From: Ryan O'Connor <rocifier@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Fri, 17 Jan 2020 21:39:41 -0800
Subject: Re: [EE] Measurement noise, signal superimposed on H-Bridge
 operation.
Thread-Topic: [EE] Measurement noise, signal superimposed on H-Bridge
 operation.
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Here's one I'm working on currently. Note C5,C10,C12 and C6,C11,C13 which
are all localized bypass as close to the FETs as you can get them (similar
board positions to the schematic parts).

Ryan

On Sat, 18 Jan 2020 at 09:11, Jason White <whitewaterssoftwareinfo@gmail.co=
m>
wrote:

> Update: adding a 100nF decoupling capacitor between the Vin and the
> floating GND close to the power connector reduced EMI by an order of
> magnitude (400mv vs 10V pk-pk). Some is still present.
>
> 1) unfortunately no.
> 2) the FETs are SOT26, I can't try that very easily
> 3) I decouple the drivers themselves quite well. The unregulated Vin
> switched by the bridge had no decoupling prior to me just adding it
> now.
> 4) I don't, but I am stuck with it in the short term.
> 5) I might try, but the circuit layout is such that there already is a
> central ground point (the FET). The H-Bridge is to the left of the
> point and the power supply and logic is all to the right of the point.
> 6) The ground node is "floating" a NMOS FET can disconnect ground to
> protect the circuit if the supply voltage gets too high. The ground
> plane goes through the FET to the power connector.
>
> On Fri, Jan 17, 2020 at 2:44 PM Sean Breheny <shb7@cornell.edu> wrote:
> >
> > Lots of possibilities:
> >
> > 1) Can we see the whole circuit?
> > 2) Try adding ferrite beads in the gate lead of the mosfets (during
> turn-on
> > and turn-off there can be a very high gain which can amplify RF
> oscillation)
> > 3) How well do you bypass the power and ground close to the h-bridge?
> > 4) Why do you want shoot-thru?
> > 5) Consider separate ground and power "islands" for the h-bridge and th=
en
> > connect them to the rest of the circuit at only one point each (and hav=
e
> > lots of bypass caps sprinkled about the fets, linking the power and gnd
> > islands)
> > 6) Why does your diagram show a block called h-bridge which is itself
> > switched by another low-side fet?
> >
> >
> > On Fri, Jan 17, 2020, 1:38 PM Jason White <
> whitewaterssoftwareinfo@gmail.com
> > wrote:
> >
> > > As a follow up: I have attached a screen capture showing the waveform
> > > of the noise.
> > >
> > > The signal presents itself as 1 cycle of a sine wave at 12.5MHz
> > > followed by 12 cycles of a sine wave at 62.5MHz on a 100MHZ scope
> > > using a 25MHz differential probe. Less than 400ns in duration from
> > > start to finish.
> > >
> > > Just writing this out made me think: while I would like to eliminate
> > > the radiation from my circuit - I may or may not be able to. Perhaps =
I
> > > can filter it out of my measurements?
> > >
> > > --
> > > Jason White
> > > --
> > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > View/change your membership options at
> > > http://mailman.mit.edu/mailman/listinfo/piclist
> > >
> > --
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>
>
>
> --
> Jason White
> --
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