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MC34063A: 电感L，呲呲噪声

user4057332
Prodigy 70 points
Part Number: MC34063A

MC34063升压拓扑如下：

测试管脚1（即电感和二极管之间的PIN1）波形如下：

问题：

1、开关管脚SC(PIN1)的波形是否正常？

2、该设计中电感L我们选择的value=150uH，出现了呲呲的噪声，请帮忙解决一下。

  • 0
    TI__Guru 61255 points

    Hello user4057332,

    First I hope that I understand your questions correct as I needed to use a translator. I am sorry, but I do not speak Chinese.

    1. Is it possible that you have a very low load on the output? The switch waveform seem to be ok for low output load. The converter needs to go to discontinuous conduction mode to keep the output voltage at the target.

    2. You changed the inductor, so please share your schematic as I expect this is not the only change compared to the picture above.
    What do you mean with "high noise on the screen"? Is the device the power supply for a display?

  • 0 in reply to Brigitte
    Prodigy 70 points

    Hello Brigitte,

    1、Application circuit diagram as follow:

    2、Iload = 200mA

    3、Test waveform is Obtained at the pin1;

    4、hear the noise by the  ears ;

    please help me.

  • 0 in reply to user4057332
    TI__Guru 61255 points

    Hello user40573332,

    Thank you for the schematic.

    Please check the following 2 points:

    1. What happens if you remove the inductor from the board and connect it through wires. Does the acoustic noise change?

    2. What happens if you reduce the capacitor C1228 to 1nF

  • 0 in reply to Brigitte
    Prodigy 70 points

    Hello Brigitte

    1、If wire instead of the inductor L1204，noise disappears;

    2、If the value of the capacitor C1228 is 1nF，the switching frequency of the sc pin is faster，but the noise is still there;

    3、If the value of the inductor is 47uH，the noise is  smaller than before。but the noise is still there，the test waveform is as follows:

    The noise is still there，please。

  • 0 in reply to user4057332
    TI__Guru 61255 points

    Hello user40573332

    1. Ok, so the noise is caused by the inductor. So it is possible to change it by using a physically different inductor. You could check other 150uH inductors to check if it is gone with another physical construction of the inductor.

    2. Does the noise change in frequency (do you hear a higher tone)? Is the noise in both cases (1.5nF and 1nF) dependent on the load?

    3. The SC measurement is taken with 47uH, right? You used a 47uF inductor of the same physical construction and size, right? The switch current cause a mechanical movement in the inductor and with the inductor connected to the board, the board oscillates with this mechanical change and then you hear the noise. So normally the easiest way should be to change the 150uF inductor to one that has a different physical construction.