Hello, in my sims I often need to simulate a soft-saturable current limiter, usually for AC. The exact construction of such a limiter is not important from the core circuit's perspective. As long as its I(U) is sigmoid or arctan-like, it's fine. What's the simplest way to express such a building block in Spice? Making it out of discretes every time adds considerable obscurity to the sim and is time-consuming. Best regards, Piotr
LTSpice: how to simulate a current limiter?
Started by ●July 23, 2018
Reply by ●July 23, 20182018-07-23
On Mon, 23 Jul 2018 06:34:20 +0200, Piotr Wyderski <peter.pan@neverland.mil> wrote:>Hello, > >in my sims I often need to simulate a soft-saturable current limiter, >usually for AC. The exact construction of such a limiter is not >important from the core circuit's perspective. As long as its I(U) >is sigmoid or arctan-like, it's fine. What's the simplest way to >express such a building block in Spice? Making it out of discretes >every time adds considerable obscurity to the sim and is time-consuming. > > Best regards, PiotrHow about a current source in parallel with a diode? -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●July 23, 20182018-07-23
Am 23.07.2018 um 06:34 schrieb Piotr Wyderski:> Hello, > > in my sims I often need to simulate a soft-saturable current limiter, > usually for AC. The exact construction of such a limiter is not > important from the core circuit's perspective. As long as its I(U) > is sigmoid or arctan-like, it's fine. What's the simplest way to > express such a building block in Spice? Making it out of discretes.FUNC or Voltage Dependent Current Source using rables or polynomials. --> Help Good luck - Udo
Reply by ●July 23, 20182018-07-23
Am 23.07.2018 um 11:02 schrieb Newdo:> Voltage Dependent Current Source using rables or polynomials.::tables.
Reply by ●July 23, 20182018-07-23
I don't understand the combination of (apparently) magnetic saturation and
current limiting, but you can always use a flux based model like this for
saturation:
* Saturable Core Model, copied from:
* _SPICE Models For Power Electronics_, Meares and Hymowitz.
*
.SUBCKT INDSAT 1 2 PARAMS: VSEC=1e-4 LMAG=1e-5 LSAT=1e-7 FEDDY=1e6
F1 1 2 VM1 1.0
G2 2 3 1 2 1.0
E1 4 2 3 2 1.0
VM1 4 5 0.0
RX 3 2 1E9
CB 3 2 {VSEC/500} IC=0
RB 5 2 {LMAG*500/VSEC}
RS 5 6 {LSAT*500/VSEC}
VP 7 2 250
VN 2 8 250
D1 6 7 DCLAMP
D2 8 6 DCLAMP
.MODEL DCLAMP D ( CJO={3*VSEC/(6.28*FEDDY*500*LMAG)} VJ=25 M=0.01
RS={LSAT/VSEC} )
.ENDS
Roughly speaking, LMAG / LSAT = mu_r, VSEC is the flux at saturation, and
FEDDY is the dominant pole rolloff.
As-is, it's pretty reasonable for ferrites. Roll-off for laminated
materials is better approximated by a k*sqrt(f) impedance in parallel.
Powder materials saturate more gradually, so DCLAMP might be replaced with a
POLY in that case.
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
"Piotr Wyderski" <peter.pan@neverland.mil> wrote in message
news:pj3lse$qmc$1@node2.news.atman.pl...
> Hello,
>
> in my sims I often need to simulate a soft-saturable current limiter,
> usually for AC. The exact construction of such a limiter is not important
> from the core circuit's perspective. As long as its I(U)
> is sigmoid or arctan-like, it's fine. What's the simplest way to
> express such a building block in Spice? Making it out of discretes
> every time adds considerable obscurity to the sim and is time-consuming.
>
> Best regards, Piotr
Reply by ●July 23, 20182018-07-23
Tim Williams wrote:> I don't understand the combination of (apparently) magnetic saturation > and current limiting, but you can always use a flux based model like > this for saturation:Thanks, you solved my other problem. :-) In this case I don't have any magnetics, just want to simulate two back-to back connected depletion-mode MOSFETs/JFETs that form an AC current limiter without the need to handicraft such a limiter every time. Firstly, because it takes a lot of time to select the components properly. The second reason is the lack of good DMOSFET models in LTSpice. Fortunately the available JFETs work up to the megavolt range, but it is a kludge. I'd like to have a single box with two parameters, I_SAT and, say, the U for which I is 1-1/e of I_SAT. Or 90%, whatever. Just don't know how to create such a box in Spice. [snip something very useful] Best regards, Piotr
Reply by ●July 23, 20182018-07-23
"Piotr Wyderski" <peter.pan@neverland.mil> wrote in message news:pj52vb$49l$1@node2.news.atman.pl...> I'd like to have a single box with two parameters, I_SAT and, > say, the U for which I is 1-1/e of I_SAT. Or 90%, whatever. > Just don't know how to create such a box in Spice. >Well, you can always do what you'd do for limiting voltage: back to back diodes. Then put a gyrator in front of it, so current and voltage are swapped around. (A gyrator is just a pair of dependent sources, same as you make a DC transformer.) I can write it out and do some example circuits if you like. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
Reply by ●July 23, 20182018-07-23
On Monday, July 23, 2018 at 1:23:58 PM UTC-4, Piotr Wyderski wrote:> Tim Williams wrote: > > > I don't understand the combination of (apparently) magnetic saturation > > and current limiting, but you can always use a flux based model like > > this for saturation: > > Thanks, you solved my other problem. :-) > > In this case I don't have any magnetics, just want to simulate > two back-to back connected depletion-mode MOSFETs/JFETs that form > an AC current limiter without the need to handicraft such a limiter > every time. Firstly, because it takes a lot of time to select > the components properly. The second reason is the lack of good > DMOSFET models in LTSpice.Phil H and later moi posted the lnd150 model, it's somewhere on the web. and good from ~1-2mA and below. Then something like the DN2540 up to ~100mA. That's two models with R knobs. How much current do you need? George H. Fortunately the available JFETs work> up to the megavolt range, but it is a kludge. > > I'd like to have a single box with two parameters, I_SAT and, > say, the U for which I is 1-1/e of I_SAT. Or 90%, whatever. > Just don't know how to create such a box in Spice. > > [snip something very useful] > > Best regards, Piotr
