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Original question:

MC33063A: Vin range under IBB design

MC33063A-Q1: Not working as Inverting Converter.

Keshava Shreenidhi B
Prodigy 10 points
Part Number: MC33063A-Q1

Hi team,

Here is the circuit I am using,

When I turned it on R73 was burning. If I reduce the value to 250mohm IC is burning up. And when I connected 1ohm I got 1.2V as output.

What might be the problem? Is the inductor I selected right? 

I have a few more questions,

1. How do you select the input voltage range?

2. How do you select the switching frequency?

Thank you,

Keshava Shreenidhi B

 

  • 0
    TI__Guru 59445 points

    Hello Keshava,

    Please try to use a diode with a forward drop of less than 0.3V.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 10 points

    Hi Brigitte,

    Thanks for the quick reply.

    Right now I don't have a diode with Vf less than 0.3V but I tried with a diode with Vf = 0.44V, and there is no change in the output.

    In the datasheet, the suggested diode doesn't have Vf < 0.3V. Can you please explain to me how this will affect the circuit?

    Thank you

    Keshava Shreenidhi B

  • 0 in reply to Keshava Shreenidhi B
    TI__Guru 59445 points

    Hello Keshava,

    Diodes are increasing the forward voltage heavily with temperature. The diode drop has to be below the forward drop of the Darlington. This might not be the issue here, but this is a simple check if an issue occurs.

    R73 has to have the right power rating as well as the capability to survive spike currents. You might check both for the resistor you used first.

    For the frequency, please have a look at the datasheet, figure 1.

    Best regards,
    Brigitte

  • +1 in reply to Brigitte
    Prodigy 10 points

    Hi Brigitte,

    It was my mistake, I mounted the diode in reverse.

    After changing it, I am getting -15V. I mounted R73 = 0.75ohm, C24 = 220pF, also changed R40 = 910ohm and R43 = 10Kohm.

    Thank you so much for your help. 

    Thank you,

    Keshava Shreenidhi B