Spice modeling a PUT oscillator

Thread Starter


Joined Aug 15, 2009

I am trying to model a oscillator circuit that uses the programmable unijunction transistor 2N6027 (http://www.rapidonline.com/netalogue/specs/47-3348.pdf) . I got the spice model from www.onsemi.com/pub/Collateral/2N6027.LIB . The circuit is quite simple and consists of two series resistors (R2 and R3) used to bias the gate, which
are placed in parallel with a resistor and capacitor in series (R1 and C1)

+ R1 C1 -
| |
R2 R3

R1 = 470K
R2 = 15K
R3 = 27K
C1 = 2.2uF

The anode of the PUT is connected between R1 and C1 (at x) and the gate between R2 and R3 (at w). The oscillation is obtained between its cathode and the negative terminal of a DC power source.

I can not get my spice model (given below in ngspice format) to oscillate.

* PUT Oscillator
* Red Led
.MODEL LEDR D (IS=93.2P RS=42M N=3.73 BV=4 IBV=10U
+ CJO=2.97P VJ=.75 M=.333 TT=4.32U)
* 2N6027 NPN PUT (Programable Unijunction Transistor)
.MODEL 2N6027 NPN(IS=5E-15 VAF=100 IKF=0.3 ISE=1.85E-12
+ NE=1.45 RE=0.15 RC=0.15 CJE=7E-10 TF=0.6E-8
+ CJC=2.2E-10 TR=4.76E-8 XTB=3)
* Oscillator Circuit
v1 1 0 9
r1 1 2 470k
c1 2 0 2.2uF
r2 1 3 15k
r3 3 0 27k
q1 2 3 4 2N6027
d1 4 0 LEDR ic=0
tran 0.1 4 uic
plot v(2), v(4)

I suspect that the PUT model does not correspond to the actual PUT I am using (given in the datasheet) but do not know how to fix the problem. Will be grateful for any help.

Are there any good tutorials on how to convert an active components datasheet into a Spice model ?



Joined Jul 17, 2007
Here's a model for the 2N6027 I've used with success:
Rich (BB code):
*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
Did anyone solve this, I have tried both models and it doesn't oscillate as it stands. I built the circuit and it is fine. Is there a better model for the 2N6027?

Here's my netlist file
* D:\Martyn\Documents\LTSpice\Oscillator.asc
R1 N001 N002 18k
R2 N001 VLoad 470k
R3 N002 0 27k
C1 VLoad 0 2.2µ V=6.3 Irms=0 Rser=9 Lser=0
D1 N003 0 REDLED
V1 N001 0 6
XU1 VLoad N002 N003 X2N6027
.model D D
.lib D:\LTspiceIV\lib\cmp\standard.dio
.tran 0 5 0 0.0001
.ic V(VLoad)=0
* Red Led
.MODEL REDLED D (IS=1.41e-21 RS=8.73 N=1.54)
Last edited:
Here's my circuit. Apologies, my spice simulation contained an 18k resistor which caused the circuit to oscillate. However, my circuit from a book contained a 15k resistor which according to my simulation won't oscillate.

Cheers, Martyn