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Re: DRSSTC Noise source found
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- Subject: Re: DRSSTC Noise source found
- From: "Tesla list" <tesla@xxxxxxxxxx>
- Date: Thu, 17 Feb 2005 07:47:30 -0700
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Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>
Tesla list wrote:
Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
I found one giant source of noise on my DRSSTC. The two big poly
capacitors (10uF, 600V) right across the H-bridge have too high of
impedance and high frequencies. Polypropylene is super good at say 400kHz
but at say 25MHz they have very high resistance and loose their ability to
stop high frequency noise.
You may have to apply a consideration commonly seen in RF circuits:
Any element (including wires) has an inductance of about 1 nH/mm
of its length. So, a capacitor is actually a series LC tank, that
resonates at f=1/(2*pi*sqrt(L*C)), as usual. Above this frequency,
the element is inductive and useless as bypass capacitor.
A 10 uF capacitor with 5 cm of length would have about 50 nH
of inductance, and resonate at just 225 kHz.
The solution is to add smaller capacitors in parallel with the
big one, covering the range of frequencies that you want.
Antonio Carlos M. de Queiroz