开云体育

  1. LTspice
  2. Topics

Diode TVS like zener in LTspice??

 

Good morning....
I'd like to know why LTspice simulates a TVS diode as a zener, even though its behavior isn't exactly the same.
I'd also like to know where I can find an LTspice library for some TVS diodes, for example, that are 15 volts and others that are around 140 volts, and that are bidirectional.
Thanks...for everything.
 

开云体育

On 23/04/2025 10:04, j.bernabe1 via groups.io wrote:
I'd like to know why LTspice simulates a TVS diode as a zener, even though its behavior isn't exactly the same.
I'd also like to know where I can find an LTspice library for some TVS diodes, for example, that are 15 volts and others that are around 140 volts, and that are bidirectional.
Did you try looking on the sites of manufacturers that make TVS diodes, e.g. Diodes Inc., Littelfuse, Vishay etc?

You could always try looking on the group's Files section and put "TVS" in the search box in the top right. I got 24 hits, but not all them were relevant.

As far as LTspice simulations are concerned, actually unidirectional TVSs are similar to Zeners, but tend to higher current. Bidirectional ones are equivalent to two unidirectional ones in anti-series.

--
Regards,
Tony
 

开云体育

Actually, 'zener' embraces true Zeners , less than about 6V, and avalanche diodes, greater than about 6V.? LTspice models take account of this. TVS diodes are high-power avalanche diodes.

On 2025-04-23 09:04, j.bernabe1 via groups.io wrote:
Good morning....
I'd like to know why LTspice simulates a TVS diode as a zener, even though its behavior isn't exactly the same.
I'd also like to know where I can find an LTspice library for some TVS diodes, for example, that are 15 volts and others that are around 140 volts, and that are bidirectional.
Thanks...for everything.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only If something is true: * as far as we know - it's science *for certain - it's mathematics *unquestionably - it's religion

Virus-free.
 

??
Thanks for your reply.
I'll connect the zener capacitors in anti-series...
Wouldn't it work correctly in anti-parallel?
 

By high power, do you mean that TVSs behave like high voltage zeners when simulating?
 

开云体育

Yes, they do behave like the 'avalanche' sort of 'zener', not the true Zener, and the mostly used TVS have a fairly high breakdown voltage, but also, almost all of them have a high maximum current rating. You can see by their physical construction, using a large die, that they are designed to dissipate power, even though it occurs over a very short time scale.

On 2025-04-23 10:03, j.bernabe1 via groups.io wrote:
By high power, do you mean that TVSs behave like high voltage zeners when simulating?
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only If something is true: * as far as we know - it's science *for certain - it's mathematics *unquestionably - it's religion

Virus-free.
 

开云体育

On 23/04/2025 11:01, j.bernabe1 via groups.io wrote:
Thanks for your reply.
I'll connect the zener capacitors in anti-series...
Wouldn't it work correctly in anti-parallel?
Because both devices are just forward biassed diodes (as well). In anti-series, each diode blocks the other's forward voltage, so the total voltage "breakdown" in either direction is Vrev + Vfwd.

--
Regards,
Tony
 
Edited

On Wed, Apr 23, 2025 at 05:01 AM, <j.bernabe1@...> wrote:
Wouldn't it work correctly in anti-parallel?
If you connected them in anti-parallel, then each diode's forward voltage (very small) dominates and it would never reach the avalanche voltage in either direction.
?
[Mod note:? The following paragraph is incorrect.? LTspice does, in fact, have a TVS diode model in its library that is bidirectional, which uses the alternate diode model rather than the standard SPICE exponential (Shockley-based) diode model.? I have redacted the following paragraph:
The diodes that come built-in to LTspice'd diode library, can only be "regular" diodes that have forward and reverse directions - unidirectional only.? A bidirectional TVS can not be modeled that way; it needs to be a subcircuit, and LTspice's diode library does not include subcircuits.? The library only has parts defined by a single .MODEL statement.
?
Andy
?
 

Andy,
you're not quite right. Here is my clarification:
.model SMBJ24CA D(Ron=.65 Roff=50Meg Vfwd=25 epsilon=6 Vrev=25 revepsilon=6 Vpk=24 mfg=Littlefuse type=TVS)
.model SMCJ33A D(Ron=.4 Roff=8Meg Vfwd=.7 epsilon=100m Vrev=38.65 Vpk=33 revepsilon=4 mfg=Littlefuse type=TVS)
 

On Sat, Apr 26, 2025 at 01:14 AM, Александр Бордодынов wrote:
Andy,
you're not quite right. Here is my clarification:
.model SMBJ24CA D(Ron=.65 Roff=50Meg Vfwd=25 epsilon=6 Vrev=25 revepsilon=6 Vpk=24 mfg=Littlefuse type=TVS)
.model SMCJ33A D(Ron=.4 Roff=8Meg Vfwd=.7 epsilon=100m Vrev=38.65 Vpk=33 revepsilon=4 mfg=Littlefuse type=TVS)
A-ha.? Yes, that's true? You used the special "conduction region-wise linear model" which is very different from the regular diode model which is based on the universal Shockley Ideal Diode equation.? The special version you used is essentially a piecewise-linear approximation of the three regions of diode conduction, and makes (almost) no attempt to model the curvature of real diode I/V curves.? I think it might be unique to LTspice.? Whereas the standard Shockley model is in every SPICE program.
?
In some cases, this alternate model is good enough.? It is described as a "computationally light weight representation of an idealized diode", meaning that it trades-off accuracy for simulation speed.
?
As you noted, it is capable of modeling both forward and reverse breakdown at similar (arbitrarily large) voltages.? It can model non-physical diodes.
?
Andy
?
 

Please note that there are parameters epsilon=100m revepsilon=4. They represent quadratic sections.

1 - 11 of 11