Groups > sci.electronics.design > #452198

Re: Parasitics?

From	Sylvia Else <sylvia@not.at.this.address>
Newsgroups	sci.electronics.design
Subject	Re: Parasitics?
Date	2017-03-17 10:59 +1100
Message-ID	<ej0n7kFmn6vU1@mid.individual.net> (permalink)
References	<oaf7ro$efu$1@dont-email.me>

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On 17/03/2017 10:44 AM, rickman wrote:
> I'm running a simulation where I'm pumping charge into a capacitor to
> generate a voltage.  A transistor emitter/source is connected to the
> positive rail and the collector/drain is connected to a 1 nF cap through
> a 47k resistor.  When the base/gate is driven high to shut off the
> current I see the current go up initially then taking almost 2 us to
> shut off.  I've tried 2N3906 and BSS84 and a couple others selected
> randomly.  The switching period is around 8 uS.
>
> Is this from the parasitic capacitance in the transistor?  The BSS84
> only has 1 nC gate charge and still the effect is very pronounced.
>
> Is there a way to mitigate this effect other than using a larger cap and
> smaller resistors?
>

If your problem only related to the pnp transistor, I'd say it was 
caused by charge storage. That you're having the same problem with a FET 
suggests another problem.

Perhaps you could provide the exact circuit you're using.

Sylvia.

Thread

Parasitics? rickman <gnuarm@gmail.com> - 2017-03-16 19:44 -0400
  Re: Parasitics? bloggs.fredbloggs.fred@gmail.com - 2017-03-16 16:48 -0700
  Re: Parasitics? Sylvia Else <sylvia@not.at.this.address> - 2017-03-17 10:59 +1100
    Re: Parasitics? rickman <gnuarm@gmail.com> - 2017-03-16 20:19 -0400
  Re: Parasitics? Sylvia Else <sylvia@not.at.this.address> - 2017-03-17 12:21 +1100
    Re: Parasitics? rickman <gnuarm@gmail.com> - 2017-03-16 23:16 -0400
      Re: Parasitics? Sylvia Else <sylvia@not.at.this.address> - 2017-03-17 14:51 +1100
        Re: Parasitics? rickman <gnuarm@gmail.com> - 2017-03-17 00:57 -0400
          Re: Parasitics? bloggs.fredbloggs.fred@gmail.com - 2017-03-18 01:36 -0700
            Re: Parasitics? rickman <gnuarm@gmail.com> - 2017-03-18 05:45 -0400
              Re: Parasitics? bloggs.fredbloggs.fred@gmail.com - 2017-03-18 06:33 -0700
                Re: Parasitics? rickman <gnuarm@gmail.com> - 2017-03-18 12:22 -0400
                Re: Parasitics? Sylvia Else <sylvia@not.at.this.address> - 2017-03-24 13:30 +1100
                Re: Parasitics? rickman <gnuarm@gmail.com> - 2017-03-24 00:36 -0400
                Re: Parasitics? Sylvia Else <sylvia@not.at.this.address> - 2017-03-24 16:10 +1100
  Re: Parasitics? "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-17 01:42 -0500
    Re: Parasitics? rickman <gnuarm@gmail.com> - 2017-03-17 04:11 -0400
  Re: Parasitics? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-17 09:53 -0400
    Re: Parasitics? Cursitor Doom <curd@notformail.com> - 2017-03-17 18:52 +0000

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