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LM5180EVM-S05: Abnormal operation for 24Vout custom specification

Satoshi
Guru 19495 points
Part Number: LM5180EVM-S05

I trying to make 12Vin (or 24Vin) to 24Vout spec based on LM5180EVM-S05.

※Transformer changed default(YA7889) to the other custom, and the other external components are changed depend on Input/Output specification.

But measured waveform is abnormal, schematic and waveform are attached below.

Please let me know about correction point or any advice.

【Test Condition】

　⇒ch4(pink): Vin, ch3(Blue): SW, ch1(Yellow): Iin, ch2(Green): Vout

By the way, 24Vin condition occur unstable Iin.

Vin: 24V, Vout: 24V, Iout: 100mA

※When Iout decrease, unstable Iin become large.

Best regards,

Satoshi

  • 0
    TI__Guru 57555 points

    You will need to retain the clamp diode on the output.

    Also, the 25V ceramic capacitor will de-rate to a very small value with 24Vout.

    You will need either a 50V cap or test with an Aluminum electrolytic.

  • 0 in reply to Frank De Stasi
    Guru 19495 points

    Frank-san

    Thank you for reply,

    I changed EVM you advised, changed point are below;

    ・Add D3 diode for Vz: 27V.

    ・Add ceramic cap to C11, actual capacity is about 9.4μF. 

    Improved points are below;

    ・Vout_max is clamped 28V by D3

    ・Current is through Primary side to Secondary side

    ・When set 24V input, unstable Iin was not find 

    Vout is still abnormal, and when iout increase, audible noise also increased. 

    Is there any other correction point?

    【Test Condition】

    　⇒ch4(pink): Vin, ch3(Blue): SW, ch1(Yellow): Iout, ch2(Green): Vout

    　　※Test point ch1 is changed Iin to Iout, Iin are the same waveform from last day.

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Guru 57555 points

    First, be sure that you used the calculator tool to design you component values.

    In photo 1, I assume the output is clamped by the zener, so should be OK

    In photo 2 and 4, do you mean the Vout changed by 2.3V?

    In photo 3, do you mean the Vout changed by 11V??

  • 0 in reply to Frank De Stasi
    TI__Guru 57555 points

    I am closing this post due to inactivity.