I am just using a reference design of SMPS (from Microchip) to boost input voltage from 12V to 90V as the image below: enter image description here It's working normally but the problem is the noise at the output of 90V. I measured the amplitude Vpeak-peak of noise around 150mV and the repetition frequency is 110kHz = switching frequency of HV9110 controller.

My question is how can I reduce this noise to 20mV because it will affect on my signal analysis.

Please help me and thanks in advance!!!

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    \$\begingroup\$ What's the ESR and ESL or your output cap? Can you reduce them? Do you have space for an CLC filter on the output? \$\endgroup\$
    – winny
    Nov 15, 2018 at 15:31
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    \$\begingroup\$ What type of load is connected to the output? What type of output capacitor are you using? \$\endgroup\$ Nov 15, 2018 at 15:43
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    \$\begingroup\$ can you add more output capacity? And: really, 150 mV of ripple at 90 V does sound like very little. Where does that 20 mV requirement come from? \$\endgroup\$ Nov 15, 2018 at 15:49
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    \$\begingroup\$ The PCB layout has a large impact on the noise voltage. Can you attach your PCB layout? \$\endgroup\$
    – Steve G
    Nov 15, 2018 at 15:52
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    \$\begingroup\$ It'd be really important to know what kind of load you attach to the output, like @PeterKarlsen asked 18h ago! \$\endgroup\$ Nov 16, 2018 at 10:34

1 Answer 1


For the Boost convertor like other convertor you have output ripple and EMI. For output ripple reduction the best way is adding a good CLC filter. Increasing the value of C12 and C16 could have direct effect on your output ripple. For the EMI reduction adding an Snubber RC circuit over the D8 diode or from its anode to ground is also a good practice. Reducing the switching speed of M3 also has direct effect on the generated EMI.

Please look at the following document:


Texas Instrument document "slva790" is also a good guide for EMI reduction.

  • \$\begingroup\$ note that reducing the switching speed typically increases the necessary size of output capacitance. \$\endgroup\$ Nov 16, 2018 at 10:33

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