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Author Topic: Simulation of Devices & Possibilities  (Read 4359 times)

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Posts: 1859
I'm looking for LTSpice or Spice simulation to show the difference between a triode, JFet and MosFet.

Specifically, tubes have one important difference - they are all diodes, at all times. With the exception of interelectrode capacitance, there is no reverse conduction while 'ON'.

As I test the scenario with the Si rectifier in line with a 5U4GB I see the SS allows reverse current (albeit short and little) while the tube does not. The result is the tube rectifier truly rectifies the noise generated by the SS.
I have the concern that a SS switch may allow full conduction of reverse current if it happens when the switch is still on and the reverse pulse is fast enough.

This would explain why I see so much more energy depleted in a fixed time when firing several of my experiments using a variety of SS devices, as compared to a trigger tube with heater.


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
Group: Guest
Yep!
Steven stated clearly that he would never have discovered the process if not for electron tubes.

The charactor we are looking for will not simulate because its only the desirabe things within convention that simulate.

In this context tubes would be useless compared to ss . and sims would  rule !

In the 5u4 thread I have tried to point out that sims dont even do predictable, known but not commonly well exploited  ss noise.

as Darren pointed out noise, is a seperate function of sims  .

   

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It is rare that I put a circuit in a sim. Most of the time I do it is when I can't get to my bench or I'm messing with something digital. (digital = headache for me)

I would have more fun writing or hacking the software than using it  ;D

The reality is ... circuit simulators are great tools (I said 'tools') and I'm not good at wielding one.

I'm starting to think one of the key points to learn with the SS/tube combination is you need to have a tube rectifier in series with SS to bring it more in-line with what is needed. Perhaps it is to show that the series tube rectifier actually enhances the ESD snap-back effect of Si diodes? It does seem to do so.




---------------------------
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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Posts: 43
I'm looking for LTSpice or Spice simulation to show the difference between a triode, JFet and MosFet.

Specifically, tubes have one important difference - they are all diodes, at all times. With the exception of interelectrode capacitance, there is no reverse conduction while 'ON'.

As I test the scenario with the Si rectifier in line with a 5U4GB I see the SS allows reverse current (albeit short and little) while the tube does not. The result is the tube rectifier truly rectifies the noise generated by the SS.
I have the concern that a SS switch may allow full conduction of reverse current if it happens when the switch is still on and the reverse pulse is fast enough.

This would explain why I see so much more energy depleted in a fixed time when firing several of my experiments using a variety of SS devices, as compared to a trigger tube with heater.

JFet's too low voltage - usless  -- but there are some great Depletion mosfets that can be switched very fast ... here's a model for Fairchilds (400V 0.5A continuous) DMOS device
.subckt XDN2540 1 2 3
Ld 1 d 3.5n
Lg 2 g 4.5n
Ls 3 s 7.5n
M1 d g s s DN2540
Rg g s 1G
.MODEL DN2540 VDMOS(KP=0.1989 RS=0.21 RD=18.3839 RG=2.0 VTO=-2.1
+LAMBDA=0.001 CGDMAX=20p CGDMIN=0p CGS=199p TT=1152n a=1.0
+IS=1.47E-08 N=1.576 RB=0.006897 m=0.454 Vj=0.1 Cjo=155.0pF)
.ends

next fastest is Fairching NMOS

.subckt XFDU3N40 1 2 3
Ld 1 d 4.5n
Lg 2 g 7.5n
Ls 3 s 7.5n
M1 d g s s FDU3N40
Rg g s 1G
Db s d dbody
.MODEL FDU3N40 VDMOS(KP=1.6168 RS=0.034 RD=3.2491 RG=16.56 VTO=4.7
+LAMBDA=0.001 CGDMAX=124p CGDMIN=0p CGS=169p TT=302n a=0.57
+IS=1.81E-10 N=1.356 RB=0.042578 m=0.377 Vj=0.1 Cjo=229.0pF)
.model dbody d ron=0.1 vrev= 630 vfwd=2
.ends

Tube models are availble in LTSpice forum (yahoo) - I can get them if you have trouble locating

cheers

mark snoswell :)
   
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Posts: 43
   
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