacitor too.

    Finally, you need to measure the output voltage too.


    WARNING: 120VDC is very dangerous. You look novice in the subject so I advice you to start with voltages less than 48VDC.
     
  6. niemand

    Thread Starter New Member

    Jun 2, 2013
    4
    0
    Hi mike, thanks for your reply.
    First a bit about myself: Im aerospace student trying to build a windturbine system. The circuit will be used to step down the generator ouput(28-100VDC) of the windturbine in order to charge a battery(24VDC).

    >>WARNING: 120VDC is very dangerous. You look novice in the subject so I >>advice you to start with voltages less than 48VDC.
    Thanks for the advice, as a Novice I will start testing with low voltages, the result should be the same

    >>Finally, you need to measure the output voltage too.
    As I understand it, I dont need to measure the output voltage as I will have a battery holding the voltage at the output. My idea is to controll input voltage(and the generator rpm) by the duty cycle, as D=V_out/Vin and V_out is fixed by the battery... Does this concept make sense?, please correct me if not.

    >>The current sensor is better to be placed before the output capacitor to >>measure transient current through the capacitor too.
    I placed the current sensor in front of the battery with the purpose of measuring the current flowing to the battery, not to test the transients.

    >>Also, you don't need the diode on the output.
    The reason I put this diode there is to protect the battery from current in the wrong direction..why is this not needed?

    I selected now SUM110P08-11L-E3 MOSFET, but how do I select the high-side driver IC? what circuit can I use to connect the mosfet to the driver, where do I place the capacitors and buffers?
    Can I use the 24 V Battery with a voltage divider for the 10-15 V IC supply, or will the current be too high?

    Thank you!
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Good idea.

    What if the battery gets overcharged?

    What will discharge the battery?

    At steady state you will measure only the battery current but during transients you will measure both battery and capacitor current.

    Keep the diode!

    Search for IR's high side gate drivers. It is better to use a voltage regulator IC to regulate down to 12V.
     
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