noiseswitch-mode-power-supplyswitching
I am just using a reference design of SMPS (from Microchip) to boost input voltage from 12V to 90V as the image below:
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!!!
You did the right thing: Conducted the null-experiment where you touch the probe tip to the ground connection. Right there you know that the signals you see are picked up by your probe setup. And you are right in thinking it's related to the loop size formed by the ground lead (try muffling around the ground lead and see the signal amplitude change).
The first thing to do is to repeat the measurement using the small spring-clip as a ground lead instead of the long "pig-tail".
To reduce the levels, maybe verify that you need to do so first... So conduct a better measurement as described. And a shielded cable maybe a really good idea if you need that signal to go anywhere useful. SMA is one possible connector.
Next idea may be to hunt for the source of the 640kHz (or 320kHz). Very likely related to the power supply somehow.
Also, did you design the system with very low power distribution network impedance across the frequencies of interest? (See my pdntool.com and similar resources for help on this)
It's in the datasheet:
The outputs are floating. You can connect any one of them to ground (but normally we'd connect the 0 V / Common to ground to give a symmetrical supply.
The voltage you're seeing on the output is due to stray capacitance between the mains side and the output side. There isn't enough to provide any useful power so, for example, if you were to connect a lamp between any one of the outputs and mains earth there wouldn't be enough power to light it. Your multimeter input impedance is high enough to give a reading without loading the stray voltage.
Best Answer
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:
http://www.westmichigan-emc.org/archive/SMPS_Teune_Mee.pdf
Texas Instrument document "slva790" is also a good guide for EMI reduction.