Groups > sci.electronics.design > #452201

Re: Parasitics?

From	rickman <gnuarm@gmail.com>
Newsgroups	sci.electronics.design
Subject	Re: Parasitics?
Date	2017-03-16 20:19 -0400
Organization	A noiseless patient Spider
Message-ID	<oaf9tk$k45$1@dont-email.me> (permalink)
References	<oaf7ro$efu$1@dont-email.me> <ej0n7kFmn6vU1@mid.individual.net>

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On 3/16/2017 7:59 PM, Sylvia Else wrote:
> 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.


Version 4
SHEET 1 2820 1128
WIRE 368 -272 144 -272
WIRE 512 -272 368 -272
WIRE 816 -272 512 -272
WIRE 1024 -272 816 -272
WIRE 1216 -272 1024 -272
WIRE 144 -224 144 -272
WIRE 368 -224 368 -272
WIRE 816 -208 816 -272
WIRE 512 -112 512 -272
WIRE 368 -96 368 -144
WIRE 416 -96 368 -96
WIRE 464 -96 416 -96
WIRE 816 -96 816 -128
WIRE 144 -64 144 -144
WIRE 192 -64 144 -64
WIRE 224 -64 192 -64
WIRE 368 -64 368 -96
WIRE 368 -64 304 -64
WIRE 512 16 512 -16
WIRE 592 16 512 16
WIRE 640 16 592 16
WIRE 800 16 720 16
WIRE 832 16 800 16
WIRE 896 16 832 16
WIRE 800 48 800 16
WIRE 800 128 800 112
FLAG 816 -96 0
FLAG 1024 -272 Vdd
FLAG 800 128 0
FLAG 832 16 Bias
FLAG 592 16 Fcntl
FLAG 192 -64 Fout
FLAG 416 -96 Gate
SYMBOL voltage 144 -240 R0
WINDOW 123 -97 26 Left 2
WINDOW 39 -277 71 Left 2
WINDOW 3 -412 109 Left 2
SYMATTR Value2 AC 1
SYMATTR SpiceLine Rser=0.01 Cpar=1fF
SYMATTR Value PULSE(0 3.3 3us 10ns 10ns 2us 8us 1000)
SYMATTR InstName V1
SYMBOL voltage 816 -224 R0
WINDOW 123 24 132 Left 2
WINDOW 39 0 0 Left 2
WINDOW 3 24 102 Left 2
SYMATTR Value 3.3
SYMATTR InstName V2
SYMBOL res 624 0 M90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 4700
SYMBOL cap 816 48 M0
WINDOW 0 43 20 Left 2
SYMATTR InstName C1
SYMATTR Value 1µF
SYMBOL res 320 -80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 1k
SYMBOL res 352 -128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R6
SYMATTR Value 100k
SYMBOL pmos 464 -16 M180
SYMATTR InstName M1
SYMATTR Value BSS84
TEXT 304 160 Left 2 !.tran 6ms
TEXT 304 96 Left 2 !.options plotwinsize=0
TEXT 32 96 Left 2 !.ic V(Vf)=1.61\n.ic V(Bias)=2.7
TEXT 304 128 Left 2 !.PARAM Tol = 1.0


-- 

Rick C

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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