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Original question:

MC33063A: Design Calculator

MC33063A: Feed Forward Resistor

Jayal Pansuriya
Prodigy 40 points
Part Number: MC33063A

Tool/software:

Hi,

I would like to add feed forward resistor(R5 shown below) to play with frequency and on/off time so just wondering if feed forward resistor is safe to use for MC33063A? 

Kind Regards,

Jayal

  • 0
    TI__Guru 65200 points

    Hello Jayal,

    Do you know that this device does not have a fixed frequency? So why not reducing the capacitor instead of adding a resistor if you want to increase the switching frequency?

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 40 points

    Hi Brigitte,

    Thank you for quick response,

    Yes, I'm aware that device does not have fixed frequency. However, there should be a way to calculate operating frequency? 

    Apart from that feed forward resistors allow to modify voltage ripple by modifying Ton time.

    Kind Regards,

    Jayal Pansuriya

  • +1 in reply to Jayal Pansuriya
    TI__Guru 65200 points

    Hello Jayal,

    The operating frequency is dependent on the speed of the rise of the inductor current, so it is not really possible to be calculated besides the frequency that the device will show when the switch current does not trigger the switch current limit set by the external sense resistor.

    The device has a very specific functionality. I recommend using a newer device with a fixed frequency if you need to set the operating frequency in a certain range.

    Best regards,
    Brigitte