Hello, I have a resistor R5 with some current flowing through it. It is possible to plot I(R5) by simply selecting the resistor. But is it possible to plot dI(R5)/dt? If yes, then how? An example circuit: Version 4 SHEET 1 916 680 WIRE 256 16 144 16 WIRE 464 16 336 16 WIRE 592 16 464 16 WIRE 720 16 592 16 WIRE 848 16 720 16 WIRE 464 48 464 16 WIRE 592 48 592 16 WIRE 720 48 720 16 WIRE 848 48 848 16 WIRE 848 64 848 48 WIRE 144 112 144 16 WIRE 416 112 384 112 WIRE 800 112 768 112 WIRE 384 144 384 112 WIRE 464 144 464 128 WIRE 464 144 384 144 WIRE 544 144 544 112 WIRE 592 144 592 128 WIRE 592 144 544 144 WIRE 672 144 672 112 WIRE 720 144 720 128 WIRE 720 144 672 144 WIRE 768 160 768 112 WIRE 848 160 848 144 WIRE 848 160 768 160 WIRE 464 176 464 144 WIRE 592 176 592 144 WIRE 720 176 720 144 WIRE 848 176 848 160 FLAG 144 192 0 FLAG 464 240 0 FLAG 592 240 0 FLAG 720 240 0 FLAG 848 240 0 SYMBOL voltage 144 96 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value PWL(0 0 1 3 2 6 3 9) SYMBOL zener 480 240 R180 WINDOW 0 24 64 Left 2 WINDOW 3 0 -35 Left 2 SYMATTR InstName D2 SYMATTR Value 1N750 SYMATTR Description Diode SYMATTR Type diode SYMBOL zener 608 240 R180 WINDOW 0 24 64 Left 2 WINDOW 3 -42 -32 Left 2 SYMATTR InstName D3 SYMATTR Value BZX84C6V2L SYMATTR Description Diode SYMATTR Type diode SYMBOL zener 736 240 R180 WINDOW 0 24 64 Left 2 WINDOW 3 -22 -29 Left 2 SYMATTR InstName D4 SYMATTR Value TFZ6_8B SYMATTR Description Diode SYMATTR Type diode SYMBOL zener 864 240 R180 WINDOW 0 24 64 Left 2 WINDOW 3 -25 -38 Left 2 SYMATTR InstName D5 SYMATTR Value UMZ7_5K SYMATTR Description Diode SYMATTR Type diode SYMBOL res 352 0 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 1 SYMBOL njf 416 48 R0 SYMATTR InstName J1 SYMATTR Value U309 SYMBOL njf 544 48 R0 SYMATTR InstName J2 SYMATTR Value U309 SYMBOL njf 672 48 R0 SYMATTR InstName J3 SYMATTR Value U309 SYMBOL njf 800 48 R0 SYMATTR InstName J4 SYMATTR Value U309 TEXT 110 216 Left 2 !.tran 4
LTspice differentiation
Started by ●November 15, 2016
Reply by ●November 15, 20162016-11-15
On Wed, 16 Nov 2016 00:04:13 +0100, Piotr Wyderski wrote:> Hello, > > I have a resistor R5 with some current flowing through it. > It is possible to plot I(R5) by simply selecting the resistor. > But is it possible to plot dI(R5)/dt? If yes, then how? > An example circuit:Not directly, but you can make a current-dependent voltage source that has a Laplace transfer function for the gain. It'll need to be of the form H = s / (tau * s + 1), because SPICE doesn't like nekkid differentiators. -- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
Reply by ●November 15, 20162016-11-15
On Tue, 15 Nov 2016 17:17:00 -0600, Tim Wescott <tim@seemywebsite.com> wrote:>On Wed, 16 Nov 2016 00:04:13 +0100, Piotr Wyderski wrote: > >> Hello, >> >> I have a resistor R5 with some current flowing through it. >> It is possible to plot I(R5) by simply selecting the resistor. >> But is it possible to plot dI(R5)/dt? If yes, then how? >> An example circuit: > >Not directly, but you can make a current-dependent voltage source that >has a Laplace transfer function for the gain. It'll need to be of the >form H = s / (tau * s + 1), because SPICE doesn't like nekkid >differentiators.Or just use a buffer and a C-R circuit. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●November 15, 20162016-11-15
On Wed, 16 Nov 2016 00:04:13 +0100, Piotr Wyderski <piotr.wyderski.no.spam@gmail.com> wrote:>Hello, > >I have a resistor R5 with some current flowing through it. >It is possible to plot I(R5) by simply selecting the resistor. >But is it possible to plot dI(R5)/dt? If yes, then how? >An example circuit: > >Version 4 >SHEET 1 916 680 >WIRE 256 16 144 16 >WIRE 464 16 336 16[snip]>SYMATTR Value U309 >TEXT 110 216 Left 2 !.tran 4If the x-axis is time, simply add to the plot... d(I(R5)) At least that's how I do it in PSpice, which is Berkeley Spice compliant. In LTspice YMMV. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website.
Reply by ●November 15, 20162016-11-15
On Tue, 15 Nov 2016 15:25:33 -0800, John Larkin wrote:> On Tue, 15 Nov 2016 17:17:00 -0600, Tim Wescott <tim@seemywebsite.com> > wrote: > >>On Wed, 16 Nov 2016 00:04:13 +0100, Piotr Wyderski wrote: >> >>> Hello, >>> >>> I have a resistor R5 with some current flowing through it. >>> It is possible to plot I(R5) by simply selecting the resistor. >>> But is it possible to plot dI(R5)/dt? If yes, then how? >>> An example circuit: >> >>Not directly, but you can make a current-dependent voltage source that >>has a Laplace transfer function for the gain. It'll need to be of the >>form H = s / (tau * s + 1), because SPICE doesn't like nekkid >>differentiators. > > Or just use a buffer and a C-R circuit.Killjoy. -- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
Reply by ●November 15, 20162016-11-15
On Tuesday, November 15, 2016 at 6:03:55 PM UTC-5, Piotr Wyderski wrote:> Hello, > > I have a resistor R5 with some current flowing through it. > It is possible to plot I(R5) by simply selecting the resistor. > But is it possible to plot dI(R5)/dt? If yes, then how? > An example circuit: >In general differentiation blows up at high frequency, (where things are changing faster) and you have to roll it off. <snip ltspice circuit> George H.
Reply by ●November 15, 20162016-11-15
On Tue, 15 Nov 2016 20:08:22 -0600, Tim Wescott <tim@seemywebsite.com> wrote:>On Tue, 15 Nov 2016 15:25:33 -0800, John Larkin wrote: > >> On Tue, 15 Nov 2016 17:17:00 -0600, Tim Wescott <tim@seemywebsite.com> >> wrote: >> >>>On Wed, 16 Nov 2016 00:04:13 +0100, Piotr Wyderski wrote: >>> >>>> Hello, >>>> >>>> I have a resistor R5 with some current flowing through it. >>>> It is possible to plot I(R5) by simply selecting the resistor. >>>> But is it possible to plot dI(R5)/dt? If yes, then how? >>>> An example circuit: >>> >>>Not directly, but you can make a current-dependent voltage source that >>>has a Laplace transfer function for the gain. It'll need to be of the >>>form H = s / (tau * s + 1), because SPICE doesn't like nekkid >>>differentiators. >> >> Or just use a buffer and a C-R circuit. > >Killjoy.I like to build my own test equipment in Spice. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●November 16, 20162016-11-16
George Herold wrote:> In general differentiation blows up at high frequency, > (where things are changing faster) and you have to > roll it off.I think it is a general question of doing math operations on the sim results, which AFAIK is not something very user-friendly in LTspice. Exporting the results and finishing processing in, say, Octave is doable, but very inconvenient. Another option is to co-simulate your own analog computer the John Larkin's way, but if the operation is more complex, this approach quickly runs out of steam. c.
Reply by ●November 16, 20162016-11-16
On 16/11/16 00:04, Piotr Wyderski wrote:> Hello, > > I have a resistor R5 with some current flowing through it. > It is possible to plot I(R5) by simply selecting the resistor. > But is it possible to plot dI(R5)/dt? If yes, then how?Copy the current at R5 with a current-controlled current source and apply this current to an auxiliary inductor. The voltage across the inductor will be L*dI(R5)/dt Pere
Reply by ●November 16, 20162016-11-16
On Wednesday, November 16, 2016 at 6:36:43 AM UTC-5, circuitmaker wrote:> George Herold wrote: > > > In general differentiation blows up at high frequency, > > (where things are changing faster) and you have to > > roll it off. > > I think it is a general question of doing math operations > on the sim results, which AFAIK is not something very > user-friendly in LTspice. Exporting the results and finishing > processing in, say, Octave is doable, but very inconvenient. > Another option is to co-simulate your own analog computer > the John Larkin's way, but if the operation is more complex, > this approach quickly runs out of steam. > > c.Yeah, my mistake. Late at night and too quick a read. George H.
