Title: UJT SPICE Model Notes
By: Don Kuenz

Abstract: 
  This page compiles notes and models, from various
  online sources, which pertain to a collection of
  UJT SPICE models.

Keywords: ltspice, spice, ujt

UJT SPICE Model Notes

Contents

Overview

SPICE [1] and LTSpice [2] both lack UniJunction Transistor (UJT) [3] models for common devices. This webpage seeks to mitigate the omission with a compilation of pertinent notes and models.

UJT Model Collection

2N6027


*Programable Unijunction Transistor pkg: TO-226AA
.SUBCKT X2N6027 1 2 3
************** K1 G K2
Q1 2 4 3 NMOD
Q2 4 2 1 PMOD
.MODEL NMOD NPN(IS=5E-15 VAF=100 IKF=0.005 ISE=1.85E-12 NE=1.45
+ RB=10 RE=0.5 RC=0.5 CJE=3.5E-11 VJE=0.75 CJC=1.1E-11 VJC=0.75 TR=4.76E-8
+ TF=16N VJS=0.75 )
.MODEL PMOD PNP(IS=2E-15 VAF=100 IKF=0.005 ISE=1.9E-12 RB=10 RE=0.5
+ RC=0.5 CJE=3.5E-11 VJE=0.75 TF=1.6E-8 CJC=1.1E-11 VJC=0.75 TR=5.1E-8
+ TF=16N VJS=0.75 )
.ENDS X2N6027
LTSpice symbol: 

Version 4
SymbolType CELL
LINE Normal 16 16 16 80
LINE Normal 48 72 48 96
LINE Normal 16 72 48 72
LINE Normal 48 24 48 0
LINE Normal 16 24 48 24
LINE Normal 4 68 16 64
LINE Normal 4 60 16 64
LINE Normal 4 60 4 68
LINE Normal -32 32 -64 32
LINE Normal 0 64 -32 32
LINE Normal 4 64 0 64
WINDOW 3 56 72 Left 2
SYMATTR Value X2N6027
SYMATTR Prefix X
SYMATTR Description UJT
SYMATTR SpiceModel X2N6027
SYMATTR ModelFile 2N6027.sub
PIN 48 0 NONE 0
PINATTR PinName K1
PINATTR SpiceOrder 1
PIN -64 32 NONE 0
PINATTR PinName G
PINATTR SpiceOrder 2
PIN 48 96 NONE 0
PINATTR PinName K2
PINATTR SpiceOrder 3

2N2646


* Motorola IP=.5U IV=6M VB1(sat)=3 Rbb=6.1K Vob1=3.6: E, B1, B2
.SUBCKT X2N2646 1 2 3
DE 1 4 EMITTER
VE 4 5 DC 0
HVE 6 0 VE 1K
RVE 0 6 1MEG
BBB 5 7 I=0.00028*V(5,7)+0.00575*V(5,7)*V(6)
CBB 5 7 35P
RB1 7 2 38.15 RMOD
RB2 3 5 2.518K RMOD 
.MODEL RMOD R TC1=.01
.MODEL EMITTER D (IS=21.3P N=1.8)
.ENDS X2N2646
LTSpice symbol: 

Version 4
SHEET 1 880 680
WIRE 272 224 272 176
WIRE 272 336 272 304
WIRE 480 336 272 336
WIRE 272 352 272 336
WIRE 160 384 32 384
WIRE 272 512 272 448
FLAG 176 16 0
FLAG 352 16 0
FLAG 176 -64 V+
FLAG 272 176 V+
FLAG 352 -64 Sig
FLAG 32 384 Sig
FLAG 272 512 0
FLAG 480 336 Out
SYMBOL Misc\\2N6027 224 352 R0
WINDOW 0 56 29 Left 2
SYMATTR InstName U1
SYMBOL voltage 176 -80 R0
WINDOW 123 0 0 Left 2
WINDOW 39 -149 14 Left 2
SYMATTR InstName V1
SYMATTR Value 5
SYMATTR SpiceLine Rser=1m
SYMBOL voltage 352 -80 R0
WINDOW 123 0 0 Left 2
WINDOW 39 51 54 Left 2
SYMATTR InstName V2
SYMATTR Value PULSE(0 3 0 100n 100n 1m 2m)
SYMATTR SpiceLine Rser=0
SYMBOL res 256 208 R0
SYMATTR InstName R1
SYMATTR Value 1K
SYMATTR SpiceLine tol=1 pwr=0.1
TEXT -184 -64 Left 2 !.tran 0 10m 0

Default N-Channel UJT


*Default N-Channel Unijunction Transistor
.SUBCKT XUJT 1 2 3
DE 1 4 EMITTER
VE 4 5 DC 0
HVE 6 0 VE 1K
RVE 0 6 1MEG
BBB 5 7 I=0.00028*V(5,7)+0.00575*V(5,7)*V(6)
CBB 5 7 35P
RB1 7 2 38.15 RMOD
RB2 3 5 2.518K RMOD 
.MODEL RMOD R TC1=.01
.MODEL EMITTER D (IS=21.3P N=1.8)
.ENDS XUJT

Jim Thompson's Comparison

In 2013 Jim Thompson ran a simulation to compare the trio of UJT SPICE models. He then summarized his impressions in the usenet thread shown below:


Don wrote:
> Jim Thompson wrote:
>> Jim Thompson wrote:
>>>RobertMacy wrote:
>>>>Jim Thompson wrote:
>>>>> RobertMacy wrote:
>>>>>
>>>>>> ..snip...
>>>>>>
>>>>>> Did you look through the 100+MB of Alex Bordodynov's models?
>>>>>>
>>>>>> I only could download one set, not the larger set, so couldn't peruse.
>>>>>
>>>>> I've seen that name on the LTspice list.  Do you have a link to his
>>>>> site?
>>>>>
>>>>> ...snip...
>>>>
>>>>His models usually are accurate and have conversion speed enhancements. He
>>>>supplied two links, circa July 5, 2013, posted to the LTspice group, which
>>>>I trashed after downloading each. Big mistake!
>>>>
>>>>LTspiceIV.zip is 37MB of 'tiny' little .asc files so you have an idea how
>>>>many models are in there.
>>>>LTSPICE.DOC is 67MB and dialup download took HOURS!!! only to find out
>>>>today that when unzipping, comes up 'corrupted' download again!
>>>
>>>Thanks.  That will allow me to find it.  As you know, I keep a record
>>>of everything... even an LTspice list directory "Pre_2013" ;-)
>>>
>>>Found it.  How do I download, it's all in Russian, and I can't get the
>>>download to start :-(
>>
>> Here you go...
>>
>>     http://us.ua/1162032/
>>
>> Kill the pop-up on the lower left, then you can download.
>
>Thank you for sharing Jim. Here's a more Anglo friendly link.
>
>http://ltwiki.org/index.php5?title=Components_Library_and_Circuits

Here's something to fret over, compare Unijunction models, wonder
which is real...

  http://www.analog-innovations.com/SED/CompareUnijunctionModels.pdf

Jim's website went dark after his demise. See Note [4] for a downloadable copy of Jim's comparision.

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Notes


© 2020 Don Kuenz