TVS diode in LT spice

.model SMCJ33A D(Ron=.4 Roff=8Meg Vfwd=.7 epsilon=100m Vrev=38.65
Vpk=33 revepsilon=4 mfg=Littlefuse type=TVS)

That's in the standard library. It behaves like a symmetric zener.

Why? Does "type" do that? There are unipolar TVS diodes, too.

tirsdag den 8. november 2022 kl. 20.12.57 UTC+1 skrev John Larkin:
> .model SMCJ33A D(Ron=.4 Roff=8Meg Vfwd=.7 epsilon=100m Vrev=38.65 
> Vpk=33 revepsilon=4 mfg=Littlefuse type=TVS) 
> 
> That's in the standard library. It behaves like a symmetric zener. 

it shouldn't and when I just tried it didn't. Vfwd 0.7V, Vrev 38.65  
if I change Vfwd and Vrev ot the same it gets symmetrical

> Why? Does "type" do that? There are unipolar TVS diodes, too.

type and mfg is not part of the model parameters if you try to make a model with them you get and error,
afaict they are just for the selection dialog

On Tue, 8 Nov 2022 11:36:04 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>tirsdag den 8. november 2022 kl. 20.12.57 UTC+1 skrev John Larkin:
>> .model SMCJ33A D(Ron=.4 Roff=8Meg Vfwd=.7 epsilon=100m Vrev=38.65 
>> Vpk=33 revepsilon=4 mfg=Littlefuse type=TVS) 
>> 
>> That's in the standard library. It behaves like a symmetric zener. 
>
>it shouldn't and when I just tried it didn't. Vfwd 0.7V, Vrev 38.65  
>if I change Vfwd and Vrev ot the same it gets symmetrical

Try this:

Version 4
SHEET 1 880 680
WIRE 16 96 -16 96
WIRE 80 96 16 96
WIRE 192 96 160 96
WIRE 224 96 192 96
WIRE -16 128 -16 96
WIRE 224 128 224 96
WIRE -16 224 -16 192
WIRE 224 224 224 192
FLAG 224 224 0
FLAG -16 224 0
FLAG 16 96 A
FLAG 192 96 B
SYMBOL TVSdiode 208 128 R0
WINDOW 0 63 22 Left 2
WINDOW 3 52 45 Left 2
SYMATTR InstName D1
SYMATTR Value SMBJ24CA
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL current 80 96 R270
WINDOW 0 50 31 VRight 2
WINDOW 3 80 -24 VRight 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 50m 1)
SYMBOL TVSdiode -32 128 R0
WINDOW 0 63 22 Left 2
WINDOW 3 52 45 Left 2
SYMATTR InstName D2
SYMATTR Value SMCJ33A
SYMATTR Description Diode
SYMATTR Type diode
TEXT 272 216 Left 2 !.tran 0 4 0



What am I missing?

tirsdag den 8. november 2022 kl. 21.05.45 UTC+1 skrev John Larkin:
> On Tue, 8 Nov 2022 11:36:04 -0800 (PST), Lasse Langwadt Christensen 
> <lang...@fonz.dk> wrote: 
> 
> >tirsdag den 8. november 2022 kl. 20.12.57 UTC+1 skrev John Larkin: 
> >> .model SMCJ33A D(Ron=.4 Roff=8Meg Vfwd=.7 epsilon=100m Vrev=38.65 
> >> Vpk=33 revepsilon=4 mfg=Littlefuse type=TVS) 
> >> 
> >> That's in the standard library. It behaves like a symmetric zener. 
> > 
> >it shouldn't and when I just tried it didn't. Vfwd 0.7V, Vrev 38.65 
> >if I change Vfwd and Vrev ot the same it gets symmetrical
> Try this: 
> 

D1 is symmetric, as expected from the model; Vfwd = Vrev
.model SMBJ24CA D(Ron=.65 Roff=50Meg Vfwd=25 epsilon=6 Vrev=25 revepsilon=6 Vpk=24 mfg=Littlefuse type=TVS)

D2 is not, as expected from the model; Vfwd != Vrev 
.model SMCJ33A D(Ron=.4 Roff=8Meg Vfwd=.7 epsilon=100m Vrev=38.65 Vpk=33 revepsilon=4 mfg=Littlefuse type=TVS)

> 
> What am I missing?

don't know,  what do you see?

https://imgur.com/OPZl629

On Tue, 8 Nov 2022 12:37:01 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>tirsdag den 8. november 2022 kl. 21.05.45 UTC+1 skrev John Larkin:
>> On Tue, 8 Nov 2022 11:36:04 -0800 (PST), Lasse Langwadt Christensen 
>> <lang...@fonz.dk> wrote: 
>> 
>> >tirsdag den 8. november 2022 kl. 20.12.57 UTC+1 skrev John Larkin: 
>> >> .model SMCJ33A D(Ron=.4 Roff=8Meg Vfwd=.7 epsilon=100m Vrev=38.65 
>> >> Vpk=33 revepsilon=4 mfg=Littlefuse type=TVS) 
>> >> 
>> >> That's in the standard library. It behaves like a symmetric zener. 
>> > 
>> >it shouldn't and when I just tried it didn't. Vfwd 0.7V, Vrev 38.65 
>> >if I change Vfwd and Vrev ot the same it gets symmetrical
>> Try this: 
>> 
>
>D1 is symmetric, as expected from the model; Vfwd = Vrev
>.model SMBJ24CA D(Ron=.65 Roff=50Meg Vfwd=25 epsilon=6 Vrev=25 revepsilon=6 Vpk=24 mfg=Littlefuse type=TVS)
>
>D2 is not, as expected from the model; Vfwd != Vrev 
>.model SMCJ33A D(Ron=.4 Roff=8Meg Vfwd=.7 epsilon=100m Vrev=38.65 Vpk=33 revepsilon=4 mfg=Littlefuse type=TVS)
>
>> 
>> What am I missing?
>
>don't know,  what do you see?
>
>https://imgur.com/OPZl629
>

Oh, they hijacked Vfwd. I missed that.

I got up at 5 AM. That's my excuse.