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I am using this proportional valve driving circuit: enter image description here

The valve is 24V, 2W, driven with a 2kHz PWM. I hear an acoustic noise coming from the EMI-Filters L49, L77. I know that the noise is coming from the filters, because when I short them, I do not hear it anymore.

Question 1: does this operation reduce the lifetime of the filters?

Question 2: how to reduce the noise? Do I need the EMI filter, or is some kind of standard ceramic capacitor better? The NFM41PC204 is discontinued anyway, so I need to select something else - what should I take care of? Is there a better filter arrangement in general for this task?

G. B.
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    It appears you have a very high Q series resonance with 120uH and 200 nF on each side and the very high resonant currents make the ceramic caps piezo -acoustic. Can you define the valve mH, DCR and what you want to achieve with specs ? – Tony Stewart EE75 Feb 02 '21 at 18:12
  • @TonyStewartSunnyskyguyEE75 The 120uH looks like a common mode choke- There should only be a fraction of that value as differential inductance. However, it's pretty clear that the feed through caps are singing. – John D Feb 02 '21 at 18:19
  • Yes of course. so essentially drive many amp spikes across the caps with/without load being directly across the 0.1 Ohm switch. – Tony Stewart EE75 Feb 02 '21 at 18:25
  • The valve is a bürkert 2871 (do not mind the frequency, I tried multiple settings). There is no electrical spec. in the datasheet, except the 24V DC, max 5W, max 220mA. What I have to achieve is proportional control of the valve. What I want to achieve is proportional control without the cap singing, or at least without ruining the capacitor. – G. B. Feb 03 '21 at 05:10
  • @G. B. -- The [datasheet](https://www.burkert.com/en/Media/plm/DTS/DS/DS2871-Standard-EU-EN.pdf) is indeed stingy with details, but that is typical. You can deduce the DC resistance from what they give you, and I suggest measuring valve impedance every decade from 30Hz to 30kHz. (measure V and I small signal with a mid-level DC current load superimposed). After that you can plan out the circuit more easily. In any case do damp that common mode resonance! – Pete W Feb 03 '21 at 14:53

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