# Spice modeling a PUT oscillator

Discussion in 'General Electronics Chat' started by bthomas, Jun 13, 2011.

1. ### bthomas Thread Starter Member

Aug 15, 2009
11
1
Hi

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 -
|---/\/\/\/\------x-------||----------|
| |
|__/\/\/\/\___w__/\/\/\/\____|
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
.control
tran 0.1 4 uic
plot v(2), v(4)
.endc
.end

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 ?

regards
Thomas

2. ### SgtWookie Expert

Jul 17, 2007
22,183
1,729
Here's a model for the 2N6027 I've used with success:
Code ( (Unknown Language)):
1. *Programable Unijunction Transistor pkg: TO-226AA
2. .SUBCKT X2N6027 1 2 3
3. ************** K1 G K2
4. Q1 2 4 3 NMOD
5. Q2 4 2 1 PMOD
6. .MODEL NMOD NPN(IS=5E-15 VAF=100 IKF=0.005 ISE=1.85E-12 NE=1.45
7. + 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
8. + TF=16N VJS=0.75 )
9. .MODEL PMOD PNP(IS=2E-15 VAF=100 IKF=0.005 ISE=1.9E-12 RB=10 RE=0.5
10. + 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
11. + TF=16N VJS=0.75 )
12. .ENDS X2N6027

3. ### martynwheeler New Member

Feb 18, 2014
2
0
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
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
.model D D
.lib D:\LTspiceIV\lib\cmp\standard.dio
.tran 0 5 0 0.0001
* Red Led
.MODEL REDLED D (IS=1.41e-21 RS=8.73 N=1.54)
.lib PUJT.LIB
.backanno
.end

Last edited: Feb 18, 2014
4. ### crutschow Expert

Mar 14, 2008
13,523
3,392
Post the circuit diagram of the complete oscillator circuit.

5. ### martynwheeler New Member

Feb 18, 2014
2
0
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