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Audible Noise from MC34063

SS_hwdesign
Prodigy 250 points
Other Parts Discussed in Thread: MC34063A

I am using MC34063 in Step Down mode to achieve 5V, 700 mA from 24V VDC Input.

During the testing with Resistive load (e.g. 80 mA to 600 mA) continuous Humming Noise is listened.

Is it due to the Lmin Inductor or issue with Timing Capacitor (Ct).

  • 0
    TI__Guru**** 151276 points

    Saurabh,

    First check the output frequency on pin 2. If the frequency is in the audio range, then the noise may be becoming from the inductor. Does the noise change with load (and resulting frequency change)?

    What value are you currently using for CT, L and Rsc?

  • 0 in reply to Ron Michallick
    Prodigy 250 points

    Ron,

    Thank you.

    Our design includes - (1) Ct = 470 pF / 50V   (2) Lmin = 220 uH & (3) Rsc = 0.4 Ohm

    As per our Design considerations, we have kept Operating Frequency of IC @ 50 KHz ( observed at Pin 2 )

    I have conducted several Tests on this.

    As Audio Noise problem observed we tried to tune the frequency and checked few combinations for Ct.

    Please refer the chart below - 

     

  • 0 in reply to SS_hwdesign
    TI__Guru**** 151276 points

    Saurabh,

    I want to make sure that I understand correctly. Audible sound wave are being produced directly by the MC34063A circuitry and are not coming from the input supply, load or other means. 30kHz and up should not cause audible vibrations in the inductor or silicon. It is possible to determine what component is generating the sound? 

  • 0 in reply to Ron Michallick
    Prodigy 250 points

    Ron,

    Yes, Audible Noise is coming from MC34063 Circuitry only and not through Input Supply / Load.

    Actually, components used in circuitry are SMD's and hence we can not identify the exact component causing this noise.

    Can't we identify the cause  - 

    1. Either it is parameters of MC34063 itself ( Ct Tuning, Output circuit etc)

    2. or the external components used 

    Have you ever gone through such problem in past ?

    If so, we can also try your observations from that.

  • 0 in reply to SS_hwdesign
    TI__Guru**** 151276 points

    Saurbh,

    This is my first experience with audible noise in a system where the operating frequency is supersonic. The most likely component to make noise is the inductor. Remove inductor from board then add a short wires (~5cm) between PCB and inductor. Test to see if sound changes (inductor cannot resonate with board now); use an insulator object (vibration conductor) touching board then inductor with the other end of object near your ear to see where sound originates.  

  • 0 in reply to Ron Michallick
    Prodigy 250 points

    Ron,

    After few experiments, we have concluded that - 

    1. IC 34063 is operating at 28 KHz, which is quite closer to Audible Noise frequency.

        We have modified Ct value.

    2. We have also replaced Inductor

    Now we are getting almost Noise Free Power Supply.

    Thank you for the support provided.

    Saurabh 

  • 0 in reply to SS_hwdesign
    Intellectual 425 points

    Hi saurabh

    I am facing the same noise problem. Can you please share, what modifications you did in ct  and inductor values?

  • 0 in reply to PARTH JOSHI
    Prodigy 20 points

    Hello,

              I also facing same issue in MPQ4473 DC-DC IC, it creates noise in the light load condition. Its due to I got 4.7KHz frequency noise  in the input side inductor filter due to output load. I tried to tune output & Input capacitor and input inductor but no use. then I use 100pF feed forward capacitor in the feedback pin (Output to FB pin) it reduces the feedback noise, which reduce input noise and at the same time it reduce Humming noise in the inductor. please check any noise you are getting in 20 to 20KHz range in the inductor side, which create vibration the core of the inductor , some time ceramic capacitor also create noise